identification of pbt and vpvb substance results of …echa.europa.eu/documents/10162/13628/... ·...

SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION

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IDENTIFICATION OF PBT AND vPvB SUBSTANCE

RESULTS OF EVALUATION OF PBT / vPvB PROPERTIES

This dossier covers three substances manufactured and supplied as detailed below.

Substance name: Dioctyltin dichloride EINECS number: 222-583-2 EINECS name: Dichlorodioctylstannane CAS number: 3542-36-7 Registration number(s): 05-2114350016-61

Molecular formula: C 16H34Cl2Sn

Structural formula: Composition: mono-constituent product 94.5 – 100 per cent dioctyltin dichloride; (typically 96.04 per cent dioctyltin dichloride; impurities 3.05 per cent octyltin trichloride, 0.68 per cent trioctyltin chloride, 0.23 per cent hexadecane) (JS Organotin Consortium REACH registration, 2010). Substance name: Dioctyltin bis(2-ethylhexyl mercaptoacetate) EINECS number: 239-622-4 EINECS name: 2-Ethylhexyl 10-ethyl-4,4-dioctyl-7-oxo-8-oxa-3,5-dithia-4-

stannatetradecanoate CAS number: 15571-58-1 Registration number(s): 05-2114362069-46 Molecular formula: C 36H72O4S2Sn

Structural formula:


2

Composition: multi-constituent product 67 – 76 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate); 24 – 33 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurities 2.5 – 5.5 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 0.3 per cent 2-ethylhexan-1-ol (Organotin Consortium REACH registration, 2010)

Substance name: Octyltin tris(2-ethylhexyl mercaptoacetate) EINECS number: 248-227-6 EINECS name: 2-Ethylhexyl 10-ethyl-4-[[2-[(2-ethylhexyl)oxy]-2-oxoethyl]thio]-4-octyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate CAS number: 27107-89-7 Registration number(s): 05-2114085657-35 Molecular formula: C 38H74O6S3Sn

Structural formula: Composition: marketed mono-constituent product 99.7 – 100 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurities 0 – 0.3 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 0 – 1 per cent 2-ethylhexan-1-ol; 0 – 1 per cent 2-ethylhexyl mercaptoacetate marketed multi-constituent products 60 – 68 per cent octyltin tris(2-ethylhexyl mercaptoacetate); 30 – 35 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate); impurities 0 – 2 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 1 per cent 2-ethylhexan-1-ol (Joint REACH registration, 2010).

Summary of how the substances meet the CMR (Cat 1 or 2), PBT or vPvB criteria, or are considered to be substances of an equivalent level of concern

In line with REACH Article 13.1 and Annex XI this evaluation is made taking into account the data available for dioctyl tin and monooctyl tin derivatives using a grouping and read-across approach. This evaluation considers bioaccumulation and other data submitted by


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Industry in response to Commission Regulation 465/2008. The grouping and read-across approach is justified on the basis that dioctyltin dichloride, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) are rapidly hydrolysed to common or structurally similar intermediate products (either dioctyltin hydroxide/oxide or octyltin hydroxide/oxide) and that these hydrolysis products are the environmentally relevant form of the substance. Furthermore, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) are generally supplied as multi-constituent products that can contain a high concentration of both substances.

Overall it is concluded that the three substances considered, dioctyltin dichloride, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) do not meet the PBT or vPvB criteria. Although they are considered to be potentially persistent (in that they do not biodegrade rapidly but rather hydrolyse rapidly to either dioctyltin hydroxide/oxide or octyltin hydroxide/oxide that are themselves potentially persistent) and toxic, the available evidence suggests that the substances and hydrolysis products do not meet the Annex XIII criteria for bioaccumulation.

Carrying out aquatic testing in general for these substances is difficult owing to their poor solubility, rapid hydrolysis, and difficulties with their analysis. In particular, conducting a fish bioconcentration test for these substances is technically challenging owing to the rapid hydrolysis and the lack of analytical methodology to allow determination of the individual substances present to which organisms are exposed. This results in the following uncertainties in the B-assessment:

• The individual substances actually present in solution are not known; it was possible only to measure concentrations on the basis of total tin or total mono- and dioctyltin species. This would be important if the observed uptake was the result of exposure to a minor component in water (for example if the accumulative component made up only a small fraction of the total mono- or dioctyltin compounds present in the test medium). In such a case, the actual BCF for the individual substance may be higher than that determined based on the total tin, total mono- or total dioctyltin compounds. The analytical difficulties mean that it is not technically possible to investigate further whether or not this is the case.

• The available data do not provide any information on the accumulation of the monooctyltin compound or its degradation products. Based on read-across, it can be expected that the bioaccumulation potential of the octyltin hydroxide/oxide hydrolysis products would be similar to (or possibly even lower than) that of the dioctyltin hydroxide/oxide. However this read-across is another source of uncertainty in the overall evaluation.

• The lack of a definitive hydrolysis rate for the test substance is important in relation to the bioconcentration test, if hydrolysis had actually been much slower than has been concluded from the available data. In this case, conclusions about the bioaccumulation potential of the hydrolysis products could not be drawn from this study. Again, the analytical difficulties mean that it is not technically possible currently to investigate further whether or not this is the case. Further evaluation of the oxide could be warranted if, in the future, more definitive hydrolysis data suggested that the test substance was more stable than concluded here.


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Hydrolysis of both dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) would also result in formation of 2-ethylhexyl mercaptoacetate. This substance is not considered to meet the PBT criteria as it has a low predicted BCF.


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Contents

1 Identification of the Substance and physical and chemical properties ..............................7

1.1 Name and other identifier of the substance.................................................................7

1.2 Composition of the substances..................................................................................10

1.3 Physico-chemical properties .....................................................................................14

2 Manufacture and uses ......................................................................................................17

3 Classification and labelling..............................................................................................17

4 Environmental fate properties..........................................................................................20

4.1 Degradation ...............................................................................................................21

4.1.1 Abiotic degradation............................................................................................21

4.1.2 Biotic degradation..............................................................................................24

4.1.3 Summary and discussion of persistence ............................................................26

4.2 Environmental distribution........................................................................................27

4.2.1 Adsorption..........................................................................................................27

4.2.2 Distribution modelling.......................................................................................27

4.2.3 Other information...............................................................................................28

4.2.4 Summary of environmental distribution ............................................................28

4.3 Bioaccumulation........................................................................................................28

4.3.1 Screening data....................................................................................................28

4.3.2 Measured bioaccumulation data ........................................................................30

4.3.3 Other supporting information ............................................................................35

4.3.4 Summary and discussion of bioaccumulation....................................................35

4.4 Secondary poisoning .................................................................................................37

5 Human health hazard assessment.....................................................................................38

6 Human health hazard assessment of physicochemical properties ...................................39

7 Environmental hazard assessment ...................................................................................39

7.1 Aquatic compartment (including sediment)..............................................................39

7.1.1 Toxicity test results ............................................................................................39

7.1.2 Fish.....................................................................................................................39

7.1.3 Aquatic invertebrates .........................................................................................41


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7.1.4 Algae and aquatic plants ....................................................................................43

7.1.5 Quantitative structure-activity relationships (QSARs) ......................................45

7.1.6 Sediment organisms...........................................................................................45

7.1.7 Other aquatic organisms ....................................................................................45

7.1.8 Summary of aquatic toxicity data ......................................................................45

8 PBT and VPVB.................................................................................................................49

8.1 Comparison with criteria from Annex XIII...............................................................49

8.2 Assessment of substances of an equivalent level of concern ....................................51

8.3 Emission characterisation..........................................................................................51

8.4 Conclusion of PBT and vPvB or equivalent level of concern assessment................51


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JUSTIFICATION

Note: Most of the data for dioctyltin and monooctyltin compounds have been reviewed and internationally agreed previously under the OECD HPV programme (OECD, 2006a and 2006b). The three substances subject to this assessment have been registered under REACH and non-confidential information not found in the OECD assessment from these registration dossiers has been used in this assessment. Where information has been found to conflict, that presented in the REACH registration has been used as it is understood this is more relevant for the EU.

1 IDENTIFICATION OF THE SUBSTANCE AND PHYSICAL AND CHEMICAL PROPERTIES

1.1 Name and other identifier of the substance

Name: Dioctyltin dichloride

EC Number: 222-583-2

CAS Number: 3542-36-7

IUPAC Name: Stannane, dichlorodioctyl-

Molecular Formula: C16H34Cl2Sn

Structural Formula:

Molecular Weight: 416.04 g/mol

Synonyms (and registered trade names):

Dichlorodioctylstannane

Name: Dioctyltin bis(2-ethylhexyl mercaptoacetate)



IUPAC Name: 8-Oxa-3,5-dithia-4-stannatetradecanoic acid, 10-ethyl-4-4-dioctyl-7-oxo-, 2-ethylhexyl ester

Molecular Formula: C36H72O4S2Sn

Structural Formula:


8

Molecular Weight: 751.8


Dioctyltin bis(2-ethylhexyl thioglycolate)

2-Ethylhexyl 10-ethyl-4,4-dioctyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate

Name: Octyltin tris(2-ethylhexyl mercaptoacetate)



IUPAC Name: 8-Oxa-3,5-dithia-4-stannatetradecanoic acid, 10-ethyl-4-[[2-[(2-ethylhexyl)oxy]-2-oxoethyl]thio]-4-octyl-7-oxo, 2-ethylhexyl ester

Molecular Formula: C38H74O6S3Sn

Structural Formula:

Molecular Weight: 841.9 g/mol


Octyltin tris(2-ethylhexyl thioglycolate)

2-Ethylhexyl 10-ethyl-4-[[2-[(2-ethylhexyl)oxy]-2-oxoethyl]thio]-4-octyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate


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The report draws on information for these three substances, and information for the following three related substances as appropriate.

• Diisooctyl 2,2’-[(octylstannylidyne)bis(thio)]diacetate, also known as dioctyltin bis(isooctyl mercaptoacetate) or dioctyl tin bis(isooctyl thioglycolate); CAS No 26401-97-8. This is a dioctyltin structural isomer of dioctyltin bis(2-ethylhexyl mercaptoacetate).

• Trichlorooctylstannane, also known as octyltin trichloride; CAS No 3091-25-6. This is a monooctyl tin derivative.

• Triisooctyl 2,2’2’’-[(octylstannylidyne)tris(thio)]triacetate, also known as octyltin tri(isooctyl mercaptoacetate) or octyltin tri(isooctyl thioglycolate); CAS No 26401-86-5. This is a monooctyl tin structural isomer of octyltin tris(2-ethylhexyl mercaptoacetate)


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As discussed in Section 1.2 the substance octyltin trichloride is particularly relevant for this assessment as: a) it is present in substantial quantities in some commercially supplied dioctyltin dichloride products and b) the commercially supplied octyltin trichloride products will contain substantial amounts of dioctyltin dichloride. Therefore information on octyltin trichloride in particular is included in the evaluation where relevant.

The two isooctyl thioglycolate derivatives are structural isomers of either dioctyltin bis(2-ethylhexyl mercaptoacetate) or octyltin tris(2-ethylhexyl mercaptoacetate). The OECD (2006a and 2006b) evaluations indicate that there is little actual experimental information available relevant to the PBT assessment for these two isooctyl thioglycolate derivatives and concludes that the information for either dioctyltin bis(2-ethylhexyl mercaptoacetate) or octyltin tris(2-ethylhexyl mercaptoacetate) can be used interchangeably for these two isooctyl thioglycolate derivatives, as the compounds produce the same dioctyl- or octyltin hydrolysis products.

In line with REACH Article 13.1 and Annex XI this evaluation is made taking account of the data available for dioctyltin and monooctyl tin derivatives using a grouping and read-across approach. This grouping and read-across approach is justified on the basis that dioctyl tin dichloride, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) are rapidly hydrolysed to common or structurally similar intermediate products (either dioctyltin hydroxide/oxide or octyltin hydroxide/oxide) and these hydrolysis products are the environmentally relevant form of the substance. Furthermore, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) are generally supplied as multi-constituent products that can contain a high concentration of both substances.

1.2 Composition of the substances

The following information is taken from the respective OECD evaluations of the substances (OECD, 2006a and 2006b) and the relevant REACH registrations. The information from the two sources differs somewhat. The OECD assessment describes the substances as multi-constituent and gives a wide concentration range for the main component in each product. The REACH registrations list the mono-constituent material and then possible marketed multi-constituent products (that are covered by the registration of the mono-constituent material) and give more information on impurities. For this assessment, the information from the REACH registrations is more relevant as the latter should more accurately describe the forms marketed in the EU.

Dioctyltin compounds

Dioctyltin dichloride

Commercially supplied dioctyltin dichloride always contains octyltin trichloride. According to the REACH registration, the purity of the substance is 94.5 – 100 per cent. The registrations include a composition containing 96.04 per cent dioctyltin dichloride, 3.05 per cent octyltin trichloride, 0.68 per cent trioctyltin chloride and 0.23 per cent hexadecane, the latter three substances listed as impurities (JS Organotin Consortium REACH registration, 2010).


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According to the OECD assessment, the dioctyltin dichloride content of the commercially supplied products varied between 10 per cent by weight to 99 per cent by weight, however only the commercially supplied products with dioctyltin dichloride contents of 50 per cent or more are considered to be dioctyltin dichloride products (products containing less than 50 per cent of dioctyltin dichloride are considered to be octyltin trichloride products). In all products the sum of dioctyltin dichloride, octyltin trichloride and other minor impurities (trioctyltin chloride and tin tetrachloride) account for approximately 99.5 per cent of the manufactured product by weight.

According to both sources, the commercially supplied products do not contain chemical additives.

In summary, the composition of dioctyltin dichloride products in the EU is typically as follows:

94.5 – 100 per cent dioctyltin dichloride; (e.g. 96.04 per cent dioctyltin dichloride; 3.05 per cent octyltin trichloride; 0.68 per cent trioctyltin chloride; 0.23 per cent hexadecane).

Dioctyltin bis(2-ethylhexyl mercaptoacetate)

Dioctyltin bis(2-ethylhexyl mercaptoacetate) products always contain octyltin tris(2-ethylhexyl mercaptoacetate). According to the REACH registration, they are only marketed as multi-constituent products. Dioctyltin bis(2-ethylhexyl mercaptoacetate) is registered as a (not marketed) mono-constituent material described as having a purity of ≥ 80 percent. Two marketed products are included in the registration, containing

• 67 – 76 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 24 – 33 per cent octyltin tris(2-ethylhexyl mercaptoacetate), with impurities of 2.5 – 5.5 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one (CAS 15535-79-2), 0 – 2 per cent 2-ethylhexyl mercaptoacetate (CAS 7659-86-1) and 0 – 0.3 percent 2-ethylhexan-1-ol (CAS 104-76-7);

• 30 – 35 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 60 – 68 per cent octyltin tris(2-ethylhexyl mercaptoacetate), with impurities of 0 – 2 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate and 0 – 1 per cent 2-ethylhexan-1-ol (Organotin Consortium REACH registration, 2010).

In this assessment, the latter is considered to be an octyltin tris(2-ethylhexyl mercaptoacetate) product.

According to the OECD (2006a) assessment, the dioctyltin bis(2-ethylhexyl mercaptoacetate) content of commercial products typically ranges from 20 per cent to 95 per cent. Only the products with dioctyltin bis(2-ethylhexyl mercaptoacetate) contents of 50 per cent or more are considered to be dioctyltin bis(2-ethylhexyl mercaptoacetate) products (those with contents less than 50 per cent are considered octyltin tris(2-ethylhexyl mercaptoacetate) products). Other trace impurities that may be present in the commercial products include trioctyltin compounds (typically <0.2% calculated as tin), residual amounts of 2-ethylhexyl mercaptoacetate, mono- and di-octyltin mercaptoacetate chlorides, or alkyl isomers such as


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isooctyl or iso-hexadecyl groups bonded to tin (typically <0.5% calculated as tin (OECD, 2006a).

According to both sources, the commercially supplied products generally do not contain chemical additives.

In summary, the composition of dioctyltin bis(2-ethylhexyl mercaptoacetate) products in the EU is typically as follows:

67 – 76 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate); 24 – 33 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurities 2.5 – 5.5 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 0.3 percent 2-ethylhexan-1-ol.

Monooctyltin compounds

Octyltin tris(2-ethylhexyl mercaptoacetate)

Octyltin tris(2-ethylhexyl mercaptoacetate) products always contain dioctyltin bis(2-ethylhexyl mercaptoacetate), either as part of their composition or as an impurity; according to the REACH registration, they are marketed as mono- and multi-constituent products. The following compositions are included in the registration.

Marketed mono-constituent product:

• 99.7 – 100 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurities 0 – 0.3 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 0 – 1 per cent 2-ethylhexan-1-ol, 0 -1 per cent 2-ethylhexyl mercaptoacetate;

Marketed as multi-constituent products; composition covered by registration of individual constituents:

• 60 – 68 per cent octyltin tris(2-ethylhexyl mercaptoacetate), 30 – 35 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate); impurities 0 – 2 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 1 per cent 2-ethylhexan-1-ol.

• 24 – 33 per cent octyltin tris(2-ethylhexyl mercaptoacetate); 67 – 76 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate); impurities 2.5 – 5.5 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 0.3 per cent 2-ethylhexan-1-ol1.

No description, but listed in the registration:

• >97 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurity 1 - 3 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate).


1 In this assessment, this is considered a dioctyltin bis(2-ethylhexyl mercaptoacetate) product


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According to the OECD (2006b) assessment, the commercially supplied octyltin tris(2-ethylhexyl mercaptoacetate) products contain between 5 per cent and 80 per cent octyltin tris(2-ethylhexyl mercaptoacetate) with the remainder consisting of dioctyltin bis(2-ethylhexyl mercaptoacetate) and other minor impurities. However, only the products with octyltin tris(2-ethylhexyl mercaptoacetate) contents of 50 per cent or more are considered to be octyltin tris(2-ethylhexyl mercaptoacetate) products.

In summary, the composition of octyltin tris(2-ethylhexyl mercaptoacetate) products is typically as follows.

Marketed mono-constituent product: 99.7 – 100 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurities 0 – 0.3 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 0 – 1 per cent 2-ethylhexan-1-ol, 0 -1 per cent 2-ethylhexyl mercaptoacetate;

Marketed as multi-constituent products; composition covered by registration of individual constituents:

60 – 68 per cent octyltin tris(2-ethylhexyl mercaptoacetate), 30 – 35 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate); impurities 0 – 2 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 1 per cent 2-ethylhexan-1-ol.

Octyltin trichloride (supporting information)

Based on the above discussion (OECD, 2006b), the composition of octyltin trichloride products is typically as follows:

≥50 to ~90 per cent octyltin trichloride

~10 to <50 per cent dioctyltin dichloride

The REACH registrations for dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) both indicate that 2,2-dioctyl-1,3,2-oxathiastannolan-5-one (CAS 15535-79-2; EC number 239-581-2) is present in multi-constituent products as an impurity in the range 0 – 5.5%, depending on the product. This substance has the following structure:


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No information on this substance has been located.

1.3 Physico-chemical properties

The physico-chemical property data are summarised in Tables 1 - 3. The data are taken from the OECD assessments (OECD, 2006a and 2006b) unless otherwise indicated.

Table 1 Summary of relevant physico-chemical properties: Dioctyltin Dichloride

REACH ref Annex, §

Property Value Comments/ Klimisch code

V, 5.1 Physical state at 20°C and 101.3 kPa

White powder

White/off white solid block

OECD (2006a)

Harlan (2010)

V, 5.2 Melting / freezing point

45°C - 47°C

45.8°C

OECD (2006a) (4)

Harlan (2010) (2)

V, 5.3 Boiling point 175°C at 130 Pa

230°C (decomp.)

OECD (2006a) (4)

Harlan (2010) (2)

V, 5.5 Vapour pressure at 25°C

5.2×10-4 Pa OECD (2006a) (2)

V, 5.7 Water solubility at 20°C

0.24-0.28 mg/l

(data waiver submitted under REACH owing to hydrolytic instability)

OECD (2006a). Values estimated from water accommodated fraction (WAF) data (4)

V, 5.8 Partition coefficient n-octanol/water (Kow, log value) at 25°C

5.8

(data waiver submitted under REACH owing to hydrolytic instability)

OECD (2006a). QSAR estimated value (EPISUITE KOWWIN v1.67). It is not clear whether the substance falls within the model’s applicability domain (4)

VII, 5.19 Dissociation constant (pKa)

Not applicable.


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Table 2 Summary of relevant physico-chemical properties: Dioctyltin Bis(2-ethylhexyl mercaptoacetate)a

REACH ref Annex, §



Yellowish liquid

Clear, colourless to slightly yellow liquid

OECD (2006a)

NOTOX (2010)


-90 to -70°C

-39°C

OECD (2006a) (2)

Arkema (2007) (4)

V, 5.3 Boiling point ≥260°C (decomposition)

≥275°C (decomposition)

OECD (2006a) (2)

NOTOX (2010) (1)


≤2.50×10-4 Pa Baltussen (2010a) (2)


<0.1 mg/l

(data waiver submitted under REACH owing to hydrolytic instability)b

OECD (2006a). QSAR estimated value. (EPISUITE, WSKOW v1.41). It is not clear whether the substance falls within the model’s applicability domain (4)


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OECD (2006a). QSAR estimated value. (EPISUITE KOWWIN v1.67). It is not clear whether the substance falls within the model’s applicability domain (4)


Not applicable

Note: a) OECD (2006a) indicates that as dioctyltin bis(2-ethylhexyl mercaptoacetate) and dioctyltin bis(isooctyl mercaptoacetate) are isomers the physico-chemical data can be used interchangeably for these two substances.

b) See discussion under Table 3 below.


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Table 3 Summary of relevant physico-chemical properties: Octyltin Tris(2-ethylhexyl mercaptoacetate)a

REACH ref Annex, §



Colourless liquid OECD (2006b)


-80 to -70°C OECD (2006b) (2)

V, 5.3 Boiling point ≥250°C (decomposition) OECD (2006b) (2)


2.87×10-3 Pa

[4 Pa at 25°C]

Baltussen (2010b) (1)

[QSAR estimated value from OECD (2006b)] (4)


0.51-2.71 mg/l


OECD (2006b). Values estimated from water accommodated fraction (WAF) data (4)


14.4


OECD (2006b). QSAR estimated value. (EPISUITE KOWWIN v1.67). It is not clear whether the substance falls within the model’s applicability domain. (4)


Not relevant.

Note: a) OECD (2006b) indicates that as octyltin tris(2-ethylhexyl mercaptoacetate) and octyltin tris(isooctyl mercaptoacetate) are isomers the physico-chemical data can be used interchangeably for these two substances. The log Kow value for octyltin tris(isooctyl mercaptoacetate) is calculated to be 14.1.

b) See discussion below.

OECD (2006a and 2006b) notes that the determined water solubility of the substances (using a WAF method) may overestimate the actual solubility of the substance as there may be contributions from more water soluble impurities and the substance may decompose in water (analyses were generally based on total tin or were not species-specific in the case of mono- or dioctyl tin analysis).

Following the OECD assessments, a further attempt was made to investigate the vapour pressure, water solubility and octanol-water partition coefficient of dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate). It was reported for both substances that it was not technically feasible to carry out the water solubility or octanol-water partition coefficient studies owing to the instability of the substances in water and the lack of substance-specific analytical methods (Baltussen, 2010a and 2010b). However, no definitive information is available on the rate at which hydrolysis proceeds as a function of pH (see Section 4.1.1.2). This uncertainty is discussed further in relation to the bioconcentration study (section 4.3.2), in which test media preparation and exposure occurred in reasonably quick succession (unlike in the ecotoxicity studies; see section 7.1.1).

The results for the vapour pressure studies are briefly reported below.



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The test was carried out using the isothermal thermogravimetric effusion method based on the OECD TG 104 (Baltussen, 2010a). The method is valid for vapour pressures in the range 10-8 to 10-3 Pa. In brief, the method involved applying the substance to a roughened glass plate and measuring the weight loss of the substance as a function of time over a defined temperature programme. The data were then used to derive the evaporation rates (VT) at defined temperatures (T) of 150°C, 160°C and 170°C and the evaporation rate at 20°C was obtained by regression analysis of a plot of log VT against 1/T and the log VT value at 20°C was obtained by extrapolation of this curve to 20°C. The vapour pressure at 20°C was obtained by calibration of the method using standards of known vapour pressure. Three sets of measurements were carried out on the samples (two using a temperature programme starting at 30°C and one using a temperature programme starting at 100°C). The vapour pressure at 20°C estimated using the method was 1.30×10-4 Pa in the first experiment, 2.50×10-4 Pa in the second experiment and 1.18×10-5 Pa in the third experiment. Baltussen (2010a) commented that the significant differences between the individual measurements may result from reaction/degradation of the substance during the measurement. However, as the substance tested had a purity of 95.9%, another possible explanation for the variability seen that was not considered by Baltussen (2010a) may be that the presence of significant impurities could have affected the results in different ways under the different temperature programmes used (no information was given on possible impurities). Overall the results can be taken to show that the vapour pressure of the test substance is ≤2.5×10-4 Pa at 20°C.


The test with octyltin tis(2-ethylhexyl mercaptoacetate) was carried out using essentially the same isothermal thermogravimetric effusion method as above (Baltussen, 2010b). In this case the substance tested had a purity of 98% and two determinations of the log VT versus 1/T were carried out (at 140°C, 150°C and 160°C). In this case the agreement between the two determinations was very good, and the vapour pressure was determined to be 2.87×10-3 Pa at 20°C.

As supporting information, the key physico-chemical properties of octyltin trichloride are a vapour pressure of 0.5 Pa at 25°C, a water solubility of 0.33 mg/l and a log Kow of 2.1 (OECD, 2006b).

2 MANUFACTURE AND USES

Not relevant for this type of dossier.

3 CLASSIFICATION AND LABELLING

The following classifications are given in Annex VI to Regulation (EC) No 1272/2008. Self-classification by the REACH registrants is included.


18



Entry in Table 3.1 of Annex VI.

Acute Tox. 3 H331 Toxic if inhaled

STOT RE 1 H372 Causes damage to organs through prolonged or repeated exposure

Aquatic Chronic 3 H412 Harmful to aquatic life with long lasting effects


T; R23-48/25 Toxic by inhalation.

Toxic: danger of serious damage to health by prolonged exposure if swallowed.

R53* May cause long-term adverse effects in the aquatic environment.

* GHS Aquatic Chronic 3 classification is equivalent to R52/53. There is no indication why this disparity exists.

Self-classification in REACH registration (according to Regulations 67/548/EEC and (EC) No 1272/2008):

GHS DSD

Acute Tox. 2 H330

Skin sens 1B H317

Repr. Cat. 2 H361

STOT RE 1 H372

Aquatic Chronic 3 H412

R48/25-43-62-63

R53*

* GHS Aquatic Chronic 3 classification is equivalent to R52/53, while R53 is equivalent to Aquatic Chronic 4. There is no indication why this disparity exists.


No classification listed in Annex VI to Regulation (EC) No 1272/2008.

Self-classification in REACH registration (according to Regulations 67/548/EEC and (EC) No 1272/2008):

GHS DSD

Acute Tox. 4 H302

Skin sens 1B H317

R48/25 R43 R63; Xi: R38; Xn: R22; N: R50/53


19

Repr. Cat. 2 H361

STOT RE 1 H372

Aquatic Chronic 1 H410




Self-classification in REACH registration (according to Regulation (EC) No 1272/2008)*.

>99 per cent octyltin tris(2-ethylhexyl mercaptoacetate), <1 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate):

Aquatic Chronic 1 (M factor 10)

H410 Very toxic to aquatic life with long lasting effects

>90 per cent octyltin tris(2-ethylhexyl mercaptoacetate), 3 - 10 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate):

Repr. Cat 2 H361 Suspected of damaging fertility or the unborn child

STOT rep. exp. 2 H373 May cause damage to organs through prolonged or repeated exposure



>97 per cent octyltin tris(2-ethylhexyl mercaptoacetate), <3 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate):

STOT rep. exp. 2 H373 May cause damage to the thymus through prolonged or repeated exposure



>70 per cent octyltin tris(2-ethylhexyl mercaptoacetate), 10 – 30 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate):


STOT rep. exp. 1 H372 Causes damage to organs through prolonged or repeated exposure




20

<70 per cent octyltin tris(2-ethylhexyl mercaptoacetate), >30 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate):

Skin sens. 1 H317 May cause an allergic skin reaction.


STOT rep. exp. 1 H372 Causes damage to organs through prolonged or repeated exposure



Note: *Several self-classifications according to relative quantities of octyl- and dioctylstannane are presented in the registration.

Self-classification in REACH registration (according to Regulation 67/548/EEC):

>99 per cent octyltin tris(2-ethylhexyl mercaptoacetate):

DSD

Xi:R38

N: R50/53

Irritating to skin,

Dangerous for the environment; very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment



4 ENVIRONMENTAL FATE PROPERTIES

Most of the information for this section has been taken from the OECD assessments for the dioctyltin dichloride and selected esters category (OECD, 2006a) and the monooctyltin chloride and selected esters category (OECD, 2006b). This is supplemented by information reported in the earlier PBT Factsheets for the three substances produced under the Existing Substances Regulation (ECB, 2004a, 2004b and 2004c).

As these data sources have been agreed internationally or in the EU, only the key findings are reported. Where new data have become available since the OECD assessments were completed a more detailed description of the study has been included.

In order to facilitate the PBT and vPvB assessment the available data have been separated, as far as possible, into data for the dioctyl tin compounds and data for the monooctyl tin compounds. In addition, a further distinction is made between data obtained for the three


21

substances that are the subject of this evaluation and data for other similar substances that are used for read-across.

4.1 Degradation

4.1.1 Abiotic degradation

4.1.1.1 Atmospheric degradation

The reaction of the substances with atmospheric hydroxyl radicals has been reviewed in OECD (2006a) and OECD (2006b). The rate constant for reaction with hydroxyl radicals, and the estimated atmospheric half-lives were estimated using the AOPWIN v1.91 program. The results are summarised in Table 4. For all three substances the estimated atmospheric half-life is low (of the order of 4-7 hours). As for the other predictions, it is not clear if the substances were within the applicability domain of the model.

Table 4 Summary of atmospheric half-lives for dioctyltin and monooctyltin compounds (taken from OECD (2006a and 2006b))

Substance Hydroxyl radical rate constant (cm3 molecule-1 s-1)

Estimated atmospheric half-live (hours)


Dioctyltin dichloride 40×10-12 6.5


66×10-12 3.9

Monooctyltin compounds)


59×10-12 4.3


20×10-12 12.9

4.1.1.2 Hydrolysis

The hydrolysis of the substances has been considered in OECD (2006a) and OECD (2006b), and the main findings of these assessments are summarised below. Further details of the main study used in these assessments have been obtained; these are also discussed below.


OECD (2006a) concluded that both dioctyltin dichloride and dioctyltin bis(2-ethylhexyl mercaptoacetate) undergo rapid hydrolysis to form, in both cases, dioctyltin hydroxide/dioctyltin oxide. The hydrolysis of both substances was studied using electrospray ionization mass spectrometry (ESI/MS) and, in both cases, it was found that the hydrolysis reaction was rapid (occurring in 10 minutes or less; the exact conditions (pH, temperature, etc.) of these measurements are not stated in OECD (2006a)). Further details of this study are available and are given below.


22

The ESI/MS study was conducted to determine whether dioctyltin compounds in water behave like dibutyltin compounds and form oxides relatively quickly (Yoder, 2003). Dioctyltin oxide was also of interest to the study’s authors but no detectable amount could be dissolved in any solvent (however, no information is provided on the solvents that were used). The sensitivity of the method for detecting dioctyltin species was about 100 ng/ml (all concentrations quoted relative to tin). Two sample preparation methods were used: 1) test substances were first dissolved in acetonitrile and water was added (to give a ratio of 1:1 acteonitrile to water) immediately prior to analysis, or 2) test substances were dissolved in acetonitrile, which was subsequently removed under nitrogen, then water was added to the resulting powder; solutions were then shaken for 24 hours before analysis (these were called “water contact experiments”).

In the acetonitrile/water solutions, as analysis was conducted immediately after addition of water to test substance solutions in acetonitrile, the author concluded that the results should give some indication of the rapidity of hydrolysis (ion intensities were normalized relative to the highest intensity peak for tin in the initial analysis to indicate concentrations). For both substances, at lower sample concentrations (e.g. 125 ng/ml (as tin)), almost all of the parent compound was converted to the oxide in less than 10 minutes (analysis took about 10 minutes, and in that time the parent dioctyltin material had virtually disappeared). An apparent relationship was found between the relative quantities of the parent substance and the oxide hydrolysis product measured in solution, depending on the concentration at which the parent substance sample had been prepared; at 1000 ng/ml, the parent compound dominated but the oxide was apparent, whereas at 125 ng/ml the oxides became predominant. It was noted, however, that this may be an artefact of the relative solubilities of the substances in solution and that the oxide might have been at its saturation concentration; in an experiment in which the 1000 ng/ml loading was analysed against time, the tin parent concentration decreased eight-fold while the oxide ion intensities hardly changed. It must be borne in mind that all of the concentrations tested appear to be above the solubility limits of the dichloride and mercaptoacetate dioctyltins, so the interpretation can be taken further to suggest that the dissolution kinetics of the parent will be the limiting factor for the rate of hydrolysis in this study.

In the water contact experiments (sampled shaken with water for 24 hours prior to analysis) only the oxide was visible in the dioctyltin bis(2-ethylhexyl mercaptoacetate) spectrum, whereas both the oxide and the parent chloride were present in the dioctyltin dichloride spectrum. Given the duration over which the samples were shaken with water prior to analysis, the result with dioctyltin dichloride may seem surprising. The study report does not indicate the concentration at which the water contact samples were prepared, but it is possible that the test concentration was above water solubility so that dissolution kinetics would limit the rate of hydrolysis. The concentration of oxide in the water contact samples was estimated from the dioctyltin bis(2-ethylhexyl mercaptoacetate) and dioctyltin dichloride standards. The oxide concentration was estimated as 10 – 40 ng/ml for the dioctyltin bis(2-ethylhexyl mercaptoacetate) sample and 30 – 120 ng/ml for the dioctyltin dichloride sample.

Overall, it is not possible to conclude definitively on the hydrolysis rate of the dioctyl compounds from this study, although it does indicate that it is rapid (half lives of minutes to hours). This is important in the interpretation of the bioaccumulation test data for the 2-ethylhexyl mercaptoacetate substituted substance (see section 4.3.2).

The hydrolysis reaction of dioctyltin dichloride liberates hydrogen chloride. The reaction of dioctyltin bis(2-ethylhexyl mercaptoacetate) liberates the corresponding thioester group. For


23

dioctyltin dichloride it was found that reaction is an equilibrium, but reformation of the dioctyltin dichloride from the dioctyltin hydroxide/dioctyltin oxide would only be significant if an excess of chloride is present. Equation 1 below shows a possible pathway for hydrolysis, with postulated sequential nucleophilic substitution of labile ligands followed by rearrangement and loss of water to give the tin oxide from the hydroxide. Alternatively, the second ligand could leave through rearrangement without the nucleophilic attack of a second water molecule, depending on how good a leaving group R is (equation 2).

ppt) ( OSn(octyl) (OH)Sn(octyl) Sn(R)OH(octyl) SnR(octyl) 222222 OH-R-R- 2-- ↓= → →← →←

Eqn 1

ppt) ( OSn(octyl) Sn(R)OH(octyl) SnR(octyl) 2222RH-R-

- ↓= → →←

Eqn 2

where R = Cl or (2-ethylhexyl mercaptoacetate)*

*substitutions of 2-ethylhexyl mercaptoacetate ligand unlikely to be reversible

In the case of dioctyltin bis(2-ethylhexyl mercaptoacetate), the thioester group itself undergoes further hydrolysis to form thioglycolic acid and 2-ethylhexanol (hydrolysis of the ester linkage).

Based on the OECD (2006a) evaluation and information in the REACH registrations it can be concluded that in the environment, both dioctyltin dichloride and dioctyltin bis(2-ethylhexyl mercaptoacetate) will hydrolyse rapidly to the same tin species (dioctyltin hydroxide/dioctyltin oxide). The dioctyltin oxide formed is less soluble than either of the two parent substances and may precipitate out of solution. OECD (2006a) concluded that the octyl groups in these hydrolysis products would be reasonably stable to further hydrolysis.


OECD (2006b) notes that there are no experimental data available for octyltin tris(2-ethylhexyl mercaptoacetate) (nor for either of the two similar substances octyltin trichloride or octyltin tris(isooctyl thioglycolate)). However, using a read-across approach from the data for the above dioctyltin compounds and other similar dibutyltin compounds it was concluded that octyltin tris(2-ethylhexyl mercaptoacetate) would be expected to hydrolyse rapidly (within minutes to hours) in solution to form octyltin hydroxide which would eventually precipitate out of solution as the oxide.

Based on the OECD (2006b) evaluation and the information above it can be concluded that in the environment, octyltin tris(2-ethylhexyl mercaptoacetate) will hydrolyse rapidly to the corresponding octyltin hydroxide/octyl tin oxide species. OECD (2006b) concluded that the octyl group in these hydrolysis products would be reasonably stable to further hydrolysis.

Similarly for the supporting substance, octyltin trichloride, OECD (2006b) concluded that, although there are no specific studies with octytin trichloride, by read-across, rapid hydrolysis to the octyl tin hydroxide/oxide species would be expected in an equilibrium reaction. It was also concluded that reformation of the octyltin trichloride would not be significant in the absence of an excess of chloride.


24

New data

New studies have been considered to investigate the hydrolysis as a function of pH of dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate). However for both substances it was reported that it was not technically feasible to carry out such studies owing to the instability of the substances in water and the lack of specific analytical methods for the test substances (Baltussen, 2010a and 2010b).

Other work done in relation to the analytical method development for the bioconcentration tests (see Section 4.3.2) explored the stability of the derivatised and extracted diocyltin species (DOT) (Baltusssen, 2009b), which is relevant here when considering the stability of the tin – carbon bond in the parent substances and hydroxide/oxide hydrolysis products. As part of this study, the substance was dissolved in ISO-medium at a nominal concentration of 1 µg/l and the concentration of all dioctyltin species (DOT) in the medium was determined over 18 days (see Section 4.3.2 for further details of the analytical method). The concentration of DOT was found to decrease over time, declining to around 0.2 µg/l after 18 days. The decline in concentration was found to follow first order kinetics and the half-life was calculated to be 5.5 days. The temperature of the experiment was 15°C. The pH of the medium used was not given. The method used by Baltusssen (2009b) would have detected all DOT present, and does not give any information on any initial hydrolysis of the parent. Furthermore, the study does not necessarily indicate that the DOT (and by inference the hydroxide/oxide hydrolysis products) is unstable in ISO medium; adsorption or precipitation may have been occurring over time causing the observed decrease in concentrations. This interpretation is consistent with the conclusion of the OECD assessments (OECD 2006a and b) and the discussion above.

4.1.2 Biotic degradation

The available biodegradation data are summarised in OECD (2006a and 2006b) and are outlined below.


The results of biodegradation screening tests for dioctyltin dichloride and dioctyltin bis(2-ethylhexyl mercaptoacetate) are summarised in

Table 5.


25

Table 5 Summary of biodegradation screening tests for dioctyltin compounds (taken from OECD (2006a))

Method Result (% biodegradation)

Conclusion Comment/ Klimisch code


OECD TG 301F – Manometric Respirometry Test

0% after 28 days Not readily biodegradable

Purity of substance tested was 99.9%. Test concentration 27.3 mg/l. Study extended to 39 days (no biodegradation noted) (1)


Directive 92/69/EEC, C.4-D – Manometric Respirometry Test (test

29-43% after 28 days

Not readily biodegradable

Purity of substance tested was 99.4%. Test concentration 50 mg/l. Test prolonged to 74 days (40 – 50% biodegradation) (1)

Directive 84/449/EEC, C.5 – Modified Sturm Test

11-19% after 28 days


Purity of substance tested was 90%. (1)


23% after 28 days Not readily biodegradable

Purity of substance was 70%. (1)

Based on these test results it is concluded that both dioctyltin dichloride and dioctyltin bis(2-ethylhexyl mercaptoacetate) are not readily biodegradable. OECD (2006a) concluded that the degradation seen in the experiments with dioctyltin bis(2-ethylhexyl mercaptoacetate) probably results from the (partial) degradation of the 2-ethylhexyl mercaptoacetate ligands once they have been liberated from the tin by hydrolysis.


The results of biodegradation screening tests for octyltin tris(2-ethylhexyl mercaptoacetate) are summarised in Table 6.


26

Table 6 Summary of biodegradation screening tests for monooctyltin compounds (taken from OECD (2006b))

Method Result (% biodegradation)

Conclusion Comment/ Klimisch code


Directive 92/69/EEC, C.4-D – Manometric Respirometry Test

32-44% after 28 days (concentration 50mg/l)


Purity of substance was 99.63%. test extended to 39 days (50 – 60%) (1)


40% after 28 days (concentration 11.7 mg/l);

28% after 28 days (concentration 22.7 mg/l)


Purity of substance was 70% (30 % DOTC). (1)


OECD TG 301F – Manometric Respirometry Test

0.9% after 28 days


Purity of substance tested was 100%

Based on these results it can be concluded that neither octyltin tris(2-ethyl mercaptoacetate), nor the supporting substance octyltin trichloride is readily biodegradable.

The OECD (2006a and 2006b) evaluations also reported the results of a ready biodegradation test using 2-ethylhexyl mercaptoacetate itself. This was not readily biodegradable (15% degradation after 29 days in an OECD TG 301B study).

4.1.3 Summary and discussion of persistence

Based on the available information, the dioctyltin and monoctyl tin compounds considered are not readily biodegradable.

Degradation in the atmosphere is predicted to occur rapidly by reaction with hydroxyl radicals, with a half-life of the order of a few hours, although this is unlikely to be an important pathway given the substances’ low vapour pressure.

Hydrolysis of the substances is expected to occur rapidly in aquatic systems. The initial hydrolysis products formed are dependent on whether the substance is a dioctyltin substance or a monooctyltin substance as the octyl groups attached to the tin atom appear to be more resistant to hydrolysis than the other groups in the substances considered. Thus both dioctyltin dichloride and dioctyltin bis(2-ethylhexylmercaptoacetate) will form essentially the same hydrolysis product in the environment, dioctyltin hydroxide/oxide. Similarly both octyltin trichloride (supporting substance) and octyltin tris(2-ethylhexylmercaptoacetate) will form octyltin hydroxide/oxide.

As the hydrolysis reaction appears to be rapid (half-lives of a few minutes to hours) it can be expected that, on release to the environment, the substances considered will be rapidly converted to the corresponding dioctyltin hydroxide/oxide or octyltin hydroxide/oxide and so


27

it is the properties of these hydroxide/oxide products that are most relevant to the PBT assessment.

As such hydrolysis would also occur under the conditions of the ready biodegradation tests, the results of these tests will reflect the biodegradability of the dioctyltin hydroxide/oxide or octytin hydroxide/oxide and the released organic ligand. As none of the substances tested were readily biodegradable it can therefore be concluded that the dioctyltin hydroxide/oxide and octytin hydroxide/oxide are also not readily biodegradable and so potentially persistent.

The hydrolysis reaction of dioctyltin dichloride and the supporting substance octyltin trichloride is to some extent reversible. Although significant reformation of the dioctyltin dichloride or octytin trichloride from the dioctyltin hydroxide/oxide and octytin hydroxide/oxide would not be expected to occur in freshwater environments the same may not necessarily be true in marine environments where higher chloride concentrations are present. However there is no information available about whether or not the reverse reaction can occur under the pH conditions prevalent in the marine environment (i.e. pH around 7.5 - 8).

The hydrolysis of both dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptacetate) will result in the release of 2-ethylhexyl mercaptoacetate itself. This substance is not readily biodegradable but can undergo hydrolysis to form thioglycolic acid and 2-ethylhexanol.

4.2 Environmental distribution

4.2.1 Adsorption

The three substances under consideration all have high log Kow values (5.8-15) and so would be expected to adsorb strongly onto sediment and soil. The supporting substance, octyltin trichloride, has a much lower log Kow of 2.1 and so will adsorb less strongly to sediment and soil than the other three substances.

Given that an important degradation mechanism for these substances appears to be hydrolysis, adsorption may be a very important property in determining the overall fate in the environment. For example, if adsorption to suspended material is significant, then this may result in a longer overall environmental half-life in sediment (or the aquatic compartment) than may be suggested based on rapid hydrolysis alone. However, there are no data available to demonstrate that this may be the case.

No information on the adsorption of the hydrolysis products octyl or dioctyl tin hydroxide/oxide was located. The study summarized in section 4.1.1.2 by Baltusssen (2009b) does suggest that dioctyltin oxide would be adsorptive, which is also indicated by its predicted log Kow value (9.26).

4.2.2 Distribution modelling

Distribution modelling using a Level III fugacity model has been carried out for the three substances as part of the OECD (2006a) and (2006b) evaluations. The results of this modelling indicate that the three substances are predicted to partition primarily to sediment


28

(45%-74%) and soil (22%-38%). For the supporting substance, octyltin trichloride, the modelling indicated that this substance would partition primarily to water (69%), soil (20%) and air (11%) rather than sediment, presumably owing to the lower log Kow value for this substance. However, the relevance of this modelling is questionable given the hydrolytic instability of the substances and the lack of information on adsorption, as stated above.

4.2.3 Other information

No other relevant information.

4.2.4 Summary of environmental distribution

The available information suggests that the substances dioctyltin dichloride, dioctyltin bis(2-ethylhexylmercaptoacetate) and octyltin tris(2-ethylhexylmercaptoacetate) will partition preferentially to the soil and sediment compartments. The effect of adsorption to sediment on the hydrolysis of the substances in the environment is not known.

The environmental distribution behaviour of the supporting substance octyltin trichloride is different to the above three substances, with the substance predicted to partition primarily to the water, soil and air compartments.

4.3 Bioaccumulation

4.3.1 Screening data

The log Kow values for the three substances are as follows (see Section 1.3):


Dioctyltin dichloride Log Kow = 5.8

Dioctyltin bis(2-ethylhexyl mercaptoacetate) Log Kow = 15


Octyltin tris(2-ethylhexyl mercaptoacetate) Log Kow = 14.4

Octyltin trichloride (supporting substance) Log Kow = 2.1

All log Kow values are estimated values and so are uncertain. Based on these, dioctyltin dichloride, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) would meet the screening criteria for bioaccumulative (B) and very bioaccumulative (vB). However the predicted log Kow for the supporting substance octyltin trichloride is below the screening criteria cut-off of 4.5 for B or vB.

The estimated log Kow value for dioctyltin oxide is 9.26 (KOWWIN v1.67). For dioctyltin dihydroxide the estimate is 6.00, and for a potential hydrolysis product of octyltin tris(2-ethylhexyl mercaptoacetate) (the octyltin hydroxy oxide) the estimated log Kow is 2.16. As


29

for the parent substances, these values are also uncertain but the first two estimates suggest the dioctyl hydrolysis products meet the screening criteria.

In addition to these log Kow values, OECD (2006a) and OECD (2006b) contain estimates for fish bioconcentration factors (BCFs) obtained using the USEPA BCFWIN software. These estimates are summarised below.


Dioctyltin dichloride BCF = 630

Dioctyltin bis(2-ethylhexyl mercaptoacetate) BCF = 100


30


Octyltin tris(2-ethylhexyl mercaptoacetate) BCF = 100

Octyltin trichloride (supporting substance) BCF = 8.9

Based on these data, OECD (2006a and 2006b) concluded that although dioctyltin dichloride, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) have high log Kow values, the substances would be expected to have only a low potential for bioaccumulation. Again, the log Kow values used to estimate these BCFs are predicted using a model which may not be validated for these types of substance.

OECD (2006a and 2006b) also estimated the fish bioconcentration factors for 2-ethylhexyl mercaptoacetate (which is likely to be released on hydrolysis of both dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate). The log BCF was estimated to be 0.8 (i.e. BCF = 6.3).

4.3.2 Measured bioaccumulation data

No measured bioaccumulation data are reported in OECD (2006a and 2006b) for any of the dioctyltin and monooctyl tin compounds considered. Since the OECD evaluations were completed, further experimental data on bioconcentration have become available. These are summarised below.



Preliminary Study

A preliminary bioconcentration study was conducted with a 14C-radiolabelled test substance in rainbow trout (Oncorhynchus mykiss), originally to investigate the duration of the uptake phase required in the definitive test (Bogers, 2006). The report for the study indicates that the 14C radiolabel was present at the 1-position in one of the octyl chains in the test substance. Information on radiopurity and other substance information is not available. Two test concentrations were run with nominal concentrations of 1 µg/l and 10 µg/l in a flow-through system, with the radiolabelled test substance present at a concentration of 0.2 µg/l in both tested substances (the radiolabelled material was mixed with “cold” test substance). The uptake phase lasted for 5 days and the depuration phase for 10 days. Liquid Scintillation Counting was used to analyse the amount of radioactivity associated with the water and fish tissue during the uptake phase and depuration phase. Exposure concentrations varied by less than 20% of nominal values. Four analyses for radioactivity during the exposure period indicated that the radiolabelled substance was steadily taken up by the fish in both test groups, achieving concentrations of about 0.16 µg/g whole fish wet weight and 0.44 µg/g whole fish wet weight in the 1 µg/l and 10 µg/l treatments, respectively, at the end of 5 days’ uptake. Information from the laboratory indicates that whole fish were sampled, without removal of skin. Steady state was not reached in either group. Concentrations appeared still to be increasing exponentially after 5 days. The report includes plots of (concentration ratio based) BCF for both test concentrations; the highest value is for the low dose group at the end of exposure, where a BCF of about 170 was reached. The results indicated that the higher dose concentration exceeded the water solubility of the test substance (based on relative


31

uptake of the substance into fish tissue). During the 10 day depuration phase fish tissue concentrations in the low dose test group hardly decreased, and decreased from about 0.44 to 0.29 µg/g whole fish wet weight in the high dose group (two measurements were taken in each group, at the start and end of depuration). Neither a steady state nor a kinetic BCF can be derived from these results with any degree of certainty. Further details on the study are not available. The results showed that a definitive study needed to be conducted, which is described below.

Definitive Study

A definitive bioconcentration test has been carried out for dioctyltin bis(2-ethylhexyl mercaptoacetate) with rainbow trout (Oncorhynchus mykiss) (Bouwman, 2010d). Owing to problems with the radiolabelled test substance2 and the realization of an analytical technique for the “cold” test substance, the study was run using the “cold” substance (purity 97.5%). No information is available on impurities present in the test substance. The methodology used was OECD TG 305 and details of the test are as follows.

The fish used in the test had an initial mean weight of 1.74 g. The test was carried out using a flow-though system with a flow-rate of 10 l/hour (giving approximately 4 volume replacements in each tank per day). Stock solutions of the test substance were prepared in acetone (two concentrations were prepared, 2.5 and 25 mg/l) and these were dosed into the dilution water in the mixing chamber at a dilution of 1:10,000 in order to give nominal test concentrations of 0.25 µg/l and 2.5 µg/l in the tank. At this dilution, the concentration of acetone in the tank would be 0.1 ml/l. A control was run containing acetone alone at this concentration. The dilution water used had a mean pH of 7.6 (range 7.4-7.8) and a hardness of 180 mg/l as CaCO3. The mean temperature during the test was 14 °C (range 13.0 to 15.3 °C) and the dissolved oxygen concentration ranged from 8.5 mg/l to 9.8 mg/l.

The flow-through system was operated for 12 days prior to the start of the test in order for the concentration of the test substance to stabilise. After this time the fish were added to the tanks (maximum fish loading 0.42 g fish/l per day) and the uptake of the substance was monitored at various time points for up to 30 days. The fish were fed pelleted fish food at a rate of 2% of body weight per day during the uptake. Fish (one replicate for the control and two replicates for each treatment group, each replicate consisting of 2 fish) were sampled on days 1, 3, 7, 14, 21, 28 and 30 of the uptake. Water samples (one sample per control and each treatment group) were sampled on days -1, 0, 1, 3, 7, 14, 21, 28 and 30 of the uptake phase.

Mortalities or other adverse effects were <10% in the control group and the two treatment groups. The mean measured exposure concentrations (±standard deviation) were 0.19±0.05 µg/l and 2.6±0.4 µg/l in the two treatment groups. The variation of the water concentration over the course of experiment was within 20% of the mean concentration for the higher concentration but the variation was slightly higher at the lower concentration owing to the low concentrations measured (close to the detection limit of the analytical method used). A more detailed discussion of the measured concentrations and analytical method used is given below.

Analysis of the fish revealed that the concentrations of the test substance were below the limit of quantification in all samples (<0.25 mg/kg). Assuming that the limit of quantification

2 Analysis of the radiolabel showed that its purity was very low; however it was not clear if this was the same substance as used in the preliminary BCF test, and this analysis appeared to have been carried out a number of years after the preliminary BCF study.


32

represents the maximum concentration of the substance in fish, the equivalent BCF factor can be estimated as <1,300 l/kg for the group exposed to a concentration of 0.19 µg/l and <100 for the group exposed to 2.6 µg/l. As no detectable concentrations of the test substance were evident in the fish at day 30 it was decided that no depuration phase was needed in this study.

Given that these BCF values are based on the limit of quantification in fish and that no test substance was measured in the fish at either test concentration these data suggest that the BCF for the test substance is <<2000.

In order to provide more evidence that the BCF is relatively low, Bouwman (2010d) also analysed the fish from day 30 for the presence of total tin. The concentration of total tin present in the fish was found to be 0.027 mg Sn/kg for the 0.19 µg/l exposure group and 0.054 mg Sn/kg for the 0.26 µg/l treatment group. In order to calculate the BCF, Bouwman (2010d) corrected the measured water concentrations to take account of the percentage tin, giving corrected water concentrations of 0.15 µg Sn/l and 0.92 µg Sn/l. Using these concentrations the BCF based on total tin were 178 at the lower treatment group and 58 at the higher treatment group. These analytical data, in particular the correction applied to the water concentrations, are considered further below.

The lipid contents of the fish used in the test was reported to be around 4% at the start of the test and reached around 6% at the end of the test3. Thus the lipid content of the fish were close to the default lipid content of 5% recommended in the REACH Guidance Document and so normalization to 5% is not considered necessary in this case.

Interpretation of the data

A key factor in interpreting the results of the definitive test is the analytical method used and so this is considered in detail. Firstly, it is important to note that there is no substance-specific method available that can currently analyse dioctyltin bis(2-ethylhexyl mercaptoacetate) with sufficient sensitivity and so an indirect method has to be used. The method was designed to detect both monooctyltin compounds and dioctyltin compounds. The method used for water and fish is similar and is summarised in a number of reports (Appendix VI of Bouwman (2010d) and Baltussen (2009a, 2009b and 2009c). The method involves simultaneous derivatization and extraction of monooctyltin and dioctyltin compounds using sodium tetraethyl borate solution and subsequent analysis of the diethyl derivative using gas chromatography mass spectrometry (GCMS). Monoheptyltin trichloride and/or diheptyltin dichloride were used as internal standards and octyltin trichloride was used as an analytical standard. The method will detect all monooctyltin (the term MOT will be used here) and dioctyltin (DOT) compounds present in the samples (provided these undergo the derivitisation step) and so does not, in this case, distinguish between dioctyltin bis(2-ethylhexyl mercaptoacetate) itself or any degradation products or impurities that contain the dioctyltin group.

Using this method the following limits of quantification were determined for MOT and DOT for water and fish.

3 The lipid contents are given in Appendix 1 of the test report (Bouwman, 2010d). Here the lipid content of the fish at day 30 in the control and two treatment groups are all given as 6%. However the weight data for the two treatment groups appears to suggest that the lipid contents were closer to 4.4% for these two groups (for example for the 0.25 µg/l (nominal) group the lipid weight is given as 0.58 g for a sample weight of 13.09 g (i.e. 4.4% lipid) and for the 2.5 µg/l (nominal) group the lipid weight is given as 0.58 g for a sample weight of 13.25 g (i.e. 4.4% lipid).


33

Limit of quantification MOT DOT

Water 0.25 µg/l 0.25 µg/l Fish 0.25 mg/kg 0.25 mg/kg

For the water analysis the mean recoveries from procedural recovery samples were generally between 86% and 105% for DOT and 78%-139% for MOT, except on one day when very low recoveries were evident for both DOT and MOT (recovery 1.8-6.3%; the results on this day were considered inaccurate) and one further day for MOT (recovery 44%).

The measured concentrations of MOT in the test water samples were generally below the limit of quantification in both exposure groups (MOT was occasionally detected at concentrations close to the limit of quantification in samples from the high treatment group). DOT was detectable in all water samples from both treatment groups. The mean level of DOT measured in the water samples was 0.19 µg/l in the low exposure group and 2.6 µg/l in the high exposure group. These concentrations are used above in the estimation of the BCF from the experiment. The concentration measured in the low exposure group is close to, but just below, the limit of quantification and this may explain the higher variability in the measured concentration in this treatment group compared with the higher exposure group.

For the fish samples, the mean recoveries from procedural recovery samples were between 87% and 134% for MOT and 88% and 119% for DOT. The concentration of both MOT and DOT was below the limit of quantification in all of the fish samples from the treatment groups in the study.

Overall the analytical methodology used appears to be robust for MOT and DOT. The method should detect any mono- or dioctyltin substances (including dioctyltin bis(ethylhexyl mercaptoacetate) and any transformation products containing the dioctyltin group) but will represent the sum of mono- or dioctyltin substances rather identifying specific mono- or dioctyltin substances. Furthermore, the inherent difficulties in analyzing for these types of substances means that the limit of quantification in fish was high at 0.25 mg/kg in comparison to that in water and this was not sufficiently sensitive to allow determination of the actual concentration present in the fish (both MOT and DOT were below the limit of quantification). However the detection limit for water was sufficiently low (0.25 µg/l) to allow analytical verification of the exposure concentrations for DOT. When these exposure concentrations for DOT are considered in relation to the limit of quantification for fish, it appears that the BCF would be <1,300 for the low exposure group and <100 for the high exposure group.

The method used for analyzing total tin concentrations in the fish is outlined in Baltussen (2009d) and Appendix VI of Bouwman (2010d). The method essentially involved digestion of a sample of fish using nitric and hydrochloric acid in a microwave and analysing the concentration of tin present using inductively coupled plasma mass spectrometry (ICPMS). The limit of quantification of the method was 0.025 mg/kg and the mean recoveries from procedural recovery samples were in the range 98% to 104%. The total tin concentration in the exposed fish samples on day 30 were 0.027 mg Sn/kg for the low exposure group and 0.054 mg Sn/kg for the high exposure group. As this method is not specific for any given organotin compound these values will represent the total tin concentration for all tin-containing substances present in the samples.


34

No total tin analysis was carried out on the water concentration and so the measured concentrations of DOT and MOT were converted to the equivalent level of tin. When carrying out this conversion, Bouwman (2010d) assumed that the percentage tin in DOT was 29.5% and the percentage tin in MOT was 37%, by mass. The total tin concentration in water was then estimated from the measured concentration of DOT and MOT by applying these percentages; the total tin concentration was the sum of tin from these two sources. In the case of MOT, as it was not quantifiable in water, the limit of quantification was used in the calculation. This led to total tin concentration of 0.15 µg/l at the low exposure concentration and 0.92 µg/l at the high exposure concentration. This correction as applied in Bouwman (2010d) can be questioned in two respects.

1. The use of the limit of quantification for MOT may result in an overestimate of the total tin concentration in water (and hence an underestimate of the resulting BCF). This is particularly relevant at the lower test concentration where the concentration of DOT is itself close to the limit of quantification. It may be more appropriate to ignore here any contribution from MOT (particularly as the dioctyl tin substance tested had a purity of ~97.5%).

2. Although the analytical method measures DOT and MOT in water, the method is calibrated such that if the test substance does not degrade in the test the concentration of the substance itself will be the same as indicated for DOT. Therefore, it may be more relevant to use the percentage tin in dioctyltin bis(2-ethylhexyl mercaptoacetate) than the percentage tin in DOT. The percentage tin in dioctyltin bis(2-ethylhexyl mercaptoacetate) is 15.8%, by mass.

Taking into account these two factors, the revised total tin concentrations in test media can be estimated to be around 0.030 µg Sn/l at the low exposure concentration and 0.41 µg Sn/l at the high exposure concentration, compared to the concentrations of 0.15 µg/l and 0.92 µg/l as derived by Bouman (2010d). Comparing these concentrations with the measured total tin concentration in the fish (0.027 mg Sn/kg and 0.054 mg Sn/kg respectively) would lead to revised estimates for the BCFs based on total tin of around 900 l/kg at the low exposure concentration and 130 l/kg at the high exposure concentration. Again it should be stressed that these values represent the total tin concentration in the fish from all sources (i.e. including any transformation products) and not just exposure to parent dioctyltin bis(2-ethylhexyl mercaptoacetate).

One final factor to consider with this study is that, as no time trend data on the actual concentration of the substance in the fish are available (i.e. for analysis of total tin), it is not possible to ascertain whether or not steady state was reached during the test.

A key consideration for this study is that the analytical method used, based on MOT and DOT, would determine all monooctyltin and dioctyltin substances present in solution and the fish (i.e. the parent substance and hydrolysis products). Therefore the rate at which the parent substance hydrolyses in the test system is very important, given the method used to prepare exposure solutions. If hydrolysis was much slower than might be expected for the substance (see section 4.1.1.2), then the study results will be relevant for the parent substance but give little information on the hydrolysis product dioctyltin oxide. Conversely, if hydrolysis in the test system was very rapid, then the uptake seen would represent, at least in part, that of the hydrolysis products rather than the parent compound. If the latter situation predominated, then the basis for this category assessment holds and a conclusion for bioaccumulation potential of the substance based on the hydrolysis products is reasonably straightforward.


35

However if this is not the case (and hydrolysis did not predominate), then it is difficult to use this study to conclude on the bioaccumulation potential of the common hydrolysis product(s).

Overall, although the results of this study do not lead to the determination of a definitive value for the BCF of dioctyltin bis(2-ethylhexyl mercaptoacetate) or its hydrolysis products, they nevertheless provide strong evidence that the BCF is well below the 2,000 l/kg cut-off for a bioaccumulative substance in relation to the Annex XIII criteria. The available data suggest that the BCF is perhaps around 1,000 l/kg as a maximum.


No new data are available. Although the above study does include the analysis of MOT, as MOT was not detectable in either the water phase or the fish nothing can be inferred from the study as to the actual accumulation potential of MOT. The DOT study may be acceptable for read across to MOT for the reasons given in the introduction to this document and section 1.1. The REACH registration of octyltin tris(2-ethylhexyl mercaptoacetate) includes the DOT study.

4.3.3 Other supporting information

Although full details have not been seen for this evaluation, the PBT factsheets produced under the Existing Substances Regulation for dioctyltin dichloride (ECB, 2004a) and dioctyltin bis(2-ethylhexyl mercaptoacetate) (ECB, 2004b) refer to a BCF test carried out on dioctyltin maleate (CAS 16091-18-2, EC 240-253-6) (a more soluble substance than the dioctyl tins assessed here) which showed a low BCF. This would support the limited bioconcentration seen in the new study with dioctyltin bis(2-ethylhexyl mercaptoacetate) reported in Section 4.3.2.

The hydrolysis product dioctyltin hydroxide is predicted to have a reasonably high log Koa (10.3; KOAWIN v1.10) based on a predicted Henry’s Law constant of 1.27 10-6 atm.m3/mol (HenryWin bond estimate) and log Kow of 6 (KOWWIN v1.67), which means there may be the potential for it to bioaccumulate in air breathing organisms. The available human health toxicokinetic and repeated dose toxicity dataset in the REACH registrations do not allow an assessment of this; no organ-specific analysis seems to have been conducted for dioctyltin dichloride or dioctyltin bis(2-ethylhexyl mercaptoacetate). The key repeated dose toxicity study for dioctyltin dichloride (read across to the mercaptoacetate) shows weight effects on the thymus.

4.3.4 Summary and discussion of bioaccumulation

Experimental fish bioconcentration data are available only for dioctyltin bis(2-ethylhexyl mercaptoacetate). Carrying out a fish bioconcentration test for these substances is technically challenging owing to the rapid hydrolysis of the substance and the lack of analytical methodology to allow determination of the individual substances present. On first inspection there is an apparent disparity between the results of the preliminary bioconcentration study and the definitive study, in that uptake was noted in the former. The concentrations measured in the preliminary study after 5 days’ uptake (based on radioanalysis) were around the detection limit possible in the definitive study for DOT or MOT (about 0.16 and 0.44 µg/g


36

against a LOQ of 0.25 µg/g). The author of the preliminary study stated that if the increase in concentration was extrapolated to 30 days for the low dose preliminary study (based on the curve of the uptake), the BCF would have been about 1000 (this assumes first order uptake kinetics based on four uptake data points). This is not out of line with the results of the definitive study considering the lower exposure concentrations (0.19 and 0.26 µg/l as opposed to about 1 and 10 µg/l) and the fact that measurements of total tin at the end of exposure in the definitive study showed the presence of tin (at concentrations of 0.027 and 0.054 µg/g for the low and high doses, respectively). However, it is difficult to take interpretation of the preliminary study further given the sparse details available on the test substance, and the fact that measurement of radioactivity is even less-substance specific than the analytical technique used in the definitive study.

Nevertheless the available definitive study can be taken to show that accumulation from water of the tin-species, in whatever form it was present (if rapid hydrolysis occurred in the test it is likely to be as the hydrolysis products dioctyltin hydroxide/oxide), results in a BCF that is perhaps around 1,000 l/kg as a maximum.

The main uncertainty in this evaluation stems from the fact that the actual individual substances present in solution are not known (only the total tin or total mono- and dioctyltin compounds were determined), and that definitive hydrolysis data are not available. If the uptake seen resulted from exposure of a minor component in water (for example if the accumulative component made up only a small fraction of the total mono- or dioctyltin compounds present) as, in this case, the actual BCF for the individual substance may be higher than that determined based on the total tin, total mono- or total dioctyltin compounds. If hydrolysis was actually much slower than expected (see section 4.1.1.2), then conclusions about the bioaccumulation potential of the hydrolysis products would be difficult to draw from this study. The analytical difficulties mean that it is not technically possible to investigate further whether or not either of these situations is the case.

The measured accumulation in the fish bioconcentration study is consistent with the findings of the OECD (2006a and 2006b) evaluations, which concluded that the bioaccumulation potential of these substances was low. However the OECD (2006a and 2006b) bioaccumulation evaluation was based on QSAR estimates, and did warn that the methods used for estimation the BCF had not been validated for chemicals containing metals in their molecular structure so that the estimated BCFs should be used with caution.

The available test does not provide any information on the accumulation of the monooctyltin compounds as the concentration of these species in both the water and fish were below detectable concentrations. Based on read-across from the dioctyltin compounds it can be expected that the bioaccumulation potential of the octyltin hydroxide/oxide hydrolysis products would be similar to or possibly lower than (based on their lower lipophilicity), that of the dioctyltin hydroxide/oxide. However this read-across is another source of uncertainty in the overall evaluation.

The available information suggests that 2-ethylhexyl mercaptoacetate released from hydrolysis of dioctyltin bis(2-ethylhexyl mercaptoacetate) or octyltin tris(2-ethylhexyl mercaptoacetate) will have a low potential for bioaccumulation.

Overall, the available fish bioconcentration results are strongly suggestive that the BCF of the dioctyltin substances is perhaps around 1,000 l/kg as a maximum but more probably much lower than this (around 100 l/kg or less).


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4.4 Secondary poisoning

Not relevant for this dossier.


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5 HUMAN HEALTH HAZARD ASSESSMENT

Of the substances considered only dioctyltin dichloride is currently included in Annex VI to Regulation (EC) No 1272/2008 and classified for human health effects. The current classification for this substance is as follows.


Acute Tox. 3 H331 Toxic if inhaled.

STOT RE 1 H372 Causes damage to organs through prolonged or repeated exposure.


T; R23-48/25 Toxic by inhalation.

Toxic: danger of serious damage to health by prolonged exposure if swallowed.

Based on the classification of R48, dioctlytin dichloride would meet the Annex XIII criteria for T.

According to the REACH registrants, dioctyltin bis((2-ethylhexyl mercaptoacetate) products are self-classified as STOT re 1 (H372) and multi-constituent octyltin tris(2-ethylhexyl mercaptoacetate) products that contain 10 per cent or more dioctyltin bis((2-ethylhexyl mercaptoacetate) are self-classified STOT re 1 (H372), equivalent to R48 under the old system.

The toxicity of the dioctyltin compounds is reviewed in detail in OECD (2006a). A category approach was used whereby read-across from oral data for dioctyltin dichloride to dioctyltin bis(2-ethylhexyl mercaptoacetate) was justified on the basis of rapid conversion of the thioesters to dioctytin dichloride under the physiological conditions present in mammalian gastric contents (0.07 M HCl). Therefore on this basis, as the R48 classification for dioctyltin dichloride is relevant to oral exposure, it can be assumed that dioctyl tin bis(2-ethylhexyl mercaptoacetate) would also meet the Annex XIII criteria for toxic (T). On a similar basis (i.e. that under the conditions prevalent in gastric contents chlorination can occur to form dioctyltin dichloride) it can also be assumed that the hydrolysis product dioctyltin hydroxide/oxide would also meet the Annex XIII criteria for T.

The toxicity of monooctyltin compounds is reviewed in detail in OECD (2006b). Using similar arguments as above, the OECD (2006b) review concluded that the oral toxicity data for octyltin trichloride was an appropriate surrogate for octyltin tris(2-ethylhexyl mercaptoacetate) (and by extension for dioctyltin hydroxide/oxide). OECD (2006b) concluded that the NOAEL from the key 90-day oral study with octytin trichloride was approximately 7 mg/kg bw/day with another 90-day oral study giving a LOAEL of 1.4-4.8 mg/kg bw/day based on decreased thymus weights.


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No classifications for mammalian toxicity for the monooctyltin compounds considered are reported in Annex VI to Regulation (EC) No 1272/2008. The REACH registration of octyltin tris(2-ethylhexyl mercaptoacetate) includes a proposal for self-classification of the substance both as a mono-constituent product and a multi-constituent product (where the substance is present with dioctyltin bis(2-ethylhexyl mercaptoacetate); see section 3). For multi-constituent products with 10 per cent or greater of the dioctyl, STOT rep. exp. 1 (H372) is proposed.

6 HUMAN HEALTH HAZARD ASSESSMENT OF PHYSICOCHEMICAL PROPERTIES


7 ENVIRONMENTAL HAZARD ASSESSMENT

7.1 Aquatic compartment (including sediment)

7.1.1 Toxicity test results

7.1.2 Fish

The available toxicity data to fish for the dioctyltin and monoctyltin compounds considered have been reviewed in OECD (2006a and 2006b) and these data are summarised in Table 7 (dioctyltin compounds) and Table 8 (monooctyltin compounds).

Table 7 Summary of fish toxicity test for dioctyltin compounds (taken from OECD (2006a) unless otherwise indicated)

Species Test substance purity

Duration Result Comment/ Klimisch code


Brachydanio rerio 99.91% 96 h LC50 >0.24 mg/l

NOEC ≥0.24 mg/l

Semi-static test using dilutions of a WAF. Analysis as DOT. (2)


Brachydanio rerio 87.2% 96 h LC50 >25 mg/l

NOEC ≥25 mg/l

Semi-static test using dilutions of a WAF. Analysis as total Sn. (2)

Brachydanio rerio 70% 96 h LC50 >20 mg/l

NOEC ≥20 mg/l

Static test using a co-solvent/emulsifier. Analysis as DOT. (2)


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Table 8 Summary of fish toxicity test for monooctyltin compounds (taken from OECD (2006b) unless otherwise indicated)





NOEC ≥2.3 mg/l


Brachydanio rerio 70% 48 h LC50 = 2.3 mg/l

NOEC = 0.36 mg/l

Static test. Analysis as MOT. (2)

Cyrpinus carpio 98% 95 h LC50 >0.95 mg/l

NOEC ≥0.95 mg/l

Static test using dilutions of a WAF. Analysis as MOT. Bouwan (2010a). See below for details. (2)



NOEC ≥0.33 mg/l

Static test using dilutions of a WAF. Analysis as Total Organic Carbon.

In summary, acute effects in fish were observed in one test with octyltin tris(2-ethylhexyl mercaptoacetate) only. Since the OECD (2006a and 2006b) evaluations were completed a further acute toxicity study has become available. The results are summarised below.


A 96-hour toxicity test has been carried out using octyltin tris(2-ethylhexyl mercaptoacetate) with carp (Cyrpinus carpio) (Bouwman, 2010a). The method used was a static procedure following OECD TG 203. The substance tested had a purity of 98%. The test was carried out using dilutions of a water accommodated fraction (WAF) obtained from a 100 mg/l loading. The WAF was prepared by stirring the test substance with the test medium for one day followed by a one day stabilisation period. The WAF was filtered through glass wool prior to use. The WAF dilutions used were 1.0, 10 and 100%. The 100% WAF solution was reported to be “slightly hazy” indicating that undissolved test material (or hydrolysis products) was present. The non-specific concentration of octyltin tris(2-ethylhexyl mercaptoacetate) present in the 100% WAF solution was determined as total monooctyltin compounds (MOT) using the method discussed in 4.3.2. Two determinations revealed the initial concentration to be 1,805 µg/l and 849 µg/l; the variability in the values was thought to reflect the fact that not all of the substance (or its hydrolysis products) was dissolved. The concentration in the 100% WAF solution determined at 24 hours was 466-511 µg/l and the concentration determined at 96 hours was 997-1,044 µg/l. A precipitate was observed to be formed with time in the 100% WAF solution. The mean concentration measured over the entire 96-hour exposure period was determined to be 945 µg/l.

The water used in the test was ISO medium and had a pH of 7.5—7.7 and a hardness of 180 mg/l as CaCO3. The dissolved oxygen concentration was in the range 5.5 mg/l to 9.1 mg/l and the temperature was 21°C over the duration of the test.

No mortalities or visible effects were evident in any of the exposed carp when compared with the control carp. Although there is some uncertainty over whether or not all of the test


41

substance was dissolved in the 100% WAF solution, the results can be taken to show that no adverse effects occurred over 96 hours at the solubility limit of the test substance.

7.1.3 Aquatic invertebrates

The available toxicity data to aquatic invertebrates for the dioctyltin and monoctyltin compounds considered have been reviewed in OECD (2006a and 2006b) and these data are summarised in Table 9 (dioctyltin compounds) and Table 10 (monooctyltin compounds).

Table 9 Summary of invertebrate toxicity test for dioctyltin compounds (taken from OECD (2006a) unless otherwise indicated)




Daphnia magna 99.9% 48 h EC50 >0.28 mg/l

NOEC ≥0.28 mg/l

Semi-static test using dilutions of a WAF. Analysis as DOT. (Key study in REACH registration) (2)


NOEC ≥0.005 mg/l


Daphnia magna 99.8% 21 d EC50 >0.87 mg/l

LOEC = 0.87 mg/l

NOEC = 0.41 mg/l (parental survival)

Semi-static using co-solvent/emulsifier. Analysis as DOT. (2)


Daphnia magna 95% 48 h EC50 = 0.17 mg/l

NOEC = 0.07 mg/l

Static using co-solvent/emulsifier. Analysis as DOT. (2)

Daphnia magna No data 24 h EC50 > 0.06 mg/l

NOEC ≥0.06 mg/l

Static test using dilutions of a WAF. Analysis as total Sn. (2)

Daphnia magna 87.2% 21 d EC50 >3.2 mg/l

LOEC = 1.4 mg/l

NOEC = 0.29 mg/l (reproduction and parental survival)

Semi-static using dilutions of a WAF. Analysis as total Sn. (2)


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Table 10 Summary of invertebrate toxicity test for monooctyltin compounds (taken from OECD (2006b) unless otherwise indicated)




Daphnia magna 70% 48 h EC50= 1 mg/l

NOEC = 0.1 mg/l

Static test. Nominal concentrations. (2)

Daphnia magna 98% 48 h EC50 = 0.039 mg/l

NOEC = 0.029 mg/l

Static test using dilutions of a WAF. Analysis as MOT. Bouwman (2010b). See below for further details. (2)

Daphnia magna 60.9% 21 d LOEC = 0.16 mg/l

NOEC = 0.036 mg/l




NOEC ≥0.33 mg/l

Static test using dilutions of a WAF. Analysis as Total Organic Carbon.

Since the OECD (2006a and 2006b) evaluations were completed a further acute toxicity study has become available. The results are summarised below.


A 48-hour toxicity test has been carried out using octyltin tris(2-ethylhexyl mercaptoacetate) with Daphnia magna (Bouwman, 2010b). The method used was a static procedure following OECD TG 202. The substance tested had a purity of 98%. The test was carried out using dilutions of a water soluble fraction (WAF) obtained from a 100 mg/l loading. The WAF was prepared by stirring the test substance with the test medium for one day followed by a one day stabilisation period. The WAF was filtered through glass wool prior to use. The WAF dilutions used were 10, 18, 32, 56 and 100%. The non-specific concentration of octyltin tris(2-ethylhexyl mercaptoacetate) present in the WAF solutions was determined as total monooctyltin compounds (MOT) using the method discussed in 4.3.2. The concentrations were determined both at the start of the test and at the end of the test. The measured concentrations were found to be relatively stable over the 48 hour test period at the three highest concentrations (89-114% of the initial value after 48 hours) but the measured concentration was found to decrease slightly over the 48 hour period for the two lowest concentrations (62-70% of the initial value after 48 hours). The average measured concentration present in the solutions over the entire test period were determined to be 19, 29, 49, 75 and 124 µg/l for the 10, 18, 32, 56 and 100% WAF dilutions respectively (two measurements were taken for each dilution at each sampling time and the results of the two measurements were generally consistent).

The water used in the test was medium M7 and had a pH of 7.7-7.9 and a hardness of 180 mg/l as CaCO3. The dissolved oxygen concentration was in the range 9.1-9.3 mg/l and the temperature was 19.1-19.7°C over the duration of the test.


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No immobilisation or visible effects were evident in the 19 µg/l and 29 µg/l treatment groups when compared with the control group. The percentage immobilised daphnia at higher concentrations was 95% at 49 µg/l, 100% at 75 µg and 100% at 124 µg/l compared with 0% in the control group. The 48-hour EC50 was determined to be 39 µg/l (95%-confidence interval 36-43 µg/l) and the 48-hour NOEC was 29 µg/l.

At the higher test concentrations a large number of the Daphnia were observed to be trapped at the surface (particularly after 24 hours). These organisms were re-immersed into the solution prior to recording the mobility. It is not clear if this reflects the presence of a surface film of undissolved test substance or not.

7.1.4 Algae and aquatic plants

The available toxicity data to aquatic invertebrates for the dioctyltin and monoctyltin compounds considered have been reviewed in OECD (2006a and 2006b) and these data are summarised in Table 11 (dioctyltin compounds) and Table 12 (monooctyltin compounds).

Table 11 Summary of algal toxicity test for dioctyltin compounds (taken from OECD (2006a) unless otherwise indicated)




Scenedesmus subspicatus

98.8 72 h EC50 >0.002 mg/l

NOEC ≥0.002 mg/l

Test using dilutions of a WAF. Analysis as total Sn. (2)



95% 72 h EC50 = 0.17 mg/l

NOEC = 0.04 mg/l

Test using co-solvent/emulsifier. Analysis as DOT. (2)


No data 72 h EC50 >0.06 mg/l

NOEC ≥0.06 mg/l

Test using dilutions of a WAF. Analysis as total Sn. (2)


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Table 12 Summary of algal toxicity test for monooctyltin compounds (taken from OECD (2006b) unless otherwise indicated)




Pseudokirchneriella subcapitata

98% 48 h LOEC = 0.009 mg/l

NOEC = 0.0009 mg/la

Test using dilutions of a WAF. Analysis as MOT. Bouwman (2010c). See below for further details. (2)


54% 72 h EC50> 0.44 mg/l (growth)

EC50 = 0.18 mg/l (biomass)

NOEC = 0.007 mg/l

Test using dilutions of a WAF. Analysis as MOT. (2)



100% 72 h EC50= 0.22 mg/l (growth)

EC50 = 0.13 mg/l (biomass)

NOEC = 0.045 mg/l

Test using dilutions of a WAF. Analysis as MOT.

Note: a) The large step in concentrations tested precludes a reliable estimate of the NOEC in this study.

Since the OECD (2006a and 2006b) evaluations were completed a further acute toxicity study has become available. The results are summarised below.


A toxicity test has been carried out using octyltin tris(2-ethylhexyl mercaptoacetate) with the freshwater algal species Pseudokirchneriella subcapitata (Bouwman, 2010c). The method used followed OECD TG 201. The substance tested had a purity of 98%. The test was carried out using dilutions of a water soluble fraction (WAF) obtained from a 100 mg/l loading. The WAF was prepared by stirring the test substance with the test medium for one day followed by a one day stabilisation period. The WAF was filtered through glass wool prior to use. The WAF dilutions used were 1, 10 and 100%. The non-specific concentration of octyltin tris(2-ethylhexyl mercaptoacetate) present in the WAF solutions was determined as total monooctyltin compounds (MOT) using the method discussed in 4.3.2. The initial concentration determined in the 100% WAF solution was 18 and 27 µg/l. The concentration was found to decrease to 37% of the initial value after 24 hours and 23% of the initial value after 72 hours. The time weighted average concentration over the entire test period in the 100% WAF solution was 8.8 µg/l.

The water used in the test was medium M2 and had a pH of 8.2-8.3 at the start of the test and a pH of 8.2 at the end of the test. The water harness was of 24 mg/l as CaCO3. The test temperature was between 22.7-23.1°C over the duration of the test.


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The inoculum concentration used was 1×104 cells/ml. After 72 hours incubation the cell density was 151.4×104 cells/ml in the control group, 156.2×104 cells/ml in the 1% WAF dilution group, 155.5×104 cells/ml in the 10% WAF dilution group and 126.4×104 cells/ml in the 100% WAF group. The cell yield was statistically significantly reduced (by around 16.5%) compared to the control group for the 100% WAF group(α=0.05 level).

The mean growth rate over 0-72 hours was 0.0698 d-1 in the control group, 0.0702 d-1 in the 1% WAF dilution group, 0.0701 d-1 in the 10% WAF dilution group and 0.0673 d-1 in the 100% WAF dilution group. The reduction in growth rate over 72 hours for the 100% WAF group was 3.6%. These data were not analysed statistically by Bouwman (2010c) as the reduction in growth rate was <10%. When the growth rate over specific time periods was considered it was evident that most of the reduction in growth rate occurred over the first 24-hour period.

Overall these data show that the effects on biomass but not growth rate occurred in the 100% WAF group (~8.8 µg/l). No significant effects are evident at the next lowest treatment level of a 10% WAF (no analytical verification of the level of substance present was undertaken but presumably this would be around 0.9 µg/l). However, the large step in concentrations tested precludes a reliable estimate of the NOEC.

7.1.5 Quantitative structure-activity relationships (QSARs)

No QSAR estimates of the toxicity of the substances are reported as no reliable QSARs are available for organometallic compounds containing tin.

7.1.6 Sediment organisms

No data are available.

7.1.7 Other aquatic organisms

No data are available.

7.1.8 Summary of aquatic toxicity data

A number of aquatic toxicity data are available for the substances of interest. For fish, only the results of acute toxicity tests are available. These data show no effects at the solubility limit of the substances, except in one case with an LC50 above 1 mg/l where sufficiently high concentrations could be maintained.

Long-term NOEC data are available for some substances for both aquatic invertebrates and algae. These data are more relevant for the PBT analysis as the Annex XIII criteria are based on long-term NOEC values. The relevant lowest long-term NOECs (excluding the limit values) are summarised below.


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Daphnia magna

Dioctyltin dichloride 21-d NOEC = 0.41 mg/l

Dioctyltin bis(2-ethylhexyl mercaptoacetate) 21-d NOEC = 0.29 mg/l

Alga

Dioctyltin dichloride No NOEC established

Dioctyltin bis(2-ethylhexyl mercaptoacetate) 72-h NOEC = 0.04 mg/l


Daphnia magna

Octyltin tris(2-ethylhexyl mercaptoacetate) 21-d NOEC = 0.036 mg/l

Octyltin trichloride (supporting information) No NOEC available

Alga

Octyltin tris(2-ethylhexyl mercaptoacetate) 72-h NOEC = 0.007 mg/l

Octyltin trichloride (supporting information) 72-h NOEC = 0.045 mg/l

The quoted (no) effect concentrations are given in terms of the equivalent concentration of parent compound; in most tests the concentration present was verified by an indirect measurement (usually total Sn or MOT or DOT) and the (no) effect concentrations were back-calculated from this assuming all of the tin, MOT or DOT present was the parent substance. However, as discussed in Section 4.1.1.2 all of the substances tested are likely to be rapidly hydrolysed under the conditions used in the tests and so the organisms in the test would be exposed to the hydrolysis products in addition to, or rather than, the parent compound. To investigate this further the above NOECs must be converted from mg/l of parent compound to mmol/l. The NOECs on a molar basis can then be converted to the equivalent concentration of the main likely hydrolysis products, dioctyl tin hydroxide/oxide for the dioctyl tin compounds and octyl tin hydroxide/oxide from the monooctyl tin compounds4. The effect of carrying out this transformation is shown below.


Daphnia magna

4 The actual identities of the respective hydroxide/oxide compounds is unclear from OECD (2006a and 2006b) but may possibly include oligomeric/polymeric structures. For the conversion here it is assumed that, at least initially, the substances are dioctyltin dihydroxide (molecular weight 378.7 g/mol) or octyltin trihydroxide (molecular weight 282.7 g/mole).


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Dioctyltin dichloride 21-d NOEC = 9.9×10-4 mmol/l

~0.37 mg/l as dioctyltin hydroxide


21-d NOEC = 3.9×10-4 mmol/l

~0.15 mg/l as dioctyltin hydroxide

Alga

Dioctyltin dichloride No NOEC established


72-h NOEC = 5.3×10-5

mmol/l ~0.020 mg/l as dioctyltin hydroxide


Daphnia magna


21-d NOEC = 4.3×10-5 mmol/l

~0.012 mg/l as octyltin hydroxide


No NOEC available

Alga


72-h NOEC = 8.3×10-6 mmol/l



72-h NOEC = 1.3×10-4 mg/l


When compared on this basis essentially the same conclusions are reached as those based on the parent compounds.

The hydrolysis products from the 2-ethylhexyl mercaptoacetate derivatives will include the 2-ethylhexyl mercaptoacetate ligand. The OECD (2006a and 2006b) evaluations report the following toxicity data for 2-ethylhexyl mercaptoacetate itself: 48-h LC50 for fish = 9 mg/l, 48-h LC50 for Daphnia magna = 0.38 mg/l, 72-h EC50 for algal growth = 0.91 mg/l, 72-h EC50 for algal biomass = 0.41 mg/l and 72-h NOEC for alga <0.5 mg/l. These results show that the acute toxicity of the 2-ethylhexyl mercaptoacetate itself is generally of a similar order to that seen in some of the tests with the tin derivatives, suggesting that at least some of the toxicity seen may have been a result of release of the 2-ethylhexyl mercaptoacetate ligand from hydrolysis of the substance. This may be particularly relevant to the octyltin tris(2-ethylhexyl mercaptoacetate) substance as this, on hydrolysis, will release three molecules of 2-ethylhexyl mercaptoacetate) into solution for every one molecule of octyltin hydroxide/oxide.

Overall the available ecotoxicity test results suggest that only octytin tris(2-ethylhexyl mercaptoacetate) would meet the T criterion based on the ecotoxicity results. It is possible that some of the toxicity seen with this substance could result from release of 2-ethylhexyl mercaptoacetate into solution.


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Assuming that hydrolysis does occur in these tests, then the best estimates for the toxicity of the dioctyltin hydroxide/oxide or octyltin hydroxide/oxide hydrolysis products probably come from the experiments with dioctyltin dichloride or octyltin trichloride, where the chloride released would be unlikely to complicate the interpretation of the results. Note that no true NOEC was established with alga in the test with dioctyltin dichloride.


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8 PBT AND VPVB

8.1 Comparison with criteria from Annex XIII

Persistence

A substance is considered to be persistent (P) if it has a half-life >60 days in marine water or >40 days in fresh or estuarine water, or >180 days in marine sediment or >120 days in freshwater or estuarine sediment or soil. A substance is considered to be very persistent (vP) if it has a half-life >60 days in marine, fresh or estuarine water, or >180 days in marine, freshwater or estuarine sediment, or soil.

The available biodegradation screening studies suggest that dioctyltin dichloride, dioctytin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) are potentially persistent based on lack of ready biodegradability.

Hydrolysis of the substances is likely to occur rapidly in aquatic systems. The initial hydrolysis products formed are dependent on whether the substance is a dioctyltin substance or a monooctyltin substance as the octyl groups attached to the tin atom appear to be more resistant to hydrolysis than the other groups in the substances considered. Thus both dioctyltin dichloride and dioctyltin bis(2-ethylhexylmercaptoacetate) will form essentially the same hydrolysis product in the environment, dioctyltin hydroxide/oxide. Similarly both octyltin trichloride (supporting substance) and octyltin tris(2-ethylhexylmercaptoacetate) will form octyltin hydroxide/oxide.

As the hydrolysis reaction appears to be very rapid (half-lives of a few minutes to hours) it can be expected that, on release to the environment, the substances considered will be rapidly converted to the corresponding dioctyltin hydroxide/oxide or octyltin hydroxide/oxide and so it is the properties of these hydroxide/oxide products that are most relevant to the PBT assessment.

As such hydrolysis would also occur under the conditions of the ready biodegradation tests, the results of these tests will reflect the biodegradability of the dioctyltin hydroxide/oxide or octytin hydroxide/oxide and the released organic ligand. As none of the substances tested were readily biodegradable it can therefore be concluded that the dioctyltin hydroxide/oxide and octytin hydroxide/oxide are also not readily biodegradable and so potentially persistent.

Bioaccumulation

According to Annex XIII of REACH, a substance is considered to be bioaccumulative (B) if it has a bioconcentration factor (BCF) >2,000 l/kg or very bioaccumulative (vB) if it has a BCF >5,000 l/kg. However, the REACH Annex XIII criteria has recently been revised in terms of using a weight of evidence approach in the assessment of B and vB in addition to the numerical criteria.

Bioconcentration data are available for only one of the three substances considered in this evaluation (dioctyltin bis(2-ethylhexyl mercaptoacetate)).

Carrying out a fish bioconcentration test for these substances is technically challenging owing to the rapid hydrolysis of the substance and the lack of a suitable analytical methodology to allow determination of the individual substances present. The main uncertainty in this


50

evaluation stems from the fact that the actual individual substances present in solution are not know, only the total tin or total mono- and dioctyltin compounds. This would be important if the uptake seen resulted from exposure of a minor component in water (for example if the accumulative component made up only a small fraction of the total mono- or dioctyltin compounds present) as, in this case, the actual BCF for the individual substance may be higher than that determined based on the total tin, total mono- or total dioctyltin compounds. Furthermore, if hydrolysis was actually slower than concluded, then the available test would only give limited information on the bioaccumulation potential of the common hydrolysis product. The analytical difficulties mean that it is not technically possible to investigate further whether or not either of these situations is the case.

Overall, the available fish bioconcentration results are strongly suggestive that the BCF of these substances is perhaps around 1,000 l/kg as a maximum (but more probably lower than this (around 100 l/kg or less)). Therefore, based on the currently available information the substances are considered not to meet the B criterion.

The available test does not provide any information on the accumulation of the monooctyltin compounds. Based on read-across from the dioctyltin compounds it can be expected that the bioaccumulation potential of the octyltin hydroxide/oxide hydrolysis products would similar to, or possibly even lower than (based on its lower lipophilicity), that of the dioctyltin hydroxide/oxide. However this read-across is another source of uncertainty in the overall evaluation.

Toxicity

A substance fulfils the toxicity criterion (T) when:

- the long term no observed effect concentration (NOEC) for marine or freshwater organisms is less than 0.01 mg/l; or

- the substance is classified as carcinogenic (category 1 or 2), mutagenic (category 1 or 2) or toxic for reproduction (category 1, 2 or 3)5; or

- there is other evidence of chronic toxicity, as identified by the classifications T, R48, or Xn, R48, according to Directive 67/548/EEC6.

Based on the classification of R48, dioctlytin dichloride would meet the Annex XIII criteria for T.

The toxicity of the dioctyltin compounds is reviewed in detail in OECD (2006a). A category approach was used whereby read-across from oral data for dioctyltin dichloride to dioctyltin bis(2-ethylhexyl mercaptoacetate) was justified on the basis of rapid conversion of the thioesters to dioctytin dichloride under the physiological conditions present in mammalian gastric contents (0.07 M HCl). Therefore on this basis, as the R48 classification for dioctyltin dichloride is relevant to oral exposure, it can be assumed that dioctyl tin bis(2-ethylhexyl mercaptoacetate) would also meet the Annex XIII criteria for toxic (T). On a similar basis

5 The CLP Regulation (EC) No 1272/2008 will amend this to be substances classified as carcinogenic (category 1A or 1B), germ cell mutagenic (category 1A or 1B), or toxic for reproduction (category 1A, 1B or 2). 6 The CLP Regulation (EC) No 1272/2008 will amend this to be “there is evidence of chronic toxicity, as defined by the classifications STOT (repeated exposure), category 1 (oral, dermal, inhalation of gases/vapours, inhalation of dust/mist/fume) or category 2 (oral, dermal, inhalation of gases/vapours, inhalation of dust/mist/fume, according to Regulation (EC) No 1272/2008”.


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(i.e. that under the conditions prevalent in gastric contents chlorination can occur to form dioctyltin dichloride) it can also be assumed that the hydrolysis product dioctyltin hydroxide/oxide would also meet the Annex XIII criteria for T.

No classifications for mammalian toxicity for the monooctyltin compounds considered are reported in Annex VI to Regulation (EC) No 1272/2008. The REACH registration of octyltin tris(2-ethylhexyl mercaptoacetate) includes a proposal for self-classification of the substance both as a mono-constituent product and a multi-constituent product (where the substance is present with dioctyltin bis(2-ethylhexyl mercaptoacetate); see section 3). For multi-constituent products with 10 per cent or greater of the dioctyl, STOT rep. exp. 1 (H372) is proposed.

Octyltin tris(2-ethylhexyl mercaptoacetate) does however meet the Annex XIII criteria for T-based on the toxicity to algae. The situation as to whether the hydrolysis product, octyltin hydroxide/oxide would meet the Annex XIII criteria based on the ecotoxicity data is less certain as, on hydrolysis, octytin tris(2-ethylhexyl mercaptoacetate) would release 2-ethylhexyl mercaptoacetate into solution and this could contribute to some of the toxicity seen.

8.2 Assessment of substances of an equivalent level of concern


8.3 Emission characterisation

Since this dossier relates to evaluation of the data in the context of whether the PBT criteria are met, emission characterisation is not relevant.

8.4 Conclusion of PBT and vPvB or equivalent level of concern assessment

Overall it is concluded that the three substances considered, dioctyltin dichloride, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) do not meet the PBT or vPvB criteria. Although they are considered to be potentially persistent (in that they do not biodegrade rapidly but rather hydrolyse rapidly to either dioctyltin hydroxide/oxide or octyltin hydroxide/oxide that are themselves potentially persistent) and toxic, the available evidence suggests that the substance/hydrolysis products do not meet the Annex XIII criteria for bioaccumulation.

Carrying out aquatic testing in general for these substances is difficult owing to their poor solubility, rapid hydrolysis, and difficulties with their analysis. In particular, conducting a fish bioconcentration test for these substances is technically challenging owing to the rapid hydrolysis and the lack of analytical methodology to allow determination of the individual substances present to which organisms are exposed. This results in the following uncertainties in the B-assessment:

• The individual substances actually present in solution are not known; it was possible only to measure concentrations on the basis of total tin or total mono- and dioctyltin species. This would be important if the observed uptake was the result of exposure to a minor component in water (for example if the accumulative component made up


52

only a small fraction of the total mono- or dioctyltin compounds present in the test medium). In such a case, the actual BCF for the individual substance may be higher than that determined based on the total tin, total mono- or total dioctyltin compounds. The analytical difficulties mean that it is not technically possible to investigate further whether or not this is the case.

• The available data do not provide any information on the accumulation of the monooctyltin compound or its degradation products. Based on read-across, it can be expected that the bioaccumulation potential of the octyltin hydroxide/oxide hydrolysis products would be similar to (or possibly even lower than) that of the dioctyltin hydroxide/oxide. However this read-across is another source of uncertainty in the overall evaluation.

• The lack of a definitive hydrolysis rate for the test substance is important in relation to the bioconcentration test, if hydrolysis had actually been much slower than has been concluded from the available data. In this case, conclusions about the bioaccumulation potential of the hydrolysis products could not be drawn from this study. Again, the analytical difficulties mean that it is not technically possible currently to investigate further whether or not this is the case.

Given the inherent difficulties in carrying out a BCF test for these substances, the fact that the available data suggests that the B criterion is not met, and the need to minimise vertebrate testing, it would be difficult to justify further testing in relation to the B criterion. Further information on the level of hydrolysis that occurred under the exposure test conditions of the definitive BCF study for dioctyltin (2-ethylhexyl mercaptoacetate) would greatly help in the interpretation of this test data, however current analytical techniques mean this is not possible. If such information showed that the level of hydrolysis was lower than concluded here because of the study’s dosing system, such that exposure to the parent substance predominated, then there may be grounds for evaluating further the bioaccumulation potential of the common hydrolysis product dioctyltin oxide. However given its very low solubility, it would appear this would not be possible following OECD Test Guideline 305 methodology.

For both dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) hydrolysis would also result in formation of 2-ethylhexyl mercaptoacetate. This substance is not considered to meet the PBT criteria as it has a low predicted BCF.


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INFORMATION ON USE, EXPOSURE, ALTERNATIVES AND RISKS

No information has been sought on alternatives.

OTHER INFORMATION


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REFERENCES

Arkema (2007). FASCAT (R) 8231 Catalyst, Material Safety Data Sheet, Arkema Inc, 2007.

Baltussen E (2009a). Development and validation of an analytical method for the analysis of monooctyltin species in water. NOTOX Project 488001. NOTOX B.V., the Netherlands, 23 October 2009.

Baltussen E (2009b). Implementation and validation of an analytical method for the analysis of dioctyltin species in dioctyltin bis(2-ethylhexyl thioglycolate) solutions in iso-mium and determination of their stability. NOTOX Project 468822. NOTOX B.V., the Netherlands, 23 October 2009.

Baltussen E (2009c). Development and validation of an analytical method for the analysis of monooctyltin and dioctyltin species in fish. NOTOX Project 488002. NOTOX B.V., the Netherlands, 23 October 2009.

Baltussen E (2009d). Development and validation of an analytical method for the analysis of total tin in fish. NOTOX Project 491916. NOTOX B.V., the Netherlands, 16 November 2009.

Baltussen E (2010a). Determination of physico-chemical properties of dioctyltin bis(2-ethylhexyl mercaptoacetate). Vapour pressure, water solubility, partition coefficient, flash-point, auto-ignition temperature, hydrolysis as a function of pH and adsorption coefficient. NOTOX Project 492799. NOTOX B.V., the Netherlands, 20 May 2010.

Baltussen E (2010b). Determination of physico-chemical properties of octyltin tris(2-ethylhexyl mercaptoacetate). Vapour pressure, water solubility, partition coefficient, flash-point, auto-ignition temperature, hydrolysis as a function of pH and adsorption coefficient. NOTOX Project 492800. NOTOX B.V., the Netherlands, 20 May 2010.

Bogers M (2006). Bioconcentration test in rainbow trout with di[1-14C]octyltin bis(2-ethylhexyl mercaptoacetate) (flow-though). NOTOX Project 402042. NOTOX B.V., the Netherlands, 12 January 2006.

Bouwman L M (2010a). 96-Hour acute toxicity study in carp with octyltin tris(2-ethylhexyl mercaptoacetate) (static). Draft Report (Version 1), NOTOX Project 492803. NOTOX B.V., the Netherlands, 28 May 2010.

Bouwman L M (2010b). Acute toxicity study in Daphnia magna with octyltin tris(2-ethylhexyl mercaptoacetate) (static). Draft Report (Version 1), NOTOX Project 492802. NOTOX B.V., the Netherlands, 28 May 2010.

Bouwman L M (2010c). Fresh water algal growth inhibition test with octyltin tris(2-ethylhexyl mercaptoacetate) (static). Draft Report (Version 1), NOTOX Project 492801. NOTOX B.V., the Netherlands, 28 May 2010.

Bouwman L M (2010d). Bioconcentration test in rainbow trout with dioctyltin bis(2-ethylhexyl mercaptoacetate) (flow-though). NOTOX Project 488003. NOTOX B.V., the Netherlands, 12 May 2010.

ECB (2004a). PBT Factsheet for dichlorodioctylstannane. PBT Working Group – PBT List No. 16. Revision 9, November 2004. European Chemicals Bureau.


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ECB (2004b). PBT Factsheet for 2-ethylhexyl-10-ethyl-4,4-dioctyl-7-oxo-8-oxa-3,3-dithia-4-stannatetradecanoate. PBT Working Group – PBT List No. 15, Revision 9, November 2004. European Chemicals Bureau.

ECB (2004c). PBT Factsheet for 2-ethylhexyl-10-ethyl-4-[[2-[(2-ethylhexyl)oxy]-2-oxoethyl]-thio]-4-octyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate. PBT Working Group – PBT List No. 99, Revision 6, November 2004. European Chemicals Bureau.

Harlan (2010). Butler RE & White DF, “Determination of General Physico-Chemical Properties”, report number 3109/0006, Harlan laboratories Ltd, 2010. Data owner: Organo Tin REACH Consortium.

OECD (2006a). SIDS Initial Assessment Report and SIDS Dossiers for dioctyltin dichloride and selected thioesters category. SIAM 23, Jeju, South Korea, 17-20 October 2006. Organisation for Economic Co-operation and Development (OECD).

OECD (2006b). SIDS Initial Assessment Report and SIDS Dossiers for mono-octyl tin chloride and selected thioesters category. SIAM 23, Jeju, South Korea, 17-20 October 2006. Organisation for Economic Co-operation and Development (OECD).

Yoder R (2003). Electrospray Ionization Mass Spectrometric Study of Dioctyltin Compounds in Solution. May 2003.

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