organochlorines and heavy metals in the harbour seal phoca vitulina from the german north sea coast

Marine Biology 41, 99-106 (1977) MARINE BIOLOGY �9 by Springer-Verlag 1977

Organochlorines and Heavy Metals in the Harbour Seal Phoca vitulina from the German North Sea Coast

H.E. Drescher 1 , U. Harms 2 and E. Huschenbeth 2

1 Neue Universit~it Kiel, Institut fllr Haustierkunde; Kiel, Germany (FRG) and

2 Bundesforschungsanstalt f~ir Fischerei; Hamburg, Germany (F RG)

Abstract

Samples of various tissues and organs from healthy, sick and dead harbour seals (Phoca vitulina) from the North German Waddensea collected during the years 1974- 1976 were analysed for copper, zinc, total mercury, cadmium, lead, and organochlorine pesticide residues (PCB, DDT, Lindane and Dieldrin). The investigations were carried out in order to increase our knowledge about the actual degree of heavy metal and organochlorine pesticide accumulation in these animals. The study was also directed towards a comparison of healthy and sick young seals and those found dead for a possible relation between the condition and concentration of pol- lutants in the organs. There was great variation within all series of compounds investigated, but in general the analytical data obtained indicated that high amounts of heavy metals and organochlorine pesticides can be present even in young seals. An age-specific increase in the mercury and cadmium content in liver samples could be demonstrated. The results are compared with data published by British and Dutch authors for other North Sea regions, and with a few exceptions, no significant differences can be established: cadmium (kidney) and DDT (blubber) contents in areas off the British coast are usually higher than corresponding values for seals from the German coast. There was no clear evidence that the concentrations of any of the compounds investigated had negative effects on the health of the seals. However, possible combined effects cannot be excluded.

I ntroduction

High concentrations of heavy metals and organochlorine residues in North Sea seals from the British coast and the Dutch Waddensea have been demonstrated in earlier reports and publications (Koeman and van Genderen, 1966; Holden, 1972; Heppleston, 1973; Heppleston and French, 1973; Koeman et al., 1975), but there is little information on the situ- ation in the German Bight.

Even though the seal is a highly mobile animal, regional differences in

sex, and health. The major effort was concentrated on the analysis of liver samples for heavy metals and of blubber samples for PCB and organochlorine pesticide residues. Additionally, some brain and kidney samples were investigated in order to provide a better knowledge of the pattern of the distribution of the contaminants between the various organs.

A high mortality rate has been observed in seals during their first and second year of life. This is mostly due to skin diseases and parasites in con- nection with malnutrition. The present

concentrations of metals, PCB, and pesti- study was also directed towards a compar- cides have been found, as demonstrated ison of healthy and sick young seals and for seals along the British coasts by Holden (1972).

This report gives data obtained on Phoca vitulina from the Waddensea of Schleswig-Holstein (FRG). Distributions of the heavy metals copper, zinc, cadmium, lead, and mercury, as well as PCB, DDT, Lindane, and Dieldrin were detected by the analysis of samples from selected organs in harbour seals of known age,

those found dead for a possible relation between the condition and the concentration of metals, PCB and pesticides in the organs.

MaterialsandMethods

Tissue samples of liver, kidney, brain and blubber were collected from 63 spec-

100 H.E. Drescher et al. : Organochlorines and Heavy Metals in Phoca vitulina

imens of Phoca ~tulina shot or found dead zinc during the years 1974-1976. The samples were deep-frozen at -2OoC until examina- The concentrations of zinc in Phoca ~tu- tion. The condition of the seals was lina investigated in this survey ranged examined and classified under the cate- from 27.0 to 56.0 mg/kg for the liver, gories "healthy", "sick", or "found dead't 10.8 to 15.0 mg/kg for the brain, and Age determination was performed on young seals by skeletal characteristics, and on older seals by grinding canine teeth for examination of the cementum layers. The age (in months) was calculated back to I July; this date is the peak of the pupping season which, in the northern part of the German Waddensea, lasts for about 3 weeks.

Heavy Metals

16.3 to 32.5 mg/kg for the kidney. As obvious from these data, the various organs displayed clear distinctions as to zinc content.

For zinc, no particular pattern emerged that could be attributed to the age of the seals (Fig. I).

Copper

The level of copper in the liver tissue Sample solutions for analyses of the ranged from 2.6 to 17.0 mg/kg, and in heavy metals zinc, copper, cadmium, lead, the brain from 2.4 to 4.0 mg/kg. Kidney and mercury were prepared by wet diges- values were similar to those of the tion of the organic material with concen- brain, ranging from 2.3 to 4.0 mg/kg. trated nitric/perchloric acid as de- In general, the liver values exhib- scribed by Harms (1975).

Measurements were performed by atomic absorption spectrophotometry: (I) contents of the elements zinc and copper were determined by means of an air- acetylene flame; (2) a flameless tech- nique with a heated graphite tube served to determine the elements lead and cadmium; (3) the concentration of total mercury was estimated according to the so- called "cold-vapour atomic-absorption method".

A "Perkin-Elmer" model 300 atomic- absorption spectrophotometer equipped with a deuterium arc background correc- tor and a "Perkin-Elmer" HGA-72 heated graphite atomizer was employed for flameless atomic absorption spectroscopy (AAS). For flame AAS, a "Beckman" model 440 A atomic-absorption spectrophotometer equipped with a "Beckman Autolam Burner II" (three-slotburner head) was used.

PCB and Organochlorine Pesticides

Pesticides were determined by gaschroma- tography using two different columns: (a) DC 200; (b) 8% QFI and 4% SF96. For cleaning, dry columns of alumina were used. PCB was separated from the pesticides by means of silica, as described by Holden and Marsden (1969). The ap- paratus consisted of a Hewlett-Packard 5750 research gas-chromatograph, and a standard solution of PCB Aroclor | 1254 was used.

Results

The results are presented in Tables I-3 and Figs. I-4. All values are based on wet weight.

ited a wide variation of almost I order of magnitude (Fig. I); however, the validity of an age-related increase in the liver tissue could not be deduced from the data obtained.

Mercury

The amount of total mercury in the tissues analysed indicated that the liver contained the highest concentrations, ranging from 1.5 to 160 mg/kg, followed by the kidney with values from 1.6 to 12.5 mg/kg. The brain concentrations were significantly lower (0.11 to 1.4 mg/ kg).

Within the limits of the sample size and in contrast to zinc and copper, the contamination level of mercury in the liver tissue increased with age, as shown in Fig. 2.

On an average, the livers of 10 to 12-month-old seals contain about 10 mg/ kg Hg. Five years later, the mercury level varies between 59 and 160 mg/kg. An age-specific increase in the mercury content in tissues of seals has also been demonstrated by other authors (Heppleston and French, 1973; Sergeant and Armstrong, 1973; Koeman et al., 1975; Smith and Armstrong, 1975).

Cadmium

Cadmium levels ranged from 0.010 to 0.200 mg/kg in the liver and 0.002 to 0.024 mg/kg in the brain. Within all brain samples analysed, values lower than 0.010 mg/kg dominated.

The kidney data provided clear evidence for the fact that cadmium is main-

H.E. Drescher et al.: Organochlorines and Heavy Metals in Phoca vitulina 101

Zinc and Copper 100

E 10

8 ~ ~ ~ 5 -- ~ ~'~o

5 10 50 100 Age [months)

Fig. i. Phoca vitulina. Zinc (circles) and copper (squares) levels in livers of harbour seals of different age classes

100

50

E

10

I1J

r

o 5 A

Mercury

A I

10

Age ( m o n t h s )

I l ' ~ l

I I

] I

50 100

Fig. 2. Phoca vitulina. Age accumulation of mercury in livers of harbour seals

ly concentrated in this organ. The values estimated ranged from 0.06 to 0,380 mg/kg, and a large percentage of the data was higher than 0.100 mg/kg. Simi- lar to mercury, cadmium levels in liver and kidney increase in older individuals (Fig. 3 and Table I).

Lead

With a few exceptions, the lead contents in liver and kidney were lower than 0.50 mg/kg. The liver values ranged from 0.10 to 0.57 mg/kg (Fig. 3), and the kidney values fell nearly into the same range (O.14 to 0.55 mg/kg). The brain values were generally lower, the contents ranging between 0.04 and 0.20 mg/ kg. In the kidney and liver there is a tendency for the lead concentration to increase with increasing age. There is a significant increase in lead content in the liver of the 6 to 8 year age-class compared with the liver of the 19 to 24 month age-class.

Lead and Codmium

I~176 fill 0501o o

..~ 0.10

~176 I 0.011

I 5 10 50 100

Age Imonths

Fig. 3. Phoca vitulina. Lead (circles) and cadmium (squares) levels in livers of harbour seals of different age classes

PCB

The PCB content in the blubber of harbour seals from the North German Wadden- sea ranged from 27.3 to 564 mg/kg (Ta- ble 2). High contamination with PCB, up to the maximum content, was already no- ticeable in very young seals. In the brain, liver and kidney, the PCB contents were comparably low, ranging from

0.25 to 2,96 mg/kg in the brain, 0.06 to 2.7 mg/kg in the liver, and from O.18 to 1.22 mg/kg in kidney tissue. A specific relation to age could not be found (Fig. 4).

DDT

Residues of DDT and its metabolites were also relatively high in young seals (Ta-

102 H.E. Drescher et al.: Organochlorines and Heavy Metals in Phoca vitulina

Table i. Phoca vitulina. Heavy metal contents of kidney, liver and

brain of harbour seals from German North Sea coast. Values are means

(underlined), ranges and sample sizes (in parentheses). -: No data

Age class Cu (mg/kg) Zn (mg/k~) Cd (m�/kg) Kidney Liver Brain Kidney Liver Brain Kidney

0-6 months - 6. i 2.7 - 39.4 14.O -

2.8-13.5 2.5-2.9 27.0-56.0 14.o-14.0 (27) (2) (27) (2)

7-12 months 3.3 7.0 3.1 22.2 39.6 12.8 O.iO 3.0-4.0 3.3------10.5 2.4------4.0 18.8-26.5 27". 5-50.5 10.8-15.0 O.O6-O.15

(9) (11) (7) (9) (10) (7) (9)

13-18 months - 5.7 3.O - 42.2 13.3 2.6-10.8 2.5-3.5 34.0-49.0 13.O-14.O

(ii) (4) (ii) (4)

19-24 months 3.2 10.6 3.2 26.5 37.3 13.O 0.22 2.5-3.8 6.O-17.O 23.3-32.5 29.0-50.0 0.19-0.29

(4) (4) (1) (4) (4) (1) (4)

3 -5 y e a r s - 2 . 8 3 . 4 - 2 7 . 5 14 .0 (1) (1) (1) (1)

6-8 years 2.5 10.7 .... 4.0 18.8 36.:0 13.O 0..31 2.3-2.8 8.5-14.8 16.3-20.0 29.O-41.O 0.26-0.38

(3) (4) (i) (3) (4) (I) (3)

Total N (16) (58) (16) 16) (57) (16) (16)

Table 2. Phoca vitulina. Organochlorine residues in the brain and blubber of

harbour seals from German North Sea coast. Values are means (underlined), ran-

ges and sample sizes (in parentheses); tr: trace

Age class % Fat PCB (mg/kg) .. DDT (mg/kg) TDE (mg/kg) Brain Blubber Brain BlUbber Brain Blubber Brain

O-6 months

7-12 months

13-18 months

19-24 months

3-5 years

6-8 years

6 . 6 87.1 1 .14 167 .8 0 . 0 5 2 4 .26 0 . 0 1 7 5.7------7.5 7 2 . 5 - 9 8 . 7 0 . 5 3 - 1 . 5 3 "27 .3 -480 .7 0 . 0 3 4 - 0 . 6 4 1 . 1 6 - 1 0 . 7 0 . 0 i 1 -0 .033

(3) (24) (3) (24) (3) (24) (3)

- 93.9 - 135.5 2.19 75.5-100.0 61.0-208.0 0.6-5.72

(12) (12) (12)

7.42 88.33 1.38 162.8 O. 05 3.14 O. 0____~2 6.19-8.05 59.8-99.9 0.252-2.96 28.5-564.0 0.026-0.085 0.56-8.34 0.008-0.038

(4) (11) (4) (Ii) (4) (11) (4)

98.2 87.3 1. 15 96.7-100.0 50.3-i 36.0 0.92-1.4

(4) (4) (4)

7.9 85.6 0.48 71. i 0.023 1.88 0.006 (1) (1) (1) (1) (1) (1) (1)

96.3 164.6 - 1.88 - 93.3-99.1 32.3-256.0 O. 54-3.06

(4) (4) (4)

H.E. Drescher et al. : Organochlorines and Heavy Metals in Phoca vitulina 103

Table i (continued)

Pb (mg/k~) Hg (m@/kg) Liver Brain Kidney Liver Brain Kidney Liver Brain

0.018 0.006 - 0.23 0.09 - 3.5 0.38 O.O1-O.O42 O.O02-O.O14 0.10-O.57 O.O8-O.10 1.5------8.9 0.22-0.52

(27) (35 (27) (3) (27) (3)

0.024 0.005 O. 32 0.23 O. 11 3.3 6.7 0.61 O.O18-O.030 0.003-0.007 O.18-O.48 O.11-O.55 0.O8-O.16 1.6-5.9 1.6-26.5 0.42-0.94

(Ii) (7) (9) (ii) (75 (95 (ii) (7)

0.028 0.003 - O.17 O. ii - 15.3 0.45 O.01 -0.063 0.002-0.004 0.10-O.28 0.04-0.20 1.8-53.O O.11-O.82

r (4) (11) (4) (11) {4)

0.032 0.004 0.38 0.23 0.10 3.9 11.2 0.35 0.025-0.038 o.14-0.55 0.1"4-0.30 3.1-4.7 7.7L14.7

(45 (i) (45 (4) (15 (45 (4) (1)

0.042 0.004 - 0.25 o.ii - 29.9 0.41 (i) (i) (i) (15 (I) (i)

o. 135 0.01 0.46 0.46 0.2 7.9 96.0 1.4 0.05-0.20 0.40-0.51 0.39-0.53 3.9-----12.5 59.o-160.o

(45 (i) (3) (4) (i) (3) (4) (i)

(58) (17) (16) (58) (17) (16) (58) (17)

Table 2 (continued)

DDE (mg/kg) Lindane (mg/kg) Dieldrin (mg/kg) ZDDT (mg/k~) Blubber Brain Blubber Brain Blubber Brain Blubber Brain Blubber

1.08 0.026 4.83 tr O.31 tr O.19 0.093 0.3-2.28 O.013-o.o39 1.9-11.7 0.04-0.78 0.06-0.56 O.O58-O.127

(24) (3) (24) (24) (24) (3)

1.62 - 3.98 0.36 0.35 0.54-2.78 1.76-10.6 0.24-0.98 O.14-O.8

(125 (125 (125 (12)

i.o5 0.03 4.56 tr 0.29 tr O.14 0.1 0.36-2.5 0.005-0.065 O.98-17.14 O.16LO.54 0.04-0.36 O.O-----39-0.161

(11) (4) (11) (11) ( i1 ) (11)

2.31 2.54 - 0.34 0.54 - 2.O4-2.7 1.92-3.O 0.26-0.56 O.14-O.90

(4) (4) (4) (4)

0.49 0.009 2.22 tr 0.34 tr 0.31 0.038 (15 (15 (15 (15 (15 (15

2.07 2.29 - 0.27 - O.15 - 0.86-2.84 1.18-3.O8 0.24-0.35 O.1-O.2

(4) (4) (4) (4)

10.3 4.4-23.3

(24)

7.7 2.9-14.7

(12)

8.8 2.2.-27.2

(11)

6.0 5 .5-6 .2

(45

4.6 (15

6.3 4.6-7.8

(4)


Table 3, Phoca vitulina. Organochlorine residues in kidney and liver of harbour seals from German North Sea coast. Values are means and sample sizes (in parentheses); tr: trace. No data were available for 0 to 6 months nor 13 to 18 months age classes

Age class % Fat PCB (mg/kg) DDT (mg/kg) TDE (mg/kg) DDE (mg/kg) Lindane (mg/kg! Dieldrin (mg/k 9) ~DDT (mg/kg) Kidney Liver Kidney Liver Kidney Liver Kidney Liver Kidney Liver Kidney Liver Kidney Liver Kidney Liver

7-12 months 2.64 2,57 0.87 2.02 0,13 0.07 0.08 0.13 0.04 0.05 tr 0,006 tr (2) (2) {2) (2) (2) (2) (2) (2) (2) (2) (2)

19-24 months - 1.62 0.38 - 0.05 - 0.04 - 0.03 - 0.005 - (2) (2) (2) (2) (2) (2)

3-5 years . . . . . . . . . . . . .

6-8 years 0.92 1.7 O,22 0.49 0.03 0.02 0.01 0.02 0.o1 0.02 tr 0.006 tr (2) (1) (2) (1) (2) (1) (2) (1) (2) (1) (1)

o.016 0.25 0.25 (2) (2) (2)

o.01 0.ii (2) (2)

0.024 0.05 0.06 (i) (2) (i)

Table 4. Phoca vitulina. Percentage of DDT, TDE and DDE in total DDT content in blubber of healthy, sick and dead harbour seals from German North Sea coast. Values are means • standard de- viations

Condition Sam- % DDT % TDE % DDE ple size

Healthy 18

Sick 19

Found dead 19

33.2• 24.6~16.1 42.3•

34.7~10.8 16.4• 49.O~7.4

35.1~ 9.8 14.1• 5.3 51.8•

500

I00

s0

E O O

10

I I 1

Y

PC B + Z' DDT

ii ii II IL ~

& 1_4 [11 o

i : I~++ H iO i-Lii I - ~ Vl

5 10

Age [ m o n t h s )

J

i .U i I

II o PCB [] /ZDDT--

I 50 100

Fig. 4. Phoca vitulina. PCB and total DDT levels in blubber of harbour seals of different age classes

bles 2 and 3), but there were no significant differences between the age classes (Fig. 4). In blubber samples, total DDT ranged from 2.2 to 27.2 mg/kg, while in all kidney, liver and brain samples, the amount was below 0.6 mg/kg.

On an average, the relative amount of DDE in total DDT was significantly higher than DDT or TDE (Table 4). This was true for healthy, sick and dead specimens. There was no significant differ- ence in the percentage of DDT in total DDT between the three conditions. The percentage of TDE in seals found dead was lower than in sick specimens, and significantly lower than in healthy seals. Great differences were found in the percentages of DDE: compared to healthy seals, %DDE was significantly higher in sick and dead individuals (Table 4).

Lindane and Dieldrin

These insecticides could be detected in seal fat in low quantities, Lindane ranging from 0.04 to 0.98 mg/kg and Dieldrin from 0.04 to 0.90 mg/kg. Both insecticides were present in similar amounts in all age classes. In brain, liver, and kidney, the amount of detect- able Lindane and Dieldrin was below 0.02 mg/kg in all samples.

Discussion and Conclusions

There was great variation within all series of compounds investigated. Phoca vitulina specimens older than 2 years are under-represented in this study, and will have to be included in later investigations. The results reveal that high amounts of heavy metals and organochlorine residues can be present even in young seals. It is of interest to compare these results with data obtained in other North Sea regions.

The mercury content in organs of seals from the German coast is in the same range as for seals from the east coast

H.E. Drescher et al. : Organochlorines and Heavy Metals in Phoca vitulina 105

of Britain (Heppleston and French, 1973). In seals from the Dutch Waddensea, however, higher levels in liver and brain have been recorded (van Haaften, 1975; Koeman et ai.,1975). The ranges of cadmium and zinc in seal liver tissue are approximately the same in the German and Dutch areas (Koeman et al., 1973). Cad- mium concentrations in the kidney are ~I00 high in areas off the British coast; the mean values for different areas m range from 2.2 to 11.6 mg/kg (Heppleston ~ 50 and French, 1973). Also, lead concentrations of British harbour seals are higher (Roberts et al., 1976).

High PCB concentrations were found in the fat of seals from the North German Waddensea. These values are comparable with those of harbour seals from other North Sea regions (Koeman and van Gen- deren, 1966; Heppleston, 1973). Total DDT values in German seals were approximately I order of magnitude lower than the PCB's (Fig. 4). The range is comparable with the occurrence of DDT in Dutch seals (Koeman and van Genderen, 10~ 1966), but DDT contents of seal blubber from the coasts of Britain are usually higher (Holden, 1972). In the Baltic Sea, 500 the PCB content of seal blubber is just as high as in the North Sea, but DDT concentrations are much higher (Olssen et

al., 1975). The range of Dieldrin content is similar in German and British seals E 100 (Heppleston, 1973). No data on Lindane m in marine mammals from the North Sea ~ 50 could be found in the literature.

As suggested by Holden (1972), there is the tendency for high DDT and PCB values to occur together in the same individual. Such relation between PCB and total DDT values can also be deduced from the data in Fig. 5. The regression equation for PCB and total DDT concentrations in blubber is y = 16.13 x + 5.27, and the correlation coefficient amounts to 0.83.

There may exist a dependency between PCB concentration in fat and the condition of nutrition in harbour seals, as expressed by blubber thickness (Fig. 6). Taking into account the variation of the data, PCB values increase in healthy and sick seals as blubber thickness de- creases.

500

0

X x

o

O o ~ o

x

X x �9

O

0%

1 5 10

Z DDT (mg/kg)

Fig. 5. Phoca vituiina. Relation between PCB and total DDT content in fat of healthy, sick and dead harbour seals

x heat thy 0 sick

�9 dead

, J I , , [ , I 50 100

O

@ � 9 1 4 9 0 X X

�9 ,

�9 o o

-- 0 8 ~ X �9 •

�9 � 9 0 x 0 �9 5 x

0 X

X �9 x x h e a l t h y

O s ick

�9 dead

I 50

I I I I 0 10 20 30 ~0

Blubber th ickness imm)

Fig. 6. Phoca vitulina. Relation between PCB content in fat and blubber thickness in healthy, sick and dead harbour seals

The amount of heavy metals, PCB and or~anochlorine pesticides in the organs of seals is dependent on the quantity and quality of the food eaten by the seal. It is of interest to compare the

At a critical thickness (between 10 concentrations of the compounds found in to 15 mm), PCB values seem to drop again, the harbour seal with those in its food. as observed in dead seals. This could be The main food items of harbour seals caused by a reduction of PCB in the re- from the Waddensea are flatfish, whiting maining fat and increasing concentrations and herring (Havinga, 1933). Huschenbeth in other organs, as observed in birds by (1973) and Harms (1975) have investigated Waddington et al. (1973). TO verify this these fish species from the German North hypothesis, a larger sample of seals and Sea: there is a tendency for higher val- tissues from various organs will have to ues of cadmium, zinc and copper to be be investigated, present in seal than in plaice and cod;


no clear evidence exists for lead being higher in the seal than in the fishes. Concentrations of mercury are up to 1000 times higher in the seal than in the fishes. PCB and all compounds of organochlorine pesticides are higher in the seal. The highest accumulation rate is displayed by PCB, the concentration in seals being approximately 1000 times higher than in the fishes, and the amount of total DDT, Dieldrin and Lindane being approximately 100 times higher in seals

than in fishes. No explanation can be given at pres-

ent for the different relative amounts of DDE in total DDT between healthy and sick/dead selas (Table 4).

So far, there is no evidence that any of the compounds investigated has solely physiological effects on seals. Possible effects of combinations of various pol- lutants, however, cannot be excluded.

Acknowledgement. These investigations are part of a research project on biology and con- servation of Phoca vitulina carried out in the northern part of the German Waddensea.

Literature Cited

Haaften, J.L. van: Seal research in the Waddensea. In: Proceedings from the Symposium on the Seal

in the Baltic, June 4-6, 1974, Liding~, Sweden, pp 30-32. Solna: National Swedish Environment Protection Board 1975

Harms, U.: The levels of heavy metals (Mn,Fe,Co, Ni,Cu,Zn,Cd,Pb,Hg) in fish from onshore and offshore waters of the German Bight. Z. Lebensmittelunters. u.-Forsch. 157, 125-132 (1975)

Havinga, B.: Der Seehund in den Holl~ndischen Gew[ssern. Tijdschr. ned. dierk. Vereen. 3,

79-111 (1933) Heppleston, P.B.: Organochlorines in British

grey seals. Mar. Pollut. Bull. 4, 44-45

(1973) - and M.C. French: Mercury and other metals

in British seals. Nature, Lond. 243, 302-304

(1973) Holden, A.V.: Monitoring organochlorine con-

tamination of the marine environment by the

analysis of residues in seals. In: Marine pollution and sea life, pp 266-272. Ed. by M. Ruivo. London: F.A.O. 1972

- and K. Marsden: Single stage clean up of animal tissue extracts for organochlorine residue analysis. J. Chromat. 44, 481-492 (1969)

Huschenbeth, E.: Zur Speicherung von chlorierten Kohlenwasserstoffen in Fisch. Arch. FischWiss. 24, 105-116 (1973)

Koeman, J.H. and H. van Genderen: Some prelimi- nary notes on chlorinated hydrocarbon residue insecticides in birds and mammals in the Netherlands. J. appl. Ecol. 3, (Suppl.), 99-106 (1966)

-, W.H. Peeters, C.H.M. Koudstaal-Hol, P.S.Tjioe and J.J.M. de Goeij: Mercury-selenium cor- relations in marine mammals. Nature, Lond. 245, 385-386 (1973)

-, W.S.M. van de Ven, J.J.M. de Goeij, P.S.T. Tjioe and J.L. van Haaften: Mercury and selenium in marine mammals and birds. Sci. total Envir. 3, 279-287 (1975)

Olsson, M., A.G. Johnels and R. Vaz: DDT and PCB levels in seals from Swedish waters. The occurrence of aborted seal pups. In: Proceed- ings from the Symposium on the Seal in the Baltic, June 4-6, 1974, Liding6, Sweden, pp 43-65. Solna: National Swedish Environment Protection Board 1975

Roberts, T.M., P.B. Heppleston and R.D. Roberts: Distribution of heavy metals in tissues of the common seal (Phoca vitulina). Mar. Pollut. Bull. (In press)

Sergeant, D.E. and F.A. Armstrong: Mercury in seals from eastern Canada. J. Fish. Res. Bd Can. 30, 843-846 (1973)

Smith, G. and F.A.J. Armstrong: Mercury in seals, terrestrial carnivores, and principal food items of the Inuit, from Holman, N.W.T. J. Fish. Res. Bd Can. 32, 795-801 (1975)

Waddington, J.I., G.A. Best, J.P. Dawson and T. Lithgow: PCBs in the Firth of Clyde. Mar. Pollut. Bull. 4, 26-28 (1973)

Dr. H.E. Drescher Neue Universit~t Kiel Institut fir Haustierkunde Olshausenstr. 40-60 2300 Kiel Germany (FRG)

Date of final manuscript acceptance: December 3, 1976. Communicated by O. Kinne, Hamburg

organochlorines and heavy metals in the harbour seal phoca vitulina from the german north sea coast

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