solomon 2003 probabilistic risk assessment
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Probabilistic hazard assessment of environmentally occurring
pharmaceuticals toxicity to fish, daphnids and algae by
ECOSAR screening
Hans Sanderson *, David J. Johnson, Christian J. Wilson, Richard A. Brain,
Keith R. SolomonCenter for Toxicology, University of Guelph, Bovey Building, Gordon Street, Guelph, Ont., Canada N1G 2W1
Received 8 April 2003; received in revised form 30 May 2003; accepted 30 May 2003
Abstract
The risks associated with occurrence of pharmaceuticals in water resources are mostly unknown. In the absence of
extensive toxicological data, we scanned all the compounds observed in the environment for toxicological properties by
(Quantitative) Structure Activity Relationship ((Q)SAR). The results of the probabilistic distribution of environmental
and effect concentrations and hazard quotients (HQs) do not indicate significant acute risks prior to application ofassessment factors. Compared with measured effect concentrations SAR predictions were more sensitive 80% of the
time. The long-term effects of subtle and chronic changes, additive or synergistic effects and effects on other endpoints
e.g. reproduction, behavior, metabolism, bacterial resistance etc. are still uncertain. (Q)SARs can be important
prioritization tools for subsequent experimental risk assessment of pharmaceuticals in surface waters, due to the
prevalent lack of ecotoxicological data.
# 2003 Elsevier Ireland Ltd. All rights reserved.
Keywords: Pharmaceuticals; ECOSAR; EC50; Probability; Hazard quotients
1. Introduction
Recently medical and personal care products
have received increasing attention from environ-
mental and health agencies across the European
Union and in North America. Surveys and reports
on the occurrence of pharmaceuticals in the
environment (primarily surface waters) show that
medical compounds are ubiquitous (Daughton
and Ternes, 1999). Pharmaceuticals are created
with the intent of causing a biological effect, they
often have similar types of physio-chemical beha-
vior that are characteristic of harmful xenobiotics
e.g. they are able to pass membranes, and they are
relatively persistent in order to avoid being in-
activated before having their therapeutic effect.
* Corresponding author. Tel.: '/1-519-824-4120x54794; fax:
'/1-519-837-3861.
E-mail address: hsander@uoguelph.ca (H. Sanderson).
Toxicology Letters 144 (2003) 383/395
www.elsevier.com/locate/toxlet
0378-4274/03/$ - see front matter # 2003 Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/S0378-4274(03)00257-1
mailto:hsander@uoguelph.camailto:hsander@uoguelph.ca -
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These compounds are excreted through feces and
urine as a mixture of metabolites and unchanged
substances. They, therefore, predominately enter
the environment via wastewater effluent, aggra-
vated by the fact that, in practice the majority of
people flush unused drugs down the drain or
dispose of it with household garbage (Jones et
al., 2001). Other sources include, direct application
in aqua farming, manure run-off, as run-off from
the application of sewage sludge and manure on
farmland as fertilizers (Halling-Srensen et al.,
1998), via hospital effluent (Kummerer, 2001) or,
finally, via landfill leaching (Richardson and
Bowron, 1985). Since the sophistication of analy-
tical methods has increased, so has the range ofdetection of xenobiotics in the environment.
Hence, pharmaceuticals have been proven to occur
in surface water (Kolpin et al., 2002). Even if the
environmental half-life of the parent pharmaceu-
tical compounds may not be relatively great
compared, this is compensated, however, by con-
tinuous replacement of the compounds in the
environment, which serves to sustain perpetual
life-cycle exposure for aquatic organisms (Daugh-
ton and Ternes, 1999).
The quantities of several of pharmaceuticalsused throughout the world are comparable to
agrochemicals (Jones et al., 2001). Directives by
the US Food and Drug Administration (FDA)
since 1995 (CDER, 1995) and in the EU since 1993
for human and veterinary compounds (Straub,
2002) stipulating that an environmental risk as-
sessment should be part of the approval procedure
of new medical substances. Few new medical
substances have been subjected to a complete
risk assessment (Halling-Srensen et al., 1998)
primarily due to the fact that in most instancesthe calculated environmental concentrations lie
below the proposed cut-offvalues, making further
ecotoxicological studies unnecessary. However,
the importance of identifying emergent risks such
as pharmaceuticals in the environment is reflected
in the fact that pharmaceuticals are one of the top
five goals of the Strategic Plan 2000 for the US
Environmental Protection Agencys Office of Re-
search and Development (Daughton and Ternes,
1999).
The current US regulatory guidance requires
new pharmaceuticals to undergo standard acute
toxicity tests (algae, Daphnia magna and fish) if
the predicted or measured environmental concen-tration (PEC/MEC) of the active ingredient is !/1
mg l(1. In the EU the cut-off PEC value is 0.01 mg
l(1, and no environmental concerns are apparent
no further testing is deemed necessary. In the
second tier a crude predicted no-effect concentra-
tion (PNEC) for the aquatic compartment is to be
extrapolated by dividing the lowest E(L)C50 from
standard tests by an assessment factor of up to
1000 in the EU. If the PEC/PNEC is B/1 no
further assessment is necessary. The third tier is a
case-by-case study. Regulations may result inlabeling or restricted use (e.g. in hospitals, in-
surgery, etc.) (Straub, 2002). Due to the scarcity of
ecotoxicological data and the presence of pharma-
ceuticals in water, the primary question is whether
medical substances at low environmentally realis-
tic concentrations (parts per billions or trillions)
will have any effect at all on different trophic levels
and/or on ecosystems.
This analysis combines the findings of pharma-
ceuticals in surface waters in the US (Kolpin et al.,
2002) with those found in the EU reported insurveys and reviews by Richardson and Bowron
(1985), Halling-Srensen et al. (1998), Daughton
and Ternes (1999), Ayscough et al. (2000), Jones et
al. (2001), Kummerer (2001), Halling-Srensen et
al. (2002) and Sturer-Lauridsen et al. (2002). We
performed an ecotoxicological (Quantitative)
Structure Activity Relationship ((Q)SAR) screen-
ing (ECOSAR) of all the compounds reported in
the aquatic environment in an attempt to frame
the above question. We include; MECs and the
effect concentration where 50% of the organisms
either die or in other ways are adversely impaired(EC50). Covered are values for fish (96 h and 14
days), daphnids (48 h and 21 days) and algae (48
h), chronic effects values are included when
available (/75%) from the ECOSAR for all
model species. Effect measures in the ECOSAR
are based on data reported by the industry to the
OECD or USEPA, and are all according to
USEPA toxicity test guidelines for algae (typically
growth inhibition of Selenastrum capricornutum;
lethality and reproduction of D. magna, and fish
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Fathead minnows (Pimephales promelas ) personal
communication, Nabholz, 2003).
The exact toxic mode of action of the pharma-
ceuticals to non-target test organisms is not knownnor accounted for in the SARs. The specificity of
the pharmacodynamic activity and the ecotoxico-
logical mode of action of pharmaceuticals does not
easily translate into an ecotoxicological mode of
action of pharmaceuticals. The concentrations of
pharmaceuticals needed to elicit intended pharma-
codynamic responses will exceed environmental
concentrations by factors in the range of 104/106
(Seiler, 2002). Furthermore, if the effect is driven
by receptors that may be lacking in non-target
organisms, concentrations needed to evoke anyeffect may then be even higher: as, e.g. serotonin
reuptake inhibitors, beta-blockers etc. are not
present in most plants and insects. However,
more basic mechanisms of cellular functions like
those connected with signal transduction or cell
division that are generally well conserved in
evolution and can thus be identified throughout
the living world from unicellular to mammal
organisms are targeted by more recently developed
pharmaceuticals (Seiler, 2002).
Due to the data scarcity and unknown risksassociated with pharmaceuticals in the environ-
ment the European Commission Scientific Com-
mittee on Toxicity, Ecotoxicity and the
Environment (CSTEE) recognizes that a prioriti-
zation procedure needs to be developed for
pharmaceuticals and their environmental risk
assessment. To ensure harmonization, this should
follow the general scheme for chemicals as de-
scribed in the White Paper for future chemicals
strategy (EU, 2001a). The main tool for prioritiza-
tion stressed therein is the use of QSARs (EU,
2001b).The most extensively validated and used QSAR
is the USEPA EPIWIN suit with ECOSAR.
ECOSAR predictions does not replace the need
for experimental assessment of the environmental
risks posed by pharmaceuticals, but can serve as
an initial prioritization tool to estimate potential
hazards of pharmaceuticals in the environment.
ECOSAR has previously been successfully (low
false negative rates) applied to screening pharma-
ceuticals (Jones et al., 2002) and other complex
compounds such as fragrance materials (Salvito et
al., 2002).
2. Methods
2.1. ECOSAR
The SARs in the ECOSAR are used to predict
the aquatic toxicity of chemicals based on the
similarity of structure to chemicals for which the
aquatic toxicity has been previously measured.
Since 1981, the US Environmental Protection
Agency has used SARs to predict the aquatic
toxicity of new industrial chemicals in the absenceof test data. The acute toxicity of a chemical to fish
(both fresh and saltwater), water fleas (daphnids),
and green algae has been the focus of the devel-
opment of SARs. These organisms are group
model-organisms and thus not specific species.
SARs are developed for chemical classes based
on measured test data that have been submitted by
industry or they are developed and structural
similarities. Using the measured aquatic toxicity
values and Kow values, regression equations (cur-
rently more than 150 for more than 50 chemicalclasses) can be developed for a class of chemicals.
Inserting the Kow into the regression equation and
correcting the resultant value for the molecular
weight of the compound may then calculate
toxicity values for new and similar yet non-
assessed chemicals (Nabholz, 2001). The ECOSAR
class program is a computerized version of the
ECOSAR analysis procedure as currently prac-
ticed by the Office of Pollution Prevention and
Toxics (OPPT). It has been developed within the
regulatory constrain of the Toxic Substances
Control Act (TSCA) and is a pragmatic approachto SAR as opposed to a theoretical approach
(Meyland and Howard, 1998). The ECOSAR
program can freely be downloaded via the USEPA
(http://www.epa.gov/oppt/exposure/docs/episui-
tedl.htm). A validation assessment of ECOSAR
predictions has been performed and they indicate
an 87/90% agreement between predictions and
measured data for more than 2000 different
chemicals and with B/3% false negatives (Nab-
holz, 2001).
H. Sanderson et al. / Toxicology Letters 144 (2003) 383/395 385
http://www.epa.gov/oppt/exposure/docs/episuitedl.htmhttp://www.epa.gov/oppt/exposure/docs/episuitedl.htmhttp://www.epa.gov/oppt/exposure/docs/episuitedl.htmhttp://www.epa.gov/oppt/exposure/docs/episuitedl.htmhttp://www.epa.gov/oppt/exposure/docs/episuitedl.htmhttp://www.epa.gov/oppt/exposure/docs/episuitedl.htm -
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2.2. Probabilistic risk assessment
Probabilistic risk assessment (PRA) methods are
being assessed and considered for incorporationinto risk assessment procedures in a number of
regulatory jurisdictions. The method used in this
analysis has been implemented by the USEPA
(Hendly and Giddings, 1999). The use of PRA
recognizes that there are no absolutes in risk
assessment. Instead there are continuums of po-
tential exposure and effect situations and a range
of certainty, which can be reported (Solomon et
al., 2000). This is the same in any risk assessment
ranging from economic, ecological, or nuclear
power plant safety. Implicit in the term risk (orin positive terms chance) dwells a distribution of
probabilities, which can be more or less thor-
oughly elucidated (Bernstein, 1996). The use of
distribution curves for exposure (MECs) and
toxicity (in this case ECOSAR estimated EC50
values for fish, daphnids and algae) allows the
application of joint probability method to describe
the nature of risks posed by the MECs of
pharmaceuticals and the estimated effect concen-
trations. The straight-line transformations are
conv
erted by probit transformation for the prob-ability (ranked percentages) (1. axis) versus log-
transformation of the concentrations (2. axis). The
analysis was preformed in an EXCEL spreadsheet
designed to perform the double probability eco-
toxicology risk assessment procedures outlined in
Solomon et al. (2000). Overlap between the
measured concentrations and the estimated effect
concentrations are then indicative of the existence
of risk.
2.3. Hazard quotients
We also calculated the hazard quotient (HQ)
(MEC/EC50) for the compounds: Values B/1
indicate an insignificant risk and no need for
further risk assessments in a tiered procedure
(Maund et al., 2001), depending on the assessment
factors that are being applied, whose values vary
between the US and the EU. A conservative
assessment factor of 106 has been proposed to
apply for ECOSAR predictions of fragrances by
Salvito et al. (2002), whereas the USEPA typically
applies an assessment factor of 2/10 to ECOSAR
predictions. The application of assessment factors
is a risk management decision outside the scope of
this paper, which focuses on the characterizationof environmental hazards associated with pharma-
ceuticals reported in surface waters; assessment
factors is thus not considered.
2.4. Conservative approach
The highest environmental concentration of
pharmaceuticals found in water, and the lowest
effect concentration from the ECOSAR estima-
tions, respectively, were used in the analysis, to
secure homogeneity and initially optimal conser-vatism throughout the test. A few chemicals found
in the aquatic environment could not be estimated
in ECOSAR due to lack of SMILES notation for
the compounds (Meyland and Howard, 1998). The
precision of the ECOSAR predictions increases for
compounds where ECOSAR identifies an SAR
that allows assessment of excess toxicity beyond
the narcotic toxicity towards aquatic organisms
(personal communication, Nabholz, 2002). This
was the case for !/90% of the compounds
scanned. Most modern pharmaceuticals are opti-mized for a specific pharmacodynamic modes of
action, which the ECOSAR will not identify,
pharmaceutical targets, e.g. membranes, enzymes,
or bacterial components, are not restricted to
mammalian physiology, as many of these are
ubiquitously present on many levels of biological
organization (Seiler, 2002). Furthermore, the avail-
able experimental ecotoxicological data for human
and veterinary pharmaceuticals were compared
with the ECOSAR estimates. The chemicals White
Paper (EU, 2001b), stresses the foundation and
application of the precautionary principle, there-fore, we used only the lowest EC50 predictions and
the highest MECs including inside sewage treat-
ment plant concentrations in this analysis.
3. Results
Table 1 illustrates the available concentration
data of pharmaceuticals in environmental water
samples from the EU and the US (/2002) in the
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open literature (Richardson and Bowron, 1985;Halling-Srensen et al., 1998; Daughton and
Ternes, 1999; Ayscough et al., 2000; Jones et al.,
2001; Kummerer, 2001; Halling-Srensen et al.,
2002; Sturer-Lauridsen et al., 2002; Kolpin et al.,
2002; Schulman et al., 2002). The list depicts the
differences found in the EU and the US for
compounds of potential need for environmental
risk assessment and for significant bioaccumula-
tion. The differences detected for certain com-
pounds between the US and the EU surveys, could
either indicate significant differences in use pat-
terns, wastewater treatment, manure and sludgemanagement, environmental conditions or simply,
and most likely, differences in analytical focus.
Twenty-three of the substances were in worst-
case scenarios detected at levels !/1 mg l(1, thus
fulfilling the FDA the requirements for an envir-
onmental risk assessment. All of them fulfilled the
EU criteria of 0.01 mg l(1, which is virtually the
detection limit. Thirteen had potential for signifi-
cant bioaccumulation (log Kow!/3). Bezafibrate,
Dextropropoxyphene, Gemfibrozil, Ibuprofen,
Methaqualone and Tolfenamic acid (or 8%) ful-filled both risk characteristics.
Fig. 1 illustrates that acute risks are probably
not significant, as there is no overlap between the
distribution of the MECs and the estimated EC50
values. There are 1/2 orders of magnitude in
difference between the environmental concentra-
tions and the effect concentrations at the level
where 10% (10th centile) of the compounds effect
concentrations would be exceeded 5% (95th cen-
tile) of the time. The probability of the highest
MEC exceeding the 10th centile of EC50s for fish,daphnids and algae are all 0.3%. In a theoretical
worst-case scenario there might be an overlap of
probabilities for the lowest fish EC50 and the least
frequent and highest environmental concentration.
3,4,5,6-Tetrabromo-o-cresol has the lowest EC50
for fish, 0.01 mg l(1 while its environmental
concentration is 0.0001 mg l(1 (see Table 1 and
Fig. 2), so the theoretical overlap is not a
consistent risk, before application of assessment
factor.
Fig. 1. Displays the percent rank distribution of the environmental concentrations from the literature and the effect concentrations in
mg l(1 derived from the ECOSAR screening.
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On average, the order of susceptibility amongthe three endpoints was: algae]/daphnids!/fish.
Note that the cytostatic pharmaceuticals (Cyclo-
phosphamide and Ifosfamide) represent a special
high risk for mammals and potentially other
trophic levels in the environment, as these are
known to be carcinogenic, mutagenic and embry-
otoxic (Kummerer, 2001).
More than 99.9% of the ranked HQs (Maund et
al., 2001) in Fig. 2 are less than 1, before
application of an assessment factor. On average,
the MECs were five orders of magnitude smallerthan the related effect concentrations. This indi-
cates no significant environmental risks based on
the ECOSAR estimates and the available MECs.
For the exact HQs for each individual compound
and endpoint see Table 1.
Because most (Q)SAR models (including ECO-
SAR) uses lipophilicity, plus additional excess
toxicity due to structure to develop models to
predict toxicity these models should, when possible
be authenticated by comparing modeled versus
measured data (Nabholz, 2001). In this case itmaybe extra important as 82% of the compounds
were hydrophilic, thus we compared the modeled
predictions with data from the open literature.
Figs. 3/5 is a graphically representation of mod-
eled versus experimental EC50 data for fish,
daphnids and algae (Halling-Srensen et al.,
2002; Sturer-Lauridsen et al., 2002; Wilson et al.,
2002; Johnson et al., 2002) for 20 different
pharmaceuticals reported to occur in surface
waters that have experimental data for either
fish, daphnids and/or algae. In 80% of the caseswhere both measured and modeled data were
available, the ECOSAR EC50 estimations were
the lower (or over-protective) than the measured
effect concentration. Cleuvers (2003) found that
for all endpoints and compounds he tested the
QSAR derived EC50 predictions were lower than
the measured EC50 values, even though only
Clofibrinic acid had a log Kow!/3. He concluded
that the compounds he worked with all acted
unspecifically by non-polar narcosis and that
Fig. 2. Graphical illustration of ranked HQs (MEC/EC50) for pharmaceuticals reported in the environment for fish, daphnids and
algae. More than 99.9% of the HQs were B/1 with an approximately median of 10(5, before application of an arbitrary assessment
factor.
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toxicity thus may be associated with log Kowrather than any specific toxic action in the non-
target organism (Cleuvers, 2003).
4. Discussion
The HQs were derived by comparing the highest
MECs from the literature with the lowest ECO-
SAR prediction, indicating low acute risk to
aquatic organisms (median HQ:/10(5). How-
ever, if an assessment factor of 1000, as advised
in the EU, is applied to the (Q)SAR predictions
14% of the compounds HQ would exceed 1 and
require further testing, which is consistent with
findings of 13% for high volume pharmaceuticals
exceeding 1 (EU, 2001a). Caution, due to uncer-
tainty connected to the regressions in the ECO-
SAR, has been raised by Kaiser et al. (1999). In
80% of the cases where both an experimental and
modeled effect concentration were available, the
estimated values were lower than the correspond-
ing lowest measured effect concentration (see Figs.
3/5). Intra- and inter-laboratory variability ofstandard single species toxicity tests needs to be
taken into account when assessing the sensitivity
and quality of SAR estimates versus experimental
values. Personne and Janssen (1994) have found
that the average coefficient of variation (CV0/
S.D./mean)/100) in single species laboratory
bioassays exceeds 25% and can be as high as
50% in some cases. Furthermore, changes in
laboratory environmental factors such as tempera-
ture, light or pH can modulate the toxicity of
Fig. 3. Measured fish effect concentration from the literature vs. ECOSAR estimated fish effect concentration for 20 different
pharmaceuticals.
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compounds by up to two orders of magnitude
(Personne and Janssen, 1994).
The EU-Directive 93/67/EEC classifies com-
pounds according to their EC50 values: B/0.1
mg l(10/extremely toxic to aquatic organisms;
0.1/1 mg l
(1
0/v
ery toxic to aquatic organisms;1/10 mg l(10/toxic to aquatic organisms; 10/100
mg l(10/harmful to aquatic organisms; B/100 mg
l(10/non-toxic to aquatic organisms. According
to EU-Directive 93/67/EEC, the anti-fungal
3,4,5,6-tetrabromo-o -cresol was extremely toxic;
12% of all the compounds found in surface waters
were toxic, 41% were harmful and 47% were non-
toxic. Thus despite low risks, more than half of
these pharmaceuticals may due to their intrinsic
toxicity cause unwanted harm in aquatic environ-
ments and are liable to be labeled N;R50/53
(Dangerous for the environment; very toxic to
aquatic organisms, may cause long-term adverse
effects in the aquatic environment) or R52/53
(Harmful to aquatic organisms, may cause long-
term adverse effects in the aquatic environment)according to EU-Directive 93/67/EEC).
The current battery of ecotoxicological testing
of chemicals is not tailored for a risk assessment of
pharmaceuticals in terms of mechanistic knowl-
edge and statistical analysis in terms of replication
and statistical power (Weiss, 1998). As most
pharmaceuticals are designed to affect mammalian
physiology, it is not known what effects they could
have on other forms of life, e.g. aquatic fauna or
plants (Seiler, 2002). Knowledge of the availability
Fig. 4. Measured daphnids effect concentration from the literature vs. ECOSAR estimated daphnids effect concentration for 20
different pharmaceuticals.
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of pharmaceuticals to cellular targets is required
for an effective risk assessment. Due to the
continued low exposure the effects of most interest
will be chronic and subtle effects on the organisms
function, reproduction, behavior, metabolism,
genotoxicity etc. (Jones et al., 2001). The currentprotocols are primarily designed to suit other
chemicals such as pesticides, where acute effects
on algae, aquatic insects or fish are expected
because the ecotoxicological modes of action of
the compounds are better elucidated. Moreover,
the risk management and risk communication
process is also more complex for pharmaceuticals
than other chemicals as pharmaceuticals intui-
tively are perceived as good, therapeutic com-
pounds, and the environmental risks are easily
outweighed, as pharmaceuticals benefits to hu-
mans are a greater priority (Henschel et al., 1997).
5. Conclusions
Due to the low MECs acute risks are not likely,
simple extrapolation of effects from higher con-
centrations does not necessarily have relevance at
lower concentrations. !/50% of the reported
pharmaceuticals were intrinsically toxic potentially
leading to the necessity for labeling in the EU. The
complicated issue of mixtures and additive, syner-
gistic or antagonistic effects need to be addressed
(Cleuvers, 2003) along with assessment of chronic,
population and ecosystem effects. Without these
Fig. 5. Measured algae effect concentration from the literature vs. ECOSAR estimated algae effect concentration for 20 different
pharmaceuticals.
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analyses and careful consideration of the statistical
power and detectability of the test (Sanderson and
Petersen, 2002), it would be unwise as well as
statistically and scientifically false to conclude thatpharmaceuticals are not causing effects in the
environment at all (Jones et al., 2001). The present
analyses indicate that the regulatory and risk
management context concerning pharmaceuticals
in the aquatic environment is more complicated
than risk management of other chemicals. The
uncertainty concerning pharmaceutical mode of
action in environmentally relevant non-target
organisms, mixture interactions, degradation pro-
ducts, bioavaliability, low acute risks, but intrinsic
toxicity and bacterial resistance contributes to therisk management challenges. Ultimately, the en-
vironmental risk assessment and management
framework for pharmaceuticals must balance these
uncertainties on a case-by-case basis against the
human health benefits of pharmaceuticals. QSARs
can be used as a prioritization tool for the risk
assessment and management of pharmaceuticals.
Acknowledgements
The authors greatly acknowledge The Canadian
Network of Toxicology Centers for supporting
this work.
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