1
Ecological Risk Characterization
Introduction:
Risk characterization integrates the available data on effects and exposure
assessments to evaluate the risk of toxicological impacts on organisms exposed
to the chemical of interest. In this exercise, we will evaluate risks using the
“quotient method”. The quotient method involves comparing Predicted Exposure
Concentrations (PECs) to Predicted No Effect Concentrations (PNEC). We will
also evaluate whether there is potential for bioaccumulation of triclosan.
Risk Characterization:
In the Exposure Assessment exercise, you calculated PECs (µg/L) for
triclosan in surface waters at a distance of 1,000 metres from sources of municipal
wastewater using dilution scenarios with 10th, 50th and 90th percentile dilution
factors. The 10th percentile dilution factors are considered to be conservative
estimates of the exposure of aquatic organisms to down-the-drain chemicals.
Consider all three dilution scenarios as PEC values for the quotient method for
quantitative risk characterization.
Risks in the Aquatic Environment:
From the Effects Assessment exercise, evaluate the data for the acute
toxicity of aquatic organisms exposed to triclosan. From the previous Effects
Assessment tutorial, utilize the various endpoints of acute toxicity in aquatic
organisms, including your calculations for mortalities of daphnia and medaka, and
the acute toxicity data from the literature. Also, review the endpoints for chronic
toxicity, which includes the data on reproduction in Daphnia magna and
Ceriodaphnia dubia, and in post-embryonic amphibian development (i.e. from
Marlatt et al., 2015). Use NOEC data for your estimates of the PNEC. If there were
no NOECs determined in the individual toxicity tests, estimate the NOEC by
dividing the LC50 (or EC50) by a factor of 100, or by dividing the LOEC by a factor
of 10.
2
Using an Excel spreadsheet, log-transform all of the NOECs for acute
toxicity and determine the mean NOEC and the 95% confidence limits around the
mean. Take the lower 95% confidence limit as a “conservative” estimate of the
PNEC for aquatic organisms exposed to triclosan. Using this PNEC for acute
toxicity, determine the ratio of PEC to PNEC (PEC/PNEC) for aquatic organisms
exposed to triclosan in wastewater effluents at a distance of 1,000 meters
downstream of the source under 10th, 50th and 90th percentile dilution scenarios. If
the ratio is =1, then there is a risk of adverse effects to aquatic organisms exposed
to triclosan in surface waters.
Determine the risk quotient using NOEC data for chronic toxicity in
Ceriodaphnia dubia (i.e. reproduction) and in post-embryonic frogs (i.e.
development) exposed to triclosan at a distance of 1,000 meters downstream from
the source under 10th, 50th and 90th percentile dilution scenarios.
Risks in the Terrestrial Environment:
From the Effects Assessment exercise, evaluate the data for the acute
toxicity of terrestrial organisms (i.e. cucumber, red wiggler worm) exposed to
triclosan in soil. Use the NOEC data for your estimates of the PNEC. For the most
sensitive endpoint (i.e. toxicity to cucumber), apply an assessment (i.e. “safety”)
factor of 10 to the NOEC to account for the fact that there are very few toxicological
data for terrestrial organisms exposed to triclosan. Determine the ratio of PEC to
PNEC (PEC/PNEC) for terrestrial organisms exposed to triclosan in agricultural
soils where biosolids were applied. If the ratio is =1, then there is a risk of adverse
effects to terrestrial organisms exposed to triclosan in soil.
Bioaccumulation Potential:
The log Kow value for triclosan is 4.8, so this compound may bioaccumulate
in exposed organisms; especially through bioconcentration from water in aquatic
organisms. There are various empirical relationships between log Kow and
bioconcentrations factors (BCF) for aquatic organisms that have been proposed in
the literature:
3
log BCF = 0.542 log Kow + 0.124 Neely et al. (1974)
log BCF = 0.85 log Kow – 0.70 Veith et al. (1979)
log BCF = log Kow – 1.32 Mackay (1982)
Using each of these relationships, estimate the BCF for aquatic organisms
exposed to triclosan. Compare these values to the BCF values that have been
determined experimentally for organisms exposed to triclosan (Table 1).
Table 1: Data on bioconcentration factors estimated for triclosan in aquatic
organisms.
Test Organism Exposure BCF Reference
Zebra fish Lab exposure 2,532 – 4,157 Orvos et al. 2002
Common carp Lab exposure 15-90 NITE 2005
White fish Field samples 2,000 – 5,200 Balmer et al 2004
Algae Field samples 700 – 1,500 Coogan et al 2007
Snail Field samples 1,200 Coogan et al 2008
References:
Balmer ME et al. 2004. Occurrence of methyl triclosan, a transformation product
of the bacteriocide triclosan, in fish from various lakes in Switzerland. Environ
Sci Technol 38:390-395.
Coogan MA et al. 2008 Snail bioaccumulation of triclocarban and triclosan and
methyl triclosan in a North Texas, USA stream affected by wastewater
treatment plant runoff. Environ Toxicol Chem 27:1788-1793.
Coogan MA et al 2007. Algal bioaccumulation of triclocarban, triclosan and methyltriclosan
in a North Texas wastewater treatment plant receiving stream.
Chemosphere 67:1911-1918.
Mackay D. 982. Correlation of bioconcentration factors. Environ Sci Technol
16:274-278.
Neely BW et al. 1974. Partition coefficient to measure bioconcentration potential
of organic chemicals in fish. Environ Sci. Technol 8:1113-1115.
4
NITE(National Institute of Technology and Evaluation of Japan) 2005.
Biodegradation and bioconcentration of existing chemical substances under
the Chemical Substances Control Law.
http://www.safe.nite.go.jp/denglish/kizon/KIZON_start-hazkizon.html.
Orvos DR et al. 2002. Aquatic toxicity of triclosan. Environ. Toxicol Chem 21:1338-
1349.
Veith GD et al. 1979. Measuring and estimating the bioconcentration factor of
chemicals in fish. J Fish Res Bd Can 36:1040-1048.
Assignment:
Risk Characterization and Management
1. Present your ecological risk assessments for aquatic and terrestrial
organisms exposed to triclosan by completing all of the steps described in
the Exposure Assessment, Effects Assessment and Risk Characterization
tutorials. Describe any of the steps in this procedure that are “conservative”
approaches for calculating a risk quotient (i.e. based on worst case
scenarios). Based on these calculations, if you were to recommend further
studies to more fully assess the risks of triclosan in the environment (i.e. a
Phase II, Tier B assessment), what would they be?
2. Estimate the Bioconcentration Factors (BCFs) for triclosan in aquatic
organisms using the three empirical relationships provided above. Compare
these data to the BCF values that have been determined experimentally
(Table 1) and comment on any differences or similarities. The log Kow value
of 4.8 for triclosan was determined at a pH = 7. However, for chemicals
that can ionize, such as triclosan, the Kow will vary with pH. Triclosan is a
phenolic compound with a pKa value of 7.9. In aquatic environments at the
upper range of the pH for natural waters (i.e. apprioximately pH=8), would
you expect that triclosan would show greater or lesser potential for
bioaccumulation than at a lower pH of 7?
3. “Risk Management” involves developing actions or policies that will reduce
or eliminate the risk of adverse effects to organisms. Risk management
5
could involve banning or phasing out a chemical. Is there justification for
using this approach to prevent adverse effects to aquatic and terrestrial
organisms exposed to triclosan? An alternative approach is to take steps
to reduce the amount of a chemical released into the environment. Discuss
ways in which this approach could be used to reduce the risks to aquatic
and terrestrial organisms exposed to triclosan.

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1
Ecological Risk Characterization
Introduction:
Risk characterization integrates the available data on effects and exposure
assessments to evaluate the risk of toxicological impacts on organisms exposed
to the chemical of interest. In this exercise, we will evaluate risks using the
“quotient method”. The quotient method involves comparing Predicted Exposure
Concentrations (PECs) to Predicted No Effect Concentrations (PNEC). We will
also evaluate whether there is potential for bioaccumulation of triclosan.
Risk Characterization:
In the Exposure Assessment exercise, you calculated PECs (µg/L) for
triclosan in surface waters at a distance of 1,000 metres from sources of municipal
wastewater using dilution scenarios with 10th, 50th and 90th percentile dilution
factors. The 10th percentile dilution factors are considered to be conservative
estimates of the exposure of aquatic organisms to down-the-drain chemicals.
Consider all three dilution scenarios as PEC values for the quotient method for
quantitative risk characterization.
Risks in the Aquatic Environment:
From the Effects Assessment exercise, evaluate the data for the acute
toxicity of aquatic organisms exposed to triclosan. From the previous Effects
Assessment tutorial, utilize the various endpoints of acute toxicity in aquatic
organisms, including your calculations for mortalities of daphnia and medaka, and
the acute toxicity data from the literature. Also, review the endpoints for chronic
toxicity, which includes the data on reproduction in Daphnia magna and
Ceriodaphnia dubia, and in post-embryonic amphibian development (i.e. from
Marlatt et al., 2015). Use NOEC data for your estimates of the PNEC. If there were
no NOECs determined in the individual toxicity tests, estimate the NOEC by
dividing the LC50 (or EC50) by a factor of 100, or by dividing the LOEC by a factor
of 10.
2
Using an Excel spreadsheet, log-transform all of the NOECs for acute
toxicity and determine the mean NOEC and the 95% confidence limits around the
mean. Take the lower 95% confidence limit as a “conservative” estimate of the
PNEC for aquatic organisms exposed to triclosan. Using this PNEC for acute
toxicity, determine the ratio of PEC to PNEC (PEC/PNEC) for aquatic organisms
exposed to triclosan in wastewater effluents at a distance of 1,000 meters
downstream of the source under 10th, 50th and 90th percentile dilution scenarios. If
the ratio is =1, then there is a risk of adverse effects to aquatic organisms exposed
to triclosan in surface waters.
Determine the risk quotient using NOEC data for chronic toxicity in
Ceriodaphnia dubia (i.e. reproduction) and in post-embryonic frogs (i.e.
development) exposed to triclosan at a distance of 1,000 meters downstream from
the source under 10th, 50th and 90th percentile dilution scenarios.
Risks in the Terrestrial Environment:
From the Effects Assessment exercise, evaluate the data for the acute
toxicity of terrestrial organisms (i.e. cucumber, red wiggler worm) exposed to
triclosan in soil. Use the NOEC data for your estimates of the PNEC. For the most
sensitive endpoint (i.e. toxicity to cucumber), apply an assessment (i.e. “safety”)
factor of 10 to the NOEC to account for the fact that there are very few toxicological
data for terrestrial organisms exposed to triclosan. Determine the ratio of PEC to
PNEC (PEC/PNEC) for terrestrial organisms exposed to triclosan in agricultural
soils where biosolids were applied. If the ratio is =1, then there is a risk of adverse
effects to terrestrial organisms exposed to triclosan in soil.
Bioaccumulation Potential:
The log Kow value for triclosan is 4.8, so this compound may bioaccumulate
in exposed organisms; especially through bioconcentration from water in aquatic
organisms. There are various empirical relationships between log Kow and
bioconcentrations factors (BCF) for aquatic organisms that have been proposed in
the literature:
3
log BCF = 0.542 log Kow + 0.124 Neely et al. (1974)
log BCF = 0.85 log Kow – 0.70 Veith et al. (1979)
log BCF = log Kow – 1.32 Mackay (1982)
Using each of these relationships, estimate the BCF for aquatic organisms
exposed to triclosan. Compare these values to the BCF values that have been
determined experimentally for organisms exposed to triclosan (Table 1).
Table 1: Data on bioconcentration factors estimated for triclosan in aquatic
organisms.
Test Organism Exposure BCF Reference
Zebra fish Lab exposure 2,532 – 4,157 Orvos et al. 2002
Common carp Lab exposure 15-90 NITE 2005
White fish Field samples 2,000 – 5,200 Balmer et al 2004
Algae Field samples 700 – 1,500 Coogan et al 2007
Snail Field samples 1,200 Coogan et al 2008
References:
Balmer ME et al. 2004. Occurrence of methyl triclosan, a transformation product
of the bacteriocide triclosan, in fish from various lakes in Switzerland. Environ
Sci Technol 38:390-395.
Coogan MA et al. 2008 Snail bioaccumulation of triclocarban and triclosan and
methyl triclosan in a North Texas, USA stream affected by wastewater
treatment plant runoff. Environ Toxicol Chem 27:1788-1793.
Coogan MA et al 2007. Algal bioaccumulation of triclocarban, triclosan and methyltriclosan
in a North Texas wastewater treatment plant receiving stream.
Chemosphere 67:1911-1918.
Mackay D. 982. Correlation of bioconcentration factors. Environ Sci Technol
16:274-278.
Neely BW et al. 1974. Partition coefficient to measure bioconcentration potential
of organic chemicals in fish. Environ Sci. Technol 8:1113-1115.
4
NITE(National Institute of Technology and Evaluation of Japan) 2005.
Biodegradation and bioconcentration of existing chemical substances under
the Chemical Substances Control Law.
http://www.safe.nite.go.jp/denglish/kizon/KIZON_start-hazkizon.html.
Orvos DR et al. 2002. Aquatic toxicity of triclosan. Environ. Toxicol Chem 21:1338-
1349.
Veith GD et al. 1979. Measuring and estimating the bioconcentration factor of
chemicals in fish. J Fish Res Bd Can 36:1040-1048.
Assignment:
Risk Characterization and Management
1. Present your ecological risk assessments for aquatic and terrestrial
organisms exposed to triclosan by completing all of the steps described in
the Exposure Assessment, Effects Assessment and Risk Characterization
tutorials. Describe any of the steps in this procedure that are “conservative”
approaches for calculating a risk quotient (i.e. based on worst case
scenarios). Based on these calculations, if you were to recommend further
studies to more fully assess the risks of triclosan in the environment (i.e. a
Phase II, Tier B assessment), what would they be?
2. Estimate the Bioconcentration Factors (BCFs) for triclosan in aquatic
organisms using the three empirical relationships provided above. Compare
these data to the BCF values that have been determined experimentally
(Table 1) and comment on any differences or similarities. The log Kow value
of 4.8 for triclosan was determined at a pH = 7. However, for chemicals
that can ionize, such as triclosan, the Kow will vary with pH. Triclosan is a
phenolic compound with a pKa value of 7.9. In aquatic environments at the
upper range of the pH for natural waters (i.e. apprioximately pH=8), would
you expect that triclosan would show greater or lesser potential for
bioaccumulation than at a lower pH of 7?
3. “Risk Management” involves developing actions or policies that will reduce
or eliminate the risk of adverse effects to organisms. Risk management
5
could involve banning or phasing out a chemical. Is there justification for
using this approach to prevent adverse effects to aquatic and terrestrial
organisms exposed to triclosan? An alternative approach is to take steps
to reduce the amount of a chemical released into the environment. Discuss
ways in which this approach could be used to reduce the risks to aquatic
and terrestrial organisms exposed to triclosan.

1
Ecological Risk Characterization
Introduction:
Risk characterization integrates the available data on effects and exposure
assessments to evaluate the risk of toxicological impacts on organisms exposed
to the chemical of interest. In this exercise, we will evaluate risks using the
“quotient method”. The quotient method involves comparing Predicted Exposure
Concentrations (PECs) to Predicted No Effect Concentrations (PNEC). We will
also evaluate whether there is potential for bioaccumulation of triclosan.
Risk Characterization:
In the Exposure Assessment exercise, you calculated PECs (µg/L) for
triclosan in surface waters at a distance of 1,000 metres from sources of municipal
wastewater using dilution scenarios with 10th, 50th and 90th percentile dilution
factors. The 10th percentile dilution factors are considered to be conservative
estimates of the exposure of aquatic organisms to down-the-drain chemicals.
Consider all three dilution scenarios as PEC values for the quotient method for
quantitative risk characterization.
Risks in the Aquatic Environment:
From the Effects Assessment exercise, evaluate the data for the acute
toxicity of aquatic organisms exposed to triclosan. From the previous Effects
Assessment tutorial, utilize the various endpoints of acute toxicity in aquatic
organisms, including your calculations for mortalities of daphnia and medaka, and
the acute toxicity data from the literature. Also, review the endpoints for chronic
toxicity, which includes the data on reproduction in Daphnia magna and
Ceriodaphnia dubia, and in post-embryonic amphibian development (i.e. from
Marlatt et al., 2015). Use NOEC data for your estimates of the PNEC. If there were
no NOECs determined in the individual toxicity tests, estimate the NOEC by
dividing the LC50 (or EC50) by a factor of 100, or by dividing the LOEC by a factor
of 10.
2
Using an Excel spreadsheet, log-transform all of the NOECs for acute
toxicity and determine the mean NOEC and the 95% confidence limits around the
mean. Take the lower 95% confidence limit as a “conservative” estimate of the
PNEC for aquatic organisms exposed to triclosan. Using this PNEC for acute
toxicity, determine the ratio of PEC to PNEC (PEC/PNEC) for aquatic organisms
exposed to triclosan in wastewater effluents at a distance of 1,000 meters
downstream of the source under 10th, 50th and 90th percentile dilution scenarios. If
the ratio is =1, then there is a risk of adverse effects to aquatic organisms exposed
to triclosan in surface waters.
Determine the risk quotient using NOEC data for chronic toxicity in
Ceriodaphnia dubia (i.e. reproduction) and in post-embryonic frogs (i.e.
development) exposed to triclosan at a distance of 1,000 meters downstream from
the source under 10th, 50th and 90th percentile dilution scenarios.
Risks in the Terrestrial Environment:
From the Effects Assessment exercise, evaluate the data for the acute
toxicity of terrestrial organisms (i.e. cucumber, red wiggler worm) exposed to
triclosan in soil. Use the NOEC data for your estimates of the PNEC. For the most
sensitive endpoint (i.e. toxicity to cucumber), apply an assessment (i.e. “safety”)
factor of 10 to the NOEC to account for the fact that there are very few toxicological
data for terrestrial organisms exposed to triclosan. Determine the ratio of PEC to
PNEC (PEC/PNEC) for terrestrial organisms exposed to triclosan in agricultural
soils where biosolids were applied. If the ratio is =1, then there is a risk of adverse
effects to terrestrial organisms exposed to triclosan in soil.
Bioaccumulation Potential:
The log Kow value for triclosan is 4.8, so this compound may bioaccumulate
in exposed organisms; especially through bioconcentration from water in aquatic
organisms. There are various empirical relationships between log Kow and
bioconcentrations factors (BCF) for aquatic organisms that have been proposed in
the literature:
3
log BCF = 0.542 log Kow + 0.124 Neely et al. (1974)
log BCF = 0.85 log Kow – 0.70 Veith et al. (1979)
log BCF = log Kow – 1.32 Mackay (1982)
Using each of these relationships, estimate the BCF for aquatic organisms
exposed to triclosan. Compare these values to the BCF values that have been
determined experimentally for organisms exposed to triclosan (Table 1).
Table 1: Data on bioconcentration factors estimated for triclosan in aquatic
organisms.
Test Organism Exposure BCF Reference
Zebra fish Lab exposure 2,532 – 4,157 Orvos et al. 2002
Common carp Lab exposure 15-90 NITE 2005
White fish Field samples 2,000 – 5,200 Balmer et al 2004
Algae Field samples 700 – 1,500 Coogan et al 2007
Snail Field samples 1,200 Coogan et al 2008
References:
Balmer ME et al. 2004. Occurrence of methyl triclosan, a transformation product
of the bacteriocide triclosan, in fish from various lakes in Switzerland. Environ
Sci Technol 38:390-395.
Coogan MA et al. 2008 Snail bioaccumulation of triclocarban and triclosan and
methyl triclosan in a North Texas, USA stream affected by wastewater
treatment plant runoff. Environ Toxicol Chem 27:1788-1793.
Coogan MA et al 2007. Algal bioaccumulation of triclocarban, triclosan and methyltriclosan
in a North Texas wastewater treatment plant receiving stream.
Chemosphere 67:1911-1918.
Mackay D. 982. Correlation of bioconcentration factors. Environ Sci Technol
16:274-278.
Neely BW et al. 1974. Partition coefficient to measure bioconcentration potential
of organic chemicals in fish. Environ Sci. Technol 8:1113-1115.
4
NITE(National Institute of Technology and Evaluation of Japan) 2005.
Biodegradation and bioconcentration of existing chemical substances under
the Chemical Substances Control Law.
http://www.safe.nite.go.jp/denglish/kizon/KIZON_start-hazkizon.html.
Orvos DR et al. 2002. Aquatic toxicity of triclosan. Environ. Toxicol Chem 21:1338-
1349.
Veith GD et al. 1979. Measuring and estimating the bioconcentration factor of
chemicals in fish. J Fish Res Bd Can 36:1040-1048.
Assignment:
Risk Characterization and Management
1. Present your ecological risk assessments for aquatic and terrestrial
organisms exposed to triclosan by completing all of the steps described in
the Exposure Assessment, Effects Assessment and Risk Characterization
tutorials. Describe any of the steps in this procedure that are “conservative”
approaches for calculating a risk quotient (i.e. based on worst case
scenarios). Based on these calculations, if you were to recommend further
studies to more fully assess the risks of triclosan in the environment (i.e. a
Phase II, Tier B assessment), what would they be?
2. Estimate the Bioconcentration Factors (BCFs) for triclosan in aquatic
organisms using the three empirical relationships provided above. Compare
these data to the BCF values that have been determined experimentally
(Table 1) and comment on any differences or similarities. The log Kow value
of 4.8 for triclosan was determined at a pH = 7. However, for chemicals
that can ionize, such as triclosan, the Kow will vary with pH. Triclosan is a
phenolic compound with a pKa value of 7.9. In aquatic environments at the
upper range of the pH for natural waters (i.e. apprioximately pH=8), would
you expect that triclosan would show greater or lesser potential for
bioaccumulation than at a lower pH of 7?
3. “Risk Management” involves developing actions or policies that will reduce
or eliminate the risk of adverse effects to organisms. Risk management
5
could involve banning or phasing out a chemical. Is there justification for
using this approach to prevent adverse effects to aquatic and terrestrial
organisms exposed to triclosan? An alternative approach is to take steps
to reduce the amount of a chemical released into the environment. Discuss
ways in which this approach could be used to reduce the risks to aquatic
and terrestrial organisms exposed to triclosan.