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A model to predict threshold concentrations for toxic effects of chlorinated benzenes in sediment

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Title: A model to predict threshold concentrations for toxic effects of chlorinated benzenes in sediment
Authors: Duda, D. J., Fuchsman, P. C., Barber, T. R.
Source: Environmental Toxicology & Chemistry. Sep1999, Vol. 18 Issue 9, p2100. 0p.
Subjects: Ecological risk assessment, Modeling (Sculpture)
Abstract: A probabilistic model was developed to predict effects threshold concentrations for chlorinated benzenes in sediment. Based on published quantitative structure-activity relationships relating the toxicity of chlorinated benzenes to the degree of chlorination, congeners with the same number of chlorine substitutions were considered toxicologically equivalent. Hexachlorobenzene was excluded from the assessment based on a lack of aquatic toxicity at the water solubility limit. Theequilibrium partitioning approach was applied in a probabilistic analysis to derive predicted effects thresholds (PETs) for each chlorinated benzene group, with model input distributions defined by published log Kow values and aquatic toxicity data (LC50s and acute to chronic ratios) extracted from the published literature. The probabilistic distributions of PETs generally increased with chlorination, with 20th percentile values ranging from 3.2 mg/kg1%OC for chlorobenzene to 67 mg/kg1%OC for tetrachlorobenzene congeners. The toxicity of total chlorinated benzenes in sediment can be assessed by applying the PETs in a toxic index model, based on theassumption that multiple chlorinated benzene congeners will show approximately additive toxicity, as characteristic of nonpolar narcotic toxicants. The 20th percentile PET values are one to two orders of magnitude higher than published screening-level guidelines, suggesting that the screening-level guidelines will provide overly conservative assessments in most cases. Relevant spiked sediment toxicity data arevery limited but seem consistent with the probabilistic model; additional testing could be conducted to confirm the model's predictions. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:A probabilistic model was developed to predict effects threshold concentrations for chlorinated benzenes in sediment. Based on published quantitative structure-activity relationships relating the toxicity of chlorinated benzenes to the degree of chlorination, congeners with the same number of chlorine substitutions were considered toxicologically equivalent. Hexachlorobenzene was excluded from the assessment based on a lack of aquatic toxicity at the water solubility limit. Theequilibrium partitioning approach was applied in a probabilistic analysis to derive predicted effects thresholds (PETs) for each chlorinated benzene group, with model input distributions defined by published log Kow values and aquatic toxicity data (LC50s and acute to chronic ratios) extracted from the published literature. The probabilistic distributions of PETs generally increased with chlorination, with 20th percentile values ranging from 3.2 mg/kg1%OC for chlorobenzene to 67 mg/kg1%OC for tetrachlorobenzene congeners. The toxicity of total chlorinated benzenes in sediment can be assessed by applying the PETs in a toxic index model, based on theassumption that multiple chlorinated benzene congeners will show approximately additive toxicity, as characteristic of nonpolar narcotic toxicants. The 20th percentile PET values are one to two orders of magnitude higher than published screening-level guidelines, suggesting that the screening-level guidelines will provide overly conservative assessments in most cases. Relevant spiked sediment toxicity data arevery limited but seem consistent with the probabilistic model; additional testing could be conducted to confirm the model's predictions. [ABSTRACT FROM AUTHOR]
ISSN:07307268