Citation:

Belanger, S., A. Beasley, J. Brill, J. Krailler, K. Connors, G. Carr, M. Embry, M. Barron, R. Otter, AND A. Kienzler. Comparisons of PNEC Derivation Logic Flows Under Example Regulatory Schemes and Implications for ecoTTC. REGULATORY TOXICOLOGY AND PHARMACOLOGY. Elsevier Science Ltd, New York, NY, 123:104933, (2021). https://doi.org/10.1016/j.yrtph.2021.104933

Impact/Purpose:

This manuscript compares methods (logic flows) for developing Predicted No Effect Concentrations and their application in the ecological threshold of toxicological concern (ecoTTC) approach to toxicity extrapolation for groups of toxicologically or chemically similar compounds. Logic flows are flow charts that show which data and extrapolation factors could be used to compute a PNEC value. The impact of this research includes communication of an important tool that will facilitate chemical screening and hazard assessment of chemicals that have limited data. The paper proposes approaches to toxicity chronic/sublethal toxicity extrapolation that will improve the application of the ecoTTC approach to species and chemicals with limited data. Ultimately advancement of the approach and application in chemical assessments will make chemical screening and prioritization more efficient and cost effective by identifying those compounds of low risk and those chemicals of greatest concern to public health and the environment.

Description:

Derivation of a Predicted No Effect Concentration (PNEC) for aquatic systems is the primary deterministic form of hazard extrapolation used in environmental risk assessment. Depending on the breadth of taxonomic inclusion (algae, invertebrates, fish) and test data type (acute, chronic), different regulatory jurisdictions apply safety, assessment, or application factors (AFs) to the most sensitive measured endpoint to derive the PNEC for a chemical. To assess differences in estimated PNEC values, two representative PNEC determination methodologies were applied to the comprehensive curated public database and computational tool of the EnviroTox Platform (www.EnviroToxdatabase.org). PNECs were derived for 3647 compounds using derivation procedures based on historic US EPA and a modified version of the current European Union chemical registration procedures with some modifications to allow for comparisons. Ranked probability distributions of PNEC values were developed and the 5th percentile of each distribution was calculated for the entire dataset and for selected subsets, including scenarios where full acute or full chronic data sets were available. The lowest PNEC values were for organotin, specific pyrethroid pesticides, and dibenzo(furan/dioxin) compounds, indicating categorization based on chemical attributes and modes of action would lead to improved extrapolations. Fifth percentile PNEC values for all data included were approximately 50% lower when full acute or chronic datasets were included. Algae, under-represented in available ecotoxicity data, were more frequent drivers of PNEC values than invertebrates or fish. Greater inclusion of algal inhibition studies in chemical assessments will be important in understanding chemical hazards. The PNEC derivation logic flows summarized here are embedded in the EnviroTox Platform and provide for transparent and consistent derivation of PNEC and 5th percentile PNEC distribution calculations.

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