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Quantifying Conservatism in Ecological Threshold for Toxicological Concern and Chemical Toxicity Distributions: Case Study of Chemicals with Regulatory Water Quality Values
Citation:
Adriana, B., M. Barron, K. Connors, M. Embry, AND K. Fay. Quantifying Conservatism in Ecological Threshold for Toxicological Concern and Chemical Toxicity Distributions: Case Study of Chemicals with Regulatory Water Quality Values. SETAC North America, Toronto, Ontario, CANADA, November 03 - 07, 2019.
Impact/Purpose:
Predictive methods that address aquatic hazards of chemicals remain essential as thousands of compounds have yet to be tested. The Threshold for Toxicological Concern (TTC) is well-established for assessing human safety but has only recently been explored in the ecological context. TTC establishes an exposure level for chemicals, below which no appreciable risk is expected based on toxicity values for related chemicals. This approach has been extended to encompass ecological resources via ecoTTCs. These are summaries of the distribution of a large array of aquatic species level toxicity data on diverse chemical substances as ecosystem Predicted No Effect Concentrations (PNECs). EcoTTCs enable the prediction of untested chemicals based on similarly acting chemicals that share a structural attribute, mode of action, or functional use. An ecotoxicological database has been recently developed based on an assessment of published data and international chemical management programs. The ecoTTC concept may be useful for assessing chemicals at early tiers of the risk assessment process, providing hazard perspective on chemicals that toxicity data, guiding product development discussions, and assisting read across or category justifications. This will be one of several case-studies that are underway to explore the feasibility of the eco-TTC approach based on several decision-contexts including prioritization and screening, chemical risk assessment, site specific risk assessment, mixtures, product development, criteria development
Description:
Ecological Thresholds for Toxicological Concern TTC (ecoTTC) summarize a large array of species-level toxicity data as a probabilistic distribution of Predicted No-Observed Effect Concentrations (PNECs). These probability distributions enable the prediction of untested chemicals based on grouping via a structural attribute, mode of action, or functional use. The approach may be useful for assessing chemicals at early tiers of the risk assessment process, providing hazard perspective on chemicals that lack QSARs, guiding product development discussions, and assisting read across or category justifications. Because PNECs can be regionally-based in their development and apply different uncertainty/safety factors, PNEC distributions can vary substantially. A chemical toxicity distribution (CTD) can be used to develop hazard concentrations with user developed levels of uncertainty and conservatism. The purpose of this presentation is to share initial findings of a case study assessing conservatism in ecoTTC and CTD approaches. Aquatic toxicity-based water quality standards (e.g., Water Quality Criteria and Standards; Environmental Quality Standards) provide benchmarks for assessing the conservatism in ecoTTC and CTD approaches. EcoTTC and CTD estimates were compared to existing criteria and screening benchmark values from regulatory jurisdictions for several groups of chemicals. Groupings were based on: 1) availability of aquatic criteria values from more than one regulatory jurisdiction; 2) sufficient data to develop ecoTTC and CTD estimates; and 3) identified and articulated grouping criteria (e.g., common mode of action, chemical functional classes, and presence on priority lists). This presentation will provide an overview of the case study, the approaches utilized, rationale for group selection, and a quantitative comparison of the degree of conservatism in ecoTTC and CDT approaches. Guidance will be provided to new users of the ecoTTC tool to explore case studies and applications to chemical evaluation strategies.
