The Threshold for Toxicological Concern (TTC) is well-established for assessing human safety of indirect food-contact substances and has been reapplied for a variety of endpoints including carcinogenicity, teratogenicity, and reproductive toxicity. Recently, we proposed an extension to the human safety TTC concept for application in environmental situations, termed the ecological TTC (eco-TTC). Eco-TTCs summarize the wealth of ecotoxicological information as Predicted No-Observed Effect Concentrations (PNECs) on diverse chemical substances in the form of statistical (probability) distributions. Eco-TTCs enable the prediction of untested chemicals based on structural attribute (category), 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. A database with approximately 110,000 unique ecotoxicological records has been developed based on recent assessments of published data and international chemical management programs. This toxicity data is associated with physical chemistry data and curated taxonomic information for the organisms tested. A process to conclude acute and chronic effects as well as identify the PNEC for exposed ecosystems based on depth and breadth of data have been devised and several mode of action schemes are being assessed to devise a best approach for grouping compounds. Chemicals that are categorized as neutral organics are the most abundant in the dataset, therefore are candidates for an initial in-depth assessment of eco-TTC attributes. Approximately 500 chemicals in the database are included in this analysis at this time with approximately one third having complete acute or chronic data sets (all three taxa). The eco-TTC for non-polar and polar narcotics is explored in depth, with additional categories under development (phenols, esters, reactive compounds, surfactants, pesticides, and pharmaceuticals). The dataset and associated tools will be made available via a web-based platform to provide an open, transparent opportunity for stakeholders to evaluate the approach with case examples. <i>The views, conclusions and recommendations expressed in this article are those of the author and do not necessarily represent views or policies of the European Commission or the U.S. Environmental Protection Agency.</i>

Ecological Threshold for Toxicological Concern (eco-TTC): Assessing the potential of a new tool for environmental hazard assessment

253rd National Meeting (2017)

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