Ecological Thresholds of Toxicological Concern: A Review

Abstract

The ecological threshold of toxicological concern (ecoTTC) is analogous to traditional human health-based TTCs but with derivation and application to ecological species. An ecoTTC is computed from the probability distribution of predicted no effect concentrations (PNECs) derived from either chronic or extrapolated acute toxicity data for toxicologically or chemically similar groups of chemicals. There has been increasing interest in using ecoTTCs in screening level environmental risk assessments and a computational platform has been developed for derivation with aquatic species toxicity data (https://envirotoxdatabase.org/). Current research and development areas include assessing mode of action-based chemical groupings, conservatism in estimated PNECs and ecoTTCs compared to existing regulatory values, and the influence of taxa (e.g., algae, invertebrates, and fish) composition in the distribution of PNEC values. The ecoTTC continues to develop as a valuable alternative strategy within the toolbox of traditional and new approach methods for ecological chemical assessment. This brief review article describes the ecoTTC concept and potential applications in ecological risk assessment, provides an overview of the ecoTTC workflow and how the values can be derived, and highlights recent developments and ongoing research. Future applications of ecoTTC concept in different disciplines are discussed along with opportunities for its use.

Investigations On the Fish Acute Toxicity of Fragrance Ingredients Involving Chinese Fish Species and Zebrafish Embryos

“…Sensitivity comparison using CTD models and UFs derivation. The CTD approach has been often used to generate the ecological threshold of toxicological concern values for screening-level risk assessment (Barron et al, 2021), in the present study, we used CTDs to calculate threshold concentrations (e.g., TC5) for sensitivity comparison as in Wang et al (2014), who compared the sensitivity of chemicals to temperate and tropical fish.…”

Use of the Species Sensitivity Distribution Approach to Derive Ecological Threshold of Toxicological Concern (eco-TTC) for Pesticides

“…The introduction of the concept of ecological thresholds of toxicological concern (eco-TTC) has resulted from the upgrading of risk assessment procedures in recent years, the aim of which is to establish an exposure level for chemicals beneath which no significant risk to ecosystems is likely [26,27,44,45]. The use of eco-TTC reduces the need for ecotoxicological studies of untested chemicals in cases where it can be demonstrated that the expected exposure is unlikely to exceed a level of concern.…”

“…In the last few years, the concept of the ecological threshold of concern (eco-TTC) has been proposed as a pragmatic approach useful in screening-level ecological risk assessment [25][26][27]. Indeed, for chemicals with little or no ecotoxicological information, eco-TTC allows identifying the exposure threshold, below which there is a negligible risk for aquatic organisms.…”

“…In this, the eco-TTC differs from HC 5 since, following the framework of PNEC calculation, it may combine acute and chronic toxicity data and consider the use of the AFs. On the other hand, as previously noted, HC 5 values can be used to derive PNECs, which could be incorporated in the eco-TTC calculation [27].…”

Comment on Plugge et al. 2021 “Toward a Universal Acute Fish Threshold of Toxicological Concern”

“…Subsequent research under a multisector group of the Committee on Animal Alternatives in Environmental Risk Assessment, Health and Environmental Sciences Institute (HESI; 2019) resulted in a curated collection of data (the EnviroTox Database, which is referenced in Plugge et al 2021), an assessment of the implications regarding mode of action (Kienzler et al 2017(Kienzler et al , 2019, and a detailed study on the database itself (Connors et al 2019). In addition, an invited review was recently published in a special issue of Frontiers in Toxicology (Barron et al, 2021). Reference materials related to the background of all concepts explored can be downloaded directly from the EnviroTox website (Health and Environmental Sciences Institute 2019).…”