Citation:

Nichols, J., F. Gobas, M. McLeod, K. Borgi, P. Leonards, P. Ester, H. Laue, AND J. Arnot. Summary of Cefic-LRI sponsored workshop: Recent scientific developments in bioaccumulation research. In Proceedings, Cefic-LRI-Field Research, Helsinki, FINLAND, September 24, 2014. Cefic, Brussels, Belgium, 1-13, (2015).

Impact/Purpose:

Chemical bioaccumulation in fish is one of three chemical properties commonly used to evaluate the hazard associated with environmental contaminants (the others are persistence and inherent toxicity). Existing mass-balance models accurately predict accumulation for neutral organic chemicals that partition passively to tissue lipid and do not undergo substantial biotransformation. Increasingly, however, risk assessors are encountering compounds that do not exhibit these behaviors. The goal of this workshop was to review the state-of-the-science with respect to bioaccumulation assessments for fish including the development of improved methods for in vivo measurement of bioaccumulation, interpretation of measured accumulation in field-collected animals, and prediction of biotransformation using in silico and in vitro procedures. The findings of this workshop substantially advance current understanding of this topic and will be of interest to several EPA Program Offices including the Office of Pesticide Programs (OPP) and Office of Pollution Prevention and Toxics (OPPT).

Description:

Current bioaccumulation regulations in most jurisdictions include only the bioconcentration factor (BCF) and the octanol-water partition coefficient (KOW) for screening assessments. Methods for evaluating bioaccumulation continue to evolve and various other metrics have been proposed including the biomagnification factor (BMF), bioaccumulation factor (BAF), trophic magnification factor (TMF), and elimination half-life (t1/2) 1, 2.  Environmental measurements are most relevant regarding a chemical’s actual behavior in the environment; however, due to natural variability, field measurements, and hence field bioaccumulation data, can be quite variable. Environmental sampling that does not consider variability can translate to uncertainty, which reduces the precision of field-derived bioaccumulation metrics which may be important in a regulatory context. Models and guidance are recommended to develop consistent methods for collecting and interpreting field data.  The BCF does not account for chemical uptake from the diet; therefore, it may not reflect the extent of bioaccumulation that would result from an environmental exposure. However, models can be used to relate the BCF to environmentally relevant metrics such as the BMF, BAF, and TMF in a straightforward manner 3.  Current science indicates that the biotransformation rate constant (kB) represents the principal source of uncertainty in the bioaccumulation assessment of most chemicals with high bioaccumulation potential and kB is a common element to all bioaccumulation assessment metrics. It is clear that more research to improve the quantification and estimation of biotransformation rates and pathways is critical for improving bioaccumulation screening assessments. In vivo kB databases and in silico models (quantitative structure-activity relationships, QSARs) for predicting kB from chemical structure have recently been established, but more kB data are needed and a wider range of measurement techniques should be developed. In vitro and in vitro-to-in vivo extrapolation (IVIVE) methods and data to estimate clearance and kB continue to evolve and offer a promising path forward. Since kB is often the key determinant of existing and proposed bioaccumulation assessment metrics, it was suggested that kB could be used as a new screening-level criterion for bioaccumulation assessment. A combination of estimates for kB derived from different methods can be applied in a weight of evidence approach (WoE) to address uncertainty.  A weight of evidence (WoE) is suggested for screening assessments (to the greatest extent possible, often with limited data) and certainly for definitive decision-making (cases in which more data are available or can be obtained). A WoE framework has been developed for biomagnification assessment 1. A complimentary framework and formal guidance for overall bioaccumulation assessment is suggested.

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