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Assessing the bioaccumulation potential of ionizable organic compounds: Current knowledge and research priorities
Citation:
Armitage, J., R. Erickson, T. Luckenbach, C. Ng, R. Prosser, J. Arnot, K. Schirmer, AND J. Nichols. Assessing the bioaccumulation potential of ionizable organic compounds: Current knowledge and research priorities. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 36(4):882-879, (2017).
Impact/Purpose:
The bioaccumulation potential of ionizable organic chemicals (IOCs) in ecological receptors is of increasing interest to scientists and risk assessors. However, modeling tools typically applied to assess bioaccumulation were developed for neutral organic chemicals and do not adequately address key aspects of the behaviour of IOCs in vivo. The objective of this paper was to review the state of the science regarding the bioaccumulation potential of IOCs, with a focus on the availability of empirical data for fish and development of predictive models. Two case studies were presented. The first describes modeled effects of pH and biotransformation on bioconcentration of weak acids and bases, while the second employs an updated model to investigate factors responsible for accumulation of perfluoroalkylated acids (PFAA). The PFAA case study is notable insofar as it illustrates the likely importance of membrane transporters in the kidney and highlights the potential value of read across approaches in bioaccumulation assessments for IOCs. This paper provides preliminary guidance on a scientifically-based approach to bioaccumulation assessment of IOCs and will serve as an invaluable resource for those who conduct risk assessments for this important class of environmental contaminants.
Description:
The objective of the present study is to review current knowledge regarding the bioaccumulation potential of IOCs, with a focus on the availability of empirical data for fish. Aspects of the bioaccumulation potential of IOCs in fish that can be characterized relatively well include the pH-dependence of gill uptake and elimination, uptake in the gut, and sorption to phospholipids (membrane-water partitioning). Key challenges include the lack of empirical data for biotransformation and binding in plasma. Fish possess a diverse array of proteins which may transport IOCs across cell membranes. Except in a few cases, however, the significance of this transport for uptake and accumulation of environmental contaminants is unknown. Two case studies are presented. The first describes modeled effects of pH and biotransformation on bioconcentration of organic acids and bases, while the second employs an updated model to investigate factors responsible for accumulation of perfluoroalkylated acids (PFAA). The PFAA case study is notable insofar as it illustrates the likely importance of membrane transporters in the kidney and highlights the potential value of read across approaches. Recognizing the current need to perform bioaccumulation hazard assessments and ecological and exposure risk assessment for IOCs, we provide a tiered strategy that progresses (as needed) from conservative assumptions (models and associated data) to more sophisticated models requiring chemical-specific information.
