Inorganic Arsenic Concentration in Fish Governed by Trophic Level and Size, not Water Concentration: Implications for Human Health Water Quality Criteria

In 2019, the Idaho Department of Environmental Quality implemented a paired surface water and fish tissue data collection program to derive a state-specific bioaccumulation factor (BAF) for inorganic arsenic (iAs) as part of the development of new human health water quality criteria (HHWQC). No statistically significant relationship was found between total arsenic (tAs) or iAs in surface water and fish tissue. Fish body weight was the only parameter with a statistically significant effect on iAs concentration in fish tissue. The ratio of iAs to tAs in fish tissue declined significantly with both increasing trophic level and increasing body weight. The decrease in iAs concentration in fish tissue with increasing size and trophic level as well as the decrease in the proportion of tAs that is iAs with increasing trophic level are likely the result of metabolic transformation of iAs to organic As by organisms in each level of the aquatic food web. Although the linear regression-based BAF using the Idaho paired fish and water data best predicted observed iAs fish tissue concentrations compared to several alternative BAFs, it was not statistically significant (p < 0.05) and was a poor predictor (R-2 = 0.01) of iAs concentrations in fish tissue. These results illustrate that iAs, and possibly other metals, in the natural environment do not conform with commonly used bioaccumulation models and the paradigm used by the US Environmental Protection Agency for determining HHWQC. These results indicate that modifications to the paradigm are necessary, such as a fish tissue criterion as Idaho has proposed, to assure that public health is protected. Environ Toxicol Chem 2023;00:1-11. (c) 2023 SETAC