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 (R2 = 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;42:1542-1552. © 2023 SETAC.

Temperature threshold models for benthic macroinvertebrates in Idaho wadeable streams and neighboring ecoregions.

Water temperatures are warming throughout the world including the Pacific Northwest, USA. Benthic macroinvertebrates are one of the most important and widely used indicators of freshwater impairment; however, their response to increased water temperatures and their use for monitoring water temperature impairment has been hindered by lack of knowledge of temperature occurrences, threshold change points, or indicator taxa. We present new analysis of a large macroinvertebrate database provided by Idaho Department of Environmental Quality from wadeable streams in Idaho that is to be used in conjunction with our previous analyses. This new analysis provides threshold change points for over 400 taxa along an increasing temperature gradient and provides a list of statistically important indicator taxa. The macroinvertebrate assemblage temperature change point for the taxa that decreased with increased temperatures was determined to be about 20.5 °C and for the taxa assemblage that increased with increased temperatures was about 11.5 °C. Results of this new analysis combined with our previous analysis will also be useful for others in neighboring regions where these taxa occur.