In vitro bioassays for quantifying mixture effects of organic micropollutants extracted from caged fish, water, and...

Fish are exposed to countless chemicals over their lifetime, with the totality of internal exposure termed the eco-exposome. In vitro bioassays can be used to complement targeted chemical analysis to quantify the mixture effects of chemicals in fish and relate them to the effects measured in extracts of water and sediment. Fathead minnows (Pimephales promelas) were exposed in cages for 48 hr and 21 days at four field sites with diverse chemical profiles. Fish, water, and sediment were collected, extracted, and analyzed with four cell-based reporter gene assays. Water from all sites activated xenobiotic metabolism in vitro, whereas only water from a site near a wastewater treatment plant activated the estrogen receptor. Only 5% of water samples were above their effect-based trigger values (EBTs) for surface water, suggesting a low overall chemical burden. In contrast, 77% of bioactive sediment samples exceeded tentative sediment EBTs, suggesting the mixture effects of chemicals in the sediment are likely to be more problematic. Whole fish extracts activated the arylhydrocarbon receptor and oxidative stress response, with the greatest effect observed at a site affected by both legacy and more recent contamination. Interpretation of mixture effects in extracts from caged fish versus laboratory controls was confounded by background contamination of fish food, as well as endogenous chemicals. Comparison of measured mixture effects with mixture effects predicted from detected chemical concentrations and their relative effect potencies indicated that mixture effects in fish extracts were mainly dominated by chemicals detected in sediment. Sediment and water did not reliably serve as a proxy for the eco-exposome. Bioanalytical investigation of whole fish extracts provides a novel approach to comprehensively characterize the fish exposome.