Pesticides used in agriculture can end up in nearby streams and can have a negative impact on nontarget organisms such as aquatic invertebrates. During registration, bioaccumulation potential is often investigated using laboratory tests only. Recent studies showed that the magnitude of bioaccumulation in the field substantially differs from laboratory conditions. To investigate this discrepancy, we conducted a field bioaccumulation study in a stream known to receive pollutant loadings from agriculture. Our work incorporates measurements of stream pesticide concentrations at high temporal resolution (every 20 min), as well as sediment, leaves, and caged gammarid analyses (every 2-24 h) over several weeks. Of 49 investigated pesticides, 14 were detected in gammarids with highly variable concentrations of up to 140 ± 28 ng/gww. Toxicokinetic modeling using laboratory-derived uptake and depuration rate constants for azoxystrobin, cyprodinil, and fluopyram showed that despite the highly resolved water concentrations measured, the pesticide burden on gammarids remains underestimated by a factor of 1.9 ± 0.1 to 31 ± 3.0, with the highest underestimations occurring after rain events. Including dietary uptake from polluted detritus leaves and sediment in the model explained this underestimation only to a minor proportion. However, suspended solids analyzed during rain events had high pesticide concentrations, and uptake from them could partially explain the underestimation after rain events. Additional comparison between the measured and modeled data showed that the pesticide depuration in gammarids is slower in the field. This observation suggests that several unknown mechanisms may play a role, including lowered enzyme expression and mixture effects. Thus, it is important to conduct such retrospective risk assessments based on field investigations and adapt the registration accordingly.

Three years following the Gold King Mine (GKM) spill that released approximately 11 million liters of metal-laden mine drainage into the Animas River, the scientific community is still evaluating the effects of this acute environmental impact in the context of a chronically mineaffected region. People living within the region affected by the spill had two principal concerns in its aftermath: is the water safe and what are the spill effects on the plants and fish consumed by humans? These are related issues, and perhaps not easy to answer. The work reported here aims to answer the second question regarding spill effects on biota, while appreciating that doing so requires a sophisticated understanding of chemical element cycling and the interactions among the physical and biological components of the aquatic and terrestrial ecosystems within the influence of the Animas and San Juan Rivers.

The purpose of is this study was to evaluate the potential for biotransformation in the gastrointestinal tissues (GIT) of fish to impact chemical bioaccumulation. In vitro biotransformation of two polycyclic aromatic hydrocarbons, pyrene (PYR) and benzo[a]pyrene (BAP), and two organic sunscreen agents, 2-ethylhexyl-4-methoxycinnamate (EHMC) and octocrylene (OCT), was measured using S9 fractions isolated from liver tissue and tissues of the upper GIT in rainbow trout. For PYR, BAP, and EHMC, activity was substantially higher in liver S9 fractions than in GIT S9 fractions. For OCT, activity was highest in GIT S9 fractions. An existing in vitro-in vivo extrapolation (IVIVE) model for fish, which yields a whole-animal biotransformation rate constant (kMET), was expanded to consider biotransformation in the GIT. The kMET values obtained using measured rates of in vitro activity (liver and GIT) were in good agreement with kMET values measured in controlled in vivo experiments, providing strong support for the IVIVE approach. Moreover, inclusion of GIT activity into the model prediction for OCT resulted in much better agreement with the empirical kMET estimate than was obtained using a ‘liver only’ model. These findings suggest that current ‘liver only’ approaches to IVIVE modeling may underestimate in vivo whole-animal biotransformation rates for chemicals that undergo substantial biotransformation in the GIT. Thus, failure to consider biotransformation in the GIT may lead to overestimation of true levels of bioaccumulation. This dataset is associated with the following publication: Saunders, L., P. Fitzsimmons, J. Nichols, and F. Gobas. In vitro-in vivo extrapolation of hepatic and gastrointestinal biotrasnformation rates of hydrophobic chemicals in rainbow trout. AQUATIC TOXICOLOGY. Elsevier Science Ltd, New York, NY, USA, 228: 1-12, (2020).