Emerging contaminants in juvenile Chinook salmon: patterns of exposure and implications for conservation

Efforts to recover populations of threatened Chinook salmon in the Pacific Northwest may be hindered by exposure to contaminants in the juvenile life stage. Here we leverage a large dataset collected by the Washington Department of Fish and Wildlife's Toxic Biological Observation System to test for the accumulation of 219 contaminants of emerging concern (CECs) in juvenile Chinook salmon and identify chemicals that may affect salmon physiology, behavior, or fitness at current exposure levels. We also highlight results obtained from the region's two most urbanized watersheds, the Green/Duwamish and Puyallup/White, to demonstrate how these data can inform decision making to protect juvenile salmonids. We found that juvenile Chinook salmon sampled in the Puyallup/White watershed had the highest average concentrations of CECs, and that six chemicals appeared to be ubiquitous and were found in all five watersheds spanning a gradient of urbanization. In the subsequent detailed studies in the Green/Duwamish and Puyallup/White watersheds, we observed patterns in accumulation of per- and polyfluoroalkyl substances (PFAS) that revealed regions where certain analytes could be entering the rivers. In contrast, spatial patterns for pharmaceutical and personal care products (PPCPs) were less clear and indicated diffuse sources throughout the migration corridor, such as stormwater or wastewater. We recommend these results be used to target areas for source tracing studies for PFAS, and that future studies test for PPCP residues in commercial fish feed. Finally, the detection of multiple emerging contaminants in almost all composite fish samples, 11 of which exceeded available biological effects thresholds, reinforces the global call for green infrastructure projects that target source control and the removal or reduction of emerging contaminants from stormwater and wastewater.