Prioritizing contaminants of concern in the Fraser River watershed: a risk-based evaluation for outmigrating juveniles and…

The Fraser River watershed is home to 54 unique spawning populations of salmon, including 19 Chinook (Oncorhynchus tshawytscha) populations. Fraser Chinook provide 80-90% of the food source consumed by Southern Resident killer whales (SRKW, Orcinus orca) in the spring and summer. Over 90% (15/16) Fraser Chinook populations are at risk. Extensive forestry, agricultural, industrial and urban activities take place in the Fraser Valley that expose early life stages of emigrating salmon and returning adult salmon to a mix of legacy and emerging contaminants. Many of which, can elicit adverse health effects in vertebrates, including endocrine disruption and reproductive effects. However, there is limited information on the nature of contaminants discharged into British Columbia's salmon habitat and their associated effects, hampering solution-oriented opportunities for natural resource managers and stakeholders. Surface water samples were collected monthly (2018-2020) from seven urban and semi urban sites in the Fraser River watershed, and one site in the Serpentine River, a lower discharge river that flows directly into SRKW critical habitat. Samples were analyzed for over 800 contaminants in order to prioritize contaminants of concern to outmigrating juveniles and retuning adult salmon, with a special focus on Chinook salmon. Measured chemical concentrations were compared to water quality guidelines for the protection of aquatic life and chemical-specific biological activities determined in high-throughput (ToxCast) in vitro assays. A risk-based evaluation using a combination of toxicity quotients and exposure activity ratios was performed to prioritize contaminants for long-term monitoring and to identify chemicals suspected of posing a potential risk to salmon. This study is the first step toward a comprehensive risk-based evaluation for contaminants of concern to salmon in the Fraser River. Results will support the Government of Canada's Whales Initiative in its quest to identify contaminants of greatest concern to Chinook salmon and to guide SRKW recovery efforts.