A risk-based screening of organic contaminants in juvenile chinook salmon and their habitat in the Lower Fraser River and estuary, British Columbia

Many populations of anadromous Chinook salmon (Oncorhynchus tshawytscha) in the Fraser River in British Columbia, Canada, have experienced decades of decline, with 85% (14/16) of assessed populations classified as 'Endangered' or 'Threatened'. During outmigration, these juvenile Chinook stocks transit through areas impacted by heavy agricultural use and urban and industrial development in the Fraser River watershed. The lack of biologically relevant assessments of environmental contamination in salmon habitats underscores a notable gap in conservation initiatives. Here, we screened organic contaminants measured in juvenile Chinook tissue and their habitat (i.e.,, water) to identify compounds that pose a potential risk to Fraser River Chinook populations. Over 595 organic contaminants (spanning eight contaminant classes) were measured in samples from five sites in the Lower Fraser basin. One hundred and thirty out of 288 (45%) of detected contaminants in water and 82 out of 368 (22%) detected in juvenile Chinook tissue were assessed against threshold values. These thresholds included published environmental quality guidelines (EQGs) and a variety of screening benchmark values, which were derived from in vivo, in vitro, or predictive modelling data across multiple databases. Sixteen contaminants were identified as "Priority" contaminants with the potential for adverse effects, and 23 were classified as "Watchlist" contaminants worthy of secondary monitoring. These included pharmaceuticals and personal care products, pesticides, polycyclic aromatic hydrocarbons, flame retardants and polychlorinated biphenyls. This preliminary risk-based screening of organic contaminants in the Lower Fraser River serves to inform monitoring and recovery efforts for culturally-valued Chinook populations, as well as the Endangered Southern Resident killer whales that depend on them.