Tanya M Brown, Antoine E Simond, Katerina Colbourne, Samuel Turgeon, Eliza-Jane Morin, Jory Cabrol, Véronique Lesage

Characterizing the nature, significance and origins of the many different pollutants found in high trophic level marine mammals is exceedingly difficult. The operational implementation of effective Recovery and Action Plans for the endangered St Lawrence Estuary Beluga Whales (SLE beluga, Delphinapterus leucas) under the Species at Risk Act will benefit from an understanding of conservation threats, including high levels of endocrine disrupting contaminants. A science-based evaluation and prioritization of the contaminants found in their priority prey and Critical Habitat will help deliver refined guidance to support the wider conservation agenda for this population. Concentrations of over 600 contaminants from 13 contaminant classes were determined in 17 surface sediment samples collected from 2020 to 2022 throughout the SLE beluga Critical Habitat. A subset of known priority contaminants, including PCBs, organochlorine (OC) pesticides, PBDEs, Dioxins/Furans, and mercury were also analyzed in the tissues of eleven priority SLE beluga prey species collected in 2019 and 2020. Measured chemical concentrations were compared to sediment quality guidelines for the protection of aquatic life, tissue residue guidelines for the protection of wildlife consumers of aquatic biota, 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 both the belugas and their prey. Contaminant pattern and ratio analyses were used to help characterize the contribution of nearby land-based versus global sources of contaminants. This study is the first step toward a comprehensive risk-based evaluation and exposure attribution for contaminants of concern to the SLE beluga.