Blood UV absorbents in urban breeding herring gulls: Annual environmental conditions, not anthropogenic habitat use, drive exposure.

Urban-adapted wildlife foraging in coastal areas are exposed to mixtures of synthetic contaminants, including ultraviolet absorbents (UVAs), such as benzotriazole UV stabilizers (BZT-UVs) and organic UV filters (UVFs). Herring gulls (Larus argentatus), known for their foraging plasticity, are particularly susceptible to UVA exposure due to their reliance on anthropogenic habitats, including landfills, known as sinks of products containing UVAs. However, the impact of foraging habitat on exposure is unknown. We aimed to investigate this relationship in gulls along the St. Lawrence estuary near the industrial center of Québec City (QC, Canada) over two breeding seasons (2023 and 2024). Eight BZT-UVs and five UVFs were measured in the plasma and red blood cells (RBC) of breeding adults. We detected UVAs in both blood compartments of the gulls sampled, with two BZT-UVs (UV-328 and UV-P) and two UVFs (BP-3 and HMS) being the most prevalent. Year was a strong predictor for most frequently detected UVA concentrations, while both year and temperature influenced ΣBZT-UVs, ΣUVFs, HMS, and UV-P. Specifically, one year had colder environmental conditions, which contributed to higher concentrations. This study is the first to demonstrate blood compartmentalization of UVAs between plasma and RBC, with higher concentrations found in RBC. Despite UVA exposure among all individuals and predominant foraging in anthropogenic terrestrial habitats, primarily agricultural fields, we found no association between habitat types and concentrations. Our findings suggest that UVA pollution is pervasive across diverse anthropogenic habitats, highlighting the complex pathways of exposure in urban-adapted wildlife and the need for broader monitoring.