Elevated organic UV absorbents in herring gull eggs near urban areas: Spatial trends across the St. Lawrence system

Ultraviolet (UV) absorbents, such as benzotriazole UV stabilizers (BZT-UVs) and UV filters (UVFs), are mass-produced additives and contaminants of emerging concern. Monitoring seabird eggs provides valuable insights into geographic patterns of contaminant exposure across ecosystems. 8 BZT-UVs and 5 UVFs in herring gull (Larus argentatus) eggs were collected in 2022-2023 from 9 colonies across three sections (fluvial, estuary, gulf) of the St. Lawrence, one of North America's most industrialized regions. Two BZT-UVs (UV-328 and UV-329) and two UVFs (EHS and HMS) were the predominant contaminants across the system. Concentrations of UV-328 (median: 2.6 ng/g wet weight (ww)), UV-329 (median: 2.2 ng/g (ww)), and EHS (median: 5.6 ng/g (ww)) were the highest known to be reported to date in seabird eggs. Total BZT-UVs, UV-328, and UV-329 were highest near Montreal, with concentrations decreasing downstream in the estuary and gulf, correlating positively with human population density and wastewater treatment plant effluent volume. These findings suggest that anthropogenic activities across the St. Lawrence influence BZT-UV exposure in herring gulls. UVF concentrations were similar across the studied range, suggesting that factors other than the local landscape influence contamination patterns. This study provides the first overview of spatial trends in UV absorbent contamination in seabird eggs, underscoring their value as sentinels of emerging contaminants. Further investigations are required to understand the potential risks these contaminants pose to biota.