Spatial Distribution, Seasonal Variation, and Ecological Risk Assessment of Benzotriazole UV Stabilizers in Waters from Canadian Tributaries and Coastal Systems

Benzotriazole UV stabilizers (BZT-UVs) are industrial additives of emerging environmental concern, with UV-328 recently listed under the Stockholm Convention on Persistent Organic Pollutants and several congeners listed as Substances of Very High Concern in Europe. However, their distribution and fate in coastal environments remain poorly understood. This study investigated the spatial and seasonal variations of dissolved and suspended particulate matter (SPM)-bound BZT-UVs in surface water from the St. Lawrence River, Estuary and Gulf (SLREG) and the coast of Vancouver and Victoria, spanning Canada's east and west coasts. BZT-UV contamination was higher in the SLREG, with peak UV-328 levels in July, likely due to increased summer use. Most congeners were more abundant in the SPM from July to October in the St. Lawrence Estuary, while elevated UV-329 levels in April suggest a distinct source, possibly related to snowmelt. These seasonal variations may influence the exposure of local species to BZT-UVs. While the concentrations of the dissolved BZT-UVs in most samples are expected to pose minimal ecological risks, the concentrations of some BZT-UVs in a few samples from the upper estuary of the SLREG may pose moderate to high risk in summer, highlighting the need for further assessment.