From source to sink: Multimedia fate, seasonal drivers, and priority control of synthetic phenolic antioxidants in typical bays of the Bohai Sea and the Yellow Sea, China

Synthetic phenolic antioxidants (SPAs) are emerging contaminants of concern in coastal environments, yet their multimedia distribution and integrated risks remain insufficiently characterized. We investigated 10 SPAs in seawater, suspended particulate matter (SPM), sediment, and Ruditapes philippinarum at 10 sites in three bays during May and August 2025. Total operationally dissolved concentrations ranged from 948 to 9851 ng/L in May to 19,585-42311 ng/L in August, and the across-site arithmetic mean was 6.35-fold higher in August. Sediment and clam concentrations across both campaigns ranged from 26,190 to 126425 and 28,666-117083 ng/g dry weight, respectively. Structural equation modeling indicated season-dependent associations between SPA concentrations and hydrochemical and nutrient variables. Positive matrix factorization resolved four factors tentatively associated with plastics, rubber, personal care products, and petroleum/lubricants. Biomarker associations in field-collected clams indicated co-occurring physiological stress but did not establish SPA-specific causation. In the provisional weight-of-evidence screen, BHT was classified as major in both campaigns, whereas AO1010 was classified as major in May and severe in August based on the sediment partitioning parameters, dietary exposure assumptions, and toxicological screening benchmarks. The integrated assessment supports targeted monitoring of BHT and AO1010 and investigation of their probable product-related inputs, with quantitative risk prioritization conditional on these methodological uncertainties.