Occurrence, Sources, and Risks of PAHs in an Urbanized Semi-Enclosed Watershed

This research systematically examines the spatial patterns, as well as the sources and hazards, of polycyclic aromatic hydrocarbons (PAHs) within the Xiangshan Harbor Watershed, an area supporting both mariculture and agriculture. Individual PAH concentrations in river water varied between 7.15 and 1016 ng/L, while sediment concentrations spanned from 10.1 to 7665 μg/kg dry weight (dw). Hotspots were identified within the upstream portion of the Fuxi River for water and the lower section of the Xianxiang River for sediment. Positive matrix factorization (PMF) revealed that vehicular emissions were the dominant contributor of PAHs in summer and autumn, contributing 62.2% and 50.0%, respectively, whereas coal burning was the primary contributor in sediment, accounting for 48.7%. A positive correlation was found between summer river water temperature and PAH groups, particularly medium and high molecular weight PAHs. Risk assessment showed that Benz[a]anthracene and Benzo[b]fluoranthene pose a high risk in water, and sediments in the watershed present higher risks compared to those in the inner bay. The cumulative cancer risk for two age groups remained below acceptable thresholds.