Pesticides Contamination in the Xiangshan Harbor Watershed: Sources, Occurrence, and Ecological Risk Analysis

Abstract

This study investigates the spatial distribution, key sources, and environmental implications of pesticides within the primary rivers supplying the Xiangshan Harbor Watershed-a region characterized by intensive agricultural and aquaculture activities. Pesticide concentrations in river water ranged from 0.70 to 398.61 ng/L, while sediment concentrations varied from 0.09 to 12.97 μg/kg dry weight (dw). Elevated pesticide levels were primarily detected in the water of the lower Dan Harbor and the sediment of the upper XianXiang River. Agricultural runoff was identified as the predominant source of pesticide contamination, with secondary contributions from industrial activities, historical residues, and mariculture. Analysis also indicated a negative correlation between summer dissolved oxygen levels in river water and specific pesticide groups, including mefenacet and fungicides. Risk assessments showed that thifluzamide poses a high risk to water and sediments in autumn, while mefenacet presents a high risk to water in summer. Despite these environmental risks, human carcinogenic risk levels remained below the threshold of concern (1E-6), indicating acceptable limits for human health.

Keywords: Pesticide contamination, Spatial distribution, Source identification, Ecological risk assessment, Xiangshan Harbor Watershed