Spatial and temporal distribution of mercury contamination in Bombay duck (Harpadon nehereus) from southeastern coastal China.

China's southeastern coast, particularly Zhejiang, Fujian, and Guangdong, is rich in key fishery resources but also faces elevated contamination due to intensive industrial activity. The study investigated the spatial and temporal variations of mercury (Hg) in Bombay duck (Harpadon nehereus) collected from five coastal sites, the Yangtze River estuary, Hangzhou Bay, Wenzhou, Xiamen and Zhanjiang. The Hg levels and MeHg/THg ratios generally increased with decreasing latitude, with the highest Hg concentrations observed in Zhanjiang (THg: 0.2034 mg/kg, MeHg: 0.1778 mg/kg), significantly exceeding those at other sites. Weight-adjusted Hg levels showed a reversed trend between Zhanjiang and Hangzhou Bay, attributing mainly to the small fish size of the latter site, and support the need for site-specific monitoring. The monthly Hg concentrations and MeHg/THg ratios peaked in Xiamen in August, exhibiting seasonal variation patterns that correlated with monthly fluctuations in water temperature. Toxicity risk thresholds indicated that Bombay duck from Zhanjiang and Xiamen were at low to moderate risks, while Target Hazard Quotient (THQ) results suggested no potential health risks to humans from their consumption. Further ecotoxicological assessments are needed, along with investigations into the underlying mechanisms of the spatiotemporal variation in Hg methylation, assimilation and bioaccumulation.