Abstract: Sediment samples were collected from the Wulihe River historically contaminated by chlor-alkali production in Huludao City, Liaoning Province, aimed to study the past 25 years spatiotemporal variation of total and methyl mercury in the River. Under 25-year artificial management and natural purification, the total and methyl mercury contents in the sediments collected from different segments showed an overall decreasing trend, being more obvious for methyl mercury, but the total mercury content was still quite high (0.491-26.395 mg·kg^-1, averagely 13.766 mg·kg^-1), 371 times higher than the background value (0.037 mg·kg^-1) of soils in the Province. The methyl mercury content was in the range of 0.253-12.079 mg·kg^-1. The segments with heavy mercury-contamination were at the Hugong Bridge near to pollution source and the North Cishan Bridge near to the downstream estuarine.

Key words: HTO, Environmental behavior, Rice, Radioecology, Nonlinear regression