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Mercury(Hg)was utilized as electrolyte in the industrial producing of chlor-alkali and resulted large anthropogenic Hg emission globally over the last several decades.However,there remain gaps in understanding the subsequent geochemical behaviors of legacy Hg.Air surface exchange of Hg flux investigate from the vicinity agricultural surfaces shown that Hg emission was largely elevated close to the plant.The Hg isotopic composition was also measured in topsoils from those flux sampling sites.Mass-dependent fractionation(MDF)of Hg was observed(δ202Hg from-1.92‰ to 0.11‰)enriched in heavier isotopes consistent with Hg concentration increased in soils,implied largely input from previous emission from the plant.This demonstrated that high emission observed in the vicinity of the plant may a result of reemission of previous deposited Hg.Soil profiles of which brine sludge piled on shown substantially high content of Hg with rapid decreased from top to deep.For the first time,isotopic composition revealed substantial MDF during Hg precipitated from top down in soil column which may related to Hg in soil processes.The results suggest that legacy Hg of pre-contaminated chlor-alkali plant undergo complex reemission and precipitation processes with systematical isotopic fractionation.