John Wiley & Sons, Ltd.

EFFECT OF CROPPING SYSTEMS ON HEAVY METAL DISTRIBUTION AND MERCURY FRACTIONATION IN THE WANSHAN MINING DISTRICT, CHINA: IMPLICATIONS FOR ENVIRONMENTAL MANAGEMENT

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We studied the concentration of heavy metals and mercury fractionation in contaminated soil for two agricultural land use systems (paddy rice and dry‐land) at the Wanshan Hg mine in China. The average concentration of chromium, lead, copper, nickel and zinc was generally lower in paddy‐rice (PR) soil relative to corn field (CF) soil. Soil under CF production was slightly contaminated with lead (22‐100 mg/kg), copper (31‐64 mg/kg), nickel (22‐76 mg/kg) and moderately contaminated with zinc (112‐635 mg/kg). Correlation of these metals, in both soils, with the Ti concentration in soil indicates a geogenic origin for each metal (lead, r=0.48; copper, r=0.63; nickel, r=0.47; zinc, r=0.48). The mercury and antimony concentration in soil was high under both cropping systems and future remediation efforts should consider the potential environmental risk presented by these metals. The concentration of bioavailable mercury in soil ranged from 0.3‐11 ng/g across the two cropping systems. The majority of mercury (>80%) was associated with organic matter and the residual fraction. However, soil under PR production exhibited a significantly lower concentration of Fe/Mn oxide‐bound mercury than that under CF production. This may be a function of the reduction of Fe/Mn oxides in the PR soil, with the subsequent release of adsorbed metals to soil solution. Sequential change from CF to PR production as practiced in Wanshan should therefore be avoided. Mercury adsorbed to Fe/Mn oxides in CF soil could potentially be released into soil solution, and be made available for bio‐methylation under the flooded water management conditions of a rice paddy. Environ Toxicol Chem © 2014 SETAC

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