Arsenic Content and the Bioavailability in Farmland Soils Affected by Mining Activities of a Realgar Ore, South China

Investigation on arsenic (As) accumulation in soil and agricultural products collected from the areas influenced by mine tailings and spoils around Shimen realgar mine, Hunan province, China, was carried out in this study. Water solubility, fractionation and bioavailability of As were determined as well to understand the environmental risk of arsenic releasing from farmland to water system this region. The results indicated that total soil arsenic concentrations varied from 18.9 to 932mg kg-1 and the highest arsenic concentration exceeding 500mg kg-1 in soils occurred only within 500m from these arsenic sources, and relatively low content ( -1) appeared in the areas far away (>3000m) from the pollution source. Arsenic content in dryland soils decreased with the distance from the mining arsenic ore, tailings and heaps increased. Through sequential extraction procedure (SEP), it was verified that the least arsenic amount occurred for exchangeable fraction with the percentage of 1.1%, then the organically bound fraction (1.6%), and much of the arsenic in the soils was associated with relatively immobile solid phases as residual fraction ranging from 87.5% to 93.3%. The fraction of mobile species, which potentially is harmful to the environment, was found to be higher in the soils with more AsT (total arsenic) content. Through statistical analysis, it was found out that arsenic content in plants was significantly correlated (R2=0.202; P<0.01) with exchangeable As among these five As fractions in soils. Comparing extracted arsenic content in soils using distilled water (H2O-As), muriatic acid (HCl-As) and ammonium chloride (NH4Cl-As), better positive relationship occurred significantly (R2=0.226; P<0.01) between NH4Cl-As and arsenic in plant, indicating the bioavailability was most closely related to NH4Cl-As rather than total As and other chemical solvents for extracting arsenic from soil.