Assessment of arsenic fractionation, mobility, and bioavailability in mining-affected soils, and remediation measures

摘要

Arsenic (As) concentrations and fractionations were investigated for control and mining-affected soils in Spain, using chemical extraction, column leaching, microbial and cultivation studies. Total As concentrations in all contaminated soils were in the range 96-27 350 mg/kg, demonstrating extremely high concentrations. However, the majority of the plant species accumulated very low As concentrations, while a few plants accumulated relatively high As concentrations (up to 152 mg/kg). Therefore, those plant species that are highly tolerant; grow abundantly in mining-affected areas; and have high biomass and roots, are suitable candidates for the phytostabilization of these contaminated soils. Compared to the total As contents, the very low water-soluble As (0.01-0.71%), sodium acetate (0.3-3.4%), and ammonium-nitrate-extractable As (0.05-0.74% of total As) concentrations and column leaching suggest that the concentrations of readily available As were relatively low in contaminated soils. Single extraction indicated that maximum concentrations of As in these soils were extracted with ammonium oxalate and hydroxylamine hydrochloride, suggesting that the major fraction of As is predominantly bound to poorly crystalline Fe, Mn and Al oxides. The residual fractions (35-80.2% of total As) were bound with silicate minerals. We document here some important results in relation to the role of microbial and cultivation activity: indigenous bacteria can mobilize As from the contaminated soils under changing redox conditions when a source of organic matter is available; and plant cultivation can promote the exchangeable and plant-available As in contaminated soils, indicating the potential risk of environmental and food-chain contamination.