Assessment of heavy metal contamination and bioaccumulation in soybean plants from mining and smelting areas of southern Hunan Province, China.

Soybean is one of most important dicotyledonous food crops and is widely planted in Hunan Province, China. However, mining activity causes contamination of the soil in which soybean grows. To assess the impact of mining-induced soil contamination on soybean plants, a geoaccumulation index (I(geo)) was used to evaluate 20 soil samples from the mining and smelting areas of southern Hunan Province. The results indicated that Zn ranged from uncontaminated to a moderately contaminated level (I(geo)<1), Pb was at a strongly contaminated level (I(geo)>3), and Cd was at an extremely contaminated level (I(geo)>5) across the whole study area. All of the studied soybean plants were affected by heavy metal Pb and Cd contamination, and the mean concentrations in seeds were 13.9 mg/kg and 2.95 mg/kg, respectively. The estimated bioconcentration factor and translocation factor showed that the soybean roots had a strong Cd bioconcentration capability and the stems had a strong translocation capability in terms of Pb, Cd, and Zn, with preferential transference of metals to the soybean leaves. The bioavailable fraction in the soil was characterized by the exchangeable fraction of heavy metals. In the present study, the bioavailable fractions of Pb, Cd, and Zn were significantly positively correlated with the concentration of these metals in soybean tissues (roots, stems, leaves, husks, and seeds).