Distribution and availability of heavy metals in soils near electroplating factories

Comprehensive understanding of the influence of soil properties on the potential availability of heavy metals could facilitate soil environment management. This study investigated the distribution of heavy metals and their potential availability in paddy and vegetable fields around electroplating factory outlets and irrigated with its wastewater. The potential availability was assessed using secondary phase fraction (SPF) of heavy metals, including acid-soluble, reducible, and oxidizable fractions resulting from BCR sequential extraction procedure. In total, 94 of topsoil samples (0-20 cm) were collected. Total and SPF concentrations of heavy metals as well as soil physicochemical properties were determined. Multivariable statistical analyses (i.e., principal component analysis (PCA) and redundancy analysis (RDA)) were employed. Results showed that total and SPF concentrations of heavy metals in soil decreased (P<0.05) as sampling distance away from the electroplating factories increased, suggesting that sampling distance was the major parameter that affected gradient variations of both total and potential availability of soil heavy metals. According to PCA, soil samples distributed on the PCA axis representing anthropogenic effect, illustrating that the variation of soil properties resulted from irrigation with electroplating wastewater. RDA and stepwise regression indicated that soil Mn oxides, amorphous Fe oxides, silt content, and pH could explain 68.8% and 43.5% of the variation of SPF concentration in paddy and vegetable garden soil, respectively, suggesting they were the most important factors influencing the potential availability of heavy metals in soils. The potential availability of heavy metals in soil was positively correlated with soil Mn oxides but negatively associated with soil amorphous Fe oxides, indicating that Mn oxides enhanced the potential availability of heavy metals while amorphous Fe oxides reduced the potential availability.