Cadmium contamination in soils and crops in four mining areas, China

The Dexing Cu, Yangjiazhangzhi MoCu, Hongqiling Ni and Baiyin polymetallic ore deposits have been mined for several decades. Samples of paddy rice (Oryza sativa L.) and maize (Zea mays L.) as well as plough layer soils were collected from the four areas that are substantially or potentially affected by mining and smelting activities. Cadmium, Zn, pH and organic carbon in soils as well as Cd in crops were determined. The concentrations of Cd in soils vary between 0.139-2.59, 0.182-22.8, 0.157-0.812, 0.180-94.0 mg/kg in Dexing, Yangjiazhangzhi, Hongqiling and Baiyin mining areas, respectively. The median values of Cd in soils are higher than their respective regional geochemical background. According to Chinese environmental quality standard for soil (GB15618-1995), 64.4%, 78.9%, 67.5% and 94.1% of soil samples in Dexing, Yangjiazhangzhi, Hongqiling and Baiyin exceed the Maximum Allowable Concentration (MAC) of Cd for farmlands, respectively. Compared with the Chinese foodstuff safety criteria (GB2762-2012), 27.8% brown rice samples in Dexing and 14.4% maize samples in Baiyin exceed the Chinese Maximum Permit Levels (MPL) 0.2 mg Cd/kg for cereals. The spatial distribution patterns of Cd in crops are similar to that in soils, indicating the substantial influence from soil Cd contamination. The Transfer Factors (TFs) of Cd in soil-rice system are much higher than those in soil-maize system due to high uptake ability of paddy rice. Statistics demonstrates organic carbon and Zn in soils have potential effect on the Cd uptake by maize.