Abstract:

Baiyin is an important non-ferrous metal province in China. Historically, unscientific and unreasonable mineral resource development and agricultural production activities have breached the heavy metal standards in Baiyin city and its surrounding areas. The controlling factors of bioavailability and ecological risk prediction of heavy metals have always been of great interest in biogeochemical behavior research. In this study, we investigated the contamination of root soil and corn seeds in/around the Dongdagou irrigation area (Baiyin city), analyzed the changes of key soil indicators in 2007 and 2018 in the local agricultural concentration area, and evaluated the ecological risks in the corn growing area. The local soil Cd content (average 17.48 mg/kg, maximum 51.1 mg/kg) exceeds the standard in some areas. The relative Cd content in different forms is carbonate state>ion exchange state>iron and manganese oxidation state>humic acid state>strong organic state>residue state≫water-soluble state. Factors such as high pH alkaline soil and low Cd accumulation of Cd-tolerant corn varieties limited the Cd bioavailability in the soil, and the exceedance rate of corn seeds is only 8.8%. There is certain Cd pollution in the local corn concentrated planting area, but it has been effectively controlled. Over half of the points of pH, Corg and CaO content that constrain the Cd bioavailability show an increasing trend, which imply that the risk will remain low for the coming future. To better control the areas with higher Cd content than the standard, we recommended to continue to choose low Cd accumulation of Cd-tolerant corn varieties for planting, and to harvest the seeds at maturity as animal feed or develop the corn seed resource industry. We also proposed to conduct recycling of other parts, especially the roots as restoration parts, to achieve reduction while restoration.

Key words: Baiyin city, cadmium pollution, cadmium speciation, ecological risk