Geochemical Characteristics Of Cadmium Elements In The Typical Agricultural Areas In East Wanyuan,Sichuan Province

Soil is the foundation forhuman survival and development. The soil quality directly or indirectly affects the health and quality of human life. At present, soil and food safety problems occur frequently, the soil heavy metal pollution has seriously affected the development of agriculture and the safety of the ecosystem, poses a potential threat to human health.Sichuan wanyuan is known as the selenium-rich agricultural products nationwide, are relying on the resource advantage, building natural selenium-rich agricultural products base in China. Due to the soil rich in selenium, at the same time, usually associated with higher levels of cadmium, biological toxicity of cadmium has been known, how to make the plants absorb selenium effectively, and avoid the absorption of cadmium, as far as possible has always been the hotspot in the research of soil geochemistry. Find out cadmium content and form of occurrence in the typical agricultural area, study on the ability of cadmium enrichment in different plants, make a discussion for migration and transformation to cadmium in environmental media, and it will has important significance for the rational development of selenium-rich soil and environmental treatment.Sampling and analysis on the four typical agriculture Areas(Baiyang, Jiuyuan, Dazhu, Miaozi), find out the cadmiumcontent for the following aspects, the rocks, surface soil, vertical section soil, crop seeds, root soil and human hair. Exploring the transition and transform rule of the cadmium elements in rock-soil-plant-human body, and finally make the quality evaluation. After the Comprehensive research, we have obtained the following results:(1) The maximum value of cadmium content in rock samples is 3.16mg/kg, and the minimum value is 0.033mg/kg. The average cadmium content in the rocks of different age from high to low in turnis: Cambrian system>sinian system>triassic sysyrem. Cadmium in the different lithology from high to low in turn is shale〉sandstone〉limestone. The average content of cadmium in therocks of different agricultural areas in turn is Miaozi>Dazhu>Baiyang>Jiuyuan, respectively is 0.518mg/kg, 0.275mg/kg, 0.062mg/kg, 0.064mg/kg. Compared with the crustal abundance(0.2mg/kg), cadmium content in rocks of Dazhu and Miaozi are higher than the earth’s crust averages.(2) Cadmium content in the surface soil is between 0.10mg/kg and 47.8mg/kg. The average content of cadmium from high to low in turn is Miaozi>Dazhu>Jiuyuan>Baiyang, respectively is 5.72mg/kg,1.73mg/kg, 0.32mg/kg and 0.28mg/kg. Compared with the national background value(0.1mg/kg), four areas showed obvious cadmium enrichment. Cadmium content in soil vertical section gradually decreases with the depth of profile.(3) The study show that cadmium content in soil is affected by soil pH and the soil organic matter content. The soil organic matter content in Baiyang is close to Dazhu, Jiuyuan is close to Miaozi. The soil organic matter content of Baiyang, Jiuyuan and Miaozi are gradually increased by the cadmium content.Organic matter has a great control effect on the Cd distribution in the soil.(4) The available cadmium is dominated in the soil.In totally, the cadmium content of various forms from big to small in turns is:ion exchange state>residual form>Fe-Mn oxide form>carbonate bounded form>Humic acid combined with state>organically bonded state>water soluble state. The differences of the soil forms are great in the different argricultural areas.(5) With reference to the national food safety standards(GB 2762-2012), the content of cadmium in the plants in all areas is within the scope of food safety standard. The plants in all areas are safe for human.The enrichment capability of cadmium in Plants is influenced by many factors, cadmium enrichment ability for different plants are differ from each other. Rice enriched cadmium strongly than potatoes, corn and green beans.The average content of cadmium in different plants of the agriculture areas from high to low in turn is rice >corn>potatoes>green beans. As selenium rich crops, potatoes and green beans can plant widely in this area.(6) The cadmium content in human hair does not exceed upper limit value for safty, which has yet to cause harm to human body.