Ecological Risk Assessment Of Soil Cadmium In Typical Rice Planting Areas Of Hunan Province

The Dongting Lake region in Hunan Province is an important rice growing area in China.According to the relevant literature and project team survey data,in recent years,the soil pollution situation of the total area is not optimistic,especially the heavy metal cadmium（Cd）element is seriously exceeded.Along the Xiangjiang River distributed contaminated area of Cd,especially the Changsha-Zhuzhou-Xiangtan area.This paper selected the typical rice planting area in Hunan Province,and systematically collected and analyzed samples of rice and its root soil system,then we summarized the mobility of Cd and influencing factors of its enrichment coefficient（K）.We established different prediction models on the basis of the different characteristics among our study area,then we used the surface soil Cd mobility in the Dongting Lake Plain Regio to make rational land use planning in combination with different land resource safety utilization plans.It is indicated that soil pH can affect soil bioavailability of Cd.Under acidic conditions,Cd has higher bioavailability,and the enrichment coefficient decreases with increasing pH and keep low values under weak alkaline conditions.Soil S can reduce the bioavailability of soil Cd by precipitation of CdS.There is a negative correlation between enrichment coefficient and soil Ca as well as soil Fe,because they can enhance the adsorption of Cd in soil.The soil P content is related to the application of phosphate fertilizer,which will cause Cd to enter the soil during the fertilization process.We found a characteristic that the area which along the Xiangjiang River,the Cd content of soil and rice seeds is higher than other area.On the basis,we established different rice seed prediction equations:（1）Xiangjiang River Basin distribution area:log(K_Cd)=0.387-0.636log（CaO）-1.625log（S）+1.150log（P）;（2）Other area:log(K_Cd)=2.662-0.393pH-1.485log（S）+1.557log（P）-1.901log（TFe₂O₃）.Prediction of Cd content in rice seeds in study areas was made using soil geochemical survey data in the study area,the results showed that the grain contamination of rice in the Xiangjiang River Basin is more serious,especially in the areas of Zhangzhou,Changsha,Zhuzhou and Xiangtan,which are extremely consistent with the high soil value distribution area.Land planning was carried out for the study area using different land resource security zoning schemes.The results showed that without considering the pollution of rice seeds,a large number of areas will be classified as priority protection,resulting in misjudgment.On the basis of considering the excessive Cd content of rice seeds,the structural adjustment area and ecological restoration area were proposed,which provided a more reliable scientific basis for the rational planning of land resources in the study area.