Evaluation Of Soil Bioavailability In Typical Geogenesis Se-Cd Symbiosis Area By Diffusive Gradients In Thin-films

The northwest of Zhejiang Province is a typical area with high geological background of heavy metals such as cadmium.In recent years,the geochemical survey results of 1:250000land quality showed that the soil environmental quality in this region was poor,and the soil cadmium content exceeded the selected or even controlled value of soil environmental quality of agricultural land.At the same time,this region was also the largest area of soil selenium rich region in Zhejiang Province.It is urgent to carry out soil bioavailability assessment and research on Se-Cd symbiosis in this region,so as to determine soil ecological risk and serve the scientific development of Se-rich land resources.Gradient diffusion thin film technology(DGT)is an effective method to predict the bioavailability of heavy metals in soil.It can simulate the dynamic process of soil heavy metal uptake by plants.Existing studies mainly focus on the evaluation of soil heavy metal pollution caused by human sources,but few of them are applied to the evaluation of heavy metal pollution caused by natural sources.Moreover,there are few reports on the application of DGT technology to evaluate the bioavailability of soil selenium.In this study,soil samples of typical crops and their supporting roots were collected from typical black shale and black carbonate rock areas in Anji and Chun'an of Northwest Zhejiang Province.The content characteristics of heavy metals and selenium in soil and crops were analyzed.The bioavailability of selenium and cadmium in soil was evaluated by gradient diffusion thin film technology(DGT).The sources,potential ecological risks and ecological effects of heavy metals,selenium and other elements in soil in typical areas of northwest Zhejiang were comprehensively evaluated,and the main factors affecting the absorption of heavy metals and selenium by crops were discussed.The applicability of DGT method to evaluate the soil bioavailability of selenium and cadmium in the study area was evaluated.The specific research conclusions are as follows:(1)The soil heavy metals in the study area may be mainly derived from the weathering of parent rocks.(2)The evaluation results using land accumulation index,potential ecological risk index and soil environmental quality soil pollution risk control standard of agricultural land showed that the pollution proportion of Cd element in soil and crop samples was higher than that of other elements.(3)In the study area,83.1% of the 83 soil samples reached the Se-enriched soil standard(>0.4mg/kg),but the heavy metals in the Se-enriched soil exceeded the standard seriously,especially Cd,which was above moderate pollution.The selenium enrichment rate of 63 rice samples in the study area reached 68.3%,and the selenium enrichment rate of 20 Chinese cabbage samples reached 90%.(4)The accumulation of heavy metals and selenium by crops is mainly affected by the total amount of heavy metals in soil and the physical and chemical properties of soil.(5)By comparing the results of different bioavailability evaluation,it can be seen that the bioavailability evaluation of Se and Cd by DGT technique is better than that by soil solution method,traditional chemical extraction method and total volume evaluation.Moreover,the prediction effect of crop Se,Cd,soil Se,Cd,soil physical and chemical properties and the model constructed by DGT method are better and the accuracy is higher.