The Research Of Affecting Factors And Evaluation Methods Of Cadmium And Arsenic Bioavailability In Soils

At present,with the rapid development of economy,the environmental pollution problem is getting heavier and heavier.As the main gathering place of heavy metals,soil health is directly related to the food safety and human health.Thus,many studies have focused on soil heavy metal pollution.Now,the total metal cotent is always used in the soil heavy metal pollution assessment.However,only few amounts of heavy metal in the soil will be absorbed by crops due to the concealment and the buffer of the soil.Therefore,studies on bioavailability of heavy metal in the soil are more scientific and should be emphasized.In addition,in all heavy metasl,cadmium and arsenic have the strong mobility and toxicity,which bring more serious environmental health problems than other heavy metals.Thus,based on the bioavailability of heavy metal in the soil,the influencing factors of soil heavy metal bioavailability and the risk assessment methods of soil heavy metal bioavailability were explored.Meanwhile,the relieve measure of soil cadmium pollution was also carried out1.The factors affecting the bioavailability of soil cadmium and arsenicThe soils with various properties from 18 provinces and different crops are selected o explore the bioavailability of Cd and As in soil.The main results are shown as follows:The cadmium and arsenic content in plants was positively correlated with cadmium and arsenic in the soil,respectively.The bioavailability of cadmium in acidic soil is stronger than that in alkaline soil,while,arsenic shows the opposite phenomenon.The Freundlich equation constructed by the stepwise multiple linear regression could be used to predict the absorption characteristics of cadmium and arsenic.The fitting results showed that compared with the single variable?soil total heavy metal content?model,the accuracy of the multivariate?soil total heavy metal content,soil pH and soil organic matter content,etc.?model is higher,which indicating its advantage in evaluating the transfer characteristics of cadmium and arsenic from soil to plant.Moreover,the prediction equation HC5=10^{?-0.2054 pH+2.9935?}+9.2 for the threshold was obtained by the species sensitivity distribution?SSD?method.Meanwhile,the HC5 value under various pH were calculated.The predicted and observed BCF have the similar values?R²=0.95?,which indicating that the prediction equation is helpful to predict the absorption of arsenic from soil to wheat and provide the technical basis for improving the quality of the existing soil environment quality standards.?2?The risk assessment method of soil heavy metal bioavailability.At present,the traditional methods to evaluate the bioavailability of soil heavy metals are always based on total heavy metal content or the content of some chemical forms.However,the real environment behaviors of heavy metal are not be defined accurately by the traditional methods.A new method named the gradient film diffusion technique?DGT?is developing.It was based on Fick's first law of diffusion theory and widely applied in the evaluation of heavy metal pollution in water and sediment,whereas,less in soil.This work was carried out to judge the feasibility and advantages of DGT technique in evaluating the bioavailability of heavy metals by comparing the DGT technology with traditional evaluation methods?soil solution method,the step extraction,total content method?.The main results are as follows:The traditional techniques for evaluating Cd bioavailability are pH and OC dependent,while,for As,it is pH and ferric-oxide dependent.Thus,soil pH,OC,and ferric-oxide content should be considered when using traditional techniques to assess the bioavailability of Cd and As in soils.DGT measurements are independent of the soil properties.The abilities of the tested methods to predict Cd and As bioavailability declined in the following order:DGT method>soil solution method>one step extraction method>total content method.Thus,DGT are preferable in the Cd and As bioavailability assessment.?3?The study of alleviating soil cadmium pollutionThe greenhouse experiment under the condition of different modifier?lime,peat,lime+chicken manure and chicken manure,lime+peat?was carried out to explore the cadmium uptake by Brassica chinensis biomass,the cadmium content in soil,and the influence of pH.The main results are as follows:Compared with the control treatment,the application amendment significantly decreased the Cd uptake of Brassia chinensis and soil available Cd.The available cadmium content in soil treated with different amendments was significantly positively correlated?R²=0.99,P<0.05?to cadmium content in Brassia chinensis.The Cd conents in plant and soils decreased in five modifier addition treatments.The decrease was in the order of lime+chicken manure?lime+peat>chicken manure?peat?lime.All treatments except for peat could significantly increased soil pH with the order of lime+chicken manure?lime+peat?lime>chicken manure>peat.