Risk Assessment Of Agricultural Product Security And Ecological Risk In Chromium Contaminated Soils

With the rapid development of chromium(Cr)steel and leather industry in China,the accumulation of Cr pollutants in soil is increasing,and more attention has been paid to strengthening the risk control of soil Cr pollution.The establishment of suitable soil Cr environmental quality standards is the core problem in evaluating soil Cr pollution,but the current soil environmental quality standards are controversial because they do not fully take into account the practical problems of large geographical span,rich soil species and different pollutant bioavailability differences in China,so the soil Cr environmental quality standards need to be revised urgently.In order to ensure the scientificity and accuracy of the new standard,environmental risk of heavy metal Cr in soils must be evaluated by ecotoxicity test and pollutant accumulation test based on the abundant soil types in the early stage.According to the division of Cr limit values of soil environmental quality standards(GB 15618-2018),this study selected representative 21 upland soils and 14 paddy soils in China,added exogenous Cr(Ⅵ)and aged for a period of time,and then planted pepper(Capsicum frutescens L.),lettuce(Lactuca sativa L.var.ramosa Hort)and rice(Oryza.sativa L.),which people often eat.The main soil properties that affect Cr bioavailability were screened to determine the relationship with the accumulation of Cr in the edible part of the crop,and a multiple regression analysis was used to establish the Cr agricultural product safety threshold prediction model.Based on the reduction rate of the crop relative to the control group and whether the Cr concentration of the edible part exceeds the current national food safety Cr limit value as the evaluation index,combined with the previous Cr wheat root length inhibition toxicity test data,preliminarily evaluated the agricultural product safety risk and ecological safety risk of Cr-contaminated farmland soils.The results as following:(1)After a period of aging,the concentration of EDTA extracted Cr(EDTA-Cr)in the soil was greatly reduced,and it differs significantly in different soils,and Cr(Ⅵ)in the alkaline soil with low clay content is more toxic than the acid soil.It is recommended that in the revision of the environmental quality standard of Cr soil,the Cr limit value decreases with increasing soil pH.(2)Cr pollution in alkaline soil will reduce crop yield or even fail to grow,but it will not cause excessive Cr concentration of agricultural products,and the Cr concentration of soil(EC50)that causes 50%inhibition of wheat root length is far less than that of lettuce Cr critical threshold.It shows that the safety risk of agricultural products in Cr-contaminated soil is much less,and it is suggested that the research on heavy metal Cr in farmland soil should focus on the ecological safety risk.Soil organic matter content,clay,amorphous alumina and amorphous iron oxide were significantly negatively correlated with crop-to-Cr accumulation in soil,while the pH is reversed,which was associated with lower soil pH and higher organic matter,iron oxide,clay content contributing to the reduction and strong adsorption of Cr(Ⅵ).Through stepwise multiple linear regression analysis,it was determined that the extracted Cr of EDTA at pH=10 and the content of soil organic matter were the most important factors affecting the Cr concentration in the edible part of lettuce.The reliable model is:log(Crlettuce)=0.058·pH+0.499·log(CEC)-0.937·log(clay)-1.075·log(aFe)+2.110(R2=0.624，P<0.001).(3)The addition of 0.75 times Cr standard limit value in upland soil has different degrees of toxicity to pepper and lettuce after aging for 425 days and 557 days,but the same addition has no obvious adverse effects on rice growth and grain Cr accumulation after aging for 112 days.The impact shows that paddy fields have lower agricultural product safety risk and ecological safety risk than in upland soil.The above results have clarified the soil properties that affect the bioavailability of soil Cr,established a prediction model for the safety threshold value of lettuce Cr agricultural products based on soil properties,revealed that the ecological security risks of soil Cr contaminated soil are much greater than agricultural product safety risks.and provided important data supporting for risk assessment and management of Cr-contaminated soil in our country.