Evaluation Of Remediation Effect And Risk Of Heavy Metal As And Cd Contamination In Agricultural Soils By Passivation Agents

Yutai County,Shandong Province,is an important grain production base in Shandong Province and belongs to a large agricultural county,where the main grain crop is rice.A detailed survey of the contamination status of agricultural land in Yutai County in 2019 found that the soil arsenic content was slightly higher than the risk screening value,the soil cadmium levels close to risk screening value.Therefore,in this paper,the typical rice soils and contaminated areas in Yutai County were used as the study area,and the heavy metals arsenic and cadmium in agricultural soils and rice were used as the study objects to reduce the content of the effective state of heavy metals in soil by adding different passivators to the soil exogenously,so as to reduce the uptake of the effective state of heavy metals by rice.In this paper,the Bureau of Reference sequential extraction methods(BCR)and Diffusive gradients in thin-films technique(DGT)were applied to determine the active state content of heavy metals in soil,and the changes of arsenic and cadmium content in soil and the changes of arsenic and cadmium accumulation in rice were analyzed and discussed,and then the passivating agents suitable for soil pollution remediation in Yutai area were selected.At the same time,the risk assessment of heavy metal pollution in soil-crop system was conducted by using the effective state content of heavy metals,so that the ecological risk of heavy metals in the soil of the region can be predicted more scientifically.(1)The test results of seven types of passivators(medium and trace element type,soil conditioner type,straw and adsorbent material type,humic acid and organic mineral composite type,wood vinegar solution and mycorrhizal agent type,chemical material-based and biofertilizer and mycorrhizal agent type)applied to As and Cd-contaminated rice soils showed that,compared with the control without passivators,biofertilizer and mycorrhizal agent-based passivators reduced rice seed and root As,soil The effect of the chemical material-based passivators was the most significant,with a reduction of 31.9%,34.2% and60.9% in rice seed and root Cd and soil Cd,respectively.(2)The results of the analysis of the ecological risk of heavy metals based on the Nemerow index method of total soil heavy metals are that the predicted value of heavy metals Cd in soil reaches the alarm line standard and As is in the clean state;the results of the evaluation of the ecological risk value of heavy metals by the ground accumulation index method are that the predicted value of heavy metals Cd in soil is 1 level of no-medium pollution and As is 0 level of clean level.(3)The results of the potential ecological risk index analysis based on the effective state content of soil heavy metals were that Cd and As were in a low risk state;the results of the integrated quality index method for soil and agricultural products indicated that Cd and As were in a clean state.By evaluating the degree of soil environmental pollution through the effective state content of heavy metals,it was found that the integrated quality index method for soil and agricultural products fully considered the effective state content of heavy metals,the mechanism of soil heavy metal uptake by plant seeds and the efficiency of heavy metal transfer from plant roots to seeds,and more intuitively showed the potential risk of soil heavy metal uptake by human body,so as to more scientifically assess the environmental health risk of soil and agricultural products The results of the study are summarized below.