An Improved Study On Index Evaluation Of Heavy Metal Pollution In Agricultural Land In Mining Areas

Agricultural land and agricultural product safety are related to the three rural issues.Soil pollution assessment of agricultural land is an important part of the safe use of agricultural land,and it is very important for precise control of agricultural land pollution and effective soil remediation.However,there are some shortcomings in the actual application of soil pollution index evaluation,such as the evaluation results do not conform to the actual situation,especially when there are many sources of heavy metals and human intervention in agricultural land.It is also one of the current research trends to revise and improve the traditional index evaluation method.In this study,a single/composite relative soil contamination index（RPE/RIE）was improved using the land accumulation index(I_geo)to assess heavy metal contamination on agricultural land.Soil data from a total of 305 multi-year samples from the study area in 2009,2014 and 2018 were used to compare and analyze the improved single and combined contamination indices before and after the improvement.The following conclusions were drawn:（1）The study area belongs to the geological high background area,which has been polluted by heavy metals and treated.The soil p H value in 2014 was acidic,and the average concentrations of heavy metals Cd,Hg,As,Pb and Cr in the study area were 0.419,0.232,15.335,41.335 and 86.105 mg/kg,respectively;the content and coefficient of variation of Cd were high,and the pollution was more serious;The spatial distribution of the five heavy metals is high in the east and low in the west;analysis of pollution sources shows that mining and gold selection by amalgamation are the main causes of Cd,Hg and As pollution in the study area,and Cr mainly considers the influence of soil pedogenic process.（2）The traditional Nemerow comprehensive pollution index（Pn/Bn）evaluation results are extreme,especially the agricultural land around the mining area is underestimated.I_geo’s improved Nemerrow index（In）evaluation results are more in line with normal distribution,the improved composite relative pollution index（MRIE）has a 28.9%reduction in severe/very severe stains,and a corresponding increase of31.1%in mild/moderate stains%,which is more consistent with the In results.MRIE keeps the pollution level of agricultural land around the mining area unchanged,while reducing the pollution level of other non-exogenous areas,and the spatial distribution is more reasonable.（3）The traditional Nemero Integrated Pollution Index（Pn/Bn）evaluation results are extreme,especially underestimating the agricultural land around the mining area.The Nemerrow Index Improved by I_geo（In）evaluation results are more in line with normal distribution,the improved composite relative pollution index（MRIE）has a28.9%reduction in severe/very severe stains,and a corresponding increase of 31.1%in mild/moderate stains%,which is more consistent with the In results.MRIE maintains the pollution level of agricultural land around the mine area without decreasing,while decreasing the pollution level of other non-exogenously influenced areas,with a more reasonable spatial distribution.（4）The trend analysis from 2009 to 2018 found that the traditional evaluation value of RPE/RIE was inconsistent with the change of heavy metal concentration.In2009-2018,RIE did not reflect the characteristics of increase and decrease,but MRIE did;MRPE also showed the same characteristics,and the discrimination was better.The numerical structure and spatial trend of MRIE evaluation results were consistent with the change trend of heavy metal content in the study area,and were generally better than RIE..This study shows that the I_geo-based improved single/integrated relative soil pollution index（MRPE/MRIE）is better than the traditional single/integrated relative pollution index（RPE/RIE）in indicating the pollution of heavy metals in agricultural land.