Pollution Characteristics And Risk Assessment Of Soil Heavy Metals In Mine Areas In Southwest China Based On Meta Analysis

Mining is one of the biggest sources of soil heavy metals.In order to accurately understand the impact of mining on soil heavy metals,this study focused on Southwest China（Yunnan Province,Sichuan Province,Guizhou Province,Chongqing Municipality and Tibet Autonomous Region）with rich mineral resources,and collected the relevant literatures on the impact of mining on soil heavy metals;the impact of metal mining on the concentrations of soil As,Cd,Cr,Cu,Hg,Ni,Pb,and Zn was quantified by Meta-analysis,and the relationship between the selected factors（i.e.,different sub-regions,metal minerals,land-use types and distance to mine areas）and soil heavy metal concentrations were explored;Then the publication bias of the literatures data was tested;Last,the concentrations of soil heavy metals were used in soil heavy metal pollution characteristics and risk assessment.The main results were as follows:（1）The average concentrations of soil As,Cd,Cu,Hg,Pb,and Zn in mine areas in Southwest China all exceeded the corresponding screening value of soil environmental quality standard in China（GB15618-2018）;among them,Cd had the highest over-standard ratio,and its over-standard multiple of concentration was 16.22 times;soil As and Pb had higher over-standard ratios,and the over-standard multiples were 8.20 and 4.31 times;the over-standard ratioes of soil Cr and Ni were lower.Overall,the concentrations of soil heavy metals around the mine areas in Southwest China were relatively high.（2）The mining of mine in Southwest China significantly increased the concentrations of heavy metals in topsoil（p<0.05）,and its concentration increased by 322.07%as a whole;the weight effect sizes（ES₊）of single heavy metal were in the order of Cd（2.53）>Hg（2.11）>Pb（1.90）>Zn（1.56）>As（1.11）>Cu（0.87）>Ni（0.35）;compared with the background concentration,the concentrations of each soil heavy metals increased by 1155.35%,724.82%,568.59%,375.88%,203.44%,138.69%,and 41.91%,respectively;the mining in both Sichuan and Yunnan led to the higher effect sizes for soil Cd(ES_+Sichuan=3.78,ES_+Yunnan=3.21),Pb(ES_+Sichuan=2.96,ES_+Yunnan=2.33),and Zn(ES_+Sichuan=2.27,ES_+Yunnan=1.75)than those for the other heavy metals,the mining of mines in Guizhou led to the higher effect size for soil Hg（ES₊=2.49）than those for the other heavy metals;the effect size of metal mining on cultivated soil（ES₊=1.43）was higher than those on forested soil（ES₊=0.87）for soil heavy metals,of which Cd,Hg and Pb in cultivated soil were affected mostly;different types of mining had different effects on soil heavy metals,and the contribution of non-ferrous metal mine was higher than that of ferrous metal mines and coal mines;the mining of lead-zinc mine and tin mine significantly increased the concentrations of soil Cd(ES_{+lead-zinc mine}=3.62,ES_{+tin mine}=3.01),Pb(ES_{+lead-zinc mine}=2.62,ES_{+tin mine}=2.18),and Zn(ES_{+lead-zinc mine}=2.35,ES_{+tin mine}=1.35);the mining of coal mines significantly increased the concentrations of soil Hg（1.66）,As（1.31）,Cu（1.05）,and Ni（0.53）;the effect size of soil heavy metals decreased gradually with the increase of the distance from the mine area,and the less affected;for the investigated soil heavy metals in Southwest China,there were slight potential publication biases for Pb and Zn（p<0.05）.（3）The results of the geo-accumulation index assessment showed that:these I_geo values confirmed that there were different grades of heavy metal pollution in the soil of the areas,and the average I_geo indices of soil heavy metals were in the order of Cd>Hg>Pb>Zn>As>Cu>Ni>Cr;the pollution degrees caused by mining were different,the soil Cd was in strong pollution,the Hg and Pb were moderate to strong pollution,the Zn and As were moderate pollution,the Cu was slight pollution,while the Ni and Cr were nonpollution;the areas with high soil Cd and Pb pollution were mainly located in Sichuan and Yunnan,while the areas with high soil Hg pollution was mainly in Guizhou.The results of the ecological risk assessment showed that:the average ecological risk indices of the eight heavy metals were in the order of Cd/Hg>Pb/As>Cu/Zn/Ni/Cr;soil Cd and Hg in the areas had higher average ecological risks than the other six soil heavy metals（E_i>320）;soil heavy metals had an extremely high average comprehensive ecological risk（RI≥1200）,the proportion of extremely high ecological risk was 39.72%,of which Cd and Hg were the main contributors.The results of the health risk assessment showed that:hand-oral intake was the main exposure route of soil heavy metals,the average daily intake of children was the highest under non-carcinogenic risk,and the average daily intake of adult women was the highest under carcinogenic risk;soil As and Pb posed non-carcinogenic risks to children（HQ>1）,with risk value of 3.74 and 1.44;the carcinogenic risk values of soil As,Cd,Cr,and Ni were all higher than 10^-6,and there was a carcinogenic risk within the human body;soil heavy metals in the areas posed comprehensive non-carcinogenic risks（HI>1）to children,and posed unacceptable comprehensive carcinogenic risks(TCR>10^-4)to the three receptor populations,with risk value of 1.19×10^-4,1.21×10^-4,and 1.06×10^-4,respectively.Compared with the previous studies on soil heavy metals in single and a few mine areas,the above results can provide more effective decision support for soil pollution prevention and soil environmental quality protection in mine areas in Southwest China.