Distribution Characteristics And Risk Assessment Of Heavy Metals In Surrounding Soil Of A Solid Waste Disposal Center In Sichuan Basin

At present,with the continuous development of urban economy and society,there are more and more domestic medical waste,which has given birth to the disposal sites of domestic medical hazardous waste（solid waste）in suburban areas,but it has brought potential harm to the soil.The harm of different solid waste disposal centers to the soil environment varies with the types of waste,the climate of disposal areas,the terrains and the soil environment.Therefore,it is necessary to carry out the investigation and evaluation of soil environmental quality around the solid waste disposal centers,especially to explore the soil heavy metal hazards that have great impacts on human health.Therefore,this paper takes the soil around a solid waste disposal center in Sichuan Basin as the object,and uses field investigation sampling,indoor analysis and geostatistics to explore the spatial distribution characteristics and influencing factors of six heavy metals（Cu,Cr,Ni,Pb,Zn,Cd）in the soil around the solid waste disposal center.Principal component analysis,positive matrix factorization（PMF）,potential ecological risk index method and health risk method were used to evaluate the pollution degree,potential ecological risk and human health risk of heavy metals.The results provide basic data and theoretical basis for the protection and management of soil ecological environment quality around the solid waste disposal center.The main results are as follows:（1）The soil Cr,Cu,Zn,Ni,Pb and Cd in the solid waste disposal center did not exceed the risk value of agricultural land screening,however,Cr,Cu,Zn,Ni and Cd exceeded the corresponding background values by 1.12～2.75 times,with different degrees of accumulation.The maximum values of Cr,Zn and Cd exceeded the screening values and there was a potential pollution risk in the region.The high value areas of Ni,Zn,Cu,Pb and Cr in the soil are distributed near the solid waste disposal center,and the high value areas of Pb,Cu and Zn are also distributed in the northwest of the solid waste disposal center.This area has frequent traffic and more scattered family farms.The high value areas of Cr,Cd and Ni are also distributed in the southeast,which is lower than that in the solid waste disposal center.The content of heavy metals in woodland soil was higher than that in garden land and cultivated land.The content of heavy metals in soil was mainly positively affected by TP（total phosphorus）,AP（available phosphorus）and AK（available potassium）.（2）The results of correlation analysis,principal component analysis and PMF model of six kinds of soil heavy metals showed that the sources of soil heavy metals in solid waste disposal centers were mainly natural sources,waste disposal industry sources and traffic activity sources.Ni is mainly due to natural factors,Cu and Pb are mainly due to transportation,Cd and Zn are mainly affected by waste disposal industry and transportation,and Cr is mainly affected by natural factors and waste disposal industry.（3）The results of single factor pollution index,Nemerow index and potential ecological risk index of soil heavy metals showed that the contents of Cr,Zn and Cd in 12.7%,12.5%and 6.9%of the samples exceeded the standard,respectively.24.1%of the samples were at the pollution risk alert level（still clean level）,9.2%of the samples were at the mild pollution level,and 1.1%of the samples were at the moderate pollution level.The Nemerow comprehensive pollution average index（0.71）exceeds the level of pollution-free risk and belongs to the pollution risk warning level.Therefore,the solid waste disposal center increased the risk of light pollution of heavy metals in the surrounding soil and the characteristic pollutants are Cr,Zn and Cd,and there is also a moderate potential ecological risk of Cd.（4）The results of human health risk assessment showed that the sum of the health risk indexes of all heavy metals in adults and children around the solid waste disposal center was1.22×10^-1 and 9.03×10^-1respectively,which were less than 1.It did not bring non-carcinogenic or carcinogenic risks to children and adults.In summary,although there is no non-carcinogenic or carcinogenic risk of heavy metals in the soil of a solid waste disposal center in the Sichuan Basin,Cr,Cu,Zn,Ni,and Cd are accumulated,which increases the risk of mild pollution of heavy metals in soil.The characteristic pollutants are Cr and Zn,Cd,and there is also medium potential ecological risk of Cd.