Study On Comprehensive Assessment Of Environmental Risk Of Soil Metals Under Different Land Use Types

With the rapid development of the world economy,people pay more attention to soil metals pollution.At present,most studies focus on the pollution of heavy metals in soil under a single land use type.However,the differences of soil pollution and environmental risks caused by heavy metals and trace elements in different land use types in the same area are ignored.Comprehensive consideration of the pollution and environmental risks of various metals in soils with different land use types is crucial to effectively control soil metal pollution.At the same time,the potential sources of various metals in soil are different,and the contribution of metal pollution from different sources to environmental risks is also different.Therefore,quantitative evaluation of the contribution of soil metals from different sources to environmental risks can provide a powerful reference for reducing the degree of metal pollution from the source.The purpose of this paper is to investigate the level of metals pollution in soil,explore the potential sources of soil metals by combining the spatial distribution map of metal concentration with positive definite matrix decomposition method(PMF),and establish a quantitative evaluation system of environmental risks,so as to comprehensively evaluate the environmental risks of soil metals in different land use types.Taking Longtan County as an example,soil samples of industrial land,farmland and residential land in Longtan County were collected,and the concentrations of 17 metal elements were determined.In the pollution assessment,enrichment factor(EF),contamination factor(CF)and comprehensive pollution index method(PLI)were used to classify the pollution levels caused by 17 metals in different land use types.The spatial interpolation distribution map of soil metals in Longtan County was drawn by kriging interpolation method in geostatistics method,and the sources of soil metals were identified by Pearson correlation coefficient and PMF.Then,a comprehensive evaluation system of environmental risk was established,and the contribution of sources was determined by receptor model,and the contribution of potential sources of soil metals to environmental risk was quantified by combining potential ecological risk index method(RI)and human health risk evaluation method.The main research results were as follows:(1)According to the overall situation of the soil in Longtan county,the concentrations of As,Cr,Cu,Hg,Ni,Pb,Sn and Zn all exceeded the background values,among which the concentrations of As,Cr,Cu,Hg,Ni,Pb and Zn exceeded the class Ⅱ soil quality standard.The coefficient of variation of Hg,Pb,As,Cu and Zn exceeded 0.5,showing high variability of concentration distribution.The concentration of metal elements in the soil of industrial land was the highest among the three land use types,but the concentration of metal in the soil of industrial land and residential land did not exceed the soil control standard of construction land.The concentrations of As and Pb in farmland exceeded the agricultural land control standards,which were 1.54 and 1.8 times of the agricultural land control standards,respectively.(2)Hg,Pb and Sn in industrial land and Sn in farmland were moderately enriched,and the pollution level was also severe pollution.Pb in residential land was moderately seriously enriched,while the pollution levels of As,Cu,Pb and Sn were all seriously polluted.The comprehensive pollution levels of three types of land use were arranged in the order of industrial land > residential land > farmland,and only industrial land had reached the moderate pollution level.(3)The spatial prediction distribution map of metals proved that Al,As,Ba,Ga,Mg,Mn and Sr all show hot spots in the southwest of the study area,which was directly affected by the industrial zone in the southwest of Longtan District.Seventeen metals were divided into six factors by PMF.Combined with the spatial distribution map of metals,it can be summarized that As and Zn were industrial sources,Hg was mainly from coal combustion,Pb and Cu were traffic emission inputs,and Al,Cr,Mg,Mn,Sr,Ba,Cd,Co,Ga,Ni,Sn and Ti were all natural sources.(4)Hg was the metal element with the highest contribution to the ecological risk of the three land use types in Longtan District.The quantitative evaluation results showed that the highest source of ecological risk of industrial land and residential land was coal combustion,and these two land use types have reached a high risk level;However,farmland was the natural source dominated by factors 5-Ba,Cd,Co,Ga,Ni,Sn and Ti,and the farmland had the lowest risk level and was at severe risk.(5)The non-carcinogenic risk value of As,Cr,Mn and Pb to children in Longtan District exceeded the safety threshold,and the quantitative evaluation results showed that industrial emissions led by As was the biggest contribution source of non-carcinogenic risk to children.Adults in Longtan District were not affected by non-carcinogenic risks.As,Cr,Ni and Pb had extremely high comprehensive carcinogenic risks to human health,and the superposition of carcinogenic risks of Cr and Ni led to the greatest contribution of natural sources to carcinogenic risks in the study area.(6)According to the research results,six risk control measures were put forward,including establishing strict emission standards of sewage enterprises,attaching importance to monitoring trace elements,refining soil quality standards of land use types,strictly preventing traffic emission pollution,strengthening remediation of polluted soil in Longtan District and earnestly carrying out propaganda work of soil protection.The conclusion of this study provided basic data reference for monitoring and treatment of soil metals in the old industrial bases in Northeast China,and provided scientific decisionmaking basis for controlling the input of soil metals from the source.It preliminarily revealed the pollution status and potential sources of soil metals under different land use modes in the study area.Meanwhile,a comprehensive evaluation of environmental risks of soil metals was carried out with a new idea.Quantitative evaluation of the contribution of sources to environmental risks can make the evaluation results more accurate,which is of great practical significance for protecting soil ecological security and residents’ health in the old industrial bases in Northeast China.