Investigation And Source Apportionment On Heavy Metal Of Soils In Farmland Around Midong Industrial Park Of Urumqi City

Soil is not noly an important part of the global environment but also the material basis for the natural resource and agricultural production on which mankind depends.For a long period of time,human society has been driven by economic interests,ignoring the harms caused by social and economic development to the environment,causing many toxic and harmful substances(such as heavy metals)to enter the soil system and contaminating the ecological system and food safety.Humans at the top of the food chain are exposed to very serious health and safety threats mainly due to the bioaccumulation by the food chain.Qualitative identification of source categories and quantification of the contribution of each source to heavy metals in the soil is a prerequisite for the prevention and control of heavy metal pollution.In this paper,the agricultural soil around Midong industrial area in the northeast of Urumqi city of Xinjiang Province was taken as the main research area.Surface soil samples were collected,soil pollution index method and geoaccumulation index method were used to fully understand the characteristics of heavy metal pollution and enrichment.The potential ecological risk index method was used to evaluatethe potential ecological risk degree of the soil in the domain.The qualitative identification of the major potential sources of pollution in the domain was carried on using the correlation coefficient,inverse distance weighted(IDW)interpolation and principal component analusis.On this basis,the PMF receptor model was further used to quantify and analyze the potential source composition spectrum and contribution rate of heavy metals in the surface soil of the domain.The main results are as follows:(1)The heavy metals in the farmland soil around Midong Industrial Park show different degrees of accumulation or pollution.The soil cadmium(Cd)pollution is more prominent.The mean concentration of Cd in the topsoil(0-20cm)was0.46mg/kg.Compared with the national soil environmental quality secondary standards,there are 11 cadastral sites in Cd,accounting for 12.09%of the total samples.Cd geoaccumulation index above grade 1,accounts for 92.31%,indicating that Cd has a high rate of over-accumulation and serious pollution.The data of topsoil Cd concentrations was analyzed by the finite mixture model,and determining the local background value of Cd was 0.171 mg/kg.The mean concentrations of nickel(Ni)and zinc(Zn)were 47.90 mg/kg and 131.14 mg/kg,respectively,and the over-standard rates for spots were 4.40%and 3.30%.The geoaccumulative indexes above grade 1 accounted for 50.55%and 86.81%respectively.Nickel and zinc have a high cumulative rate of over-standard but the rate of contamination is low.Mercury(Hg),lead(Pb),copper(Cu),and arsenic(As)were not seriously contaminated in the study area.The arithmetic averages were 0.12 mg/kg,14.49 mg/kg,33.94 mg/kg,and12.33 mg/kg.Hg,Pb,and Cu did not exceed the national secondary standard,but the cumulative Hg exceeded the standard,and the As part exceeded the standard.(2)Analysis of Hg pollution index in the soil indicates that the average Nemero index is 0.74,which is still clean,and the maximum value is 1.63,which is in light pollution level.Soil samples above the cleanliness level accounted for 49.55%,indicating that heavy metals have the potential for pollution hazards in the soil in the study area.It is necessary to conduct further research on the soil.According to the analysis of the potential ecological risk index,28.57%of the soil Hg samples reached a moderate(Class 2)hazard level,and 35.17%of the samples reached a moderate degree of damage,indicating that Hg has a serious ecological hazard.There are 32.97%of the moderate degree of soil Cd,and 59.34%of the samples above moderate hazard,indicating that the ecological harm of Cd is also very serious.The average potential integrated ecological risk is 213.14,which belongs to moderate hazard,65.93%of the samples belong to moderate degree of damage,8.79%of samples belong to strong degree of harm,and 2.20%of samples belong to strong hazard level,indicating that it is necessary to comprehensively integrate the soil.The outliers combined with two contamination points of the box plots of the Nemero index and comprehensive ecological risk index data,it can be seen that each potential contamination sample follows the similarity principle.(3)The heavy metals showed distinctive spatial distribution characteristics.Higher Zn concentrations in the soil were mainly distributed in the north and southwest of the study area,and is in line with the Galvanized Steel Pipe Greenhouse,Machinery Manufacturing,Caigang Manufacturing Plant and Traffic lines.There is a significant positive and positive correlation between soil Ni and Cr,and the spatial distributions of them are similar.Sandaoba Middle Road passes through the high value areas of Ni and Cr North,and Changshanzi South Road has high values of Ni and Cr West.The Great Expressway is a high-value point in the south and southwest of Cr.The high soil Cd value zone is mainly concentrated in the eastern part of the study area,which is close to the industrial park.Soil Pb has two high-value areas in the west of Gumudi Town and south of Sandaoba Town.A total of four principal components were extracted using PCA analysis,which were interpreted as mixed pollution sources,sewage irrigation sources,soil parent material sources,and coal-fired emission sources related to agricultural activities,industrial activities,and transportation.(4)Analytical results of heavy metal sources based on the positive matrix factorization decomposition(PMF)model show that the fitting results of As,Hg,Zn and Pb in soil are very satisfactory,and the linear correlation(r~2)between predicted and measured values is close to 1;The fitting effects of Ni and Cr are better,r~2 is between 0.7 and 0.8,and the soil Cd fitting effect is poor(r~2=0.65).It can be seen that the overall fitting effect of the PMF model is good and basically meets the analysis requirements.The four source factors decomposed by PMF,from the factor spectrum of factor 1,it can be known that Zn,Ni,and Cr have higher concentration values than other factors in the factor,and are consistent with the source pollution component identified by the previous source,so the factor 1 is identified.For the mixed pollution sources,factor 2 contribution rates from large to small were As(72.16%),Cu(45.06%),Cr(38.95%),and Ni(34.51),all greater than 30%.Comparing the contribution matrix of principal component 3 and PMF in the rotating load matrix,it was found that Ni and Cr were from factor 1(mixed pollution source)and from factor2,and only accounted for a smaller contribution factor in factor 2.Factor 2 is similar to pre-source recognition of PC3.Therefore,factor 2 can be identified as a parent material source.Factor 3 and factor 4 have a greater contribution to Hg(74.59%),Cd(56.70%),and Pb(46.70%),respectively,making Hg and Cd and Pb the identifying elements of factor 3 and factor 4,respectively.Thus,factor 3 can be interpreted as the coal-burning source and factor 4 as the source of sewage irrigation.(5)The average contribution of factor 2(soil parent source)from the PMF model to Cd and Pb is 0.087 mg/kg and 0.090 mg/kg,respectively,and Cd(0.16 mg/kg)and Pb(11.20 mg/kg).Compared with the background value,it is obvious that the contribution value of PMF derived soil parent material is less than the background value.It shows that the model will underestimate the contribution of the parent material source,and the reliability of model analysis results must be further studied.