| Yuzhong County was typical representative of ecologically fragile area in Northwest China,and the ecological environment is relatively complex.Therefore,it was of great significance to scientifically evaluate the overall pollution level and main pollution sources of heavy metals in cultivated soil in Yuzhong County based on various methods and models for understanding the heavy metal pollution in cultivated soil in ecologically fragile areas in Northwest China.In this study,104 topsoil samples of cultivated land were collected in Yuzhong County.The contents of eight heavy metal elements(Pb,Cd,Cr,Hg,as,Cu,Zn and Ni)were determined based on ICP-MS.the pollution levers,spatial distribution and sources apportionment of heavy metals in cultivated were evaluated by using various methods and models.The main results were as follows:(1)The average contents of Pb,Cd,Cr,Hg,As,Cu,Zn and Ni in cultivated soil of Yuzhong County were 20.09,0.24,59.40,0.04,3.98,35.91,96.81,32.51mg/kg.The average contents of Cd,Hg,Cu,Zn and Ni were 1.71,1.33,1.57,1.44 and1.23 times higher than the Lanzhou soil background values,indicating that heavy metals such as Cd,Hg,Cu,Zn and Ni had accumulated to certain extent in the study area.On the contrary,the average contents of the 8 heavy metals were all lower than the national background value of soil environmental quality,and all of them exceeded the standard.(2)In order to understand the pollution status of heavy metals in cultivated soil in Yuzhong,this study accurately calculated the pollution accumulation value of 8heavy metals by using single factor index and Nerome pollution index.The results showed that the soil environment in the whole Yuzhong County was clean,and the accumulation degree of heavy metals in cultivated soil was low and at a safe level.The potential ecological risk index of 8 heavy metals showed that except Cd,the ecological risks of Pb,Cr,Hg,As,Cu,Zn and Ni at all the sampling sites were low.It Was found that Cd contributes the most to the overall ecological risk,and Cd can be used as the main pollutant control.(3)All heavy metals conform to normal distribution.Through calculation of semivariogram and model fitting,Cd,Hg and Zn were Gaussian models;Cr,As,Cu and Ni were exponential models;Pb was spherical model.The spatial distribution shows that Hg has wide range of low values in the entire study area,while elements such as Pb,Cd,Cr,As,Cu,Zn,and Ni have obvious high value areas in the entire area.Among them,Cd,Cu and Zn the widest range of high values.(4)Based on correlation analysis,Positive matrix factorization(PMF)and absolute principal component score-multiple linear regression model(APCS-MLR)to analyze the main pollution sources of 8 heavy metals.Correlation analysis shows that there are significant positive correlations between Pb and Cd,Hg,and As,between Cu and Zn,and between As and Ni,which may have similar sources.On the contrary,Cr has no significant correlation with other heavy metals,so Cr may have single source.Through the PMF model,it was concluded that Hg,Cu and Zn were mainly agricultural sources with contribution rate of 29.64%;Cr was natural source with contribution rate of 19.52%;Pb and Cd were transportation sources with contribution rate of 23.13%;As and Ni were industrial sources,with contribution rate of 27.71%.Through the APCS-MLR model,it can be obtained that Pb,Cd and Hg were sources of transportation and agricultural activities with contribution rate of 21.14%;Cr was natural source with contribution rate of 17.38%;Cu and Zn were agricultural sources with contribution rate of 32.33%;As and Ni were industrial source with contribution rate of 29.15%.In summary,the pollution sources in the study area were mainly caused by human activities. |
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