| With the rapid development of urbanization and industrialization,the problem of soil heavy metal pollution is extremely prominent.Heavy metals are persistent,non-degradable and highly toxic.Once they enter the soil environment,they are difficult to remove and repair.Therefore,it is of great significance for soil environmental protection and prevention to accurately grasp the current situation of soil heavy metal pollution and its health risks,and reveal the main pollution sources.A total of 295 surface soil samples(0?20 cm)were collected from the soils in the Yanghe watershed.Seven major heavy metal elements(Cu,Zn,Pb,Cr,Cd,Ni and As)were analyzed and determined.Based on local background values and soil secondary standards,collaborative Kriging interpolation was used to analyze their spatial distribution characteristics.Combined with cluster analysis,PCA and PMF,the sources of soil heavy metals in Yanghe watershed were explored to reveal the main sources and contributions of soil heavy metals.Based on the USEPA human exposure risk model,the non-carcinogenic risk of Cr,Ni,Cu,Zn,As,Cd and Pb elements in soil of Yanghe River Basin was evaluated,and the carcinogenic risk of Cr,As and Cd was evaluated.The main results are as follows:(1)The contents of Cu,As,Ni,Pb and Cr did not exceed the background values except Cd and Zn,but the maximum values of all heavy metals exceeded the local background values.Among different land use types,the contents of Cu and As are the highest in agricultural land,while the contents of Cr,Ni,Zn,Cd and Pb are the highest in urban industrial land.On the whole,the heavy metal pollution degree in yanghe River basin is acceptable,but the heavy metal content in local soil is much higher than the average value,which has potential pollution risk.(2)Cluster analysis,principal component analysis and PMF model were used to analyze the sources of heavy metals in soil of Yanghe River Basin.The results showed that Cr,Ni,Cu and As were mainly derived from natural processes,mainly chemical fertilizer and pesticide application.Zn and Cd mainly come from metallurgical and industrial activities.The production activities of heavy pollution industries such as mines,power plants and cement plants play a leading role in the distribution of Cd and Zn.Pb mainly comes from transportation activities,and transportation emissions contribute to Pb and Zn to a certain extent.However,in agricultural activities,the accumulation of Zn,Pb and Cd in soil will be accelerated due to the massive application of phosphate fertilizer,which will eventually exceed the natural abundance.(3)The health risk assessment results of soil heavy metals showed that there was no significant non-carcinogenic risk in the study area.The HI value of adults was4.24×10-1,and that of children was 8.38×10-1.Cd has become a major contributor to non-carcinogenic health risks in the study area,contributing 38.05%to non-carcinogenic risks of adults and 29.73%to non-carcinogenic risks of children.The most important exposure route is skin contact.The risk of cancer in the study area was also not significant,with TCR of 5.61×10-5 for adults and 8.93×10-4 for children,both less than 1×10-4.Skin contact was the main exposure route.At the same time,children suffer more carcinogenic and non-carcinogenic risks than adults. |
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