| The scope of soil heavy metal pollution is spreading and its severity is gradually increasing as a result of rapid industrialization and urbanization,endangering the quality of agricultural products,people’s health,and even the stable development of society and economy,so an increasing number of countries and regions are focusing on heavy metal pollution in soils and related research.Iron and steel smelting is one of the important industrial sources for generating and discharging heavy metals,and the expansion of large iron and steel factories and other heavy industrial enterprises in Lanshan District of Rizhao city may cause the problem of soil environmental pollution in coastal areas,so it is necessary to carry out an investigation and ecological risk assessment of heavy metal pollution in soil around Rizhao Steel Holding Group Co.,Ltd(RG)and Shandong Steel Rizhao Co.,Ltd(SG).100 surface soil samples were collected through a field survey,and the contents of nine metal elements,Cu,Zn,Pb,Cr,Cd,Ni,Mn,Fe and Mg,were determined by indoor analysis,and the content characteristics of soil heavy metals were revealed with the help of pollution index method and geostatistical analysis method.Geostatistical analysis method combined with principal component analysis(PCA)were used to initially determine the types of soil heavy metal pollution sources,and positive definite matrix The geostatistical analysis method combined with the principal component analysis(PCA)method was used to initially determine the types of soil heavy metal pollution sources,then the Positive Matrix Factorization(PMF)was applied to determine the exact sources of soil heavy metals,and complete the quantitative analysis of the contribution of pollution sources to various types of heavy metals.The following are the key findings of the study.(1)The contents of various heavy metals in the soil were higher,and the study area was at a heavy pollution level.95%of the sites exceeded the standard for Cd,and the average content in the study area was 0.90 mg/kg,which was 7.89 times of the background value.100%of the sites exceeded the standard for Ni and Pb,and the average contents were 163.93 mg/kg and 112.51 mg/kg,respectively,which were 6.75 times and 4.20 times of the soil background value,respectively.The average contents of other heavy metals exceeded the standard whose contents were higher range from 1 to 3.The results of the single factor pollution index analysis showed that Pb was in moderate and heavy pollution levels,accounting for 90%and 10%,respectively.Cd was mainly in moderate and heavy pollution levels,accounting for 24%and 62%,respectively.Ni was mainly in moderate and heavy pollution levels,accounting for 20%and 79%,respectively,and according to the Nemerow comprehensive pollution index,the study area as a whole was seriously polluted.The spatial interpolation results showed that the areas with high heavy metal contents were mostly concentrated in the northwestern farmland area,the eastern steel factories,the east of the dredging avenue,the ports and the southwestern town site,and the heavy metal contents gradually decreased to the north and west.(2)The results in relation to source analysis of heavy metal demonstrated that the sources of soil heavy metals in the study area included mixed agricultural and traffic sources,natural source,atmospheric deposition source and industrial material source,with the contribution rates of 32.68%,12.20%,27.57%and 27.54%,respectively.The contribution rates of mixed agricultural and traffic sources to Cu,Pb and Cd were larger,accounting for 46.00%,48.21%and 61.33%,respectively.The contribution rate of natural source to Mn reached 79.08%.Atmospheric deposition source was closely related to the contents of Cr and Ni,with contributions of 69.79%and 42.89%,respectively.Industrial material source mainly influenced the contents of Zn,Cd,Fe and Mg,with contributions of 52.47%,38.67%,36.44%and 58.96%,respectively,and heavy metal Cd was influenced by mixed agricultural and traffic sources and industrial material sources(3)The consequences of the environmental risk analysis showed that the proportions of sample sites with Ni at medium and high ecological risk levels were 13%and 2%,respectively,and the high value areas were mainly concentrated in the southern part of SG,the northern part of RG and the eastern part of the Shugang Avenue between the two iron and steel factories.The proportions of sample sites with Cd at considerable,high and very high ecological risk levels were 27%,37%and 23%,respectively,and the high value area was located within 4km of the center of SG.All in all,the study area was mainly at the medium ecological risk and high ecological risk levels.The results of the health risk assessment showed that soil heavy metals can cause carcinogenic risk to children and adults through three exposure pathways,and Ni was the main carcinogenic factor.The key pathway for both carcinogenic and non-carcinogenic health risks of soil heavy metals was hand-to-mouth exposure,and adults were more vulnerable to the carcinogenic risk of heavy metals than children.(4)The pollution of Cd in the study area was the most serious and was at heavy pollution and a high ecological risk levels,which could produce potential carcinogenic risk to adults,so the treatment of soil Cd pollution was urgent,and it was recommended to use physical or chemical methods with short remediation cycles.Ni produced significant carcinogenic risk to both adults and children.As a result,it was suitable to grow plants with strong absorption capacity for this heavy metal,such as Alyssum murale,and the key treatment areas were the iron and steel factories and the eastern section of Shugang Avenue between the iron and steel factories.Heavy metal pollution in the study area mainly came from agricultural activities,the iron and steel factories and transportation,so the later stage should start from strict emission of waste water,waste gas and waste residues from key industries,reducing the use of chemical fertilizers and pesticides,strengthening control of dust,and optimizing the layout of enterprises,in order to protect ecological environment and human health and advance sustainable development of economy and society. |
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