Pollution Characteristics And Health Risk Assessment Of Heavy Metals In Soil Near A Large Non-ferrous Smelter

Non-ferrous metal smelting activities have long been considered as one of the most important anthropogenic sources of heavy metals in soil.There are many non-ferrous metal smelters in China,which cause serious heavy metal contamination to the surroundings and pose a great threat to the health of people.Daye City,Hubei Province is rich in mineral resources.The long-term mining and smelting activities in Daye nonferrous smelting area(DNSA)have caused severe heavy metal pollution,and have shown a preliminary damage effect on human health.In order to investigate the pollution status of soil heavy metal in DNSA,the content levels of ten soil heavy metals in the study area were analyzed,including Co,Zn,Mn,Ni,Cu,Pb,As,Cr,Cd and Sb.The pollution characteristics and spatial distribution of heavy metals in soil were analyzed by enrichment factor(EF),pollution load index(PLI)and geostatistical methods.The correlation analysis and positive matrix factorization(PMF)model were used to quantitatively apportioned the sources of soil heavy metal.Moreover,the potential ecological risk assessment model and the human health risk model were used to evaluate the ecological risks and health risks of heavy metals in the soil.(1)The average concentrations of Co,Zn,Mn,Ni,Cu,Pb,As,Cr,Cd and Sb in the soil of DNSA were 17.85,244.22,625.15,28.76,273.51,75.03,30.77,61.89,3.24 and 3.78 mg/kg,respectively.The average contents of Co,Zn,Cu,Pb,As,Cd and Sb were higher than their background values of Hubei Province,which were 1.16,2.92,8.91,2.81,2.50,19.04 and 2.29 times of the background values,respectively.There were differences in the content of soil heavy metals under different land use patterns.The contents of Zn,Cu,Pb,As,Cd and Sb in the construction land were significantly higher than those in the agricultural land and ecological land,indicating that these six heavy metals were greatly affected by human activities;and there was no significant difference in the contents of Co,Mn,Ni and Cr under different land use patterns,indicating that human activities have less influence on these four heavy metals.The vertical distribution of heavy metal in the profile soil showed that Zn,Cu,Pb,As,Cd and Sb were obviously enriched in the surface layer,and their contents significantly decreased from the surface layer(20 cm)to the subsurface layer(40 cm),and then the contents gradually decreased with the increase of depth,indicating that the accumulation of these six heavy metals in the surface layer might mainly come from human activities such as smelting.The contents of Co and Mn increased with increasing depth,indicating that Co and Mn might be mainly controlled by the parent material.Moreover,there was no significant difference in the contents of Ni and Cr between layers,indicating that these two heavy metals were less affected by human activities and probably mainly from natural sources.The results of EFs showed that Zn,Cu,Pb,As,Cd and Sb were obviously enriched in the study area,especially Cd and Cu,with extremely high enrichment levels;the results of PLI revealed that the whole study area was in serious pollution,and 76.71% of the total sample sites were moderate pollution and serious pollution.(2)The nugget effect values of soil heavy metals in the study area decreased following the order of As > Pb > Cu > Cd > Zn > Sb > Co > Mn > Ni > Cr.The nugget effect values of Mn,Ni and Cr were 0.248,0.230 and 0.191 with higher spatial correlation,suggesting Mn,Ni and Cr were influenced by in structural factors.While the nugget effect values of As,Pb,Cu,Cd,Zn,Sb and Co were 0.684,0.574,0.541,0.529,0.517,0.436 and 0.344 with medium spatial variation,indicating As,Pb,Cu,Cd,Zn,Sb and Co were influenced by anthropogenic random factors.The distributions of Co,Cu,As,Cd and Sb in the soil of the study area were relatively consistent,which the high-value areas were mainly located near the smelter.The spatial distributions of Pb and Zn revealed that the high-value areas were located around the smelter and near the main roads in the middle of the study area.However,the spatial distributions of Mn,Ni,and Cr were different from the above heavy metals,and their hot spots were small and relatively random.(3)Through EF,spatial distribution characteristics,correlation analysis and PMF model to quantitatively identify the source of heavy metals,it can be concluded that there were four main sources of heavy metals in the study area.Copper,Cd,and As mainly came from agricultural activities such as the application of pesticides and fertilizers.Zinc and Pb were mainly contributed by traffic emission sources.Cobalt,Mn,Ni,and Cr were mainly derived from natural sources affected by parent material.Cobalt,Cu,As,Cd and Sb were mainly related to smelting activities and other industrial activities such as alloy processing and electroplating.The contribution rates of the four source factors were 12.14%,23.07%,33.46% and 31.33%,respectively.Therefore,anthropogenic activities were the dominant factor for the sources of soil heavy metal in the study area,accounting for 66.54% of the total contribution of heavy metal sources.(4)The results of ecological risk assessment showed that the average value of single potential ecological risk index of Cd(488.91)was the largest of all heavy metals,reaching an extremely high level of ecological risk,followed by Cu(44.55),reaching a medium level of ecological risk,while the average value of single potential ecological risk indexes of Co,Zn,Mn,Ni,Pb,as,Cr,and Sb were lower than 40,belonging to a slight ecological risk.Furthermore,the average value of the comprehensive ecological hazard index of the study area was 598.87,reaching a high ecological risk level,and the contribution rate of Cd was 81.64%,which should be paid attention to.The proportions of the four risk levels of low,medium,considerable and high were 6.85%,27.40%,16.44% and 49.31%,respectively.This meant that nearly half of the sample sites were at high ecological risk.(5)The total hazard index values of adults and children in the study area were 0.23 and 2.06,respectively,indicating that heavy metals in the soil of DNSA caused significant non-carcinogenic health risks to children,while the non-carcinogenic health risks to adults were still acceptable.Oral ingestion was the main exposure route of non-carcinogenic health risk in two groups.Arsenic made the largest contribution to the non-carcinogenic risk of adults,while As,Pb,Cr had a greater impact on the non-carcinogenic risk of children,especially the impact of As on children's health.The total carcinogenic risk index values of adults and children were 4.34E-05 and 9.08E-05,respectively,which were tolerable to human body.However,the total carcinogenic risk index of children was close to the threshold value(1.00E-04)and should be concerned.Oral ingestion was the main exposure pathway for carcinogenic risk of As,Cr and Cd in two groups.As and Cr contributed greatly to the total carcinogenic risk of adults and children,and were the major carcinogenic risk factors.The contribution of various sources to non-carcinogenic and carcinogenic health risks showed that the industrial activities dominated by smelting(Factor 4)were the main contribution sources of non-carcinogenic and carcinogenic risks in the study area.The results of this study will provide scientific basis for the prevention and control of soil heavy metal pollution,green production of industry and agriculture and human health protection in DNSA,and also provide reference for the construction of ecological civilization in other domestic nonferrous smelting areas.