Pollution And Potential Health Risk Assessment Of Heavy Metals In Groundwater In The Yanqi Basin

The quality and safety of groundwater is the base of the utilization and protection of groundwater resources.The accumulation and diffusion of heavy metals in groundwater not only affect the main functions of groundwater,the growth of vegetation,and the ecosystem security,but also enter human body through the circulation among various ecosystems,and thus threatening the human health,which has attracted the attentions of foreign and domestic researchers.Considering the lack of related researches on heavy metal pollution of groundwater in Yanqi Basin,Xinjiang,this study takes groundwater in Yanqi Basin as the main research object,combined with field investigation and indoor detection and analysis,the contents of six heavy metal elements,such as Cu,Mn,Cr,Cd,Ni,and Zn in groundwater were measured.Based on multivariate statistical analysis,geostatistics analysis,GIS technology,Nemerow Comprehensive Pollution Index,fuzzy mathematics and the US EPA health risk assessment model,the pollution characteristics and the potential health risk of heavy metals in groundwater in the study area are systematically studied,the spatial distribution characteristics and pollution sources of heavy metals in groundwater are discussed,the impact mechanism of heavy metals in groundwater on human health are clarified,results of this study will provide scientific basis for the safety of groundwater environment and sustainability use groundwater in the study area.The main conclusions of this study are as follows:(1)The contents of Cu,Mn,Cd,Cr,Ni,and Zn in groundwater in the study area vary from 0.009 to 0.108 mg/L,0.005 to 0.297 mg/L,0.002 to 0.011 mg/L,0.005 to 0.042 mg/L,0.000 to 0.109 mg/L,and 0.005 to 0.454 mg/L,respectively.According to class III of the national groundwater quality standard(GB/T14848-2017),contents of Cu,Cr and Ni in the study area did not exceed the limits,whereas contents of Mn,Cd,and Zn exceeded the related limits,with the exceeding rate of 10.45%,1.49% and 10.45% respectively.The average content of six elements in groundwater in the study area does not exceed the national groundwater quality standard.The variation coefficients of Cu,Mn,Cr,Ni,and Zn in the groundwater in the study area are 0.729,0.897,0.516,1.083,and 1.314,respectively,which are greater than 0.5,indicating that the distribution of heavy metals in the groundwater of the study area is uneven and the spatial variation is obvious.(2)Results of the geostatistical analysis show that the Exponential Model is the best semi-variogram model of Cd,Cu,Ni,and Zn elements in groundwater in the Yanqi Basin,where as the Spherical Model for Mn element,and the Gaussian Model for Cr element.The spatial distribution patterns of six heavy metal elements of groundwater in the study area were different,and all elements showed high value areas;(3)The average value of the pollution index of Cd,Mn,Ni,Cr,Zn,and Cu in groundwater in Yanqi Basin is 2.04,0.69,0.45,0.24,0.07,and 0.03 respectively.The comprehensive pollution index(NI)of heavy metals in groundwater is between0.23 and 2.22,with an average value of 0.73,at the slight pollution level.According to the NI value of groundwater,58.21%,29.85%,7.46%,and 4.08% of the total samples fell into the no pollution,slight pollution,low pollution and moderate pollution levels,respectively.(4)It is calculated that the potential non-carcinogenic health risk index(HI)of six heavy metals in groundwater to adult was 7.83E-01<1,and the potential non-carcinogenic health risk index for children was 1.05E+01>1,indicating that the impact of heavy metals in groundwater in the study area on adults’ health is not obvious,but it may have a certain impact on children’s health,which needs further study.(5)The correlation between Mn and Cd,Mn and Zn,Cd and Zn in the groundwater of the study area is extremely significant with the significance test of0.01 levels,and the correlation between Cu and Cd is relatively high with the significance test of 0.05 levels.The results of multivariate statistical analysis show that Mn,Cd,and Zn in the groundwater in the study area are mainly affected by human factors,while Cu and Cr are jointly affected by human factors and natural factors,and Ni is affected by natural factors.