Distribution Characteristics And Risk Assessment Of Heavy Metals In Qingshui River Basin

Arsenic(As),chromium(Cr),mercury(Hg)and lead(Pb)in water and surface sediments at 32 sampling sites in QingShui River basin were monitored in April,July and November 2018 to explore the distribution characteristics and pollution of heavy metals there.The principal component method was used to analyze the influence degree of heavy metals in the water and surface sediment of qingshui river basin and the pollution degree of each water system.Twelve river systems in qingshui river basin were classified by cluster analysis.Nemero comprehensive pollution index method and water quality index method were used to evaluate the heavy metal pollution in water.Potential ecological risk index method,land accumulation index method and pollution load index method were used to evaluate the heavy metals in the surface sediments of qingshui river basin.Through different evaluation methods,heavy metals in the water and surface sediments of qingshui river basin were studied,and their distribution patterns and pollution sources were analyzed to provide a basis for the treatment of heavy metal pollution in qingshui river basin in ningxia.The main results of this study were as follows:(1)In 2018,qingshui river basin water of heavy metals As,Hg,Pb Ⅳ class there were no more than the average content of surface water standard,and the average content of Cr more than surface water Ⅳ class standard.As,Hg and Cr showed seasonal variation rule in November>April>July,while Pb showed seasonal variation rule in November>July>April.The average annual contents of heavy metals As,Cr and Pb in the surface sediments of qingshui river basin did not exceed the background values of soil,while the average annual contents of Hg exceeded the background values of soil.As,Pb,Hg and Cr showed the seasonal variation rule in November>April>July.(2)Three principal components of heavy metals were extracted from the water and surface sediments of qingshui river basin by principal component analysis.Based on the results of one year’s analysis,the order of four heavy metals in water in qingshui river basin was Cr>Hg>As>Pb.The order of four heavy metals in sediments in qingshui river basin was Hg>As>Pb>Cr.The heavy metals As,Cr,Hg and Pb mainly come from the discharge of industrial wastewater,urban sewage and agricultural sewage around qingshui river basin,minerals replenishing water in groundwater,inorganic salts in rainwater erosion and soil and rock weathering.The ranking of the comprehensive scores of the 12 drainage systems in qingshui river basin showed that the higher pollution degree was mainly located in the middle and lower reaches of qingshui river,mainly in shayan ditch,jing ditch and xi river.(3)The heavy metals in the water of qingshui river basin were analyzed by cluster analysis.The 12 water systems of qingshui river basin in April,July and November 2018 were divided into 5 categories.The first was upstream and dongzhi rivers;The second was xianma river;The third category was middle stream,down stream,zhong river,shuangjingzi ditch,zhongwei wupai;The fourth category was xi river,zhesi ditch;The fifth category was jing ditch,shayan ditch.The heavy metal cluster analysis was conducted on the sediments,and the 12 water systems in qingshui river basin in April,July and November 2018 were also divided into 5 categories.The first was upstream and middle river;The second category was shuangjingzi ditch,zhesi ditch,dongzhi river,xianma river;The third category was the zhongwei wupai,downstream;The fourth category was the shayan ditch,middle stream;The fifth category was xi river and jing ditch.Combined with the principal component method,the pollution ranking of the twelve water systems in qingshui river basin was analyzed.The cluster analysis was mainly classified according to the similarity of heavy metal pollution degree.The classification results are not only related to the ranking of heavy metal pollution in qingshui river basin,but also related to the geographical locations and pollution sources of the 12 river systems.(4)The results of nemero comprehensive pollution index method showed that the pollution of weight metal Cr in water was the most serious,and the qingshui river basin was moderate pollution.The results of the water quality index method showed that the qingshui river basin as a whole was pollution-free.The evaluation results of the two methods were consistent with the overall change trend of the whole qingshui river basin,and the water pollution degree was mostly November>April>July.Potential ecological risk index method,land accumulation index method and pollution load index method were used to evaluate heavy metals in the sediments of qingshui river basin.The evaluation results of the three methods were basically the same,and it was believed that the surface sediments of qingshui river basin had the greatest risk of heavy metal Hg pollution.From the perspective of multi-factor index,the results of potential ecological risk index method showed that the surface sediments in qingshui river basin were low risk.The results of pollution load index method showed that the heavy metal pollution degree of surface sediment in qingshui river basin was pollution-free.From the perspective of season,the pollution degree of all water systems was mostly November>April>July.