Multi Medium Distribution Characteristics,Risk Assessment And Source Identification Of Heavy Metals In Taipu River In The Yangtze River Delta Integration Demonstration Area

Taipu River is the only representative river spanning two provinces and one city in the Yangtze River Delta Ecological Green Integration Development Demonstration Zone,and it is also an important standby water source in the upper reaches of Huangpu River.The water quality of Taipu River is not only an important manifestation of the regional environment but also of great significance to the development of the Yangtze River Delta Integration Demonstration Zone.A seasonal study on the distribution characteristics and occurrence forms of As,Cd,Co,Cr,Cu,Mn,Ni,Pb,Sb and Zn in15 sediments of Taipu River was carried out.A variety of pollution assessment methods were used to evaluate the pollution level and the health risk of heavy metals in Taipu River while multivariate statistical analysis and Pb isotopes were applied to identify the source of heavy metals in Taipu River.The main conclusions were as follows:In Huangpu River waters,the single factor pollution index showed that Mn reached light pollution in spring and autumn while Sb reached light pollution in winter;the comprehensive pollution index indicated that T1 and T6 reached heavy pollution in spring while T3 reached heavy pollution in autumn,and T7 reached heavy pollution in spring,autumn and winter.The health risk assessment demonstrated that health risks of heavy metals in Taipu River mainly came from chemical carcinogenic heavy metal elements As,Cd and Cr.Both adults and children had higher health risks at the upper and middle reaches in spring.The health risks of heavy metals in children were significantly higher than those in adults.Notice that no matter it was in wet season or dry season,the overlying and pore waters of As,Cd,Mn,Ni,Pb,and Zn were only reached class IV standard while Co,Cr,Cu and Zn could reach the class III standard.In Huangpu River sediments,the results indicated that the top four heavy metals with higher average concentrations in Taipu River sediments were Mn,Zn,Cr and Cu,whether in spring,summer,autumn or winter;in the longitudinal distribution characteristics,the concentrations of Sb,Co and Zn in each layer of sediments exceeded the background value in four seasons,resulting in relatively more serious pollution and different longitudinal distribution characteristics.The concentration of Sb decreased with the increase of depth in spring while the concentrations of Co and Zn in each layer were close in four seasons,which implied that there were migration movement of heavy metals in the layer of sediments.The concentrations of Cd,Co,Cu,Mn,Pb and Zn in the non-residue state in the four seasons all account for more than 50%with high bioavailability and high ecological risks.As and Sb accounted for a relatively high proportion of residue state in spring,autumn and winter,the four forms accounted for a relatively uniform proportion in summer,with active biological movement and enhanced bioavailability in summer,and Cr and Ni accounted for a high proportion of residue state in the four seasons;oxidizable heavy metals had strong correlation and positive correlation with TOC in summer（As,Cr,Cu,Mn and Zn）and autumn（As,Cr,Cu and Sb）.According to the analysis results of various pollution assessment methods,the pollution of Sb in the sediments of Taipu River was the most serious while the pollution of Cu,Mn,Pb and Zn in the sediments of Taipu River was more serious according to the speciation of heavy metals.The potential ecological risk index method revealed that Cd in Taipu River sediments was at moderate risk in both wet and dry seasons;Hg was at high risk in both wet and dry seasons;Sb was at low risk in both wet and dry seasons.The total risk index displayed that Taipu River sediments were at high risk in both wet and dry seasons,and all sample points were at high risk in wet season and dry season.The analysis of land use types revealed that the Taipu River basin was mainly dominated by residential land,forest land and natural water bodies.The proportion of cultivated land in the midstream and downstream was higher than that in the upstream,and the proportion of industrial land at point T7 was the highest,mainly in the textile industry and printing and dyeing industry.Although the proportion of industrial land was relatively small,local high-concentrations of industrial emissions could still cause serious ecological hazards.The results of multivariate statistical analysis displayed that As,Cd,Cr,Cu,Ni,Pb and Zn in Taipu River sediments were mainly affected by the combined influence of industrial sources,traffic sources and agricultural sources.Sb was mainly controlled by industrial sources,the textile printing and dyeing industry was the main source of Sb pollution,and Co and Mn were mainly affected by both natural and industrial sources.Pb isotope tracing results shown that Pb isotopes in Taipu River were affected by both natural and anthropogenic sources.Most of Taipu River sediments were in the range of natural Pb isotopes(²⁰⁶Pb/²⁰⁷Pb=1.18～1.20),but there were other sources.The Pb isotopes of aerosols were close to those of Taipu River sediments,and aerosols may be the source of Pb in Taipu River.