Pollution Characteristics And Risk Assessment Of Heavy Metals In Road-deposited Sediments From Urban Areas Of Yixing City

In this study,the grain size distribution and content of nutrients,organic matter and heavy metals(i.e.Zn,C u,Pb,N i and Cr)were analyzed for road-deposited sediments(RDS)in urban areas of Yixing C ity.The size distributions,sources,pollution levels and potential hazards of heavy metals were evaluated,and the results showed that:(1)The median particle size of RDS in Yixing C ity was 80.7 ?m,which was smaller than other cities.More explicitly,<22,22~38.5,38.5~150 and 150~2000 ?m RDS accounted for 2.11%,8.55%,50.71% and 38.63%,respectively.(2)The average contentrations of total nitrogen,total phosphorus,and organic matter in RDS of Yixing C ity were(1.26±0.33),(0.81±0.18)and(55.98±17.41)g/kg,respectively.The contentrations were relatively higher compared to other cities.Additionally,the contentrations of total nitrogen,total phosphorus,and organic matter were dependent on particle sizes.The contentrations of total nitrogen increased with the increase of particle sizes.The contentrations of total phosphorus decreased firstly and then increased slightly with the increase of particle sizes.<22 ?m RDS showed the highest total phosphorus concentration.However,t he concentrations of organic matter showed an opposite trend with total phosphorus,and 38.5~150 ?m RDS showed the highest concentrations.(3)The average contentrations of heavy metals(mg/kg)in RDS of Yixing C ity ranked as follows: Zn(329.03±95.92)> Pb(197.33±452.72)> Cr(128.12±61.79)> Cu(94.27±16.58)> N i(72.06±25.22).The contentrations of five heavy metals were higher than the background values of local,national and global soils.The contentrations of Zn and C u were highest in industrial and market areas.The contentrations of Pb were highest in old residential areas.The contentrations of Ni and Cr were highest in market areas.Additionally,all the heavy metals showed the lowest contentrations in >150 ?m RDS.(4)Source analysis showed that N i,Zn and Cr were mainly contributed by industrial and traffic activities.Cu was mainly contributed by the wear of brakes.Pb was mainly derived from the past emissions of Pb gasoline.No relationships between the heavy metal contentrations and total nitrogen,total phosphorus,organic matter were detected.O verall,industrial and traffic activities were the dominant sources of heavy metal pollution of RDS in Yixing City.(5)The results of geoaccumulation index(Igeo)showed that RDS in Yixing C ity were moderately to moderately/strongly polluted with Zn,moderately polluted with Cu,and no/moderately polluted with Pb,N i and Cr.The potential ecological risk index(RI)indicated that the heavy metals in RDS primarily posed low to moderately risk to local ecosystems,and 85% of which derived from C u,Cr and Pb.The health risk assessment indicated that there will be a potential non-carcinogenic risk to children,while not to adults.Additionally,the carcinogenic risk will be neglectable to populations exposed to RDS of Yixing.