Form,Source Analysis And Risk Assessment Of Heavy Metals In PM_2.5 In The Northern Suburbs Of Nanjing

As an important kind of atmospheric pollution,atmospheric particulate matter pollution has become one of the most serious environmental problems for many cities in China in recent years.The large specific surface area of atmospheric particle was easy to absorb heavy metals and other harmful substances,which could pose a threat to human health through respiration,skin exposure and other ways,and has gradually become a research hotspot.With the acceleration of urbanization and developing industrialization,human activity is considered the main source of heavy metals in the atmosphere,and the combination of heavy metals and PM_2.5directly affects their biological toxicity.Thus,a comprehensive understanding of the pollution of atmospheric heavy metals such as their pollution characteristics,possible sources and environmental and health risk,is needed for us to gain insight into the air pollution status in China,which is also crucial for the government to make the environmental policies and carry out the prevention work for urban atmospheric pollution.Atmospheric PM_2.5samples were collected continuously for a long time in Nanjing.Concentrations,morphology and the seasonal variation rules of 12 heavy metals in PM_2.5（Al,V,Cr,Mn,Co,C Ni,Cu,As,Cd,Ba,Pb,and Sr）was studied by the improved the European Community Bureau of Reference（BCR）,and the sources of heavy metals in PM_2.5were identified using the enrichment factor method,correlation analysis,principal component analysis,positive definite matrix factorization model（PMF）and Hybrid Single Particle Lagrangian Integrated Trajectory Model（HYSPLIT）.Assessed ecological and health risks of heavy metals in PM_2.5by ecological risk index model and EPA exposure model based on bioavailability modifications,and analyzed the health risk of specific pollution sources and potential source areas with CWT and HYSPLIT.The results are as follows:（1）Pollution characteristics of PM_2.5and its heavy metalsDaily average concentration of PM_2.5is（102.24±43.81）μg·m³and its seasonal variation law is winter>spring>autumn>summer,and the total contents of 12 heavy metals was（3039.23±1021.31）ng·m^-3,Al was the most abundant element among the twelve measured metals and followed by Pb,V,Cr,Sr,Mn,Cu,Ba,Ni,As,Co and Co during sampling period.The total contents of each HM in different seasons were in the following order:winter>autumn>spring>summer.Most of the studied HMs（V,Cr,Mn,Ni,As,Cd）was mainly concentrated in acid-soluble fraction（F1）with high bioaccessibility and high environmental risk,a relate high percentage of Co,Cu,Pb were present in reducible fraction（F2）with potential environmental risk,Al,Ba and Sr was mostly concentrated in residual fraction（F4）with low bioaccessibility and relatively low environmental risk.（2）Source analysis of heavy metals in PM_2.5The enrichment factors showed that V,Cr,Co,Cd,Ni,Cu,As,Cd,and Pb were severely enriched,Mn,Ba,and Sr were moderately enriched.The results of correlation,principal component analysis and positive definite matrix factor model show that the sources of heavy metals in PM_2.5are dust sources（35.5%）,coal burning sourcse（12.5%）,traffic sourcse（37.1%）,industrial sources（14.9%）.The results of the HYSPLIT show that the heavy metals in PM_2.5mainly come from the transportation of the Yellow Sea and the surrounding areas,with little local source contribution.Heavy metals in PM_2.5in Nanjing mainly came from the transportation of southern Jiangsu Province,Anhui Province and Jiangxi Province during the period of heavy pollution.（3）Risk assessment of heavy metals in PM_2.5The results of ecological risk assessment showed that Cr,Ni,As,Cd,Cu and Pb were all more harmful to human.The health risk assessment showed that the non-cancer risks of heavy metals for children is obvious with HI values more than 1 and for adults is negligible with HI values under 1.Cr,Co,As,Cd had a potential cancer risk to children and adults with ILCR values between 10^-6and 10^-4,the cancer risks of Cr for adults was obvious with ILCR values is 1.36E-04.ILCR of Industrial sources and coal sources were the main contributing sources of non-cancer risk and cancer risk.CWT and HYSPLIT reveals that Zhejiang Province,Anhui Province,and Hunan Province are main region.Therefore,the treatment of heavy metals in PM_2.5in Nanjing should not only strengthen the control of Cr,Co and As from industrial sources and coal burning sources,but also pay close attention to the local transportation situation of surrounding areas.