Pollution Characteristic,source And Health Risks Of Heavy Metals In Urban Atmospheric PM_2.5

With the rapid development of urbanization in China,environmental air pollution has gradually attracted more and more attention.Recently,atmospheric PM_2.5 has become a hot spot with its specific surface area,which can easily absorb more pollutants and can enter the lung to cause more serious health hazards.Population explosion,energy consumption,industrial production and so on are the potential sources of heavy metal pollution in the atmosphere.Human activities will discharge a large amount of heavy metal pollutants into the atmosphere,and the combination of heavy metal pollutants and PM_2.5 will cause more serious harm to the ecological environment and human health.Therefore,it is significant to analyze the characteristics,source and health risks of atmospheric PM_2.5 and its heavy metals by a variety of scientific analysis methods and simulation studies.Shanghai Minhang District and Tianjin Xiqing area were selected as the study area.Five heavy metals including Hg,As,Pb,Cd and Cr were selected as the main research objects,through a long-term sample collection and continuous observation of typical haze events.In order to explain the characteristics of heavy metals in PM_2.5,the variations of metal concentrations,chemical morphology and morphologies of heavy metals in PM_2.5 was analyzed.Combined with the following simulation models or analysis mothod,such as tracking trajectory and stable Pb isotope ratio,the sources of heavy metals in PM_2.5 were identified furthermore.The risk of carcinogenic and non-carcinogenic exposure under the inhalation pathway of different heavy metals was simulated,so as to improve the study on the characteristics,sources and health risks of heavy metals in PM_2.5 in autumn and winter finally.The results were as follows:?1?The concentrations of Cr,Pb,Cd,As and Hg in the PM_2.5.5 of Shanghai in autumn and winter were 30.18¹78.61,11.63⁷6.51,0.26³.20,0.28⁴.28,0.01⁵.83ng·m^-3,which showed a significant decline trend with the improvement of air quality.The results of cumulative index evaluation indicated that the pollution level of As in PM_2.5 was relatively low,and Pb and Cr were slightly higher polluted,while Cd and Hg were highly polluted,affected by the human activities.Pb,As and Cd in PM_2.5 had high bioavailability and strong environmental activity,and were easy to transfer to environment,which were highly influenced by human activities.While Hg and Cr were mainly in stable form,which could not be easily changed by environmental conditions.?2?Backward trajectory clustering weights trajectory analysis combined with potential source contribution?PSCF?and Concentration Weighted Trajectory?CWT?showed that the pollution incident in Shanghai was influenced by the land transportation in the local and surrounding Yangtze River Delta region?Anhui Wuhu industrial zone,Zhejiang Qiantang river basin?.The influence of the long-distance pollutants from the Southeast Asia and Taiwan region also accounted for a high proportion.However,the pollution incident in Tianjin was mainly affected by external source of pollution,especially in Shandong,Hebei and northern Jiangsu.The result of PSCF and CWT further determined the source of heavy metals in Shanghai pollution events.The exogenous heavy metal pollution mainly came from the southeastern Anhui industrial cities?Wuhu?,Zhejiang Qiantang river basin?printing and dyeing,paper making pollution?and high energy consumption enterprises in Shaoxing-Zhuji area.And the main exogenous sources in Tianjin pollution event was the Bohai sea industrial zone and industrial port city area along the coast of the yellow sea.The influence of Handan-Shijiazhuang area in Hebei province also cannot be ignored,because heavy industry?like Steel,metallurgy and so on?gathered at this area.Lead isotope ratio results also showed that the PM_2.5 pollutants in Shanghai and Tianjin were affected by different anthropogenic sources.PM_2.5 and Pb in Shanghai were affected by anthropogenic influence like metallurgy and coal burning,while those pollutants were mainly from motor vehicle emissions and coal combustion in Tianjin.?3?Potential ecological hazards and health risks of heavy metals in PM_2.5 of ShanghaiThere was a high comprehensive ecological risk of heavy metals in PM_2.5 of Shanghai,Cd and Hg had the greatest ecological risk contribution among them,and Cd had a high bioavailability in particular,which can easily lead to hazardous events.Health risk evaluation results showed that the cancer risk of different heavy metals in PM_2.5 of Shanghai was not high.Under normal respiratory exposure,the risk for teenagers was the highest,followed by the risks for adult males and adult females,sucessively.The carcinogenic risk for heavy metals in PM_2.5 indicated that the carcinogenic risk for adults was much higher than that for children.The risk of carcinogenic health has a lifelong accumulation effect.To sum up,there are different levels of heavy metal pollution in PM_2.5 in different city air,and the meteorological factors have some influence on the formation of PM_2.5and its heavy metal bioavailability.In the process of air pollution control,the actual contribution rate of different pollutant components from local pollution and exogenous pollution should be carefully integrated.