Digestion Method And Pollution Characteristics Of Heavy Metals Of The PM_2.5 In Typical Northeast Beijing

Heavy metals can be adsorbed by atmospheric particulates, removal with the spreadparticles, and present in the air for a long time with the fine particulate matter. It maylead to a great potential threat to environment and people health for its long-standing inthe air due to the toxic of the heavy metals, and the teratogenic, carcinogenic, andrespectively of part of heavy metals. In this study, we choose the fine particulate matterin Northeastern Beijing as the research object, the PM2.5samples were collected in theChina National Environmental Monitoring Center from September2012to July2013,and was digested by the microwave digestion system. The content of14heavy metalelements, including Cr, Mn, Co, Ni, Cu, As, Rb, Ag, Cd, Pb, Al, Ca, Fe, and Zn, in thePM2.5samples, were determined by ICP-MS under optimized conditions, to analysis thepollution characteristics of the heavy metals in PM2.5. Before determination, Four kindsof microwave digestion system were studied to digest the PM2.5samples collected withPTFE filter, and the optimal digestion system was established. The main conclusions areas follows:(1) When digesting the PM2.5samples collected with PTFE filter to determinate thecontent of heavy metal elements in it, the digestion system of HNO3(placed overnightafter added)+H2O2can be best satisfied with the demand of rapid, efficient and accurateanalysis of the total quantities of heavy metals on a large scale of PM2.5samples becauseof the advantages of low blank value, better stability of determination, easy to operate,green environmental protection, less harmful to health and so on, which is better than thedigestion system of HNO3+H2O2, aqua regia and aqua regia+hydrofluoric acid.(2) The concentrations of Fe, Zn, Pb, Al, Ca in PM2.5at the northeast of Beijingwere higher, ranged from0.3187~1.2242μg/m3, and the ratio in the total massconcentrations of heavy metals was94.28%. Besides the three metals of Fe, Al, Ca,which are the major elements in the earth’s crust, the content of Zn and Pb were also onthe high side, it may be related to human activities. The average concentration of thesecondly higher metals, Mn, Cu, As, ranged from0.0245~0.0799μg/m3, and the ratio inthe total mass concentrations of heavy metals was4.18%. The average concentration ofRb, Ag, Cd, Co, Ni, Cr were relatively low, and ranged from0.0008~0.0258μg/m3, andthe ratio in the total mass concentrations of heavy metals was1.54%.Compared to the data (table4-1) of Beijing in November2006，Cu and As hasfallen slightly (declines of0.13%and12.18%respectively)，while the concentration ofthe rest of the heavy metals all increased to different extent, and Pb (154.2%) and Zn(129.9%)were the highest. It may be related to the great increase of vehicle ownership inrecent years in Beijing. (3) The seasonal variation of the concentrations of heavy metals in PM2.5atNortheast Beijing can be divided into two categories, for one, as Fe, Al, Ca, the law ofthe concentration is autumn> spring> winter> summer, and for the other, Zn, Pb, Cu,Mn, Rb, Cd, Ni, the law of the concentration is autumn> spring> winter> summer. Asin the spring, autumn and winter has a little change. The concentration of Co was at alow level, and changed little in seasons.(4) Compared with the haze days, The concentrations of Cr, Ni, Rb, Pb, Fe, Zn inhaze days were significantly on the high than that in normal days, and Mn wassignificantly higher. The ratio of Pb, As, Cr, Cd in the total mass concentrations ofheavy metals was17.1%in haze days, far higher than that in the normal days, which was7.9%. With exception of Ag, the EF value of each element in haze days was higher thanthat in normal days, among of which Pb was highest (2379404.0),2.38times as much asthat in normal days(998659.2), and Cu was lowest,1.07times as much as that in normaldays, and then were Ag, Cd, As, Zn, Cu in turn, which were much larger than10. It maybe more likely to cause the enrichment of the pollution element.(5) In haze days, the health risks of heavy metals in PM2.5was generally higherthan normal days. The HQ of Mn, Cu, Ag, Pb, Zn to the children were higher than adults;The HQ to the children and adults in haze days were higher than normal days; The HI tothe children and adults were greater than1, especially to children, reach up to4.466,leading to a higher non-carcinogenic health risks. The highest HQ was Mn, leading to agreat non-carcinogenic health risks. The key to control non-carcinogenic metals in PM2.5is Mn.The ILCR of Cr, Co, Ni, As, Cd in PM2.5to the children were higher than the adult;The ILCR to the children and adult in haze days were higher than that in normal days; Inhaze days, the ILCR of Cr to adults and children, as well as the ILCR of As to adults,were higher than10-5, indicating a potential cancer risk. the ILCR of Cd to children wasclose to10-5, indicating a certain potential non-carcinogenic health risks; The ILCR ofAs to children was higher than10-4, suggesting the existence of carcinogenic risk. Inhaze days, the T(Risk) to the children and adult were higher than10-4, leading to a greatcarcinogenic risk. We must strengthen the management and control of the haze days andthe metals in PM2.5, especially the pollution sources of Cr, As, Cd.