Pollution Characterization Of Heavy Metals In Air, Soil And Precipitation In Xi’an

Due to a strong bioaccumulation effect, the heavy metals are very harmful to the environment, which is one of the hot research issues. This research collected19precipitation samples,58soil samples in different functional areas, and73atmosphericparticulate matter samples of four seasons in2012. Taking advantage of ICP-MS, itanalyzed the quality concentration of As, Pb, Cr, Cd, Hg, Cu, Zn, Mn and Ni. Then itresearched heavy metals pollution characteristics of soil, precipitation and atmosphericparticulate matter, estimated dry and wet deposition of heavy metals and proceededsource apportionment by adopting correlation analysis and factor analysis, and finally itconcluded with pollution assessment.The main conclusions are below:In2012, the concentration of heavy metals elements of atmospheric particulatematter of Xi’an trended to be greater in Spring and Winter than that in Summer andAutumn. From the perspective of particle size distribution, the heavy metals elementsmainly gathered in PM_2.5; comparing with normal weather, human factor played a moreobvious role in smog weather and earthcrust factor surpassed others in sand and dustweather. The correlation between heavy metals in PM_2.5demonstrated that correlationsof fire coal elements and traffic pollution elements played significant roles andcorrelation of earthcrust element was also remarkable. After analyzing the source ofPM_2.5by using method of factor analysis, results showed that the primary source ofPM_2.5comed from soil dust, dire coat and industry dust, automobile dust and bilmassburning dust. The health risk assessment indicated that the heavy metals of PM_2.5werewithin the range of maximum acceptable risk and there were no significant healthhazards by respiration.The content of Pb, Cd, Cu, Ni in the surface soil in part of sampling sites in different functional areas of Xi’an had surpassed national soil secondary standard, andthe over standard rates were1.66%,8.33%,3.33%,3.33%respectively. Theconcentration was on the high side for Pb, Cr, Cd, Zn in industrial zone, Cu in trafficmain roads, Hg and Ni in business district, and Cd in residential area. The soil heavymetals pollution of Xi’an mainly resulted in traffic dust and tail gas as well as theindustry “three wastes”. Integrated pollution assessment showed that the pollution levelof surface soil in functional areas of Xi’an was in a sequence of industrial zone>commercial> Transportation> agriculture> residential areas.For precipitation of Xi’an in2012, Cu, Hg, Pb and Zn exceeded standard （surfacewater primary standard） in part of the samples, with over standard rates reaching4.76%,9.52%,28.57%and71.42%respectively, among which Zn was the most serious one.Heavy metals performed distinct seasonal changes: highest in winter, followed byspring and autumn, and lowest in summer. Potential ecological risk assessment showedthat heavy metals elements of precipitation were in a slight ecological risk level.Based on enrichment factor analysis of elements in atmosphere, soil andprecipitation, it was found that the enrichment of heavy metals was obvious in rain andPM_2.5, and relatively low in soil. The amounts of dry, wet deposition of heavy metalswere93.87mg/m²·a and42.62mg/m²·a,respectively. Total amounts of heavy metalswere136.49mg/m²·a.