Pollution Characteristics And Source Analysis Of Heavy Metals In Atmospheric Deposition In Chang-Zhu-Tan Area

Non-ferrous metal smelting, exhaust gases from thermal power plants and other industries are the main sources of atmospheric heavy metals. Atmospheric heavy metals settle to the ground through atmospheric turbulence, gravity sedimentation and precipitation. It has become one of the important exogenous factors of heavy metals in soil, and it has potential threat to ecosystems and human health. Chang-Zhu-Tan has become the new rise city clusters of central China. It is approved by the State Council to be the two type society (environment-friendly and resource-saving) comprehensive matched reform experiment zone. It is also one of the old industrial bases in China. There are many small non-ferrous smelting enterprises in the past, resulting in serious heavy metal pollution in the environment. The study of heavy metals in soil and water existed as early as the Sixth, Seventh Five-Year Plans, but there are less study on heavy metals in the atmosphere.Through field sampling of atmospheric deposition in regions of Changsha, Zhuzhou, Xiangtan of Hunan Province from November 2011 to October 2012, the deposition amount and deposition fluxes of atmospheric deposition and five heavy metals include Cr, As, Cd, Pb, Zn it contains, the pollution characteristics and levels of the heavy metals are analyzed. Sources, potential ecological risks and the impact on soil of the heavy metals are studied. The main conclusions of the study are:(1) The deposition amount and deposition flux, heavy metal content in atmospheric dustfall of Chang-Zhu-Tan area, Chang-Zhu-Tan main city zone are calculated. The annual heavy metal deposition fluxes are between 100 and 103mg/(m2·yr), of which Zn is the highest, Cd is the lowest. There is little difference between the magnitudes of As, Cr and Pb; The heavy metal content is much higher in dry deposition than that in wet deposition; The distribution of annual dustfall deposition fluxes of 12 sampling sites of Zhuzhou basically show a gradually decreasing trend with the increase of distance from the Qingshuitang Industrial Park, decreasing from northwest to southeast; The heavy metal contents in dry deposition is basically higher in autumn and winter, followed by spring, lower in summer.(2) Compared with other regions, the atmospheric dustfall deposition flux of Chang-Zhu-Tan area is lower. Except Cr, deposition fluxes and contents of the other four heavy metals are all much higher in Zhuzhou city than in Chang-Zhu-Tan main city zone, and much higher than in Chang-Zhu-Tan area. The atmospheric heavy metal deposition fluxes and contents of Zhuzhou are higher. The results of Chang-Zhu-Tan area are not very different with the research results of other major cities in China.(3)A variety of method include enrichment factor, single factor pollution index, Nemerow pollution index, pollution load index and geoaccumulation index are used to analyze the dgree of contamination of heavy metals to soil. The main pollution element of Chang-Zhu-Tan area is Zn, followed by Cd, while the main pollution element of Chang-Zhu-Tan main city zone is Cd, followed by Pb and Zn, the pollution of Cr and As is lighter, only the pollution of As in Liuyang is heavier; In addition to Shaping sampling point, there are more serious pollution in all the other eight sampling points of Chang-Zhu-Tan main city zone, especially in Zhuzhou Smelter Hospital and Tiantai Mountain sampling points.(4) The principal factor analysis, correlation analysis, cluster analysis, trajectory analysis and other analysis methods are used to analyze possible sources of heavy metals. In Chang-Zhu-Tan area, Cd and Pb are most relevant, and they may be affected by industry or automotive exhaust; In Chang-Zhu-Tan main city zone, Zn, As, Cd, Pb may be more affected by industry, coal combustion and other human factors; The source of Cr is significantly different from the other four heavy metals, probably mainly from the crust or other natural sources; The heavy metals in atmospheric deposition in winter may be affected by the pollution from the north; while in summer, they are often affected by marine air masses from the southeast, the heavy metal content is lower; The potential ecological risk factor of Cd is the highest, especially in Zhuzhou Smelter Hospital and Tiantai Mountain sampling points, which are in strong ecological harm.(5)The effect of atmospheric dustfall on the content of heavy metals in soil is analyzed. The mass concentration of Cr in dustfall is not very different with which in soil, Cd, Pb, Zn content is higher than in soil; In addition to Cr, content of most heavy metals in soil will increase due to atmospheric deposition. The annual change rate of Cd in soil is maximum of Chang-Zhu-Tan area and main city zone, followed by Zn, the annual change rate of As and Pb in soil is lower.