| As a kind of rare metal,mercury（Hg）is in liquid form under standard conditions.In biosphere,total energy remains fixed.Due to its special physiochemical properties,mercury is listed as a worldwide pollutant by United Nations Environmental Programme（UNEP）and defined as a highly dangerous element by United States Environmental Protection Agency.Once entering the hydrosphere,atmosphere and soil,mercury and its compounds can be absorbed by human beings through the food chain in some special cases,and thus cause mercury poisoning and such symptoms as ataxia,impaired auditory system,speech disorder,and even nervous system damage and renal failure.Coal burning and cement productionare listed in the three major anthropogenic sources of atmospheric mercury emissions in the world.The large coal consumption by coal-fired enterprises and cement plants will release a considerable amount of mercury into the atmosphere,which will influence the mercury content around the enterprises.In this paper,the coal-fired enterprises with certain scaleand and representative NSP cement plants in Guizhou Province were selected as the research objects,so as to investigate the status quo of mercury pollution aroundthe coal-fired enterprises and cement plants through monitoring the mercury content in the atmosphere and soil in the surrounding environment.Meanwhile,the methods of mercury monitoring were also studied and analyzed.The paper is expected to provide certain theoretical basis for future development of mercury pollution control in a more targeted way and shed some practical light on enactment of laws and regulations on mercury pollution control by bioenvironment administrative agencies.Major research findings are as follows:（1）Investigation and analysis of mercury content in the surrounding environment of coal-fired enterprises（1）In this study,the Hg content in the surface soil sampled from the surrounding areas of three typical coal-fired power plants was tested.The average soil Hg content around DY power plant and AS power plant was 0.06 mg/kg0.09 mg/kg,which was lower than the limit of soil pollution risk screening value in the Soil Environmental Quality Risk Control Standards for Soil Contaminationof Agricultural Land（Trial）（GB15618-2018）,as well as the average soil Hg content in Guizhou（0.102 mg/kg）,but it was higher than the national average value（0.042 mg/kg）and the global average value（0.030 mg/kg）.The average Hg content in the surrounding soil of DL power plant was 0.94 mg/kg,which exceeded the limit of soil pollution risk screening value in the Soil Environmental Quality Risk Control Standards for Soil Contaminationof Agricultural Land（Trial）（GB15618-2018）,as well as the average soil Hg content in Guizhou,the national average value and the global average value.（2）The research results showed that,the discharge of pollutants from coal-fired power plants was the main factor of surrounding soil pollution.Compared with the research results of other power plants available in current literature,the Hg content in the surrounding soil of DL power plant was the highest,The reasons might include1.The influence of mercury emission to the atmosphere from surrounding enterprises;2.The influence of high mercury emission concentration of DL power plant itself.（3）The single factor pollution index of the surrounding soil of DY power plant was 0.1763.637,the geo-accumulation index was-0.929-0.266,and the potential ecological risk coefficient was 7.059145.490.Part of the soil within 1km of the power plant had been contaminated with mercury to varying degrees and showed potential ecological hazards.Part of the soil within 1km5km was basically unpolluted and provided with low potential ecological hazards.The single factor pollution index of soil around AS power plant was 0.3470.947,the geo-accumulation index was-0.636-0.194,and the potential ecological risk coefficient was 13.86737.867,all of which showed non-pollution from the perspective of pollution degree and mercury pollution status,butindicated low potential ecological hazardin terms of potential ecological risk coefficient.The single factor pollution index of soil around the DL power plant wasmeasured to be 3.63728.706,the geo-accumulation index was 0.3850.895,and the potential ecological risk coefficient was 145.490445.882.The soil mercury pollution within1km of the power plant was relatively serious,showing serious potential ecological risks.The soil pollution degree of the sampling siteswithin 1km5km was lower than that within 1km,but the degree of potential ecological hazard was still high.（4）It was found in this study that,there was no linear correlation between the soil Hg content and pH value around coal-fired power plants（P=0.375）.There was a significant linear correlation between Hg content and organic matter content in surrounding soil of coal-fired power plants（P=0.002,P≤0.05 could be considered as a significant correlation）.（5）The Hg concentration in the ambient atmosphere around the DL power plant was significantly higher than that around the other two power plants,but the monitoring results of the three power plants were higher than the average background value of Global Atmospheric Total Gaseous Mercury（1.52 ng/m3）,which were far less than the atmospheric mercury standard for living environment of China,namely,300ng/m3,and less than 200 ng/m3,the empirical valueof no cancer effect by element inhalation put forward by the US EPA&ATSDR in 1995.（6）The change of Hg concentration in the ambient atmosphere around the power plant wasdistributed in the shape of“几”（a Chinese character）:the Hg concentration from the boundary of coal-fired power plant to the place about 2.5km downwind increased with the increase of distance;while it decreased with the increase of instance after reaching the concentration peak value.（2）Cement mills’ambient mercury content survey,research and analysis（1）The pH of soil sample around Tongren Conch Cement Mill is 6.26-7.90,while Hg content ranges from 0.04mg/kg to 0.55mg/kg（mean:0.21mg/kg;median:0.15mg/kg）.Average mercury content is lower than the soil pollution risk screening limit in GB15618-2018 Soil Environment Quality Risk Control Standard for Soil Contamination of Agricultural Land（trial version）but higher than average mercury contents in soil in Guizhou（0.102mg/kg）,China（0.042mg/kg）and the world（0.030mg/kg）.（2）Judged from the pollution level,57.1%of sampled soil spots within 1km from Tongren Conch Cement Mill are not contaminated,14.3%are severely contaminated;75%within 1-2km are moderately contaminated;and 63%within2-3km are slightly contaminated with rest being severely contaminated.From the perspective of potential ecological hazard,57.1%of sampled soil spots within 1km are lowly hazardous,28.6%are moderately hazardous,and 14.3%are highly hazardous;75%within 1-2km are highly hazardous;and 66.7%within 2-3km are moderately hazardous with rest being highly hazardous.（3）The mercury content in the soil around cement mills studied by the present paper is not linearly related to corresponding pH value and organic content（P:0.595and 0.258,respectively）.（4）The mercury concentration in upwind air measured in Tongren Conch Cement Mill is 6.1ng/m3,whereas that in downwind air is 11.358.5ng/m3 with average value being 23.9ng/m3.The monitoring results are higher than the average background value（1.52ng/m3）of total gaseous mercury in global atmosphere but far lower than the atmospheric mercury limit in human settlement specified in the country(300ng/m-3)and also lower than the empirical cancer-free value for absorptive element（200ng/m3）proposed by U.S.Environmental Protection Agency（EPA）and Agency for Toxic Substances and Disease Registry（ATSDR）in 1995.（3）Comparison of mercury monitoring methodsAt present,a standard approach for monitoring mercury content in specific source exhaust gas is potassium permanganate solution absorption method（HJ543-2009）.Nevertheless,this approach is inapplicable to outlet exhaust gas monitoring,because its monitoring result is lower than actual result and monitoring accuracy is far inferior to that of online monitoring method（EPA Method 30A）,active carbon（AC）absorption tube offline sampling method（EPA Method 30B）drafted by United States Environmental Protection Agency and the internationally recognized Ontario Hydro method for mercury speciation analysis. |
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