Composition Characteristics And Health Risk Assessment Of Heavy Metals In PM_2.5 In Bengbu City

Heavy metals in PM_2.5,have significant biological toxicity,and may damage the normal physiological metabolism and vital organs of the human body.Therefore,understanding the pollution characteristics and sources of heavy metals in PM_2.5 is an important aspect of the research on atmospheric particulate pollution.Bengbu is located on the Qinling-Huaihe line of China’s north-south geographic demarcation,and is representative for the central inland areas of China.Exploring the pollution characteristics,sources and health risks of heavy metals in PM_2.5 in Bengbu is of great value for in-depth understanding of the pollution characteristics and environmental impacts of atmospheric fine particles in China.In this study,the PM_2.5 samples were collected in November 2018 and January,February,April,July,and October 2019 in Bengbu City.The mass concentrations of eight heavy metals,including but not limited to Cr,Mn,Fe,Ni,Cu,Zn,As and Pb,were measured by X-ray fluorescence spectrometer（XRF）.The water-soluble concentrations of the heavy metals was measured by inductively coupled plasma optical emission spectrometer（ICP-OES）.The impact of meteorological factors on the pollution characteristics of PM_2.5 and heavy metals were investigated.Air mass backward trajectory analysis,correlation analysis,enrichment factor calculation,principal component analysis,and positive matrix factorization were used to analyze the source characteristics of heavy metals.The potential ecological risks and human health risks of heavy metals had been assessed,and the impact of bioavailability on the health risk assessment of heavy metals had been preliminarily discussed.The main results are as follows:（1）During the sampling period,the average PM_2.5 concentration in Bengbu City was 65.5μg?m^-3,and the over-standard(>75μg?m^-3)rate was 30.6%.The PM_2.5 concentration was higher in autumn and winter than that in spring and summer.Poor diffusion conditions and increased emissions due to space heating were the main reasons for the serious pollution in autumn and winter,while higher temperature and higher wind speed in summer was favourable for the diffusion of pollutants.（2）The annual average concentrations of total heavy metals from high to low were Fe (297.4 ng·m^-3),Zn(96.9 ng·m^-3),Pb(42.8 ng·m^-3),Mn(23.5 ng·m^-3),Cu(18.4 ng·m^-3),As(4.7 ng·m^-3),Cr(3.6 ng·m^-3),Ni(2.7 ng·m^-3),summed at 490.0 ng·m^-3. Fe,Zn and Pb contributed 89.2%to the total concentration of heavy metals.The contribution rate of total heavy metals to PM_2.5 was the highest（1.2%）in summer and the lowest（0.5%）in winter,and a downward trend was found with the increase of PM_2.5 pollution level,which may be due to the impact of the changing gas- particle partitioning of the semi-volatile substances in PM_2.5.（3）The concentrations of water-soluble heavy metals in PM_2.5 in January 2019,from high to low,were Zn(93.0 ng·m^-3),Fe(60.9 ng·m^-3),Pb(18.8 ng·m^-3),Mn(13.7 ng·m^-3),Cu(8.5 ng·m^-3),As(3.2 ng·m^-3),Cr(1.3 ng·m^-3),Ni（0.6）.The sum of their concentrations contributed 34.8%to the total heavy metals.The water solubility of Zn,Cu,As was high（≥50%）,and the water solubility of Fe and Ni was low（about 20%）.The water solubility rate of heavy metals increased from about 28.1%under slight pollution to about 38.4%under heavy pollution,which may be related to the differences in emission sources at different pollution levels.（4）The analysis of the enrichment factor（EF）showed that the degree of influence from anthropogenic activities on heavy metal from high to low was Pb,Zn,Cu,As,Ni, Cr,Mn,Fe.The EF value of Mn and Fe≤10,while that of Pb、Zn、Cu、As were ≥100.Principal component analysis,PMF analysis,and correlation analysis showed that the main sources of heavy metals in PM_2.5 in Bengbu were industrial emissions, metal smelting/processing,coal combustion and vehicle emission,accounting more than 70%of the total contribution,but the sources of different heavy metals were significantly different.The contribution rates of various sources to the total concentration of heavy metals were:coal combustion and vehicle emission（29.4%）,dust（25.7%）,industrial emissions（24.0%）,metal smelting/processing（16.5%）,biomass burning（4.4%）.（5）The ecological risk assessment of heavy metals showed that heavy metals in PM_2.5 in Bengbu had moderate ecological hazards,and Pb,As and Cu contribute 89.2% of the ecological hazards.The human health risk assessment of heavy metals showed that the risk of non-carcinogenic effects from high to low were Mn,Cr,As, Pb,Fe,Cu,Zn,Ni,and the risk of carcinogenic effects from high to low were Cr, As,Pb,Ni.The non-carcinogenic risk of heavy metals through the PM_2.5 respiratory exposure were generally small,but there was a potential carcinogenic risk to local human beings.The non-carcinogenic effect was dominated by Mn,and the carcinogenic effect was dominated by Cr and As.When the bioavailability of heavy metals was considered,compared with the total heavy metals,the combined non- Bcarcinogenic risk value and combined carcinogenic risk value of water-soluble heavy metals decreased by 59.3%and 64.8%,respectively.The contribution of Cr in the carcinogenic effect decreased,while the contribution of As rose.