Research On Distribution Characteristics Of Mercury In The Environment Around The Coal-fired Power Plant In The Southeast Coastal Area

Mercury acts as a bioaccumulative heavy metal with strong toxicity.The emission of a small amount of mercury can lead to serious environmental problem.The coal-fired power plant is one of the most important sources of anthropogenic mercury emission.Different species of mercury that the power plant emitted will have a significant influence on the surrounding environment.In this study,the atmospheric particulate,water,soil and crops around a coal-fired power plant were collected in order to investigate the temporal and spatial variation of mercury in the atmospheric particulates and the dry and wet deposition of atmospheric mercury;the temporal and spatial variation of mercury and methylmercury(MeHg)in the river;the distribution and sources of mercury and MeHg in soil-crops system.At last,an evaluation was conducted to judge the influence of the consumption of local crops on the health of local residents.The main conclusions were summarized as follows:(1)The average mercury concentration in PM2.5 and TSP around the coal-fired power plant was 309±84.02 pg/m3 and 429±114.79 pg/m3,respectively and the mercury in atmospheric particulates was concentrated in fine portion.The variation of mercury concentration in PM2,5 and TSP showed the same tendency:winter>autumn>spring>summer.This might be due to the prevailing seawinds in the spring.The mercury concentration in the PM2.5 and TSP collected in the sampling spot in the downwind direction was higher than the other one.The variation of Cm of mercury concentration in dust fall showed spring>summer>autumn>winter and the contribution of mercury in dust fall to mercury on earth's surface was 67.57(non-downwind direction)and 99.51?g/m2·a(downwind direction).The mercury and methylmercury concentration in the rainfall was 19.46 ng/L and 0.22 ng/L,respectively.(2)The total mercury concentration in the surface waters was 22,93±11.34 ng/L.The spatial distribution of mercury in soil have no relationship with the location of the power plant,some sampling spots were influenced by the small-scale pollution sources.Particulate mercury in waters showed a significant correlation with the suspended solid,at the same time,the percentage of particulate mercury in total mercury was relatively higher(74.55%).Thus the transportation of mercury in waters was realized through the suspended solid.The percentage of dissolved mercury in total mercury(25.55%)was not high compared to particulate mercury.In this study,reactive mercury accounted only 4%of the total mercury,which is relatively lower.However,it showed a significant correlation with the MeHg.The average MeHg concentration in the waters was 0.77±0.41 ng/L.Dissolved MeHg takes a great proportion in total MeHg and it also showed a significant correlation with total MeHg.Thus,the transportation and concentration level of MeHg was mainly controlled by the Dissolved MeHg.Since hydrologic condition was different in winter and summer,the total mercury,dissolved mercury and particulate mercury concentration of waters in summer was higher than in winter.However,reactive mercury showed the opposite trend.Whether the MeHg concentration or the percentage methylmercury took account in total mercury,the value was higher in winter than in summer.(3)The concentration of total mercury in paddy soil was 0.27±0.06 mg/kg.The mercury in paddy soil was mainly existed in the forms of organic-matter-bound and residual fractions.The concentration of MeHg in paddy soil was 0.72±0.51 ng/g.Compared to the control site,the mercury content in the rice surrounding the power plant was high.While we speculate that Hg in soil is the main source for this element's presence in the root,the portion of rice plant above the ground might also absorb Hg from the atmosphere.The exchangeable and organic-matter-bound fractions of Hg in soil were the forms most easily absorbed by the rice plant roots.A major portion of MeHg in rice plants is likely derived from the MeHg in soil,while that from other forms of Hg in soil and the atmosphere might be limited.The total mercury in vegetable field was higher than paddy soil.However,the MeHg concentration in vegetable field was only half of in paddy soil.This indicated that paddy wetlands facilitate the production of MeHg.Different tissues of the vegetables might originate from different sources,soil is the main source for this mercury in the root,the the leaves might mainly absorb Hg from the atmosphere.The MeHg in the root of vegetables was probably accumulated through direct absorption from soil,while the MeHg in the leaves have more than one source.The mercury and methylmercury content in the leaves of the vegetables were both higher than in the root.In addition,our results demonstrate that without additional exposure to Hg and MeHg,the daily intake of Hg and MeHg by a local resident due to crops consumption was 0.187?g/(kg·d)and 0.007?g/(kg·d),respectively.This result would be less than the provisional tolerable intake recommended by WHO.