| Mercury is a non-essential element for biology,all its forms are toxic,and methyl mercury is the most toxic.Since the "minamata disease" in Japan in the 1950 s,the pollution of mercury and methyl mercury in the environment has attracted more and more attention.Reservoir is a typical "mercury sensitive ecosystem".Thus,the researches on mercury pollution in reservoirs are necessary.Baihua reservoir is belong to “The two Lakes and a Reservoir”,and it is one of the important sources of drinking water in Guiyang city.During 1971-1997,a large amount of untreated mercury wastewater was discharged into the Baihua reservoir from Guizhou Organic Chemical Plant(GOCP),resulting in severe mercury pollution in the Baihua reservoir and surrounding areas.Since then,there are still other sources of mercury pollution in the upper reaches of the reservoir,although mercury wasterwater has been cut off from the GOCP.According to the investigation,the total mercury in the sediments of Baihua reservoir is far greater than that in other natural reservoirs.Therefore,the mercury pollution problem of baihua reservoir is very serious.Due to the "winter storage and summer platoon",the annual change of water level has formed the water-level-fluctuating-zone with the difference of about 6m.This area collects mercury pollutants from both land runoff and reservoir water,so it can be identified as a sink of mercury.It is also washed by runoff and water,and released mercury into the water body.Therefore,it is the mercury source.Periodical change of water level drop away with soil in dry and wet alternation.This will cause the change of soil properties,and the migration of mercury transformation(especially mercury methylation)have a major impact.At present,some issues(e.g.the distribution characteristics of mercury,especially methyl mercury;the species of mercury in the soil;whether the soil is affected by the upstream mercury pollution sources;whether there is ecological risk in soil mercury).There is still a lack of systematic research on those.In addition,according to the investigation,the flora of the Baihua reservoir shown the dominance of single species and single species,indicated the ecological fragility.Systematic research is still lack on total and methyl mercury distribution characteristics in plants,and whether these plants suited for soil mercury repair.Therefore,the researches on these problems mentioned above is aimed at exploring the environmental geochemical processes and ecological risks of the mercury,as well as providing references for the soil mercury ecological restoration in this area.The results are as follows:(1)The total mercury concentration in soils was between 67.9~796.8 ug/kg(264.6 ± 151.0 ug/kg).The methylmercury contents was between 0.183 and 31.268 ug/kg(2.724 ± 3.276 ug/kg).The concentrations of mercury and methylmercury were higher than those in uncontaminated areas,but lower than those in heavily contaminated areas.This indicated the concentrations of total and methyl mercury in soils were at moderate levels in water-level-fluctuating-zone of Baihua reservoir.(2)The total methyl mercury concentrations were significantly changed in the surface soils.The average contents of total mercury in each region is shown as flooded area > unflooded area > semi-flooded area.The methylmercury was followed: flooded area > unflooded area > semiflooded area.There is no obvious accumulation of total and methyl mercury in soils vertially.(3)The soil mercury formation in baihua reservoir is mainly composed of organic complexation,strong binding state,sulfide bond state,and low water soluble and acid soluble mercury.(4)The evaluation results show that the soil mercury in baihua reservoir has high pollution risk and should be taken seriously.(5)The concents of THg in leaves,stalks,and roots were 6.6~160.1 ug/kg(70.2 ± 26.2ug/kg),10.0~112.1 ug/kg(38.3 ± 23.0 ug/kg),and 11.2~11.2 ug/kg(49.8 ± 27.1 ug/kg).The concentrations MeHg in leaves,stalks,and roots were 0.199~0.861 ug/kg(0.425 ± 0.144 ug/kg),0.176~0.950 ug/kg(0.357 ± 0.161ug/kg),0.154~0.867 ug/kg(0.457 ± 0.169 ug/kg),respectively.Compared with other natural or mercury deposits,the concentrations of mercury and methyl mercury in the plants of the baihua reservoir were at moderate levels.(6)Based on bioconcentration factor of total and methyl mercury,eight plant species and one species were selected for total mercury and methyl mercury restoration in soils.The Solanum nigrum Linn.and Plantago asiatica L.can be considered as the pioneer plants for the ecological restoration of soil total mercury and methylmercury,respectively. |
PDF Full Text Request