Adsorption-desorption And Abiotic Methylation Of Mercury In Soils

It was difficult to remove through water leaching and microbial degradation, once themercury contaminated the soil. It was often quickly assimilated and strong adsorption andlong-term stagnation slip by soils, on account of its strong affinity with the soil. However,it was not static and can be activated, occurrd the morphological change or generated withorganic matter, converting to organic mercury. The adsorption-desorption was bound tooccur by mercury in soils, methlation was an important process for the mercurybiogeochemical cycle yet. Therefore, investigating the adsorption-desorption behavior aswell as the methylation of inorganic and methyl mercury in soils, as for calculatingenvironmental effects and comprehending bioavailability, ecological impact assessment ofmercury was essential; and these would provide the certain basis for remediation ofmercury pollution in farmland.The main contents and results were listed as follows:1. A method for the determination of inorganic mercury and methyl mercury in soilsby high performance liquid chromatography （HPLC） with alkaline digestion wasestablished. The experiments were set up for examing the effects of KOH/methanolconcentration, digestion time and Na₂S₂O₃concentration on the extraction rates of methylmercury in the process of alkaline digestion. When the KOH/methanol concentration was25%, the digestion time was12minutes, and Na₂S₂O₃concentration was0.01mol·L^-1，thehighest extraction rate of methyl mercury in soils were obtained. After extracted withKOH/methanol, mercury and methyl mercury were derivatived and then detected by HPLC.The mobile phase was methanol+water （55+45by volume） containing0.01mol·L^-1tetra-n-alkylammonium bromides and0.025mol·L^-1sodium chloride. In optimizedconditions, the detection limits for inorganic mercury and methyl mercury were1ng·g^-1and10ng·g^-1respectively. The results indicated that the method had a simple pre-treatmentprocedure, broad linear range, good accuracy and precision, and was suitable for thedetermination of mercury speciation in soils.2. The adsorption of inorganic mercury and methyl mercury in paddy, tawny, and redsoils were studied using adsorption equilibrium experiments. The results suggested that theadsorption of mercury and methyl mercury in soils were well fitted by the Langmuirisotherm, as well as Freundlich isotherm. And the adsorption of mercury and methylmercury in these soils increased with increasing their initial concentration. The adsorptioncapacity of soils for mercury followed the order: paddy soil> tawny soil> red soil, the adsorption capacity of soils for methyl mercury followed the order: red soil> tawny soil>paddy soil; and desportion capacity of soils for mercury followed the order: red soil>tawny soil> paddy soil. The adsorption of mercury and methyl mercury were influencedby the physical and chemical properties of the soils. The higher of the organic mattercontent and cation-exchange capacity of the paddy soil, the higher of the Hg （II） adsorption.In contrast, the higher clay, and the lower pH of the red soil, the higher of methyl mercuryadsorption.3. The possibility and the effects of mercury abiotic methyl ation were preliminarilyinvestigated through sterilization closed culture experiments of soils. The results indicatedin the that closed culture conditions, the abiotic methyl ation was able to occuring ofmercury. In contrast with red soil, paddy and tawny soil’s methyl ation rate was moresignificantly.The higher of soil pH, the more methyl coblamin voting content, the moregreater initial mercury concentration and lower of sulfide ions concentration; the moreconducive to abiotic methylation of mercury.