Key factor and mechanism of abiotic methylation of mercury in contaminated soil in Chongqing, China

Mercury methylation was consisted of biotic and abiotic methylation in nature, which play decisive roles in the geochemical cycle of mercury and its compounds. The abiotic methylation has been deeply studied to the gene level, but the abiotic methylation mechanism of mercury is still unclear. This paper analyzed condition and key factors of abiotic methylation of mercury, mechanism of abiotic methylation was comprehensively expounded by electron distribution, hybridization, electronegativity and free radical theory. The corrin-like coenzyme methylcobalamin was an efficient methyl donor, and the effect of pH on the mercury abiotic methylation was the greatest. The initial mercury concentration of 500mg/L, pH = 5 and temperature 35°C were the optimal parameters for yielding methylmercury, which is the most unfavorable conditions to the nature. The abiotic methylation of mercury conforms to the second-order reaction kinetic model. Compared with solution, soil will reduce the rate and yield of abiotic methylation. The mechanism of abiotic methylation reaction of mercury should be the coexistence of carbanion transfer and methyl radical reaction.