Hisamitsu Nagase

Methylation of mercury by humic substances in an aquatic environment

Both humic acid and fulvic acid obtained from leaf mould and river sediment methylate inorganic mercury. Methylation occurs in the dark and in the absence of bacteria and is also influenced by reaction temperature, inorganic mercury concentration, humic acid and fluvic acid concentrations and solution pH. n nOther types of humic acid obtained from river sediment and those commercially available also methylated the mercuric ion. All fulvic acids fractioned by molecular weight methylate inorganic mercury, and furthermore lower molecular weight (M.W. 200) compounds which were most active in this methylation.

Mercury methylation by compounds in humic material

Extracts of humic substances in river sediment and leaf mould have the ability to methylate mercury; several compounds have been identified by GC-MS. The methylating abilities of the compounds found and known as constituents in humic material were determined. Only three compounds, 2, 6-di-tert.-butyl-4-methylphenol (BHT), p-xylene and mesitylene had the ability to methylate at pH 3.5. At pH 7, only BHT produced methylmercury, the other two compounds did not. Methylmercury production by BHT increased with increase of temperature, mercury concentration and BHT concentration, and was also influenced by pH; a high production rate was observed at pH 2 and 13.5. BHT was found in river sediment and leaf mould, and the possibility of a contribution to methylmercury formation by BHT in the environment is indicated.