Organic matter composition controls monomethylmercury formation rates in lake and river sediments

Abstract

Methylmercury (MeHg) accumulated in biomass of food web is a potent neurotoxin that is mainly produced in sediment of aquatic systems. It is well known that organic matter interacts strongly with mercury, however, the contribution of organic matter composition to the formation rate of methylmercury in sediment remains poorly understood. The relationship between organic matter composition and the formation of methylmercury was therefore investigated by examining rate constants of methylation and demethylation of sediments in lakes and rivers, as well as water and sediment qualities such as organic compositions identified using the excitation-emission matrix fluorescence spectroscopy. We identified correlation factors between sediment methylation rate constants and supplementary parameters in sediments and waters through statistical techniques such as Pearson’s correlation and Principal Component Analysis (PCA). According to the results, we found that dissolved organic carbon (DOC), chlorophyll-a (Chl-a) and total organic nitrogen (TON) were important factors increasing mercury methylation rate constants in lakes sediment. The major source of sediment organic matter was algal production, which increases Hg methylation rate by increasing Hg uptake rate of bacterial cells and/or enhancing microbial activities. In contrast to the lake, the source of sediment organic matter of the river was mainly upstream transport, which was not able to increase Hg methylation rate in surface sediment. In conclusion, the composition of sediment organic matter is highly related to the methylation rate of Hg(II) in Korean lakes and rivers, and therefore, the source and flux of organic matter should be properly managed to decrease the formation rate of MeHg.