Abstract: Mercury methylation bacteria change inorganic mercury to the highest toxic methylmercury (MeHg) under anaerobic conditions, which can result the human’s MeHg exposure by bioaccumulation and biomagnification. This article reviews the species and phylogeny of mercury methylation bacteria, methylation mechanism, spatial location of MeHg producing and the affecting factors in aquatic environments. In aquatic environments, mercury methylation occurs mainly in the anaerobic sediments of oceans, estuaries, rivers and lakes. Sulfate-reducing bacteria (SRB) and iron-reducing bacteria (IRB) are the main methylation bacteria. Their species, community structure and distribution control MeHg production and effects to human health. The studies on the biochemical mechanisms of mercury methylation show that MeHg may be produced from different metabolism pathways, but there still exist no consistent conclusions on mercury methylation mechanism. Spatial distribution of MeHg producing in sediments and the rate of mercury methylation are controlled by the distribution of mercury methylation bacteria, therefore the geochemical factors in aquatic environments affect the distribution of methylation bacteria, methylation rate and MeHg producing.

Key words: soil water content, soil temperature, dryland, mode of plastic mulch, spring maize.