Microbial mercury methylation potential in a large-scale municipal solid waste landfill, China

Landfills harbor ideal conditions for microbial mercury methylation. However, the levels and distribution of mercury (Hg) and methylmercury (MeHg), potential microbial Hg methylation, and their linkage within landfills are largely unknown. In the present study, total mercury (THg), MeHg, the Hg methylation gene (hgcA) and mer operon were quantified in 30 waste samples from different depths (0-30 m) at 5 locations within a large-scale landfill in China. The average concentrations of THg and MeHg in the solid waste samples were 1422.91 ng/g and 3.15 ng/g, respectively. THg (up to 14405.29 ng/g) and MeHg (up to 10.42 ng/g) have high concentrations in the middle part (10-15 m) along the depth profiles. The concentration of THg was strongly positively (both p < 0.05) correlated with the MeHg concentration and the relative abundance of hgcA, indicating that the THg concentration can play an important role in microbial Hg methylation. The hgcA genes were detected in most samples and mer operon were detected in all samples. Combined hgcA qPCR and metagenomics data showed that Archaea Methanofollis may mainly account for Hg methylation within landfills. These findings provide fundamental knowledge on Hg cycles in landfills.