Methylmercury and sulfate-reducing bacteria in mangrove sediments fromJiulong River Estuary, China

Estuaries are important sites for mercury (Hg) methylation, with sulfate-reducing bacteria (SRB) thought to be the main Hgmethylators. Distributions of total mercury (THg) and methylmercury (MeHg) in mangrove sediment and sediment core from JiulongRiver Estuary Provincial Mangrove Reserve, China were determined and the possible mechanisms of Hg methylation and theircontrolling factors in mangrove sediments were investigated. Microbiological and geochemical parameters were also determined.Results showed that SRB constitute a small fraction of total bacteria (TB) in both surface sediments and the profile of sediments. Thecontent of THg, MeHg, TB, and SRB were (350 150) ng/g, (0.47 0.11) ng/g, (1.4 1011 4.1 109) cfu/g dry weight (dw), and (5.0 106 2.7 106) cfu/g dw in surficial sediments, respectively, and (240 24) ng/g, (0.30 0.15) ng/g, (1.9 1011 4.2 1010) cfu/gdw, and (1.3 106 2.0 106) cfu/g dw in sediment core, respectively. Results showed that THg, MeHg, TB, MeHg/THg, salinityand total sulfur (TS) increased with depth, but total organic matter (TOM), SRB, and pH decreased with depth. Concentrations ofMeHg in sediments showed significant positive correlation with THg, salinity, TS, and MeHg/THg, and significant negative correlationwith SRB, TOM, and pH. It was concluded that other microbes, rather than SRB, may also act as main Hg methylators in mangrovesediments.