Mercury methylation from mercury selenide particles in soils.

Selenium-inhibited monomethylmercury (MeHg) production is an attractive strategy for mitigating the risks of MeHg exposure. However, it is poorly understood the methylation potential of mercury selenide (HgSe) particles during their aging in soils and sediments. Net MeHg production in three floodplain soils amended with different geochemical species of mercury selenides, i.e., dissolved inorganic mercury freshly mixed with selenite (Hg(II)+Se(IV)), HgSe nanoparticles (45.2 ± 0.5 nm) and microparticles (> 1 μm) is examined. Among mercury types, the methylation from nanoparticulate HgSe was similar to (0.05 - 0.5 % vs. 0.1 - 0.4 %, yellow brown soil) or 12.9 - 21.0 times lower (0.02 - 0.1 vs. 0.6 - 1.5 %, black soil) than that from Hg(II)+Se(IV); however, net MeHg production from HgSe nanoparticles (0.02 - 0.5 %) was 1.9 - 15.5 times greater than HgSe microparticles (< 0.05 %) in all soils. Furthermore, net MeHg production from nanoparticulate HgSe varied significantly among soil types, attributable to differences in soil organic matter contents (2.4-5.8%) and microbial methylator community among soils. These results address the importance of geochemical intermediates of mercury selenide precipitation reactions and soil properties in MeHg production, and develop Se-based remediation strategy to minimize negative effects of MeHg on environmental and human health.