Decreased bioavailability of both inorganic mercury and methylmercury in anaerobic sediments by sorption on iron sulfide nanoparticles

Methylmercury (MeHg), derived via inorganic mercury (Hg(II)) methylation by anaerobic microorganisms , is a neurotoxic contaminant causing concern worldwide. Establishing how to reduce Hg(II) methylation and MeHg bioavailability is essential for effective control of Hg pollution. Iron sulfide nanoparticles (FeS NP ) is a promising passivator for Hg(II) methylation. However, its effect on the fate of MeHg in aquatic systems remains poorly understood. This study investigated the effect of FeS NP on Hg(II) bioavailability, MeHg production and bioavailability in aquatic environments. Results demonstrated that FeS NP rapidly sorbed Hg(II) and MeHg, with sorption affected by pH, chloride ion and dissolved organic matter . Hg-specific biosensor analysis showed that Hg(II) sorbed onto FeS NP significantly reduced its bioavailability to microorganisms. Double stable isotope ( 199 Hg(II) and Me 201 Hg) addition revealed that FeS NP significantly inhibited MeHg production in anaerobic sediments . Furthermore, synthetic gut juice extraction suggested that FeS NP decrease concentrations of bioavailable MeHg and Hg(II), reducing their integration into food webs. However, the sorbed MeHg and Hg(II) in sediments can be released after FeS NP oxidation , potentially enhancing the risk of exposure to aquatic organisms. Overall, these findings increase our understanding of Hg transformation and exposure risks in aquatic systems, providing valuable information for the development of in situ Hg remediation systems.