Increased water inputs fuel microbial mercury methylation in upland soils

Area of Science:

• Environmental science
• Microbiology
• Environmental chemistry

Background:

• Mercury (Hg) methylation to neurotoxic methylmercury (MeHg) typically occurs in anaerobic environments.
• Bioaccumulation of MeHg in food webs poses human health risks.
• The potential for Hg methylation in water-inundated upland soils remains largely uninvestigated.

Purpose of the Study:

• To investigate the impact of increased water content on MeHg production in upland soils.
• To identify microbial taxa involved in Hg methylation under these conditions.
• To understand the influence of temperature and microbial syntrophy on MeHg formation.

Main Methods:

• Incubation experiments using two types of upland soils (long-term and short-term use).
• Monitoring of MeHg production under varying water saturation levels and temperatures.
• Analysis of microbial community composition, focusing on Hg methylating taxa.

Main Results:

• Significant MeHg production was observed in water-saturated upland soils.
• MeHg production strongly correlated with increased abundance of the Hg methylating taxon Geobacter.
• Elevated temperatures further boosted MeHg production by promoting specific methylators (Clostridium, Acetonema, Geobacter) and microbial syntrophy.

Conclusions:

• Upland soils can become significant methylmercury reservoirs when water content increases.
• Microbial Hg methylation is enhanced by water saturation and favorable temperatures.
• Anthropogenic activities like irrigation could exacerbate MeHg production in these environments.