The Divergent Roles of Humic- and Fulvic-Acid DOM in Regulating Hg Methylation/Demethylation in Paddy Soils.

Humic acid (HA) reduces mercury methylation while fulvic acid (FA) enhances it in paddy soils, with methylation rate constants of 0.40 and 0.91 × 10^-3 d^-1 respectively.

• Why it matters: Understanding how different DOM fractions influence mercury methylation is vital for managing food safety and health risks associated with rice cultivation.
• What they did: A year-long field study combined with incubation experiments using Hg isotope tracers examined the roles of HA and FA in regulating methylation and demethylation processes, analyzing their properties and effects across multiple sites.
• The result: Findings show that Hg-FA, with low aromaticity, has higher methylation rates, while high-molecular-weight HA promotes MeHg degradation, indicating that the balance between these DOM fractions governs net methylmercury production in paddy soils.