Flooding rice soil with organic matter traps mercury, blocks toxic form
Chang J, Yu H, Miao W, Gan C, Hu Z
Soil Health
If you grow vegetables in soil with any legacy contamination, this shows that boosting organic matter and managing water levels can physically trap heavy metals before they turn into a more dangerous, bioavailable form.
Mercury in soil can get converted by microbes into methylmercury, a much more toxic form that moves up the food chain. Scientists found that adding bits of organic matter (chunky plant debris, not fully decomposed compost) to rice paddy soil, especially when the field is kept flooded, traps mercury inside its porous structure and binds it tightly with sulfur groups, cutting available mercury by up to 82%. It also shrank the population of mercury-converting microbes, so less toxic methylmercury formed in the first place.
Key Findings
Particulate organic matter (POM) addition reduced available soil mercury by 82% under flooded conditions versus 61% under non-flooded conditions over a 120-day incubation.
Hg2+ immobilization occurred through physical entrapment in POM's porous structure plus chemisorption via sulfur- and oxygen-containing functional groups, with reactive organic sulfur as the dominant binding site.
POM suppressed methylmercury accumulation in a dose-dependent manner by lowering bioavailable Hg and decreasing abundance of the hgcA gene (linked to mercury-methylating microbes), with enrichment of keystone taxa like Vicinamibacter.
chevron_right Technical Summary
Mixing a common organic soil amendment into contaminated paddy fields, then flooding them, locked up mercury so tightly that far less of it could turn into toxic methylmercury, the form that builds up in fish and people.
Abstract Preview
Original paper
Mechanisms of POM-mediated Hg immobilization and MeHg suppression in paddy soil: a perspective of coupled geochemical and microbial processes under water management.
Particulate organic matter (POM) plays a critical role in Hg biogeochemistry, yet its immobilization mechanisms and interactions with water management remain unclear. This study investigated POM-me...
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