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Plastispheres as hotspots of microbially-driven methylmercury production in paddy soils
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Researchers found that microplastics accumulate in paddy (rice) soil and create hotspots of methylmercury production — a potent neurotoxin — because the microbial communities living on microplastic surfaces (the "plastisphere") are enriched in mercury-methylating bacteria compared to the surrounding soil. This means microplastics in agricultural fields do more than carry chemical additives: they actively amplify the conversion of mercury into its most toxic form, which can then enter rice plants and the human food supply. The findings reveal a previously unrecognized indirect health risk from microplastic contamination of farmland.
Microplastics (MPs) as emerging contaminants have accumulated extensively in agricultural ecosystems and are known to exert important effects on biogeochemical processes. However, how MPs in paddy soils influence the conversion of mercury (Hg) to neurotoxic methylmercury (MeHg) remains poorly understood. Here, we evaluated the effects of MPs on Hg methylation and associated microbial communities in microcosms using two typical paddy soils in China (i.e., yellow and red soils). Results showed that the addition of MPs significantly increased MeHg production in both soils, which could be related to higher Hg methylation potential in the plastisphere than in the bulk soil. We found significant divergences in the community composition of Hg methylators between the plastisphere and the bulk soil. In addition, the plastisphere had higher proportions of Geobacterales in the yellow soil and Methanomicrobia in the red soil compared with the bulk soil, respectively; and plastisphere also had more densely connected microbial groups between non-Hg methylators and Hg methylators. These microbiota in the plastisphere are different from those in the bulk soil, which could partially account for their distinct MeHg production ability. Our findings suggest plastisphere as a unique biotope for MeHg production and provide new insights into the environment risks of MP accumulation in agricultural soils.
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Biodegradable polylactic acid microplastics enhance methylmercury production in soils and promote mercury accumulation in rice grains in Northeastern China
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Researchers found that biodegradable polylactic acid (PLA) microplastics significantly enhanced methylmercury production in paddy field soils, leading to rice grain mercury concentrations approximately six-fold higher than controls, reaching an average of 130.46 µg/kg. PLA-MPs upregulated mercury methylation genes hgcA and hgcB, with Desulfobacterota identified as the predominant methylating taxon, raising serious food safety concerns for PLA use in mercury-contaminated agricultural soils.
Microplastics influence on Hg methylation in diverse paddy soils
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Researchers found that polyvinyl chloride microplastics (PVC-MPs) decreased bioavailable methylmercury concentrations in both red and alkaline paddy soils through alterations to dissolved organic matter composition, competitive adsorption effects, and influences on microbial communities involved in Hg methylation.
Farmland Microhabitat Mediated by a Residual Microplastic Film: Microbial Communities and Function
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Researchers studied how leftover plastic film in farmland creates a unique microbial environment called a plastisphere, where different bacteria and fungi colonize compared to the surrounding soil. The plastic surfaces attracted more pathogens and bacteria involved in nitrogen and sulfur cycling, potentially increasing nutrient loss from agricultural soil. This finding is concerning because it suggests microplastic contamination in farmland does not just sit there passively but actively changes the soil ecosystem in ways that could affect crop health and food safety.
Mechanistic Insights into the Impacts of Microplastics on the Fate of Mercury and Methylmercury in a Simplified Estuarine Model System
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Lab tests show that microplastics in coastal waters can attract mercury and feed bacteria that turn it into methylmercury, a toxic form that builds up in fish. This means microplastic pollution might indirectly boost mercury contamination in seafood, though real world confirmation is still needed before drawing firm conclusions about human health risk.
Plastisphere as a unique metabolic hotspot in river water: Impact of plastic substrate biodegradability
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A study of river water found that microplastic surfaces — even from tiny 100-micrometer particles — host distinct microbial communities called plastispheres that function as metabolic hotspots, with richer carbon and nitrogen cycling activity than the surrounding water. The biodegradability of the plastic substrate influenced which microbes colonized it and how they interacted, with biodegradable plastics supporting different communities than conventional plastics. This matters because plastisphere microbes can include potential pathogens and antibiotic-resistant bacteria, and they alter the ecological function of freshwater environments.
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