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Burial of microplastics in freshwater sediments facilitated by iron-organo flocs
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Researchers found that iron-organo flocs in freshwater sediments facilitate the burial and long-term sequestration of microplastics by aggregating plastic particles with organic matter and iron minerals, identifying this aggregation mechanism as an important pathway controlling microplastic fate in lake sediments.
Microplastics are ubiquitous in standing freshwater bodies, consequently lakes and reservoirs may be important sinks for these contaminants. However, the mechanisms governing the deposition of microplastics and their interactions with the sediments are understudied. We demonstrate how aggregation-based transport facilitates the sinking and infiltration of buoyant microplastics into freshwater reservoir sediments by employing experiments with intact sediment cores. Buoyant polyethylene microplastics were rapidly (1-4 h) incorporated into sinking iron-organic aggregates, followed by swift deposition into sediments. Ingression of microplastic bearing flocs into sediments was completed within 6 days and led to stable deposition of the incorporated particles for at least 2 months. Most microplastics were deposited in the top 2 cm of the sediments and few particles (5-15%) were re-released into the water. Our results show at least 85% burial of microplastics, indicating the significant role of freshwaters with low flow velocities in reducing microplastic loads to the oceans.
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Microbial iron reduction does not release microplastics from organo‐metallic aggregates
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Researchers tested whether microbial iron reduction — a common process in anoxic sediments — releases microplastics that had been captured in iron floc aggregates during water treatment. Despite iron reduction reducing floc structure over 120 days, most microplastics remained within the sediment and were not released back into the water column. This suggests iron-based water treatment can provide relatively stable long-term microplastic capture in sediments.
Unveiling the crucial role of iron oxide transformation in simultaneous immobilization of nanoplastics and organic matter
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Researchers tracked how nanoplastics become trapped during the transformation of dissolved iron into crystalline iron oxide minerals, finding that polystyrene nanoplastics become physically encased within forming crystals while humic acid stabilizes the system, creating a durable iron oxide-nanoplastic-organic matter composite that sequesters particles in sediments.
Biofouling, metal sorption and aggregation are related to sinking of microplastics in a stratified reservoir
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In a freshwater reservoir study, biofouling on microplastic surfaces did not cause polyethylene particles to sink, but a mixing event that brought iron-rich anoxic water to the surface triggered aggregation of PE particles with organic matter and iron minerals, causing them to sink. The study reveals that episodic environmental events, not just steady biofouling, can drive microplastic sedimentation.
Method for microplastics extraction from Lake sediments
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Researchers developed a method for extracting microplastics from organic-rich freshwater lake sediments using repeated wet oxidation and density separation. Reliable extraction methods for freshwater sediments are important for understanding how lakes accumulate microplastics transported by rivers.
Biogeochemical processes governing microplastic transport in freshwater reservoirs
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Researchers investigated how microbial activity and biogeochemical processes affect the physical transport and eventual sedimentation of microplastics in freshwater reservoirs. They found that biofouling — the colonisation of plastic surfaces by microorganisms and algae — is a key mechanism causing initially buoyant microplastics to sink and accumulate in reservoir sediments.
Research digests by email
When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.