New Publication: Nanoplastic Transport in Soil via Bioturbation by Lumbricus terrestris

Weibke Mareile Heinze, Denise M. Mitrnao, Elma Lahive, John Koestel and Geert Cornelis. Environmental Science and Tecchnology. 

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Plastic pollution is increasingly perceived as an emerging threat to terrestrial environments. The fate of nanoplastics (diameter <1 µm) in soil, and thus the spatial and temporal dimension of exposure, is particularly poorly understood. We hypothesized that bioturbation significantly contributes to nanoplastic transport in soils. Nanoplastics displacement in soil microcosms by the deep-​burrowing earthworm Lumbricus terrestris was quantified over four weeks using palladium-​doped polystyrene nanoplastics (diameter 256 nm) to overcome challenges of detecting plastic particles. Earthworms caused significant downward transport of nanoplastics, increasing with time, but nanoplastics had no detectable negative effects on the earthworms. We concluded that ingestion and subsequent excretion of nanoplastics was the primary driver of nanoplastic redistribution based on several observations. Firstly, nanoplastics were detected in depurated earthworms confirming their ingestion. Secondly, the drilosphere, i.e. the burrow walls, were found enriched with nanoplastics relatively to the soil matrix, probably because earthworms re-​used initial burrows as confirmed by X-​ray tomography. Finally, the speed of nanoplastics transport could not be explained by a bioturbation model based on local mixing only. Our results suggest bioturbation needs to be explicitly included in fate modelling of nanoplastics to avoid systematic underestimation of their mobility and understand their spatial distribution in the field.