Nanoplastic transport in soil via bioturbation by Lumbricus terrestris

Plastic pollution is increasingly perceived as an emerging threat to terrestrial environments, but the spatial and temporal dimension of plastic exposure in soils is poorly understood. Bioturbation displaces microplastics (>1 μm) in soils and likely also nanoplastics (<1 μm), but empirical evidence is lacking. We used a combination of methods that allowed us to not only quantify but to also understand the mechanisms of biologically driven transport of nanoplastics in microcosms with the deep-burrowing earthworm Lumbricus terrestris. We hypothesized that ingestion and subsurface excretion drives deep vertical transport of nanoplastics that subsequently accumulate in the drilosphere, i.e., burrow walls. Significant vertical transport of palladium-doped polystyrene nanoplastics (diameter 256 nm), traceable using elemental analysis, was observed and increased over 4 weeks. Nanoplastics were detected in depurated earthworms confirming their uptake without any detectable negative impact. Nanoplastics were indeed enriched in the drilosphere where cast material was visibly incorporated, and the reuse of initial burrows could be monitored via X-ray computed tomography. Moreover, the speed of nanoplastics transport to the deeper soil profile could not be explained with a local mixing model. Earthworms thus repeatedly ingested and excreted nanoplastics in the drilosphere calling for a more explicit inclusion of bioturbation in nanoplastic fate modeling under consideration of the dominant mechanism. Further investigation is required to quantify nanoplastic re-entrainment, such as during events of preferential flow in burrows

Fate of microplastics in sewage sludge and in agricultural soils

The aim of this study was to review microplastics (MPs) occurrence in sewage sludge from wastewater treatment plants (WWTPs) and assess implications of sludge application to agricultural soils. Sludge is a main sink for MPs in WWTPs, highlighting the importance of sludge as a route for environmental exposure. Sludge application on agricultural fields is associated with elevated MP concentrations in soils, potentially affecting soil health. However, prior to application sludge treatments may alter MP abundance and MPs properties, such as shape and size, subsequently affecting environmental risk. Knowledge gaps still exist regarding sludge treatments and their effect on MPs (size, shape abundance). Further investigation is needed to assess the risk of MPs exposure at WWTPs, explore the effects of sludge treatments on soil health, and to better understand how management at WWTPs, and in agricultural systems, affect MP properties. & COPY; 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)