Nanoplastic Transport in Soil via Bioturbation by Lumbricus terrestris

Abstract

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.

Size-Dependent Uptake and Depuration of Nanoplastics in Tilapia (Oreochromis niloticus) and Distinct Intestinal Impacts

“…32 By measuring Pd as a proxy for the NPs, they offered a robust method for detecting NPs more easily, sensitively, and quantitatively in complex samples. In terms of application, the fate of NPs in simulated activated sludge processes in a municipal sewage treatment, 33 NP transport through unsaturated porous media, 34 and NP uptake and effects on Gammarus pulex 35 have been demonstrated. Presumably, this technique may provide a new insight into the toxicokinetic properties of NPs and a better understanding of their behavior in aquatic organisms.…”

Ecological risk of microplastic toxicity to earthworms in soil: A bibliometric analysis

“…The main mechanism by which earthworms were harmed by MPs is ingestion, with a notable focus on its effects on earthworm growth (Huerta Lwanga et al, 2016;Huerta Lwanga et al, 2017a). The ingestion of MPs by earthworms affects the earthworm gut bacterial community (Wang H. et al, 2019), and earthworm gut bacteria can promote plastic degradation (Huerta Lwanga et al, 2018), thereby increasing the risk of MPs entering the groundwater (Zhang et al, 2018;Yu et al, 2020;Heinze et al, 2021). Ingestion of MPs may cause mechanical damage to the digestive organisms in earthworms, and Fourier-transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy and intestinal pathology analyses indicate that MPs can damage the intestinal tract of earthworms (Rodriguez-Seijo et al, 2017).…”

“…Furthermore, the uptake of MPs by soil organisms affects digestive processes, resulting in bioaccumulation and biomagnification effects (Wang H. et al, 2019;Li M. et al, 2021;Zhao et al, 2022). Moreover, the activities of soil organisms drive the migration of MPs from the topsoil to the subsoil (Yu et al, 2019), thus increasing the risk of MPs entering groundwater (Zhang et al, 2018;Yu et al, 2020;Heinze et al, 2021).…”

Microplastics and nanoplastics in agriculture—A potential source of soil and groundwater contamination?

“…Earthworms, microarthropods and other bioturbators can accelerate vertical transport of MnPs by creating preferential flow paths (Heinze et al 2021). Some studies have shown that this can lead to MnPs being transported to depths of up to 40-50 cm (Huerta Lwanga et al 2017;Rillig et al 2017;Rodríguez-Seijo and Pereira 2019).…”