Transport av nanoplast genom advektion och bioturbering

Micro- and nanoplastics are increasingly perceived as an emerging threat to ecosystems. They are emitted to soils through different pathways, including sewage sludge or compost applications in agriculture, or through tire abrasion and degradation of mismanaged waste. Yet, their environmental behaviour and fate in terrestrial ecosystems is still poorly investigated. In order to investigate the potential impact of different transport processes on the redistribution of plastics in natural soils, column leaching tests and bioturbation studies in microcosms were conducted using a natural topsoil and palladiumdoped polystyrene nanoplastics of 256 nm diameter. Under the influence of advection, nanoplastic retention in saturated columns was very limited. Kinetic transport parameters were obtained from saturated column tests by applying inverse modelling in HYDRUS-1D. Derived attachment efficiencies were relatively low, att = 6.25 × 10-4. In unsaturated soils, more representative of prevailing field conditions, nanoplastic mobility through percolating water was very limited. However, the burrowing activity of anecic earthworms, here Lumbricus terrestris, caused a significant redistribution and transport of nanoplastics into deeper soil layers, steadily increasing over the duration of the experiment. Observed spatial and temporal changes in nanoplastic distribution were used to determine bioturbation rates by applying a bioturbation model (kbioturb = 4.5 × 10-11). The bioturbation model systematically underestimated nanoplastics in the lower layers, indicating that further differentiation of the transport modes by soil biota might be necessary. Although mixing by earthworms was slow, the current study suggests that under field conditions bioturbation may be more important than advective transport for nanoplastics in soils. While displacement of nanoplastics likely reduces uptake and risks for terrestrial organisms and crops near the surface, potential effects in deeper soil layers are of yet unknown consequences. A wider array of nanoplastic types and sizes, as well as modes of applications is needed to allow for extrapolation of findings

Vertical distribution of microplastics in an agricultural soil after long-term treatment with sewage sludge and mineral fertiliser

Sewage sludge applications release contaminants to agricultural soils, such as potentially toxic metals and microplastics (MPs). However, factors determining the subsequent mobility of MPs in long-term field conditions are poorly understood. This study aimed to understand the vertical distribution of MPs in soils amended with sewage sludge in comparison to conventional mineral fertiliser for 24 years. The depth-dependent MP mass and number concentrations, plastic types, sizes and shapes were compared with the distribution of organic carbon and metals to provide insights into potentially transport-limiting factors. Polyethylene, polypropylene and polystyrene mass concentrations were screened down to 90 cm depth via pyrolysis-gas chromatography/mass spectrometry. MP number concentrations, additional plastic types, sizes, and shapes were analysed down to 40 cm depth using micro-Fourier transform-infrared imaging. Across all depths, MP numbers were twice and mass concentrations 8 times higher when sewage sludge was applied, with a higher share of textile-related plastics, more fibres and on average larger particles than in soil receiving mineral fertiliser. Transport of MPs beyond the plough layer (0-20 cm) is often assumed negligible, but substantial MP numbers (42 %) and mass (52 %) were detected down to 70 cm in sewage sludge-amended soils. The initial mobilization of MPs was shape- and sizedependent, because the fractions of fragmental-shaped and relatively small MPs increased directly below the plough layer, but not at greater depths. The sharp decline of total MP concentrations between 20 and 40 cm depth resembled that of metals and organic matter suggesting similar transport limitations. We hypothesize that the effect of soil management, such as ploughing, on soil compactness and subsequent transport by bioturbation and via macropores drives vertical MP distribution over long time scales. Risk assessment in soils should therefore account for considerable MP displacement to avoid underestimating soil exposure

Sample Preparation Techniques for the Analysis of Microplastics in Soil-A Review

Although most plastic pollution originates on land, current research largely remains focused on aquatic ecosystems. Studies pioneering terrestrial microplastic research have adapted analytical methods from aquatic research without acknowledging the complex nature of soil. Meanwhile, novel methods have been developed and further refined. However, methodical inconsistencies still challenge a comprehensive understanding of microplastic occurrence and fate in and on soil. This review aims to disentangle the variety of state-of-the-art sample preparation techniques for heterogeneous solid matrices to identify and discuss best-practice methods for soil-focused microplastic analyses. We show that soil sampling, homogenization, and aggregate dispersion are often neglected or incompletely documented. Microplastic preconcentration is typically performed by separating inorganic soil constituents with high-density salt solutions. Not yet standardized but currently most used separation setups involve overflowing beakers to retrieve supernatant plastics, although closed-design separation funnels probably reduce the risk of contamination. Fenton reagent may be particularly useful to digest soil organic matter if suspected to interfere with subsequent microplastic quantification. A promising new approach is extraction of target polymers with organic solvents. However, insufficiently characterized soils still impede an informed decision on optimal sample preparation. Further research and method development thus requires thorough validation and quality control with well-characterized matrices to enable robust routine analyses for terrestrial microplastics

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

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.ISSN:0013-936XISSN:1520-585

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/)