Search

Microplastic (MP) contamination is a growing concern across many environments. However, research on MP accumulation in remote soils remains limited. This study investigated MP abundance in remote soil in western Iceland, with agricultural and urban soils as references. The MP was extracted and measured using state-of-the-art methods, capturing types, sizes, and shapes. Results showed that MP was present in all samples, with the lowest average count and mass observed in the remote samples (857 (±561) counts kg -1 , corresponding to 64.37 (±47.96) μg kg -1 ) and the highest in the urban samples (26,206 (±25,345) counts kg -1 , corresponding to 2175 (±1385) μg kg -1 ), showing that increase in anthropogenic activity gives increasing MP concentrations. In the remote samples, the particles were primarily medium-sized (median = 67 μm), lightweight polyester fragments. This study also investigated the influence of soil parameters such as water content, bulk density, and particle size on MP retention in remote soils. However, no other significant correlations were found when relating the count and mass to soil parameters., (Copyright © 2024. Published by Elsevier B.V.)

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 size-dependent, 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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

This study investigated the abundance of microplastic (MP) in agricultural soil fertilised with sludge, assessing the variation in MP count and estimated mass in three long-term field trials treated excessively with sludge in 2003-2012. Ten samples were taken from each of the three fields with concentrations ranging from 2392 to 48,791 counts kg -1 , where over 50 % of the MPs were polyester and acrylic. Due to the considerable variation in concentration, the impact of the number of sub-samples on the predicted measured concentration was estimated applying a Monto Carlo simulation approach. Choosing the number of sampling points is a compromise between acceptable sampling error and available resources. The simulations showed an increasingly high risk of obtaining an outlier when taking less than approx. ten subsamples. When ending fertilisation with sludge, the estimated half-life for the MPs measured by counts was approx. 2.5 years, whereas the half-life for the MP estimated mass was approx. 4 years. Hence, smaller particles seemed to degrade and/or migrate elsewhere the fastest., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Stormwater runoff from urban areas contain a wide variety of pollutants which is typically managed using stormwater retention ponds. However, their performance with regards to emerging pollutants such as microplastics and tyre wear material remains unclear. In this study, samples of effluent water and sediments from four stormwater retention ponds were analysed for their content of microplastics and tyre wear material. Microplastics were analysed using state-of-the-art hyperspectral imaging technique while tyre wear material was analysed using pyrolysis-GC-MS. Microplastics were recovered in all samples and the mass balance revealed that on average 88% of small microplastics (<500 µm) were retain in the ponds while the removal efficiency for large microplastics (>500 µm) was 95%. Tyre wear material was identified in all sediment samples but found below the detection limit in three out of four effluent samples. On average 95% of the tyre wear material was removed by the retention ponds. The results from this study show that stormwater retention ponds are very effective in removing microplastics as well as tyre wear material from stormwater runoff., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Shape matters for microplastics, but its definition, particularly for hyperspectral imaged microplastics, remains ambiguous and inexplicit, leading to incomparability across data. Hyperspectral imaging is a common approach for quantification, yet no unambiguous microplastic shape classification exists. We conducted an expert-based survey and proposed a set of clear and concise shapes ( fiber , rod , ellipse , oval , sphere , quadrilateral , triangle , free-form , and unidentifiable ). The categories were validated on images of 11,042 microplastics from four environmental compartments (seven matrices: indoor air; wastewater influent, effluent, and sludge; marine water; stormwater; and stormwater pond sediments), by inviting five experts to score each shape. We found that the proposed shapes were well defined, representative, and distinguishable to the human eye, especially for fiber and sphere . Ellipse , oval , and rod were though less distinguishable but dominated in all water and solid matrices. Indoor air held more unidentifiable , an abstract shape that appeared mostly for particles below 30 μm. This study highlights the need for assessing the recognizability of chosen shape categories prior to reporting data. Shapes with a clear and stringent definition would increase comparability and reproducibility across data and promote harmonization in microplastic research.