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Microplastics detection in agricultural soil combining 3D Laser Scanning Confocal Microscopy with machine learning
Summary
Scientists developed a new workflow combining 3D laser scanning confocal microscopy with machine learning to detect and quantify microplastics in agricultural soils more efficiently and without hazardous chemicals. The method was validated on soil samples spiked with transparent microplastics, which are particularly difficult to identify. Faster, safer detection tools are essential for understanding how widely microplastics from plastic mulch films and organic fertilizers contaminate farmland soils.
Abstract Low-density plastics of different origins are a major source of microplastic (MP) contamination in agricultural soil systems. Although several plastic entry pathways are well known, such as the fragmentation of plastic materials used in so-called plasticulture or the contamination of organic fertilisers, including compost and sewage sludge, quantifying the MP contamination of these soil systems remains challenging and time-consuming. This study developed and rigorously tested a hazard-free workflow to overcome these limitations and expand the capabilities for detecting MP. The workflow combines 3D Laser Scanning Confocal Microscopy (Keyence VK-X1000, Japan) with machine-learning-based data analysis and was evaluated using three agricultural topsoils spiked with transparent and black low-density polyethylene and polypropylene particles (<53 µm, 53-100 µm, 100-250 µm) and polypropylene fibres (1000 µm). The method reliably detects both transparent and black MP ≥53 µm in soils with low particulate organic matter content, achieving a mean recovery rate of 80% ± 28%. Transparent MPs were reliably identified, whereas black MPs and fibres were influenced by particulate organic matter. Beyond particle count and size, the approach quantifies surface morphology using high-resolution 3D data. Four 25 g samples (100 g total soil) can be processed within three days, providing a fast, accurate, and environmentally safe tool for MP analysis in agricultural soils.