Quantification and Characterisation of Microplastics in Organic Waste-Derived Soil Amendments

Abstract

The spread of organic waste-derived amendments such as compost, anaerobic digestate and biosolids has been identified as a major source of microplastics in agricultural soil, with potential negative environmental and human health effects. Due to lacking regulatory frameworks and standard monitoring procedures, the extent of microplastic contamination in Scottish organic waste-derived soil amendments is still poorly understood. This study investigated the presence, quantity and characteristics (morphology, density and colour) of microplastics in anaerobically digested biosolids, green-waste-derived compost and food-waste-derived anaerobic digestate produced in Scotland. Microplastics (100—5000 µm) were present in all analysed samples in concentrations ranging from 34 to 160 particles g −1 dw, with the highest levels found in biosolids, followed by digestate and compost. High-density fibres represented 55.8—66.4% of microplastics in biosolids, likely polyester from the domestic washing of textiles. In addition to microplastics, > 20,000 cellulosic microfibres g −1 dw, likely textile-derived natural fibres, were detected in biosolids, and were absent in other samples. Microplastic fibres of a wider-density-range represented 72% of microplastic in compost, while high-density microplastic fragments (34%) and fibres (24%) were the most abundant microplastics in digestate. Based on the results, it was estimated that compost, anaerobic digestates and biosolids could respectively introduce 3.17 × 10 12 , 5.9 × 10 11 and 7.2 × 10 12 microplastic particles measuring 100—5000 μm to Scottish land, annually. These findings highlight the extent of microplastic contamination in terrestrial environments across Scotland, underscoring the need for standardised routine monitoring, enhanced waste management practices, and stricter regulatory measures.

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