Long-term application of organic compost is the primary contributor to microplastic pollution of soils in a wheat-maize rotation

Urban Farm DB summary

A 2023 study using an 11-year wheat–maize rotation field trial in China to test how long-term application of pig- and cow-manure compost affects soil microplastics (MPs). The composts themselves contained 3,547 and 4,520 items/kg respectively; soils under long-term application held 144–287 and 140–316 items/kg, significantly more than unamended soil, and abundance rose with application rate. Compost-derived accumulation reached 1.73 × 10⁸ to 7.22 × 10⁸ items per hectare, accounting for 43.0–75.9% of total soil MPs, with the contribution doubling when the application rate doubled. Particles under 1 mm made up 31.0% of MPs in the composts but 43.8% in amended soils, size and abundance fell with depth, and particle surfaces showed complex weathering with attached soil mineral colloids — evidence, the authors conclude, that compost-derived MPs are progressively fragmented and degraded in soil after application. Polyethylene and polypropylene fragments and polyethylene terephthalate fibres dominated.