Coarse microplastic accumulation patterns in agricultural soils during two decades of different urban composts application

Urban Farm DB summary

A 2024 analysis of archived soils from a long-term field experiment in France that received three urban composts — municipal solid waste compost, biowaste compost, and a sewage-sludge-plus-green-waste compost — over 21 years. Density fractionation followed by oxidation isolated 1,417 coarse microplastic (CMP) particles, identified by Py-GC/MS; different compost types produced different accumulation levels, and CMP content in soil rose over time. After 21 years the measured number of CMP particles matched estimates derived from compost inputs, but the measured mass did not for any of the three composts, which the authors attribute to biotic transport or to weathering and fragmentation making particles smaller. No difference in temporal pattern was found between films and fragments. The value of the study is long-term evidence that returning urban organic matter to soil also imports plastic; note that the site is farmland, not a city garden, so the figures cannot be transferred directly to citizen composting.