Microplastics in Waste-Derived Fertilisers

Waste-derived fertilising materials, including sewage sludge, compost, digestate, food-waste-derived products and commercial organic or organo-mineral fertilisers, return nutrients to farmland but can also transfer microplastics to agricultural soil. This critical review examines their occurrence across these streams, analytical constraints, fate after application and the EU regulatory framework. Reported abundances span orders of magnitude and cannot be pooled because extraction, polymer identification and reporting are not harmonised, while particle-counting and mass-based methods measure different quantities. Field evidence indicates topsoil retention and accumulation after repeated application, whereas crop transfer and field-scale ecological effects remain poorly quantified. Regulation (EU) 2019/1009 sets no microplastic-specific product limit. For compost qualifying as CMC 3 and digestate other than fresh crop digestate qualifying as CMC 5, it controls plastic impurities above 2 mm by mass, while smaller particles remain outside that criterion. Waste-derived fertilisers can therefore form a recurrent, incompletely regulated pathway for microplastic transfer to soil. Controlled studies demonstrate hazard potential for selected particles and exposure conditions, but the magnitude and likelihood of effects under field conditions remain uncertain. The immediate priority is harmonised monitoring and reporting of the sub-2 mm fraction, including a stated lower size limit, polymer-confirmed particle counts and minimum QA/QC.