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Microplastics in Waste-Derived Fertilisers
Summary
Fertilizers made from sewage sludge, compost, and food waste help recycle nutrients back into farm soil, but this review of existing research shows they can also introduce microplastics into the ground where our food grows. Current EU rules only restrict larger plastic pieces (bigger than 2mm), leaving smaller microplastic fragments largely unregulated and understudied—meaning scientists still don't know how much of this plastic ends up in crops or what it means for the food on our plates. The researchers say better, standardized testing is urgently needed to understand the real risks before we can say how worried we should be.
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.