Microplastics in composts, digestates, and food wastes: A review

Diverting food waste from landfills to composting or anaerobic digestion can reduce greenhouse gas emissions, enable the recovery of energy in usable forms, and create nutrient‐rich soil amendments. However, many food waste streams are mixed with plastic packaging, raising concerns that food waste‐derived composts and digestates may inadvertently introduce microplastics into agricultural soils. Research on the occurrence of microplastics in food waste‐derived soil amendments is in an early phase and the relative importance of this potential pathway of microplastics to agricultural soils needs further clarification. In this paper, we review what is known and what is not known about the abundance of microplastics in composts, digestates, and food wastes and their effects on agricultural soils. Additionally, we highlight future research needs and suggest ways to harmonize microplastic abundance and ecotoxicity studies with the design of related policies. This review is novel in that it focuses on quantitative measures of microplastics in composts, digestates, and food wastes and discusses limitations of existing methods and implications for policy. Core Ideas Microplastic presence is documented in composts, digestates, and food wastes. Lack of standardized methods for these materials complicates comparison between studies. Existing regulations establish w/w limits on contamination which is inconsistent with many studies. Focus on maximizing benefits of food waste diversion and minimizing risk of microplastic pollution is needed.