From waste to resource: unveiling the nexus between compost, microplastics, and agroecosystem

• Municipal waste is the major source of microplastics in compost • Measuring microplastics in different units reduce results accuracy and consistency • Smaller microplastics pose more risk to the sustainability of agroecosystems • Bioplastics can act as a non-point source of microplastics in compost • Biochar can increase microplastics’ degradation during composting process Compost is a widely used organic amendment to improve soil health and increase crop yield. However, the contamination of compost with microplastics (MPs) has emerged as a growing concern for the sustainability of agroecosystems. Despite concerns, the fate of compost bound MPs largely remained unclear. This review critically assessed the sources, characteristics and fate of MPs in the compost. The findings clarified that contaminated organic waste feedstocks were the main contributor of MPs to compost, with fibers, fragments, and films being the most observed shapes. The abundance of polypropylene (PP), Polyethylene (PE), and Polyethylene terephthalate (PET) polymers in compost reflected their widespread use in the production of everyday plastic products. The review further investigated the effect of MPs on the soil system and found that the severity of impact mainly depends on MP morphology. The results also highlighted that partial degradation of bioplastics could persist as non-point source of MPs in the compost. However, addition of biochar, strict monitoring of composting conditions, and introduction of specific microbial strains during the composting process could be possible solutions to increase the degradation of MPs.