Atmospheric microplastic emissions from organic waste composting: Field-based assessment and exposure implications

Organic compost serves as a major pathway for microplastics (MPs) entering the environment. However, atmospheric MPs pollution from composting activities remains poorly understood. This study comprehensively investigated airborne MPs pollution by comparing multiple composting techniques (reactor, stack, film-covered, and trough) using a combined approach of active and dry deposition sampling, and quantitatively assessed the associated human exposure risks. Results revealed substantial differences among composting techniques: stack composting exhibited the highest MPs abundance (16.90 items m^-3 via active sampling; 93.4 items m^-2 d^-1 via deposition sampling), whereas film-covered composting showed the lowest emissions (3.48 items m^-3 and 37.4 items m^-2 d^-1, respectively). Film-covered composting released more film-shaped MPs, polyvinyl chloride, and polyethylene, while stack composting emitted more rayon and polyamide. As composting progressed, airborne MPs abundance via active sampling significantly increased by 114.8 %, the proportion of smaller MPs (<800 μm) rose by 34.4 %, and the average size significantly decreased by 26.3 %. Human exposure risk, estimated via oral intake and inhalation pathways, increased as composting advanced, peaking during stack composting and reaching minimal levels during film-covered composting. These findings underscore composting as a significant pathway for MPs dispersion into the atmosphere and provide essential insights for optimizing composting practices to mitigation environmental contamination.