Investigation on the formation of microplastics from compostable plastic bags during the rotting process in field tests

Abstract Compostable pre-collection plastic bags can foster the separate collection of biowaste from households and reduce pollution of conventional plastics. Test conditions proposed in certification procedures (e.g., EN 13432) used to show the compostability of such materials (and products) are made under controlled and optimal laboratory conditions and extended test periods that are rarely achieved in the composting practice. Thus, it is possible that some ‘compostable’ plastic products may not be degraded satisfactorily in technical composting plants under realistic conditions, which could leave microplastic fragments in composts. Therefore, in this study, the compostability of a certified compostable plastic bag was investigated under practical conditions in two state-of-art composting plants in Austria. Expected future plastic bag quantities (resulting in 0.95–1.19 kg biowaste per pre-collection-bag) were added to test windrows and were investigated during 12 weeks for fragment sizes > 0.2 mm. The results show that the investigated materials degraded within the first four weeks and left only tiny amounts of plastic materials in a size range 0.63–0.2 mm.