Persistence in soil of microplastic films from ultra-thin compostable plastic bags and implications on soil Aspergillus flavus population

An increasing number of states and municipalities are choosing to reduce plastic litter by replacing plastic items, particularly single-use ones, with same-use products manufactured from compostable plastics. This study investigated the formation and persistence of compostable film microplastic particles (CFMPs) from ultra-thin compostable carrier bags in soil under laboratory conditions, and the potential impact of CFMPs on Aspergillus flavus populations in the soil. During a 12-month incubation period, compostable film samples in soils with small, medium or large populations of indigenous A. flavus, underwent 5.9, 9.8, and 17.1% reduction in total surface area, respectively. Despite the low levels of deterioration, the number of CFMPs released increased steadily over the incubation period, particularly fragments with size < 0.05 mm. Up to 88.4% of the released fragments had associated A. flavus and up to 68% of isolates from CFMPs produced aflatoxins. A. flavus levels associated with CFMPs increased rapidly during the initial part of the 12-month incubation period, whereas the percent aflatoxigenicity continued to increase even after A. flavus density leveled off later. During 12 months incubation, A. flavus DNA amounts recovered from CFMPs increased in soils with all levels of indigenous A. flavus, with the largest increases (119.1%) occurring in soil containing the lowest indigenous A. flavus. These results suggest that burying compostable film in soil, or application of compost containing CFMPs, may reduce soil quality and increase risk of adverse impacts from elevated aflatoxigenic A. flavus populations in soil.