Field Application of Biodegradable Microplastics Has No Significant Effect on Plant and Soil Health in the Short Term

Abstract

Bioplastics (biodegradable plastics) potentially offer an encouraging alternative to conventional (petroleum-based) plastics. However, biodegradable plastics, in practice, inevitably generate a large number of bio-microplastics (bio-MPs, diameter < 5 mm) during the degradation progress. However, the impact of bio-MPs on plant and soil health within agroecosystems remains incomplete. Here, we investigated the effect of two shapes (fiber and powder) of pure polylactic acid (PLA) bio-MPs on oat ( Avena sativa L.) and soybean ( Glycine max (L.) Merr.) growth, and soil health in a field-based study. Our results showed that PLA application at a soil loading rate of 0.2% (w/w) had no significant effect on soil enzyme activities, soil physicochemical properties (soil water content, pH, etc.), root characteristics, plant biomass, and crop yield. Thus, we conclude that soil quality, plant health, and ecosystem multifunctionality were not affected by PLA over one growing season (5 months) in the presence of either bio-MP shape (fiber and powder) for either crop species (oat and soybean). Overall, we conclude that PLA based bio-MPs may not pose a significant threat to agroecosystem functions in the short term (days to months) and may provide a viable environmentally benign solution to replace traditional non-biodegradable plastics in agroecosystems.

Keywords: Biodegradable microplastics, Soil enzyme activities, Soil quality indicator, Plastic mulch film, Ecosystem multifunctionality