Understanding the ecological impacts of biodegradable microplastics

Biodegradable plastics are being designed and increasingly used as eco-friendly alternatives to conventional plastics in an effort to combat the plastic pollution crisis. However, whether these alternative forms of plastic are eco-friendly and safe remains controversial. Here, we systematically review the literature on the ecological impacts of biodegradable microplastics (BMPs) and summarize their impacts on environmental physicochemical properties, biota, and human health. Most published studies have observed that BMP exposure has significant negative effects, including inhibited growth and reproduction in certain plants and animals, reduced microbial diversity, enrichment of pathogens, increased pollutant bioavailability in soil, heightened risks of their spread within water bodies, and exacerbated greenhouse gas emissions. Different concentrations and types (polymers, sizes, shapes, and additives) of BMPs can have different ecological consequences with aging amplifies these effects. The impact of BMPs is influenced by the physicochemical properties of environmental media, such as divergent pH responses to BMPs, which correlate strongly with soil textural classes. Clay-dominated soils exhibit strong buffering capacity that mitigates BMP-induced pH shifts, but sandy soils with limited buffering capacity demonstrate pronounced pH susceptibility to BMP amendments. This review emphasizes the need to reconsider the ecological friendliness of biodegradable plastics and assess BMPs' ecological risks. The current understanding is limited by issues such as short experimental duration and excessive dosage levels. Future long-term monitoring experiments based on environmentally relevant concentrations are imperative for comprehensively assessing the ecological risks associated with BMP pollution.