Environmental impacts of polylactic acid microplastics on terrestrial and aquatic ecosystems: More threatening compared to traditional microplastics?

The widespread use of plastics has caused significant environmental challenges, particularly the accumulation of microplastics (MPs, <5 mm) in ecosystems. While polylactic acid (PLA)-based biodegradable plastics represent a technologically advanced substitute for conventional polymers, field studies reveal that their environmental degradation frequently yields PLA MPs, creating novel ecological exposure pathways that differ from those of petroleum-based MPs. This review systematically evaluates the environmental impacts of PLA MPs, focusing on their effects on terrestrial and aquatic ecosystems. Current research reveals that PLA MPs might disrupt carbon and nitrogen cycling, alter microbial communities, and affect soil fauna and plant health, and they could act as carriers for pollutants, influence microbial diversity through plastisphere formation, and elicit toxicological responses in aquatic organisms. Meanwhile, PLA MPs have shown differences from conventional MPs in various aspects, such as providing additional soil carbon sources, affecting soil physicochemical properties, exerting oxidative stress in animals and plants, and more substantial toxic effects of co-exposure to pollutants. Despite growing evidence, knowledge gaps remain regarding the long-term fate and ecological risks of PLA MPs. This review is based on existing research findings, highlighting the necessity of comprehensive and long-term research on PLA MPs under realistic conditions, and emphasizing the systematic comparison of the environmental behavior of PLA MPs with traditional MPs. Future research needs comprehensive ecotoxicological assessments, investigations into PLA MPs' interactions with pollutants and microbial communities, standardized protocols, and comparative analyses with conventional MPs; long-term studies on degradation pathways and ecosystem impacts are required to inform sustainable plastic policies.