生分解性プラスチックの隠された危機：ポリ乳酸マイクロプラスチックは土壌中のCdおよびPbの生物学的利用能と関連する人間の健康リスクを高める

The increasing application of biodegradable plastics like polylactic acid (PLA) has raised concerns about their potential environmental impacts, especially in agricultural soils co-contaminated with heavy metals. However, the mechanisms by which PLA microplastics (MPs) regulate the environmental behavior of heavy metals remain insufficiently understood. A pot experiment was conducted to investigate the influence of PLA MPs on cadmium (Cd) and lead (Pb) dynamics, lettuce uptake, and associated human health risks in a soil-lettuce system. The results demonstrated that PLA MPs altered soil properties, dissolved organic matter composition, and microbial community structure, thereby enhancing Cd (13.0-73.8%) and Pb (8.7-60.9%) bioavailability. Consequently, PLA MPs promoted Cd accumulation and translocation in lettuce, which exhibited photosynthesis inhibition and oxidative damage. Medium and high levels of PLA MPs significantly increased non-carcinogenic (0.4-1.9-fold) and carcinogenic (0.8-2.6-fold) risks associated with heavy metals, with shoot Cd accumulation as the primary contributor. These findings highlight the ecological and health risks of biodegradable MPs, calling for a critical reassessment of their presumed environmental sustainability.