From biodegradation to biohazard: polylactic acid microplastics induced rice growth inhibition in agroecosystems

Abstract

The increasing use of biodegradable plastics necessitates critical evaluation of their environmental safety. This study investigated the effects of polylactic acid microplastics (PLA-MPs, 0.1–2.5% w/w) on rice–soil systems using controlled pot experiments integrated with enzymatic assays, rhizosphere bacterial profiling, and non-target analysis of degradation products. PLA-MPs exposure inhibited rice growth by reducing photosynthetic efficiency and root development, which was associated with decreased nitrogen availability (30–60% reduction in NH⁺₄/NO^-₃-N), altered phosphorus levels, and reduced microbial α-diversity. Foliar fertilization alleviated phytotoxic effects by improving antioxidant responses and nutrient uptake. Non-target screening identified lactic acid derivatives as dominant degradation products, with limited long-term persistence. The degradation rate of PLA-MPs was estimated at 0.065 mg·d⁻¹ under soil conditions. These results indicate that PLA-MPs, despite their biodegradable nature, can adversely affect soil nutrient cycling and crop performance. These findings emphasize the need to re-evaluate biodegradable plastic use in agriculture and promote integrated mitigation strategies to reduce microplastic-induced stress and support sustainable soil–plant systems.