Phytotoxic impacts of microplastic pollution on cellular redox homeostasis and antioxidant defences in plants: a multilevel meta-analysis

Abstract The rapid build-up of plastic pollution in land-based ecosystems is a serious abiotic stressor that directly threatens cellular redox balance in plants. To precisely evaluate the risk of oxidative stress associated with microplastic exposure, a meta-analysis was conducted in accordance with the PRISMA protocol, using a multilevel random-effects model. By combining extensive literature data, this analysis examined biomarkers such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), malondialdehyde (MDA), and hydrogen peroxide (H 2 O 2 ). The meta-analysis showed that microplastic exposure caused significant oxidative damage in plants, indicated by profound increases in reactive oxygen species, especially H 2 O 2 ( g = 3.60, 95% CI: 2.34–4.86, p < 0.001), and in lipid peroxidation, as indicated by MDA ( g = 3.58, 95% CI: 2.95–4.21, p < 0.001). In response to this cellular injury, plants displayed a statistically significant, compensatory upregulation in their enzymatic defence systems (CAT: g = 3.02, 95% CI: 2.43–3.62; SOD: g = 2.15, 95% CI: 1.81–2.49; POD: g = 1.50, 95% CI: 1.05–1.95; all p < 0.001). Additionally, moderator analyses found that Plastic Type was a crucial factor influencing these enzymatic responses. Exploratory subgroup analyses tentatively suggested that PBAT, a biodegradable polymer, was associated with stronger SOD and CAT responses than conventional microplastics; however, these subgroup estimates are based on a small number of effect sizes ( k = 4–9), were not consistent across all biomarkers (e.g., POD and H₂O₂ showed no such pattern), and should therefore be regarded as preliminary and requiring confirmation. In summary, these results provide no indication that the biodegradable polymers examined here are less phytotoxic than conventional ones; however, the small number of biodegradable-polymer comparisons means that neither a safety advantage nor a disadvantage can be established from the present evidence, and polymer-related phytotoxic risk remains an open question for agricultural sustainability.