Physiological and biochemical responses of sweet basil (Ocimum basilicum L.) to polyethylene micro- and nanoplastics exposure

Although plastic threatens terrestrial ecosystems, the effects of micro- and nanoplastics (MNPs) combination in plants remain poorly understood and need in-depth investigations. This study investigates the effects of polyethylene MNPs (0.1% w/v; Ø 200–9900 nm) on Ocimum basilicum by exposing seeds to MNPs for 5 days (Seed Treatment; ST) or hydroponically-grown 20-day seedlings for 15 days (Plant Treatment; PT). Biometric, physiological, cytological, ultrastructural responses, oxidative stress level and antioxidant responses were analyzed. In PT, transmission electron microscopy revealed MNPs presence in xylem vessel of stem, highlighting the translocation of smaller particles to aerial parts. MNPs adsorption onto roots reduced water uptake, affecting plant metabolism. ST impaired root growth, with signs of cyto-genotoxicity and oxidative damage. PT reduced CO₂ assimilation due to stomatal limitations and altered plants biometric traits, including root length (+42.6%), root biomass (−35.2%) and leaf area. Oxidative stress increased in leaves in terms of H2O2 accumulation (+47.4%) and lipid peroxidation (+22.2%). These findings underscore the detrimental impact of MNPs on basil growth. Further research is essential to elucidate MNPs uptake and translocation mechanisms, and to assess the potential risks of MNPs contamination for plant health and ecosystem integrity.