Deciphering micro/nanoplastic induced phytotoxicity with special emphasis on the cytogenotoxic effects on Allium cepa L.

Abstract

Considering the present plastic pollution crisis, this thesis work reported the phytotoxicity of polystyrene micro/nanoplastics (M/NPs) in onion with effects on seed germination, root growth, and cytotogenotoxicity. The detection of negative impacts in environmentally relevant concentrations of polystyrenes (PS) clearly showed the harmful effects of polystyrene particles on the plants health, indicating its possible negative impacts on biodiversity. The root growth rather than seed germination was negatively affected by the increasing concentrations of polystyrene particles. The tested diameter of polystyrene particles caused an imbalance in redox homeostasis through the elevated production of ROS, which in high concentrations of polystyrenes subdues the antioxidant defence and ensues in different harmful effects. Different chromosomal alterations and DNA damage potential of micro/nanopolystyrenes (M/NPS), as recorded in this work, may indicate the potential threat of micro/nanoplastics to other organisms because, the basic genetic makeup is same for all eukaryotes. The combined effects of nanoplastics and heavy metals such as Cd and Hg were also evaluated showing an increasing level of toxicity of Cd and a decreasing toxicity of Hg in the presence of polystyrene particles. This observation signifies a differential effect of plastics in modulating the toxicities of heavy metals depending on metal species. Another interesting finding of this work was the positive impact of high temperature or temperature stress (TS), but not the salinity stress (SS), in aggravating the toxicity of micro/nanoplastics. The temperature stress improves the root accumulation of polystyrene particles with notable deleterious effects on oxidative stress, microtubules stability, and organization. In this study, we have used the term micropolystyrene and nanopolystyrene interchangeably for the same diameter (100 nm or 0.1 µm) of polystyrene particles, because the selected diameter remains at the transition between micro and nano particles and there is no accepted distinction on nanoplastics size unlike metal nanoparticles. Some authors have used the term micro for this diameter, while others have used nano for the same.