Effects of selenite on the responses of lettuce (Lactuca sativa L.) to polystyrene nano-plastic stress

Nowadays, nano-plastics are widespread in agricultural soils and could be uptaken by crops to cause an increased risk for food safety. As a beneficial element for plants, selenium (Se) can alleviate oxidative damages under various environmental stresses (eg. heavy metals, heat, cold). This study investigated the single and co-applications of nano-size polystyrene (PS) (80 nm and 200 nm) and selenite (0.8 ppm and 5 ppm) in lettuce (Lactuca sativa L.). Results showed nano-PS significantly decreased the root-shoot fresh biomass ratios, inhibited physiological functions in roots and leaves (e.g. root length, chlorophyll content and net photosynthetic rate), as well as stimulated the activities of the antioxidant enzymes in roots and shoots with greater toxicity at the smaller particle size (80 nm). However, both exogenous selenite applications significantly alleviated the above toxic effects of nano-PS in lettuces, especially at a high Se level of 5 ppm. Regression Path Analysis (RPA) revealed that regulation of chlorophyll levels by Se might be a key mechanism for counteracting PS stress in lettuces, which led to the increase in indigenous defense capacity. The present findings provide a novel but safer and cleaner agricultural strategy to alleviate or minimize nano-plastics toxicity in agricultural soils for staple crops and vegetables via application of Se.