Toxicity mechanisms of photodegraded polyvinyl chloride nanoplastics on pea seedlings

Nanoplasctics (NPs), which are very small in particle size, exert toxic effect to organisms. Additionally, compared to original NPs, photodegraded NPs would pose higher toxicity. This is because their relatively higher specific surface areas and the presence of additives which can more easily leach. How original NPs and aged NPs affect plant growth has not been widely investigated. This work chose polyvinyl chloride NPs (PVC-NPs) that were subjected to up to 1000 h UV light radiation to explore the impact of PVC-NPs on the growth of pea seedlings (Pisum Sativum L.). The results indicated the existence of PVC-NPs with longer UV light radiation time and higher concentrations had more negative influences on pea seedlings’ growth such as germination rate (decreased by 10.6%–22.5%), stem length (decreased by 2.8%–8.1%), dry weight (decreased by 6.3%–7.1%) and fresh weight (decreased by 6.7%–14.8%). It was also noted that photodegraded PVC-NPs resulted in damage to leaf stomata and roots, hindering photosynthesis and absorption of nutrients and hence the decrease in chlorophyll and soluble sugar contents. According to transcriptomic investigation results, the presence of aged PVC-NPs primarily influenced protein processing in endoplasmic reticulum (upregulated metabolic pathway) and phenylpropanoid biosynthesis (downregulated metabolic pathway) of pea seedlings. These results provide an in-depth understanding of how NPs influence the growth of plants.