Sublethal Toxicity and Gene Expression Changes in Hydra vulgaris Exposed to Polyethylene and Polypropylene Nanoparticles

Plastic nanoparticles (NPs) released from plastic breakdown pervade aquatic ecosystems, raising concerns about their long-term toxic effects in aquatic organisms. The purpose of this study was to examine the sublethal toxicity of polyethylene (PeNPs) and polypropylene (PpNPs) nanoparticles of the same size (50 nm diameter) in Hydra vulgaris. Hydras were exposed to increasing concentrations of PeNPs and PpNPs (0.3–10 mg/L) for 96 h at 20 °C. Toxicity was determined based on the characteristic morphological changes and gene expression analysis of genes involved in oxidative stress, DNA repair, protein salvaging and autophagy, neural activity and regeneration. The data revealed that PpNPs produced morphological changes (50% effects concentration EC50 = 7 mg/L), while PeNPs did not. Exposure to both nanoplastics produced changes in gene expression in all gene targets and at concentrations less than 0.3 mg/L in some cases. PpNPs generally produced stronger effects than PeNPs. The mode of action of these plastic polymers differed based on the intensity of responses in oxidative stress (superoxide dismutase, catalase), DNA repair of oxidized DNA, regeneration and circadian rhythms. In conclusion, both plastics’ nanoparticles produced effects at concentrations well below the appearance of morphological changes and at concentrations found in highly contaminated environments.