Molecular effects of polystyrene nanoplastics toxicity in zebrafish embryos (Danio rerio)

Plastics pose a health hazard to living beings and the environment. Plastic degradation produces nano-sized plastic particles (NPs) that end up in terrestrial and aquatic ecosystems, including oceans, rivers, and lakes. Their presence in air, drinking water, sediments, food, and personal care products leads to a variety of exposure routes for living beings, including humans. The toxicity mechanisms of these nanomaterials (NMs) in living organisms and ecosystems are currently unknown, making it a priority to understand their effects at the mo-lecular and cellular levels. The zebrafish (Zf) (Danio rerio) is a model organism which has a high homology with humans and has been widely used to assess the hazard of different xenobiotics. In this study, the expression changes of different genes in 120 hpf Zf embryos (Zfe) after exposure to polystyrene (PS) NPs (30 nm) at con-centrations of 0.1, 0.5 and 3 ppm were investigated. The results showed that the gene encoding heat shock protein (hsp70) was down-regulated in a dose-dependent manner. The genes encoding superoxide dismutase (SOD 1 and SOD 2), apoptotic genes (cas 1 and cas 8) and interleukin 1-beta (il1 beta) were activated at the concen-tration of 3 ppm PS NP, while the anti-apoptotic gene Bcl2 alpha was inhibited at 0.5 and 3 ppm. In addition, the neurotransmitter-related gene Acetyl-Cholinesterase (ache) was significantly inhibited and the DNA repair genes (gadd45 alpha and rad51) were also down-regulated. In contrast, the mitochondrial metabolism-related gene cox1 did not alter its expression in any of the treatments. Most of the changes in gene expression occurred at the highest concentration of NPs. Overall, the results indicated that NPs generated cellular stress that caused certain al-terations in normal gene expression (oxidative stress, apoptotic and inflammatory processes, neurotoxicity and anti-apoptotic proteins), but did not cause any mortality after 120 hpf exposure at the three concentrations assayed. These results highlight the need for further studies investigating the effects, at the molecular level, of these materials in humans and other living organisms.