Toxic effects of polystyrene nanoparticles on the development, escape locomotion, and lateral-line sensory function of zebrafish embryos.

Environmental pollution by micro- and nanosized plastic particles is a potential threat to aquatic animals. Polystyrene is one of the most common plastic particles in aquatic environments. Previous studies found that polystyrene nanoparticles (PNs) can penetrate the integument and accumulate in the organs of fish embryos. However, the potential impacts of PNs on fish embryos are not fully understood. To investigate this issue, zebrafish embryos were exposed to different concentrations (10, 25, and 50 mg/L) of PNs (25 nm) for 96 h (4-100 h post-fertilization), and various endpoints were examined, including developmental morphology (body length, sizes of the eyes, otic vesicles, otoliths, pericardial cavity, and yolk sac), locomotion (touch-evoked escape response and spinal motor neurons), and lateral-line function (hair cell number and hair bundle number). Exposure to 50 mg/L of PNs resulted in significant adverse effects across all endpoints studied, indicating that embryonic development was severely disrupted, and both locomotion and sensory function were impaired. However, at 25 mg/L of PNs, only locomotion and sensory function were significantly affected. The effects were insignificant in all examined endpoints at 10 mg/L of PNs. Transcript levels of several marker genes for neuronal function and eye development were suppressed after treatment. Exposure to fluorescent PNs showed that they accumulated in various organs including, the eyes, gills, blood vessels, gallbladder, gut, and lateral line neuromasts. Overall, this study suggests that short-term exposure to a high concentration of PNs can threaten fish survival by impairing embryonic development, locomotion performance, and mechanical sensory function.

Acute exposure to polystyrene nanoplastics impairs skin cells and ion regulation in zebrafish embryos.

The presence of nanoplastics in aquatic environments is a global problem. Accumulating evidence shows that nanoplastics can accumulate in fish and influence internal organs. However, it is still unknown if nanoplastics can impair skin cells (keratinocytes and ionocytes), which play critical roles in maintaining body fluid homeostasis. In the present study, zebrafish embryos were exposed to polystyrene nanoplastics (PS-NPs; 25 nm in size, at 0, 10, 25, and 50 mg/L) for 96 h to test the effects of PS-NPs on skin functions. After exposure to 50 mg/L, the survival rate, ion (Na+, K+, and Ca2+) contents, and acid/ammonia excretion by skin cells of embryos significantly declined. The apical structure of skin keratinocytes was damaged at 10, 25, and 50 mg/L. The number and mitochondrial activity of ionocytes were reduced at 25 and 50 mg/L. Reactive oxygen species (ROS) levels indicated by CellROX staining showed that both ionocytes and keratinocytes were under oxidative stress. PS-NPs reduced the mRNA expression of antioxidant genes (sod1, sod2, cat, and gpx1a), and promoted apoptosis-related genes (casp3a). Taken together, this study suggests that PS-NPs might suppress antioxidative reactions and induce oxidative stress, leading to mitochondrial damage and cell death of ionocytes, eventually impairing skin functions including ion uptake, pH regulation, and ammonia excretion.

Characterization and toxicology evaluation of low molecular weight chitosan on zebrafish.

Chitosan is suggested as no or low toxicity and biocompatible biomaterial. Digestion of chitosan to reduce molecular weight and formulate nanoparticle was generally used to improve efficiency for DNA or protein delivery. However, the toxicity of low-molecular-weight chitosan (LMWCS) towards freshwater fishes has not been well evaluated. Here, we reported the toxic mechanism of LMWCS using zebrafish (Danio rerio) liver (ZFL) cell line, zebrafish larvae, and adult fish. LMWCS rapidly induced cytotoxicity of ZFL cells and death of zebrafish. Cell membrane damaged by LMWCS reduced cell viability. Damaged membrane of epithelial cell in zebrafish larvae induced breakage of the yolk. Adult fish exhibited hypoxia before death due to multiple damages induced by LMWCS. Although the toxicity of LMWCS was revealed in zebrafish model, the toxicity was only present in pH < 7 and easy be neutralized by other negative ions. Collectively, these data improved a new understanding of LMWCS properties.