Embryotoxicity of Polystyrene Microspheres of Different Sizes to the Marine Medaka Oryzias melastigma (McClelland, 1839)

Polystyrene microplastics effects on zebrafish embryological development: Comparison of two different sizes

Microplastics have become a great worldwide problem and it's therefore important to study their possible effects on human and environmental health. In this study, zebrafish embryos were used to compare two different sizes of polystyrene microplastics (PS-MPs), 1 µm and 3 µm respectively, at 0.01, 0.1, 1.0 and 10.0 mgL-1, and were monitored up to 72 h. Toxicity tests demonstrated that neither of the PS-MPs altered the embryos' survival and the normal hatching process. Instead, higher concentrations of both sizes caused an increase of the heart rate and phenotypic changes. The PS-MPs of both sizes entered and accumulated in the larvae at the concentration of 10.0 mgL-1 and the same concentration caused an increase of apoptotic processes correlated to redox homeostasis changes. The reported results give a realistic view of the negative effects of exposure to PS-MPs and provide new information on their toxicity, also considering their sizes.

Endocrine disruptor responses in the embryos of marine medaka (Oryzias melastigma) after exposure to aged plastic leachates

The issue of the additives leached from plastics has attracted widespread attention. More crucially, endocrine disruptor status for several leached additives has been established. However, little is known about the overall endocrine disrupting effects of aged plastic leachates. Therefore, the transcriptional responses of endocrine-related genes were assessed in the embryos of marine medaka (Oryzias melastigma), which were exposed to the leachates from aged plastics that were immersed into the simulated seawater (SW) or fish digest (FD). The results revealed that there was a great difference between the SW and FD leachates in the transcripts of endocrine-related genes. With the exception of cyp1a, all target genes had their transcripts potentially down-regulated by the FD leachates. Chgl (a biomarker for estrogens), pparβ (related to lipid metabolism), and cyp19a (related to sexual differentiation and reproduction) transcripts tended to be repressed by the SW leachates, while pparα, pparγ and cyp1a (mediating metabolism of xenobiotics) transcripts were stimulated. In addition, a redundancy analysis was carried out to determine the relationship between the leached additives and the transcriptional changes. However, the additives only partially explained the variation in the transcripts of endocrine-related genes (24.8%), indicating that other leached additives may have an impact on target gene transcription. This study provided molecular evidence of the aged plastic leachates' endocrine disrupting effects. Exploring the primary factors that affect the transcriptional alterations would require more research.

Ocean acidification enhances the embryotoxicity of CuO nanoparticles to Oryzias melastigma

Concerns are raised towards individual effects of ocean acidification (OA) and engineered nanoparticles (NPs) on marine organisms. However, there are scarce studies regarding nanotoxicity under OA conditions. We investigated the combined effects of OA (pHs, 7.70 and 7.40) and CuO NPs on the embryotoxicity of marine medaka Oryzias melastigma and the bioavailability of CuO NPs in embryos. The results showed that OA alleviated the aggregation of CuO NPs and promoted the dissolution of CuO NPs in seawater (increased by 0.010 and 0.029 mg/L under pHs 7.70 and 7.40, respectively). Synergistic effects of OA with CuO NPs on medaka embryos were observed as indicated by much higher mortality and oxidative damage. Importantly, the enhanced toxicity of CuO NPs to medaka embryos under OA conditions mainly originated from the higher bioavailability of particulate CuO (e.g., 30.28 mg/kg at pH 7.40) rather than their released Cu²⁺ ions (e.g. 3.04 mg/kg at pH 7.40). The weaker aggregation of NPs under OA conditions resulted in higher penetration of individual particles (or small aggregates) into embryos through the micropyle and chorionic pores, causing enhanced bioavailability of NPs. The obtained results provided underlying insights into understanding the risk of NPs to marine ecosystem under OA conditions.