Effects of exposure to Microplastics and Endocrine Disrupting Chemicals in zebrafish embryonic development

As the global production of plastics accelerates, the ubiquitous presence of microplastics (MPs) has emerged as a global concern. A massive number of plastic-derived pollutants are released into the environment, and these are potentially dangerous for human and wildlife health. Thus, besides MPs direct effect on organisms, these could become vectors of a wide range of contaminants, such as bisphenol A (BPA), leading to synergistic effects. Exposure to MPs and BPA has been linked to an increased risk of impaired fertility and altered hypothalamus-pituitary-gonadal function in humans. Current knowledge about possible adverse effects on development of these pollutants is still scarce. In this study, we focused on 5 and 0.5 μm polystyrene-MPs (PS-MPs), both pristine and functionalized (-COOH), that may mimic environmentally aged MPs, and BPA. We assessed the impact of MPs and BPA exposure on zebrafish embryos at morphologic and molecular level. To this purpose, we analysed embryos survival, hatching, heartbeat rate, chorion interaction, and MPs uptake. Moreover, since sexual maturation and reproduction are controlled by Gonadotropin-Releasing Hormone (GnRH) expressing neurons, a transgenic GnRH3:EGFP fish strain was used to assess alterations in GnRH3 neuron number and axonal pathfinding. Finally, GnRH and associated-gene expression were evaluated. Results suggest that PS-MPs are not toxic in vivo, adhere to the external chorion and accumulate in intestine and gills. PS-MP exposure causes a reduction in the number of GnRH3 neurons and reduces the expression of reproduction marker genes. Further in-depth investigations are needed to evaluate metabolic and developmental effects of contaminant-associated MPs.