Description

Tire wear particles (TWP) are small micro- or nano-particles resulting from the friction of tire tread against roads. These microplastics have been found in waterways, usually through rain and wind, posing a potential risk to exposed aquatic life. The goal of this project was to assess the toxicity of chemical leachate from TWP and how it may affect the health and development of aquatic life, like Danio rerio, zebrafish. We also wanted to determine if solar-simulated or dark conditions intensified the effects of TWP, considering processes like photodegradation, photochemical oxidation, etc. occur in sunlight. For this project, zebrafish were exposed to a TWP solution, treated in solar-simulated or dark conditions, of 0% (light), 0% (dark), 25% (light), 25% (dark), 50% (light), 50% (dark), 75% (light), or 75% (dark) from 0 days post fertilization (dpf) to 4 dpf. On days one through three, the mortality rate was noted and each vial or petri dish was refreshed. On the fourth day of exposure, the overall survival rate and any physical defects were noted and imaged through light microscopy. From TWP exposure, there was an increase in mortality, yolk sac edema, impaired hatching, and craniofacial malformations, and a decrease in swim bladder inflation for all the exposed light and dark groups. Pericardial edema increased for the 25% and 75% dark groups and for the 50% and 75% light groups. Spinal deformities also increased for the 50% and 75% light groups and the 50% dark group. Ethyoxyresorufin-O-deethylase (EROD) activity, a visual measurement of CYP1A metabolic activity, was also assessed in the gut, liver, and brain by exposing the embryos to 7-ethoxyresorufin (7-ER). The EROD activity conveyed an increase in CYP1A activity in the liver and brain regardless of light status and a decrease in gut CYP1A activity in both light and dark groups. Interestingly, TWPs decreased EROD activity in the gut. Overall, these results suggest a disruption of embryonic development in zebrafish when exposed to TWP and an increase in liver and brain metabolism of TWP due to potential damage in the gut microbiome, regardless of solar simulated or dark conditions.