LaPlaca SB, Rice CD, van den Hurk P. 2022. Chronic toxicity of tire crumb rubber particles to mummichog (Fundulus heteroclitus) in episodic exposures. Under review. Available at http://dx.doi.org/10.2139/ssrn.4070229
Microrubber (MR) encompasses all tire-related particles in the micro-scale and has recently drawn increased attention as a subclass of the broader group of microplastics. While tire particles have entered the environment since the introduction of rubber tires, concern regarding tire wear particles (TWP) as an environmental contaminant is relatively new. Recent studies have examined acute toxicity of MR particles and leachates to a variety of organisms. However, there is a lack of information on the long-term effects of tire particle exposure under environmentally realistic conditions. The current study examined the chronic toxicity of crumb rubber (CR) particles to the estuarine fish species, mummichog ( Fundulus heteroclitus ) under episodic exposures at environmentally relevant concentrations. Immunohistochemistry (IHC) of fish gill, intestine, and liver was performed to assess CYP1A induction in these organs. Bile fluorescence was measured as an indicator of exposure to polycyclic aromatic hydrocarbons (PAHs) from CR. DNA damage was measured through the formation of 8-hydroxy-2’-deoxyguanosine (8-OHdG) together with other oxidative stress measures as lipid peroxidation (TBARS assay), and free and oxidized glutathione (GSH/GSSG) concentrations. Upregulation of CYP1A in gill, intestine, and liver was observed especially in gill filaments and general vasculature. Increased bile fluorescence demonstrated exposure to aromatic compounds. Data for DNA damage indicated greater plasma 8-OHdG concentrations as a result of increased DNA repair. Malondialdehyde (MDA) production was decreased and total GSH was increased at higher concentrations of CR. It appeared that under long-term repeated dosing, antioxidant systems in mummichog were upregulated to deal with exogenous stressors released by the CR particles. Combined, these data demonstrate that fish exposed to tire crumb rubber particles illicit significant biomarker responses under environmentally relevant CR concentrations, but induced antioxidant and detoxification pathways may prevent mortality and serious physiological effects in F. heteroclitus when exposed to environmentally relevant concentrations of CR.