Microrubber (MR) encompasses all tire-related particles in the microscale and has recently been acknowledged as a microplastic class. While tire particles have been entering the environment since the introduction of rubber tires for vehicles, the concern regarding tire wear particles (TWP) as an environmental contaminant is relatively new. Recent studies have examined physical and chemical toxicity of MR 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 examines the chronic toxicity of crumb rubber (CR) particles to the estuarine fish species, mummichog (Fundulus heteroclitus), under a pulsed-dosing regime at environmentally relevant concentrations. Organisms were individually exposed to CR (38 – 355 µm in size) at concentrations up to 0.25 g/L every five days for 42 days total. Previous research has demonstrated that adult mummichogs can survive at concentrations up to 6.0 g/L CR. Therefore, the focus of the present study was on sublethal effects. Bile fluorescence was measured as an indicator or exposure to polycyclic aromatic hydrocarbons (PAHs) from CR. Oxidative stress was measured through the TBARS assay, free glutathione (GSH), and oxidized glutathione (GSSG). DNA damage was measured through the formation of 8-hydroxy-2’-deoxyguanosine (8-OHdG). Initial results indicate an increase in bile fluorescence as CR concentration increases, suggesting an increase in exposure to PAHs from CR which agrees with previous findings from our lab. Preliminary data for DNA damage shows greater DNA damage at higher CR concentrations. We hypothesize that sublethal effects such as increases in oxidative stress biomarkers and DNA damage result from long-term exposure to CR, even at low concentrations. The results from biomarker analyses will be discussed as well as overall conclusions on chronic effects of CR exposure to mummichogs.