Description

Tire tread particles (TTP) are microplastics (< 5 mm) released from tire abrasion against road surfaces. TTP accumulate on roads in dry weather and are transported into surface water via atmospheric deposition and stormwater runoff. Like other microplastics, TTP are persistent in the environment and may transport various environmental contaminants. Previous research has shown that tires contain known toxic chemicals, such as 6PPD (antiozonant), plasticizers, and polycyclic aromatic hydrocarbons (PAHs). There is a need to better understand the behavior of TTP in water under realistic environmental conditions including sunlight exposure. The present study investigated the leaching of chemicals from TTP in photoirradiated (sunlight) or nonirradiated (dark) laboratory-made freshwater, and the photodegradation of dissolved constituents from TTP, or leachates, under photoirradiation. To quantify leachates, dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations were measured. DOC and TDN range from 0.47 to 1.04 mg DOC/g TTP and 0.09 to 0.38 mg TDN/g TTP, depending on leaching time and presence or lack of photoirradiation. Leaching and photochemical degradation rates were also estimated by measuring fluorescence intensities over time. Fluorescence spectroscopy is a non-destructive method used in water quality studies to monitor organic compounds with fluorescent properties and collect three-dimensional excitation emission matrices (3D EEMs). Some fluorescent compounds were resistant to photodegradation, resulting in a zero order decay rate of 0.04 ± 0.0007 Raman Units (RU)/hour and first order decay rates that range from 0.015 to 0.017/hour. Others were photolabile and experienced double exponential decay, resulting in photolabile decay rates that range from 1.2 to 1.8/hour and photo-semilabile decay rates that range from 0.003 to 0.01/hour. Additionally, there are efforts in assessing the fluorescent spectral signatures of TTP-specific compounds or classes of compounds and comparing them to TTP leachates. This will improve the use of 3D EEM spectroscopy in detecting compounds from TTP. Overall, results will aim to support the advising of policy changes in California regarding the regulation of chemicals and materials used in tire manufacturing.