Photodegradation and Heterogeneous OH Oxidation Kinetics and Product Analysis of Aerosolized Triclosan Mixed with NaCl and Humic Acid

Triclosan, an antimicrobial agent incorporated in personal care and consumer products, is used to prevent bacterial contamination and material biodegradation. However, various studies have shown that triclosan exhibits toxic effects to aquatic species, persists in the environment, and poses as an endocrine disruptor. Triclosan can be leached from untreated wastewater and wastewater treatment plant effluent into ocean surface water as a contaminant. Consequently, it can become aerosolized in sea spray aerosol (SSA) and undergo degradation in the atmosphere to produce potentially more toxic transformation products, such as dichlorodibenzo-p-dioxin and chlorophenols. To understand the lifetime of triclosan in the aerosol phase in SSA, this research focuses on quantifying the kinetics and degradation lifetimes of triclosan with respect to heterogeneous oxidation by hydroxyl radicals (OH) and photosensitization reactions involving chromophoric dissolved organic matter (CDOM) mixed with inorganic salts that coexist in SSA. A potential aerosol mass oxidation flow reactor (PAM-OFR), used to simulate aerosol aging, is coupled with an extractive electrospray ionization high-resolution time-of-flight mass spectrometer (EESI-HR-ToF-MS) to study triclosan degradation kinetics and its transformation products in the aerosol phase in near real time. Results indicate that the reactive uptake of OH by single-component triclosan aerosol proceeds with a diffusion-corrected uptake coefficient of 0.15 ± 0.04. In the presence of humic acid, a CDOM proxy, the OH reactive uptake coefficient decreased to 0.09 ± 0.04, suggesting that CDOM inhibits triclosan degradation in the presence of OH radicals. Furthermore, the addition of the inorganic salt, NaCl, to the triclosan system increased the effective uptake coefficient to 0.29 ± 0.08. 2,8 dichlorodibenzo-p-dioxin (2,8 DCDD), a toxic transformation product, was potentially detected by the EESI-HR-ToF-MS in the aerosol phase indicating photodegradation as the major degradation pathway of triclosan. The half-life of triclosan in the aerosol phase with respect to heterogeneous oxidation by OH is estimated to be 18.63 ± 4.53 days. This project aims to gain a better understanding of the effects of photodegradation and OH radical heterogeneous oxidation on the lifetime of triclosan in the aerosol phase, the influence of added photosensitizer and inorganic salt, and potentially the contribution of triclosan degradation to the formation of more toxic transformation products