Chemistry Seminar - Annastacia Stubbs, PhD Candidate

Title

Pollutant Photodegradation Kinetics in Seawater and Sea Ice, and Exposure to Bleach Emissions after Disinfecting Indoor Surfaces

Abstract

This talk covers two separate projects: first, we investigate reasons for different anthracene photodegradation kinetics in aqueous and frozen saltwater compared to freshwater. Next, we determine near-source concentrations of hypochlorous acid (HOCl) during bathroom surface cleaning with a bleach-based product.

Anthracene is a polycyclic aromatic hydrocarbon (PAH), which are ubiquitous in the environment, and are considered priority pollutants in Canada and the US due to their associated health effects and toxicity to aquatic life. Oxidation processes in the environment, including photodegradation, often form reaction products that are more toxic than the parent PAH. An understanding of PAH chemical reactivity in multiple environmental compartments (e.g., air, water, soil) is therefore necessary to determine their fate and exposure risks. This is complicated by technical challenges associated with measuring reaction kinetics in atmospherically relevant samples. We observed faster anthracene photodegradation rate constants in seawater and in sea ice proxies compared to liquid and frozen freshwater samples. We have proposed mechanisms to explain these enhancements in salty aqueous environments. This research helps us better understand and predict anthracene’s and potentially other organic pollutants’ environmental fate.

People spend majority of their time indoors and the activities we do, such as cleaning surfaces, can affect indoor air quality. Bleach is a commonly used disinfectant which releases HOCl, which can negatively affect human health directly and indirectly. Room-averaged HOCl concentrations have been measured during surface cleaning, but concentrations near to the source of application, which is most likely where a person’s face would be during cleaning, have not been reported. We measured HOCl concentrations at different distances from the application source during cleaning with a bleach-based product. HOCl levels near the source were more than 10 times greater than room-averaged levels, suggesting that anyone close to the source may experience higher exposure to HOCl than what is expected based on existing reports of room averaged concentrations.