Multiphase Oxidation of Harmful Algal Bloom Toxin Aerosols: Implications for their Atmospheric Lifetimes, Fates, and Toxicity

Harmful algal blooms (HABs), intensified by climate change and eutrophication, occur when photosynthetic organisms proliferate and release toxic metabolites (“HAB toxins”) into the water column. HAB toxins can be ejected from the water surface into the atmosphere through bubble bursting during wave action. Aerosolized HAB toxins can be transported over long distances inland, exposing downwind communities to their inhalation hazards. Previous epidemiological and toxicological studies have linked this exposure to various negative respiratory health outcomes. While previous research has mostly focused on the potential for long-range transport and inhalation toxicity of someHAB toxins, their atmospheric processing remains a critical knowledge gap. Specifically, the multiphase oxidation of HAB toxin aerosols by ubiquitous atmospheric oxidants such as gas-phase hydroxyl radicals (•OH) and ozone (O3) are currently understudied and poorly understood. This oxidative processing can fundamentally alter the atmospheric lifetimes, fates, chemical composition, and inhalation toxicity of aerosolized HAB toxins. Thus, enhancing our knowledge of the multiphase oxidation of HAB toxin aerosols is essential for assessing their evolving public health threat.This project addresses existing knowledge gaps by systematically investigating the multiphase •OH and O3 oxidation of HAB toxin aerosols and its consequent impact on their toxicological characteristics. The project focuses on five prevalent HAB toxins: microcystin LR, saxitoxin, okadaic acid, cylindrospermopsin, and brevetoxin PbTx 2. The overarching goal is to elucidate the chemical transformations of HAB toxin aerosols during oxidation, quantify how aerosol matrices modulate this process, and determine the resulting evolution in their inhalation toxicity. Experiments will be performed using an oxidation flow reactor to simulate atmospheric multiphase oxidation, during which HAB toxin-containing sea spray or lake spray aerosol proxies are exposed to gas-phase •OH and O3. Ultra-performance liquid chromatography coupled to high-resolution mass spectrometry will be used to measure reaction kinetics, identify and track the formation of oxidation products, and elucidate reaction mechanisms. Scanning electron microscopy with energy dispersive X-ray spectroscopy will be used to characterize oxidative changes in aerosol morphology and mixing state. To determine how multiphase oxidation modulates the inhalation health risks of HAB toxin aerosols, composition changes will be linked to evolution in their toxicological responses, which will be evaluated using acellular (dithiothreitol) and cellular (human bronchial epithelial BEAS-2B cells) assays. Project findings will provide the fundamental data needed to refine atmospheric exposure models and enable accurate science-based public health risk assessments to protect communities near HAB-prone waterbodies.