BOOK OF ABSTRACTS 85 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Tuesday, 25 August 2026 / Hall B+C Environment, Agriculture, and Forestry SL37 Impact Of Wildland-Urban Interface Wildfires on Drinking Water: Urban Structural Ash Is a Source of Precursors for Toxic Disinfection Byproducts Susan D. Richardson, Patrick T. Justen, Erin Katie Jaynes, Coley A. Beavers, Talal Alshehri, Mahbub Alam, and Mohammed Baalousha 1 Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, 29208 2 Center for Environmental Nanoscience and Risk, Department of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, SC, 29208 Wildland-urban interface wildfires are increasing in frequency worldwide with negative implications for drinking waters due to alteration of organic matter, which enters waterways following rain events, flows downstream to water treatment plants, and forms disinfection byproducts (DBPs). Previous research focused on vegetative wildfires with nothing known about DBPs from wildland-urban interface wildfires. In this study, the water-extractable fraction of seven structural ashes and two vegetation ashes from the 2020 LNU Lightning Complex Fire in California, were treated with chlorine and chloramine. Formation of 65 DBPs was measured by gas chromatography-mass spectrometry. Non-target analysis revealed highly reactive aromatic precursors and additional DBPs. Three urban structural ash samples formed higher levels total levels of DBPs and three formed lower levels, compared to the vegetation ashes. Calculated cytotoxicity was higher in chlor(am)inated structural ash samples than vegetation ash, due to formation of toxic brominated, iodinated, and nitrogenous DBPs. Chloramination reduced total DBP formation and calculated toxicity vs. chlorination, except where iodinated DBP formation was high. Structural ash leachates had lower dissolved organic carbon levels than vegetation ash and contribute lower levels of DBP precursors. However, these precursors may increase the toxicity of drinking water due to a shift towards more toxic DBP species.
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