IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 88 Environment, Agriculture, and Forestry Tuesday, 25 August 2026 / Hall B+C significantly increased after wildfires, while the distribution of fluorescent components varied by sampling site. At the molecular level, wildfires enhanced the molecular heterogeneity of soil DOM. Among 1,103 identified CA formulas, only 174 (15.8%) were commonly present across all burned sites. These CAs were characterized by oxidized and unsaturated compounds with low MW and O/C ratios (<0.5). Notably, soil DOM shifted toward N-rich compounds, as wildfires consistently produced diverse heterocyclic N structures across all sampling sites. Chlorination of burned soil leachates enhanced toxic nitrogenous and brominated DBP formation, consistent with the fire-induced enrichment of organic N structures and inorganic bromide. While total DBP yields generally decreased, regulated carbonaceous DBP concentrations varied by soil origin. Our findings reveal that soil PyDOM across Mediterranean-type forest ecoregions is chemically heterogeneous yet shares N-rich pyrogenic molecular fingerprints. These alterations may complicate drinking water treatment by shifting DBP formation toward more concerning nitrogenous and brominated species. References 1. X. Cao, S. Li, H. Huang, et al. Wildfire impacts on molecular changes of dissolved organic matter during its passage through soil [J]. Environmental Science & Technology, 2024, 58(26): 11436−11446. 2. A. S. Wozniak, S. Mitra, A. I. Goranov, et al. Effects of environmental aging on wildfire particulate and dissolved pyrogenic organic matter characteristics [J]. ACS Earth and Space Chemistry, 2023, 8(1): 104-118. 3. H. Chen, A. T. Chow, X. Li, et al. Wildfire Burn Intensity Affects the Quantity and Speciation of Polycyclic Aromatic Hydrocarbons in Soils [J]. ACS Earth and Space Chemistry, 2018, 2(12): 1262-1270. 4. P.T. Justen, E.K. Jaynes, C. A. Beavers, et al. Impact of wildland-urban interface wildfires on drinking water: Urban structural ash is a source of precursors for toxic disinfection byproducts [J]. Environmental Science & Technology, 2025, 59(27): 14030-14040. Acknowledgement The project described in this work was supported by agence nationale de la recherche (ANR), France (Grant ANR-23CE34-0010-05).
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