Molecular-Level Perturbations of Dissolved Organic Matter Driven by Episodic Firecracker Residue Leaching

Firework festivities are widely associated with transient atmospheric pollution, yet postcombustion firecracker residues remain an overlooked source of environmental contamination. These residues, accumulated in riparian and lakeshore zones due to fire safety regulations, can continuously release pollutants into adjacent waters via leaching. However, their effects on dissolved organic matter (DOM) in aquatic systems remain poorly understood. Here, we examined DOM responses to leaching of firecracker residues in river, lake, and ultrapure waters using optical and high-resolution mass spectrometry (HRMS) analyses. Firecracker residues released DOM enriched in low-molecular-weight, sulfur-containing, and aliphatic compounds, resulting in decreased molecular weight, oxidation state, and unsaturation in natural waters. In parallel, aromatic and highly unsaturated DOM was selectively removed, indicating coupled release-adsorption processes. The extent of DOM changes induced by firecracker residues strongly depended on the initial water chemistry, with higher conductivity suppressing DOM release, whereas humic-rich waters promoted greater molecular redistribution. Our findings reveal that these solid-phase residues transform episodic festive celebrations into extended postevent perturbations in aquatic biogeochemistry. Recognizing firecracker residues not merely as physical litter, but as geochemically active drivers of DOM dynamics, is essential for managing aquatic systems affected by intensive festive activities.