Abstract: This research constructed small scaled fire-suppression experimental platforms emulating three archetypal fire scenarios-structural (building) fires, electric bicycle fires, and diesel fuel fires-to comprehensively characterize aqueous-phase properties, acute toxicity, and genotoxic potential of firefighting runoff under divergent extinguishment strategies. The objectives were to provide data support for exploring the disposal methods of firefighting runoff and the formulation/revision of relevant standards. The results revealed that fire-extinguishing runoff universally exhibited weakly acidic to circumneutral (pH value 6.4~7.4), concomitant with elevated organic burdens. Notably, total organic carbon (TOC) concentrations in structural fire runoff peaked at 3 722.5 mg/L. Toxicological quantification demonstrated that 4-nitroquinoline-N-oxide (4-NQO) equivalency concentrations in runoff (12.5~75.7 μg/L) exceeded groundwater and surface water baselines (1~520 ng/L) by orders of magnitude. Runoff derived from Class A foam deployment during structural fire suppression elicited 63.5% luminescent bacteria (Vibrio fischeri) inhibition at merely 0.1% dilution. Moreover, both acute toxicity and genotoxicity of the firefighting runoff increased with extinguishing duration, indicating that continuous scouring of combustibles enhanced the ecological toxicity of the runoff. Class A foam extinguishing agents primarily contributed to acute toxicity, while aqueous film-forming foams (AFFF) predominantly mediated genotoxic effects. These results suggest that during large-scale fires, while ensuring firefighting and rescue effectiveness, efforts should be made to minimize the application time of foam concentrates and enhance the collection and treatment of firefighting wastewater to mitigate the potential ecological toxicity risks posed by firefighting runoff.

Key words: firefighting runoff, building fire, water quality characteristics, toxicity risk