Microbial risk from wildfire residues

Abstract

Based on climate models, wildfire frequency is likely to increase by more than 15% based by 2050. While wildfire affects human lives and economy, it can also change the surface water quality by supplying the burned residues to receiving waters via stormwater runoff. This work presents the results that link wildfire residue geochemistry to bacterial viability or microbial health risk. Batch experiments were conducted by exposing Escherichia coli to pre and post-wildfire residues in stormwater. Results showed that water chemistry and particle geochemistry drastically affected bacteria viability. In the presence of sediments without wildfire residues, E. coli grew 118 times its initial concentration. In contrast, E. coli growth diminished to 25 and 8 times its initial concentration when exposed to wildfire sediments and black carbon residues, respectively. Analyzing change in nutrient availability in stormwater with and without wildfire residue, we showed that wildfire residues might adsorb nutrients and create conditions that limits bacterial growth. Live-dead assays on bacterial cells attached to wildfire residues further reveal the link between bacteria inactivation and surface chemistry of the wildfire residues. These results suggest that the deposition of wildfire residues on sediments and surface water can alter their natural microbiome. Injecting bacteria with and without wildfire residues in sand columns—a model for subsurface soil, we showed that these residues have limited impact on microbial transport through subsurface soil. Overall, change in microbial composition of water and soil affected by wildfire residues should be monitored to access the long-term health risk of wildfire.