Occurrence of benzene polycarboxylic acids in ash and streamwater after the Cameron Peak Fire
Figure 1. Cameron Peak Fire (red) and sampling sites within the CLP watershed. The inset shows the fire perimeter within the national forest (green).
The threat of wildfires to natural resources and water supplies is growing globally. Fueling these wildfires are combustion reactions which create a suite of organic compounds that are frequently detected in air, ash, soil, and water samples. Understanding the source and fate of combustion-related compounds requires an evaluation of chemicals that are both dissolved in and mobilized by water during storm events. Combustion of vegetation and surface organic soil layers by extreme wildfires exposes burned landscapes to soil erosion and alters how watersheds regulate water supplied to both aquatic habitats and downstream use.
In addition to short term, postfire responses, loss of upland and riparian vegetation, and rearrangement of stream and floodplain geomorphology alter biogeochemical processes that regulate nutrients (such as nitrogen and phosphorus), metals, and organic matter retention and losses over longer timeframes. Highly variable wildfire behavior, coupled with varying vegetation, landscape, and hydrologic factors, complicates anticipation of postfire surface water and drinking water quality.
Intense rainstorms over recently burned areas, although unpredictable, determine the watershed responses, which affect downstream drinking water treatment plants. Benzene polycarboxylic acids (BPCAs) include benzene, naphthenic, and biphenyl polycarboxylic acids. BPCAs were measured in streamwater samples for their occurrence in the watersheds, and numerous related compounds were also detected. BPCAs were detected following storm events but were absent from unburned sites and occurred at lower levels during nonstorm conditions. The most concentrated and abundant BPCA in burned samples (1,2,4-benzene tricarboxylic acid) was absent in unburned samples and thus may potentially serve as a tracer of wildfire impacts on water quality. Ash collected immediately following the fire contained the same suite of compounds as streamwater samples. The results from this study showcase the complex impacts that wildfires can have on water quality. This analysis confirms the presence of 14 BPCAs that have commercial standards, along with associated compounds. There is no evidence that they are toxic to humans, although BPCAs may be present at high postfire concentrations in aqueous systems. Nevertheless, additional work is warranted to better understand the potential human and environmental health effects of postfire BPCAs in surface water.