Wildfire mobilization of arsenic into water resources: A scoping review of current literature

Increasing wildfire activity poses a threat to water resources via the mobilization of hazardous materials such as arsenic (As). While As contamination of water resources is well studied, the fate and transport of As impacted by wildfire are not well characterized. This literature review synthesizes studies addressing the questions of: (1) Does fuel type influence how As is mobilized by wildfire?; (2) What mobilization pathways are most common for As when impacted by wildfires?; and (3) How are surface and groundwater As concentrations impacted by wildfire mobilization of As? To address this goal, articles were queried using Boolean search strings in Google Scholar, PubMed, and Web of Science and screened for relevance using PECO (Population, Exposure, Comparator, and Outcome) criteria. Twenty articles met the criteria, showing wildfire mobilization of As and changes in concentrations or loading of As to surface or groundwater. The majority of studies (16 of 20) showed an increase or a likely increase in As in waterbodies post-wildfire. Runoff to surface water was by far the dominant pathway. Average values typically did not exceed drinking water standards, although six studies reported instances where this occurred, with one reporting exceedances in treated drinking water itself. The largest value of dissolved As reported across surveyed literature (70 μg/L) was measured downgradient of a legacy mining operation post-wildfire. Higher values were also observed downstream of burned agricultural or urban areas, illustrating how human activities concentrate As, which can then be subsequently mobilized by wildfire. In contrast to surface water, groundwater impacts were inconsistent in the limited literature, with one study showing an increase in post-wildfire As, while the other two studies showed no-change. Overall, these results suggest communities may need to test drinking water supplies for As following wildfire, especially in cases where mining, agricultural, or urbanized areas are burned.