POST-FIRE TRACE ELEMENT ACCUMULATION IN SEDIMENT AND SURFACE WATER OF THE WOOLSEY WILDFIRE AREA

In an environment with growing population climatic uncertainty, wildfires affect larger populations as more people share less land. Additionally, urbanization has expanded to natural areas that are historically resilient against seasonal fires. The Woolsey fire of August 2018 claimed destroyed 1,600 structures in Los Angeles and Ventura Counties. The Woolsey fire took place in a relatively wild region close to a major metropolitan area. Our study found detectable concentrations of trace elements and certain elements with higher concentrations near burned anthropogenic structures.

We measured water and sediment samples collected in the area of the Woolsey fire data ten months post-incident. The procedure involved collecting sediment and stream water samples from burned and unburned areas, near and away from structures. Samples were filtered, acidified and diluted, then analyzed for dissolved metals by Agilent 8900 ICP-QQQ-MS using EPA standards.

Previous environmental inventories of trace metals in burned areas (Abraham et al., 2017, Water Air Soil Pollut v. 228) Burton et al., 2016, PLoS ONE v. 11) found elevated concentrations of Cu, Pb, Ni and Zn in ash from burned residences rather than wildland areas. Our data show elevated Cr, Mn, Zn, Ni, Cu, Co, and Pb in the burned areas compared to non-burned. In proximity to burned structures, concentration of Cr, Zn, Ni, Cu, along with Pb, As, Ag, and Sb are high relative to areas with no structures (findings similar to those from the ‘09 Station Fire). Concentrated As is thought to be liberated from chromated copper arsenate (CCA) treated wood found in decks and foundations (e.g., Burton et al. 2016). With discontinued use of CCA lumber after 2004, it would appear that the As is a legacy effect of earlier construction. Elevated concentrations of Pb, Zn, Ag, and Sb are speculated to be linked to combustion of various manufactured metal products from galvanized metals and plumbing, to solders and wiring. Our water samples near burned areas contain notable concentrations of trace elements mentioned. Understanding the mobilization of trace metals and other dissolved solids in post-burn areas will have implications for environmental policy and urban planning. The Woolsey Wildfire’s historic proportions and urban-adjacent setting make it an important case study.