ENVIRONMENTAL- AND HEALTH-HAZARDS CHARACTERIZATION OF ASH AND SOILS FROM WILDLAND AND RESIDENTIAL AREAS BURNED BY 2007–2009 SOUTHERN CALIFORNIA WILDFIRES

From 2007 to 2009, wildfires burned hundreds of thousands of acres in southern California, including portions of suburban residential areas from Santa Barbara to south of San Diego. We have characterized ash and burned soil samples from the 2007 Harris, Witch, Ammo, Santiago, Canyon and Grass Valley fires, the 2008 Tea fire, and the 2009 Jesusita fire. Samples from both burned wildland and residential areas were collected prior to rainfall. Water leach tests indicate that more heavily combusted residential and wildland white ashes produce highly alkaline, caustic leachates with pH as high as 13. Typical wildland ash (with intermixed white ash and less heavily combusted black ash) produces somewhat less alkaline and caustic leachates. Simulated lung fluid leaches of the ash produce similar, though less extreme, shifts in pH as those from water leaches. Bulk residential ash samples contain elevated levels of As, Pb, Sb, Cu, Zn, and Cr compared to wildland ash; some of these levels can substantially exceed average US soil levels and EPA residential soil remediation guidelines. Speciation analyses indicate that a portion of the Cr is in the more soluble, bioaccessible, and toxic hexavalent form. Limited analyses of residential ash document somewhat elevated levels of chlordane (a legacy pesticide) and naphthalene compounds but few other organohalogens or polycyclic aromatic hydrocarbons. Scanning electron microscopy reveals anthropogenic materials in the residential ash (e.g. glass fibers, metal particles) and a preponderance of inhalable- and respirable-size particles in wildland white ash. The first rainfall to hit a burned area, depending upon the burn intensity and rainfall intensity and duration, would be expected to produce alkaline, potentially caustic runoff that could be detrimental to aquatic organisms, with alkalinity diminishing over time and with distance downstream. Runoff from residential areas could contain some heavy-metal and organic contaminants that could be taken up by aquatic organisms. The abundant respirable, caustic particles in ash and the elevated heavy metals in residential ash underscore that appropriate respiratory, eye, and skin protection should be worn by those working in burned areas.