Pyrogenic Remobilization And Transport Of Toxic Metals

The effects of wildfires and deforestation on the remobilization of persistent inorganic contaminants are not completely understood. In forests, trace metal contaminants (e.g., lead) are sequestered in terrestrial sediment, soil organic matter, and vegetation, where they are relatively immobile. However, the combustion of soil organic matter and vegetation releases these contaminants in more labile forms. The associated deforestation and accelerated weathering increase the mobilization of trace metals from forests by simply increasing rates of erosion. These remobilized contaminants are transported to water bodies, increasing the loads of contaminants in these aquatic systems.This project used analyses of trace metal inventories and lead isotopic compositions to study the remobilization and transport of toxic metals with respect to forest fires and deforestation associated with land-use. Chapters 2 and 3 present the results of investigation of the pyrogenic remobilization of trace metals at two contrasting sites in California: the relatively pristine Santa Barbara and the more populated and industrialized Los Angeles Metropolitan Area. The results indicate that wildfires are increasing the remobilization and transport of persistent contaminants (e.g., lead) in both study areas. Chapter 4 presents the results of a similar study conducted in Chile, in which geochronology and lead isotopic compositions were used to investigate the impact of historic (about a century ago) slash and burn practices on the deposition of trace metals in Lake Thompson, Patagonia. The results show a positive relationship between fire size and the flux of metals to the lake. These findings are significant because the frequency and intensity of wildfires are expected to increase with global climate change. Chapter 5 presents the results of a study in which contaminant remobilization was linked to land-use practices by characterizing temporal changes in the flux of trace metals to Lake Tanganyika, Africa. The results indicate that deforestation is the predominant factor accelerating trace metals transport to the lake. This land-use associated remobilization of contaminants is projected to increase with population growth and industrialization in Africa

Trace Metal Inventories and Lead Isotopic Composition Chronicle a Forest Fire’s Remobilization of Industrial Contaminants Deposited in the Angeles National Forest

<div><p>The amounts of labile trace metals: [Co] (3 to 11 µg g⁻¹), [Cu] (15 to 69 µg g⁻¹), [Ni] (6 to 15 µg g⁻¹), [Pb] (7 to 42 µg g⁻¹), and [Zn] (65 to 500 µg g⁻¹) in ash collected from the 2012 Williams Fire in Los Angeles, California attest to the role of fires in remobilizing industrial metals deposited in forests. These remobilized trace metals may be dispersed by winds, increasing human exposures, and they may be deposited in water bodies, increasing exposures in aquatic ecosystems. Correlations between the concentrations of these trace metals, normalized to Fe, in ash from the fire suggest that Co, Cu, and Ni in most of those samples were predominantly from natural sources, whereas Pb and Zn were enriched in some ash samples. The predominantly anthropogenic source of excess Pb in the ash was further demonstrated by its isotopic ratios (<i>²⁰⁸Pb/²⁰⁷Pb: ²⁰⁶Pb/²⁰⁷Pb</i>) that fell between those of natural Pb and leaded gasoline sold in California during the previous century. These analyses substantiate current human and environmental health concerns with the pyrogenic remobilization of toxic metals, which are compounded by projections of increases in the intensity and frequency of wildfires associated with climate change.</p></div

Analytical (instrumental) precision for lead isotopic compositions.

<p>Analytical (instrumental) precision for lead isotopic compositions.</p

Analytical (instrumental) precision.

<p>Analytical (instrumental) precision.</p