Atmospheric deposition of arsenic and selenium in ombrotrophic peat bogs

Abstract
Peat bogs serve as faithful archives of atmospheric Pb deposition, and there is growing evidence that they preserve reliable records of atmospheric Hg and Cu deposition as well. Far less is known about As and Se in peat, despite their environmental relevance, because there have been so few studies; the lack of study probably is due partly to the difficulties associated with the measurement of these elements at low concentrations in complex matrices. In peat which is contaminated with anthropogenic As (e.g. bogs near smelters), and in minerotrophic peat which may be naturally enriched with this element, As can be measured in solid samples containing 1 to 100 or more ppm using XRF or INAA. Similarly, Se can be measured in blanket peats from maritime locations using either of these methods, because marine emissions of DMSe give rise to elevated Se concentrations (1 to 10 ppm) in these peats. However, in pre-anthropogenic peats from continental bogs, the concentrations of As and Se are far lower ( <0.1 ppm), and only recently bas As been reliably measured in peat samples at these levels (Krachler et al., 2002). Clearly, accurate and precise measurements are needed both to describe the geochemical cycles of these elements, and for the reconstruction of atmospheric metal deposition rates. Thus, there is a real need to develop robust and reliable analytical methods with low detection limits for the determination of As and Se in ombrotrophic peat.