Digestion of epiphytic lichens for analysis by ICP-MS, as applied to monitoring atmospheric heavy metals

Tucker, Jocelyn Ann (2003) Digestion of epiphytic lichens for analysis by ICP-MS, as applied to monitoring atmospheric heavy metals. Masters thesis, Memorial University of Newfoundland.

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Abstract

Lichens are excellent biomonitors. This study was undertaken to develop and refine a partial digestion procedure for lichen, suitable for ICP-MS analysis of trace elements, for the purpose of environmental monitoring. The developed digestion method consisted of a series of alternating dry and wet ashings utilizing nitric acid and hydrogen peroxide. Acceptable ICP-MS data were obtained for the following suite of elements: Mg, P, Ca, Mn, Co, Zn, Sr, Ba, V, Cr, Fe, Cu, Rb, Cd, Sb, Cs, and Ce. The application of the procedure to lichens from different sites indicated that sites could be distinguished by their trace element concentrations; the elements with differences included elements of environmental interest such as V, Zn, and Cu. The concentrations determined by this research for Newfoundland lichens were generally much lower than those reported by other researchers. The digestion procedure was also applied to different lichen species (Alectoria sarmentosa, Bryoria sp., and Cladonia alpestris) collected at the same site. It was found that different species yielded different trace element information, thus direct comparisons cannot necessarily be made. Digestion residues were examined by SEM-EDX to determine general compositions. The majority of these residual particles had a high silicon content, with varying amounts of other elements, particularly aluminum and potassium; these minerals were silicates, likely to be quartz, feldspars, olivines, garnets, micas, and/or clay minerals. Differences in concentration (as determined by ICP-MS) were observed in lichen samples collected from the same site in consecutive years. Some elements displayed differences between ICP-MS Runs, likely due to sample inhomogeneity. Other researchers have found that elemental concentrations can differ between species, that some elements (e.g. Cr, Fe, Ni, Cu, Zn) have higher concentrations in more polluted areas, and that the levels of some anthropogenic pollutants decrease with distance from the source; each of these points support the findings of this study.

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