Environmental pollution monitoring using lichens as bioindicators: a micro-PIXE study

Lichens are known to be very good bioindicators of environmental pollution. Epiphytic species growing on the bark of trees and shrubs are often used in assessing levels of air pollution in urbanized areas. Despite their important role in bioindication, there is still little information available on certain aspects of the physiology of lichens, such as elemental distribution within their thalli. Concentration of elements in selected parts of epiphytic lichens could indicate possible sources of pollution—either from the atmosphere or from other sources. Therefore, elemental microanalysis allows more accurate air pollution studies compared to bulk (macro) analysis. Micro-particle induced X-ray emission (PIXE) is a suitable technique that can be employed for studies of elemental distribution in lichens, with satisfactory detection limits (Clark et al., 1999; Budka et al., 2002; Ohnuki et al., 2002).