The residence time that contaminants and nutrients remain in lichen tissue differs among elements (Pucket 1985). Macronutrients, such as nitrogen, sulfur, potassium, magnesium and calcium are comparatively mobile and easily leached and therefore measurable changes in tissue concentrations can occur over weeks or months with seasonal changes in deposition (Boongaprob et al. 1989). In one study, mobile elements reached the same levels in transplants as the indigenous lichens within four to six months (Palomäki et al. 1992). Trace and toxic metals such as cadmium, lead, and zinc, are more tightly bound or sequestered within lichens.
