Spatial-Temporal Patterns of Element Concentrations in Xanthoparmelia Camtschadalis Transplanted along Roads

Lichen transplantation is a powerful tool for monitoring the deposition of atmospheric elements in areas devoid of native or expected lichens. The foliose lichen Xanthoparmelia camtschadalis (XPc) was transplanted along two busy roads in Hebei, China, and was exposed for 3, 6, 9 and 12 months. Twenty-five elements (Al, Ba, Cd, Ce, Cs, Cu, Fe, La, Mg, Mn, Na, Ni, Pb, Rb, S, Sb, Sc, Sm, Sr, Tb, Th, Ti, Tl, V, and Zn) were measured using an inductively coupled plasma mass spectrometer (ICP-MS). The concentrations of all elements were higher in post-exposure samples than in the control, suggesting severe air pollution at the exposure sites. The temporal trends of the lichen S concentration were similar to those of the atmospheric SO2 concentration. This result indicates that the release of SO2 during the winter heating period elevated the lichen S concentrations, for which XPc had an integration time of <3 months. Metal concentrations peaked after 9-month exposure at exposure sites near roads, whereas they peaked after 12-month exposure at the other sites. This result indicates that the emissions near the roads accelerated the accumulation of metals, for which XPc had an integration time of >3 months. Our results confirmed the applicability of XPc for assessing the atmospheric pollution influenced by road emissions in highly polluted regions.