Retrospective Study of Lichen Lead Accumulation in the Northeastern United States

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Abstract
Lichen samples collected from several locations in 1907-1980 were analyzed for Pb content to establish accumulation trends indicative of atmospheric Pb pollution patterns. The main collection site was Plummers Island, Maryland, a Potomac River island subjected to severe atmospheric pollution stress from automobile exhaust. A nearby island, Bear Island, more remote from traffic, was also studied for comparison. In addition, lichen samples were collected in Shenandoah National Park in western Virginia, and Aton Forest and other sites in Litchfield County, Connecticut, Present-day Pb concentrations in all species samples from Plummers Island were significantly higher than concentrations in the same-species from Bear Island, highest values being obtained for Pseudoparmelia baltimorensis and Xanthoparmelia conspersa. These values are the highest yet found for foliose and fruitcose lichen species subjected to atmospheric automobile exhaust pollution, although higher values have been reported for lichens from Pb mining areas. Significantly increased Pb concentration values were observed for lichens collected from Plummers Island in 1907-1958. During this interval, Plummers Island was remote from any specific Pb pollution source: therefore, the average background Pb pollution level apparently also increased during this time. Cladina subtenuis contained the lowest Pb concentrations in all sites, suggesting that lichen morphology influences particle trapping capacity and thus regulates the rate of Pb absorption by lichen tissues.