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Retrospective Study of Lichen Lead Accumulation in the Northeastern United States

1981; American Bryological and Lichenological Society; Volume: 84; Issue: 4 Linguagem: Inglês

10.2307/3242552

1938-4378

James D. Lawrey, Mason E. Hale,

Heavy metals in environment

Lichen samples collected from several locations in the northeastern United States from 1907 to 1980 were analyzed for lead 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. Presentday Pb concentrations in all species sampled from Plummers Island were found to be 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 fruticose 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 between 1907 and 1958. During this interval, Plummers Island was remote from any specific Pb pollution source; therefore, the average Pb pollution level appears to have also increased during this time. Cladina subtenuis was found to contain 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. Increased concern over the effects of lead pollution that are caused by the use of leaded gasoline in automobiles has stimulated a number of studies of Pb accumulation by plants, particularly cryptogams, in roadside environments (Riihling & Tyler 1968, 1971; Goodman 007-2745/81/449-456$0.95/0 This content downloaded from 157.55.39.127 on Wed, 29 Jun 2016 06:03:49 UTC All use subject to http://about.jstor.org/terms 450 THE BRYOLOGIST [Volume 84 & Roberts 1971; Smith 1976; Burkitt et al. 1972; Rao et al. 1977). These studies have demonstrated that atmospheric Pb burden is concentrated near heavily traveled roads and that significant pollution effects are not seen at distances greater than 100 m from roads. These results are consistent with the model of Pb cycling proposed by Smith (1976) for roadside systems. Despite the highly concentrated deposition pattern observed for atmospheric lead, however, cryptogam samples collected in unpolluted areas often exhibit elevated Pb concentrations (Riihling & Tyler 1968). Lead deposition rates have been found to be increasing not only in urban areas (Chow & Earl 1970), but also in areas far removed from pollution sources in the U.S.A. (Schlesinger et al. 1974). These patterns demonstrate a need to document changes in Pb burden with time. A number of retrospective heavy metal studies have been done with cryptogams since Riihling and Tyler (1968) first published on the elevated lead content of a number of species during an interval from 1860 to 1968 in Sweden. They found two distinct periods of increased Pb concentration. One occurred during the end of the nineteenth century; the other occurred after the second World War. Although they were unable to explain the first major increase in Pb concentration, they attributed the second increase to the use of leaded automobile fuel after 1940. Rasmussen (1977) and Johnsen and Rasmussen (1977) determined the concentration of several heavy metals, including Pb, for epiphytic bryophytes from rural areas in Denmark. Even in these rural areas, Pb concentration was found to have increased approximately one order of magnitude during the last quarter century. Rao et al. (1977) reported results of an unpublished study by Robitaille and LeBlanc on heavy metal accumulation by five moss species from Mount Royal, Montreal, from 1905 to 1971. Lead was found to have exhibited the greatest increases in Heterophyllium haldanianum (Grev.) Kindb. from 20 tg/g in 1905 to 110 tg/g in 1971. These results indicated a steadily increasing heavy metal pollution in the area through urbanization and industrialization. There have been relatively few retrospective studies of lichen heavy metal accumulation over time, although the few that have been published demonstrate that lichens are as effective as bryophytes as long-term integrators of atmospheric pollution burden. In central Sweden, Persson et al. (1974) studied the concentration of radiolead (Pb-210) and stable Pb in field-collected Cladonia alpestris (L.) Rabenh. (= Cladina stellaris (Opiz) Brodo) and unidentified Cladonia species from herbarium collections dating to 1882. They found a decreased ratio of Pb-210 to stable Pb after 1940, indicating an increased deposition of stable Pb at that time. In an examination of herbarium specimens dating to 1893 and fieldcollected material, Schutte (1977) found elevated Cr concentrations in the most recently collected thalli of Parmelia caperata (L.) Ach. (= Pseudoparmelia caperata (L.) Hale) and P. rudecta Ach. from several locations in Ohio and West Virginia. She attributed the increased Cr concentrations to the effects of air pollution in the region. Retrospective studies of lead concentrations in lichens are limited only by the period over which samples have been collected in a given area of interest; they should provide a long-term pollution monitoring tool. We report herein Pb concentration values for three common species collected in various locations and times. The retrospective concentration values obtained for these lichens indicate a significant rise in background Pb levels as well as greatly increased levels near heavily travelled roads.