Accumulation of mercury and other metals by the lichen Parmelia, at a minesite and a volcanic area

Young thallus tissue of the epiphytic lichen, Parmelia sulcata, and surface soil associated with its host trees were collected on Mt. Amiata for analysis of metal content including A1, Fe, Mn, Cu, Zn and Hg. The purpose of this study was to achieve a better understanding of plant-soil Hg relationships by comparisons of the Mt. Amiata minesite with the summit of an active volcano - Mt. Etna - and thereby to gain more insight into metal source and eco-physiology as factors in plant-Hg distribution. Although an Hg source-plant distance relationship clearly exists on Mr. Amiata, its precise nature is still in doubt, as it was impossible to distinguish statistically at p<0.01 among linear, log-linear, exponential, and third order polynomial regressions, even with N=47. Nevertheless, the distance-fromsource relationship for Hg was clearly unique. No significant pattern could be assigned to the other metals studied, nor was there evidence of a regular relationship between soil content and plant content except in the case of Hg. Parmelia from Mt. Amiata accumulates Hg from soil degassing which was not at all the case for its mercury source on Mr. Etna. The data also suggests that high Zn values in the lichen of Mt. Amiata may be based on long range atmospheric transport. The Zn content of Parmelia was not analyzed on Mt. Etna. Element atomic ratios, Fe/AI for example, provide good evidence for accumulation of surface soil particulates, other than cinnabar by the thallus. Finally, we conclude that widely separated populations of the same species can display biogeochemical differences that are best explained on an eco-physiological basis.