The effect of heavy metals on some aspects of lichen physiology

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Abstract
The effect of the heavy metals Cd, Co, Cu, Pb, Hg, Ni and Ag on the lichen Umbilicaria muhlenbergii (Ach.) Tuck. is described in terms of membrane integrity, chlorophyll damage and changes in photosynthetic 14C fixation. Increasing concentrations of Cu, Hg and Ag produced a gradual K loss from the thallus, while the other metals tested initiated an abrupt efflux at a specific concentration. Cu, Hg and Ag caused both a displacement and a decrease in the absorption spectrum of chlorophyll, whereas no detectable changes were induced by the other metals. The relative toxicities of these metals on photosynthesis is reflected in the series Ag, Hg > Co > Cu, Cd > Pb, Ni for short-term exposures, and Ag, Hg > Cu .gtoreq. Pb, Co > Ni for extended exposures. The tendency for the metals studied to fall into 2 distinct groups on the basis of their effects on lichen metabolism is discussed in terms of their physicochemical properties.