The effect of heavy metals on some aspects of lichen physiology

The effect of the heavy metals cadmium, cobalt, copper, lead, mercury, nickel, and silver on the lichen Umbiliearia muhlenbergii (Ach.) Tuck, is described in terms of membrane integrity, chlorophyll damage, and changes in photosynthetic 14C fixation. Increasing concentrations of copper, mercury, and silver produced a gradual potassium loss from the thallus while the other metals tested initiated an abrupt efflux at a specific concentration. Copper, mercury, and silver 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. [Formula: see text] for extended exposures. The tendency for the metals studied to fall into two distinct groups on the basis of their effects on lichen metabolism is discussed in terms of their physicochemical properties.