Lichens metal accumulation

Early studies of metal uptake by lichens presented metal sorption as an ion exchange process, and reported metal accumulation in terms of relative uptake capacity, or the capacity of one metal to displace another as an adsorbed complex. Competitive uptake studies by Puckett et al. (1973)... 

The objective of this preliminary study was to assess levels of Cd, Cu, Fe, Mn, Pb and Zn in two species of epilithic macrolichens Usnea aurantiacoatra (only found in maritime Antarctica) and Usnea antarctica (found in maritime and continental Antarctica) (57). Usnea antarctica has an antarctic circumpolar distribution continental and subantarctic regions. New Zealand and Tierra del Fuego (58). Table 6.9 shows the concentrations of Cd, Cu, Fe, Mn, Pb and Zn in specimens of the Antarctic lichens Usnea aurantiacoatra and Usnea antarctica in areas close to Jubany Station. Two different trends of trace metals accumulation have been identified, namely ... 

The capability of lichens to accumulate different elements, inclusive of trace metals, is a distinctive feature, extensively documented in the 1970s and 1980s (James, 1973 Nieboer et al., 1977, 1978 Puckett and Burton, 1981 Martin and Coughtrey, 1982 Brown and Beckett, 1984, 1985a,b Lawrey, 1984 Arndt et al., 1987 Galun and Ronen, 1988 Puckett, 1988 Richardson, 1988 Nash, 1989 Tyler, 1989). 

Helena, P., Franc, B. and Cvetka, R.L. (2004) Monitoring of short-term heavy metal deposition by accumulation in epiphytic lichens (Hypogymnia physodes (L.) Nyl.). Journal of Atmospheric Chemistry, 49, 223-30. 

Lichens and bryophytes grow very slowly, and are adapted to absorb nutrients from the atmosphere. NSA values of order 1000 m2d kg-1 can be deduced from data of Andersen etal. (1978) on the accumulation of metals by bryophytes in the Copenhagen district. In the Arctic, lichens form the basis of a food chain via reindeer to man, and the concentration of 137Cs in the lichens has given exceptionally high body burdens of 137Cs in Eskimos and Laplanders (UNSCEAR, 1967). 

Garty, J. Galun, M. (1979). Localization of heavy metals and other elements accumulated in the lichen thallus. New Phytologist, 82, 159-68. 

Lichens are adapted to accumulate all the elements necessary for their life from the atmosphere. They have no root system and absorb very little from the substrate on which they grow. Atmospheric materials, including trace metals and radionuclides, can be concentrated by particulate entrapment, ion exchange, electrolytic sorption and processes mediated by metabolic energy (Crete et al., 1992). Passive particulate trapping is, however, thought to be the dominant uptake mechanism. This is also true for mosses which absorb nutrients directly through leaf and stem surfaces. 

Lichens have been used as good bioaccumulators of atmospherically transported heavy metals by different researchers (47-53). Lichens have neither roots, nor other adsorptive structures or a waxy cuticle and for mineral nutrition are largely dependent on atmospheric depositions. Lichens act as bioaccumulators via their capacity to adsorb metals from the environment. Three mechanisms have been proposed (a) intracellular uptake via an exchange process (b) intracellular accumulation and (c) trapping of metal-rich particles (54). In spite of that, there are still some gaps in the understanding of the overall process responsible for the metal uptake and accumulation in lichens. 

A better understanding of the different trends in the accumulation of metals observed in Usnea antarctica and Usnea aurantiacoatra demand more studies, such as the estimation of the age of lichens, their growing rate and the composition of the soil and rocky substrates in eontact with them. 

Coal-fired power plants are well-known sources of SO2, NO2, heavy metals and other elements (Fig. 1). Lichens applied as monitors near coal-fired power stations in Portugal were found to accumulate heavy metals such as Fe, Co, Cr, and Sb, originating in coal and ash particles drifting through the air and positioned on the thallus (Freitas, 1994). 

Armstrong, R.A., 1997. Are metal ions accumulated by saxicolous lichens growing in a rural environment . Environ. Exp. Bot. 38, 73-79. 

Nieboer, E., Puckett, K.J., Richardson, D.H.S., Tomassini, F.D., Grace, B., 1977. Ecological and physicochemical aspects of the accumulation of heavy metals and sulphur in lichens. In International Conference on Heavy Metals in the Environment, Toronto, Ontario, Canada, October 27-31, 1975, Symposium Proceedings, Vol. 2. pp. 331-352. 

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