Improving the use of lichens as biomonitors of atmospheric metal pollution

Improving the use of lichens as biomonitors of atmospheric metal pollution is the main objective of this work. For that a better insight into the availability and location of heavy metals in lichens subjected to polluted conditions both under laboratory and field conditions was attained. The data in this work supported the hypothesis that the absence of the lichen Ramalina fastigiata near a copper mine site, located in the south of Portugal, was related with toxic levels of Cu-dust near the centre of the mine. Lichen biodiversity, measured by the parameter number of lichen species, reflected the impact of the copper-mine dust emissions. The extent of the impact was more widespread towards cast, which appears to be correlated with the frequency of the winds. The chemical analysis of in-situ samples of R. fastigiata collected at different distances and in different directions from the mine showed that Cu, K and Mg were emitted from the centre of the mine site, confirming that major sources of atmospheric dust were located there. Total inhibition of PSII (photosystem II) photochemical reactions occurred in R. fastigiata both under field and controlled conditions, when intracellular Cu concentrations exceeded a threshold of ca. 2.0 μmol g-1. No samples of this species were found under field conditions beyond the Cu threshold, suggesting that the absence of the lichen R. fastigiata might be used as an indicator of intracellular Cu concentrations above 2.0 μmol g-1 in the surroundings of the copper-mine. The fluorescence parameter Fv/Fm proved to be a good estimator of the survival capacity of R. fastigiata under field conditions and thus a useful parameter in determining the sensitivity of the lichens (photobiont) to Cu pollution. The intracellular location of Cu, K and Mg allowed to explain the physiological changes and the survival of the species in the surroundings of the copper-mine. (author)