Biological activity of material whether known in folk medicine or observed in planned screening program has been the starting point in the drug research. The general pattern is the isolation of active principles, elucidation their structures, followed by attempts for modulation of its activity potential by chemical modification. Lichens are valuable plant resources and are used as medicine, food, fodder, perfume, spice, dyes and for miscellaneous purposes throughout the world. Lichens are well known for the diversity of secondary metabolites that they produce. Compounds isolated from various lichen species have been reported to display diverse biological activities.Here we review the medicinal efficacy of lichen substances, which intends to explore the pharmaceutical potential of lichen substances.

Application of medicinal plant to cure ailments has been practiced by several civilizations. Nowadays, contamination of heavy metals and pesticide residues in medicinal plant is a serious concern, due to toxic effects on human health. The present study was designed with an aim to quantify the heavy metals and pesticide residues in the 20 medicinal herbs, frequently sold in the local market as raw material without any quality assurance. The concentrations of the elements are as follows: copper (2.42-19.14 μgg), cadmium (0.01-2.10 μgg), chromium (17.63-58.63 μgg), iron (7.61-322.6 μgg), and lead (13.00-54.47 μgg), whereas total metal concentration ranged between 44.73 and 385.15 μgg. Among the organic pesticides, HCH (1.63-6.44 μgg) and DDT (0.63-7.14 μgg) isomers were found to be present in medicinal plant material. Result showed that lead and chromium concentrations in the herbs were above the permissible limits set by WHO. These herbs should be regularly checked for quality assurance before using raw or as a herbal formulation to avoid chronic exposure of metal and pesticides to human being.

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The distribution and origin of polycyclic aromatic hydrocarbons (PAHs) in the lichen, Phaeophyscia hispidula (Ach.) Essl., collected from nine different road crossings of DehraDun, capital city of Uttaranchal (Garhwal Himalayas) were studied. The origin of PAHs was also assessed using the Phe/Ant, Flu/Pyr, Ant/Ant+Phe, Flu/Flu+Pyr and Naph/Phen concentration ratios. The total concentration of 16 PAHs ranged from 3.38-25.01 mug g(-1) with an average concentration of 12.09 +/- 9.38 (SD). The PAH ratios clearly indicates that PAH were of mixed origin, a major characteristic of urban environment. Significantly higher concentration of phenanthrene, pyrene and acenaphthylene indicates road traffic as major source of PAH pollution in the city. The study establishes the utility of P. hispidula as an excellent biomonitoring organism in monitoring of PAH from foot hill to sub temperate area of the Garhwal Himalayas.

Despite the tragic outcome, on review of case literature, we believe this case provides valuable lessons concerning the use of DMSA and DMPS to treat mercury toxicity, particularly with regard to the combined use of chelation agents and hemodialysis.