Abstract
Lichens are indicator species of air quality of a locality. Estimate of heavy metal (HM) accumulation in lichens offers an indirect measure of their levels in the atmosphere. Accumulated HMs of lichen thalli of 16 species belonging to 10 genera and their phorophytes of two characteristic areas of Brahmaputra valley were studied. Acid digested samples of thalli and phorophytes were analysed for Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb by ICP-OES. Mean concentrations of the HMs were found to be higher in lichens at the area situated close to the downtown area of the city and the Brahmaputra River. Accumulation of Cd, Cu, Fe and Ni were found to be higher in lichen thalli; however, leaves accumulated higher levels of Co and Mn. Linear regression analysis shows poor dependency of the thalli on their phorophytes indicating accumulation of metals from atmosphere. The extent of enrichment in the lichen thalli, which was evaluated by calculating enrichment factors (EFs) revealed moderate enrichment of Cr, Cu, Ni and Pb; however, Cd was found to be highly enriched. Ecological risk posed by the heavy metals were calculated and it was found that Principal Component Analysis (PCA) of the data set identifies three contributing sources: coal-fired industrial emission, crustal dust blown from dry river bed and vehicular emission.
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