Assessment of heavy metal accumulation and their translocation in plant species

Industrial processes are causing continuous discharges of effluents into open drains which enter into the soil that is being contaminated from variety of pollutants including heavy metals. The natural vegetation along the drains is under metal contamination stress. In this research work natural vegetation was primarily focused to study the accumulation of heavy metals in the plants growing in this polluted area assuming that soil has increasingly become contaminated due to discharge of industrial effluents. The purpose was to evaluate inter-population variations to estimate potential range of metal uptake and to direct the selection of the species to ensure optimal accumulation. Soil and plant sampling was carried out from the three selected sites. Seven metals (Cd, Cr, Cu, Pb, Zn, Mn and Ni) were analyzed in soil and as well as in plant tissues. For plant tissue analysis, the underground and above ground parts were separately analyzed. However, soil analysis was conducted by taking composite samples and diethylene triamine pentaacetic acid (DTPA) extractable heavy metal contents were determined. The soil up to 30 cm depth and near the drain was found to have significantly higher metal concentrations than the non contaminated sites and has low organic matter and pH while high EC was observed in the study area. Bioconcentration factor showed considerable extent of root to shoot translocation of metals among species analyzed for phytoaccumulation. The maximum accumulation being Sylibum marianum (Cr, in the whole plant but Mn and Zn in the shoot tissues only), Rumex dentatus (Pb and Ni in both tissues while Cd, Zn, Ni and Cu in the root tissues), Cannabis sativa (Cd and Cu in the root tissues only). The revegetation and colonization of these species would be an appropriate choice in such metal polluted soils.