Phytoremediation of metal contaminated soils: metal tolerance and metal accumulation in Pelargonium sp.
Phytoremediation is an innovative technology that uses plants to remove and/or degrade environmental contaminants such as heavy metals and organic compounds. Plants that possess the ability to accumulate high levels of metals in their biomass are referred to as metal accumulators. The overall objective of this research was to identify, characterize and evaluate the utility of metal accumulator plant species, specifically 'Pelargonium' sp. Physiological characterization of metal tolerance using chlorophyll ' a' fluorescence parameters (Fv/Fm, Fv/Fo) indicated that the scented geranium plants were capable of maintaining an efficient photosynthetic activity required for sustained metabolism and to overcome metal-ion mediated stress. The metal accumulation ability of scented geraniums was tested under greenhouse conditions. Scented geranium plants accumulated in excess of 0.08% Cd, 0.12% Ni, 0.30% Pb per kg of shoot dry weight (DW) and 2.70% Cd, 2.11% Ni, 6.10% Pb per kg of root DW. Additionally, scented geraniums exposed to a mixture of metals (Pb + Cd + Ni) have the ability to uptake in excess of 0.44% Cd + 0.52% Ni + 4.72% Pb per kg of root DW, as well as 0.07% Cd + 0.14% Ni + 0.17% Pb per kg of shoot DW. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies coupled with X-ray microanalysis indicated that the ability of scented geraniums to tolerate metals was due, in part, to its ability to detoxify the metal ions by formation of complexes as well as sequestration of these metal ion complexes in vacuoles, intercellular spaces and as deposits on cell membranes. The efficacy of scented geraniums to tolerate complex contaminants (Pb, Cu and hydrocarbons) under field conditions further confirmed the utility of this plant species for phytoremediation. Identification and characterization of 'Pelargonium' sp. provides the field of phytoremediation with an efficient system for remediation of metal polluted substrates.