RHIZOFILTRATION - THE USE OF PLANTS TO REMOVE HEAVY-METALS FROM AQUEOUS STREAMS

Heavy metal pollution of water is a major environmental problem facing the modern world. Rhizofiltration-the use of plant roots to remove heavy metals from water-is an emerging environmental cleanup technology. Roots of many hydroponically grown terrestrial plants, e.g., Indian mustard (Brassica juncea (L.) Czern.), sunflower (Helianthus annuus L.), and various grasses, effectively removed toxic metals such as Cu2+, Cd2+, Cr6+, Ni2+, Pb2+, and Zn2+ from aqueous solutions. Roots of B. juncea concentrated these metals 131-563-fold (on a DW basis) above initial solution concentrations. Pb removal was based on tissue absorption and on root-mediated Pb precipitation in the form of insoluble inorganic compounds, mainly lead phosphate. At high Pb concentrations, precipitation played a progressively more important role in Pb removal than tissue absorption, which saturated at approximately 100 mg of Pb/g DW root. Dried roots were much less effective than live roots in accumulating Pb and in removing Pb from the solution.