Bioavailability of heavy metals and decontamination of soils by plants

Bioavailability of heavy metals in metal-contaminated soils depends on physical, chemical and biological factors. Physical (structure, penetrability) and chemical factors (Eh, pH, speciation, concentration) give the framework in which biological factors can modify the metal availability by release of oxygen, protons, and organic acids and by association with mycorrhizal fungi. With these conditions in mind, the possibilities of the use of hyperaccumulating higher plants for the decontamination of metal polluted soils, i.e. phytoremediation, are explored. By small scale experiments it has been demonstrated that at present phytoremediation is only an economically important clean-up technique for slightly contaminated soils. Heavily contaminated soils can only be revegetated using highly metal-resistant plants. (C) 1996 Elsevier Science Ltd