ABSTRACT
Remediation methods currently used to treat soils contaminated with heavy metals are expensive, labor-intensive, and environmentally invasive. They are mainly based on civil engineering techniques, often involving excavation and removal of contaminated soil, with additional effort, time, and money then required to restore the site. A low cost remediation technique that is environmentally sound and equally protective of human health and the environment would be a valuable and viable alternative to current remediation methods. Research has been directed toward exploiting biological and chemical processes to reduce the risk associated with metal-contaminated soils. Examples of such remediation strategies are the so-called phytoremediation techniques. For phytoremediation of metal-polluted soils, two possible techniques, both aiming at a reduction of the bioavailable fraction of metals in the soil, can be distinguished: (1) phytostabilization or phytorestoration (in situ metal inactivation by means of revegetation, either with or without nontoxic metal-immobilizing or fertilizing soil amendments), and (2) phytoextraction (metal bioextraction by means of hyperaccumulating plants). Plant and soil amendments are used to extract or to change the chemical and physical form of the heavy metal contaminants in the environment, thereby decreasing their potential mobility and hazard. The use of phytoremediation techniques including the use of metal-immobilizing soil additives that can be classified as "soft" or "gentle" approaches for soil remediation shows some promise.
