Promises and Prospects of Phytoremediation.

We often think of plants primarily as a source of wood, food, and fiber. Secoridarily we may also appreciate their presence for aesthetic reasons as well as for “altruistically” providing habitat for other species. Increasingly, however, their value as an environmental counterbalance to industrialization processes is being appreciated. These processes include the burning of fossil fuels, generation of wastes (sewage, inorganic and organic solids, and effluents), and general water flow and processing. Plants have long been recognized for their consumption of CO, and, more recently, of other gaseous industrial byproducts (Simonich and Hites, 1994). Recently, their role in slowing the rate of global warming has been further appreciated in both the scientific and popular press. Their use as a final water treatment and for disposal of sludge resulting from waste water treatment is centuries old (Hartman, 1975). The extensive literature concerning water and sludge treatment and the emerging field of air pollution abatement with plants will not be discussed here. Instead, we focus on an emerging concept, ”phytoremediation,” the use of plants to remediate contamination of soil with organic or inorganic wastes. Remediation of soil contamination by conventional engineering techniques often costs between $50 and $500 per ton. Certain specialized techniques can exceed costs of $1000 per ton. With an acre of soil (to a 3-foot depth) weighing approximately 4500 tons, this translates to a minimum cost of about a quarter million dollars per acre (Cunningham et al., 1995). It is not surprising that the cleanup of contaminated sites has not been proceeding at a rapid pace. There is an active effort to develop new, more costeffective technologies to remediate contamination of such soils. For the most part these efforts are being led by engineers and microbiologists. More recently, however, green plant-based processes have begun receiving greater attention. It has long been known that the life cycle of a plant has profound effects on the chemical, physical, and biological processes that occur in its immediate vicinity. In the process of shoot and root growth, water and mineral acquisition, senescence, and eventual decay, plants can profoundly alter the surrounding soil. The effects of many of these processes are apparent on