Bioremediation refers to techniques that employ living organisms, such as microbes and plants, to extract, eliminate and/or bind toxins in forms that are not harmful to the environment. These include biostimulation, biotransformation, biostabilization and biofiltration. For instance, microalgae are used in ponds to eliminate nitrogen and phosphorous, and aquatic plants (e.g. water lentils) are used to extract heavy metals in industrial effluents. These natural processes have been employed for many years to eliminate pollutants.
Modern biotechnology techniques promise to enha nce the performance of these natural processes in pollution control. For example, mercury is a highly toxic metal that accumulates in the food chain when released in water, for example in the Minamata accident, where inhabitants of the Japanese island of Kyushu suffered the toxic effects of fish poisoned by mercury-rich industrial effluents. Since naturally thriving mercury-tolerant bacteria are rare and cannot be grown easily in culture, researchers at Cornell University inserted the metallothionein gene into Escherichia coli, which grows well in culture. The genetically engineered bacteria are placed inside a bioreactor that efficiently removes mercury from water. The bacteria are later incinerated and the accumulated mercury is recovered (European Commission,2002). Existing techniques of mercury removal are expensive and inefficient.
Phytoremediation refers to the use of plants to remove pollutants from water and soils. There are about 1.4 million polluted sites in Western Europe alone. Current techniques are costly and destroy soil structure. The use of plants that can store 10 to 500 more pollutants in their leaves and stems is cheaper and stabilizes the soil structure. Above all, the metals can be recovered from ashes and reused.
There are many hyperaccumulating plants. These plants accumulate lead, zinc, nickel, copper and cobalt, among others, at levels toxic to other plants. For example, Sebertia acuminata can contain up to 20% of nickel in its sap (nickel is generally toxic to plants at a concentration of 0.005%). Similarly, the fern Pteris vittata accumulates arsenium while conserving a very rapid growth and a high biomass. The firm Edenspace has acquired the commercialization rights of the fern (now called edenfern™) for use in phytoremediation. The potential market for Phytoremediation in the United States alone was estimated at $100 million in 2002 (Tastemain, 2002).
