Certain plants are able to extract hazardous substances such as Arsenic, Lead and Uranium from Soil and Water. One example is alpine pennycress (Brassicaceae), a plant which naturally accumulates high levels of Cadmium and Zinc from the environment. Alpine pennycress is therefore known as a hyperaccumulator of these metals, which in unnaturally high levels would be poisonous to many plants. Another example of a hyperaccumulator is the Bracken Fern. This fern extracts arsenic from the soil at a much greater rate than other plants. This arsenic is stored in the fern's leaves at as much as 200 times that present in the soil, thus enabling effective and practical clean-up programs. Sunflowers were also used to clean up uranium after the Chernobyl accident.
Breeding programs and Genetic engineering are powerful methods for enhancing natural tendencies of plants, or for introducing these tendencies into alternative types of plants which might be more suitable for the environmental conditions.
The range of biological treatments for environmental problems, as described by the term phytoremediation, actually consists of several specific processes: