What is phytoremediation?
Phytoremediation is the use of living plants to remove, immobilise or break down pollutants in contaminated soil, water or air. It relies on the same uptake system that a plant normally uses to absorb water and mineral salts through its roots. Common targets include heavy metals such as lead, cadmium, arsenic and mercury, as well as some organic pollutants.
Main methods
- Phytoextraction — plants absorb pollutants (especially metals) and store them in their roots, stems and leaves; the plants are then harvested and safely disposed of.
- Rhizofiltration — plant roots absorb or adsorb contaminants from polluted water.
- Phytostabilisation — plants immobilise pollutants in the soil around their roots, preventing them from spreading or entering groundwater.
- Phytodegradation — plants (and microbes near their roots) break down organic pollutants into harmless substances.
Hyperaccumulator plants
Some plants, called hyperaccumulators, can take up unusually large amounts of metals without being poisoned. Examples used in phytoremediation include the sunflower, Indian mustard, vetiver grass and water hyacinth (for polluted water).
Key idea
In phytoextraction the pollutant is absorbed into the plant and removed when the plant is harvested. In phytostabilisation the pollutant stays in the soil but is locked in place so it cannot spread.
Advantages and limitations
Advantages: it is relatively cheap, solar-powered, environmentally friendly and causes little disturbance to the soil compared with digging it out. Limitations: it is slow, works only as deep as the roots reach, and the polluted plant material must be disposed of carefully. There is also a risk that toxins could enter the food chain if animals eat the plants.
Example
Sunflowers were planted on soil contaminated with radioactive and heavy-metal waste; their roots absorbed the pollutants, and the plants were later harvested and removed, gradually cleaning the site.