Mopping up pollutants

Phytoremediation is the term used to describe the process whereby plants remove contaminants from the atmosphere. It has been demonstrated that some common houseplants are able to remove indoor pollutants, including benzene, formaldehyde, trichloroethane and carbon monoxide. Trace elements from the atmosphere and soil are absorbed through the leaves and roots before being biodegraded. Studies have shown that one potted plant per 100 sq ft can help clean the air in the average home or office.

In the US, one project has been under way for several years at an air force base in Carswell, Texas, where both the soil and ground water are heavily contaminated with trichloroethane. The area was extensively planted with poplars, which have made a significant improvement in pollutant levels. In the Everglades of Florida, cattail plants are used to absorb large amounts of toxic phosphorus caused by fertiliser run-off.

Phytoremediation can also be used to remove radiation from the environment, with sunflowers and marijuana being the main species used. These so-called hyper-accumulating plants are effective at removing heavy metals from both soil and ground water. Both species were used at sites around the Chernobyl nuclear power plant in Ukraine, and in one experiment sunflower plants were planted on a raft in contaminated water near the reactor. After 12 days plant caesium levels were 8,000 times and strontium levels 2,000 times that of the water.

The US Environmental Protection Agency has estimated that more than 30,000 sites in the US alone require hazardous waste treatment. The Japanese government has recently planted sunflowers near the stricken Fukushima nuclear plant, but there have been concerns from environmentalists that the radiation removed by plants is in fact merely being concentrated, increasing the risk of secondary contamination if the plant matter is not disposed of safely.