A recent article in Scientific American describes the use of transgenic plants to remove toxins from contaminated sites. The plants have genes for toxin and carcinogen metabolisis (for instance, using the enzyme cytochrome P450-3A) inserted into their DNA. The technique has been tested with plants intended to address trichloroethylene, chloroform, carbon tetrachloride, vinyl chloride, and benzene contamination. Such plants have also shown promise in removing remaining concentrations of the explosive RDX from soil in test ranges. At present, there is sometimes no choice but to scoop up huge amounts of contaminated soil and put it into landfills; plants that are able to seperate the toxins from the soil could promise to facilitate the process, as well as reduce costs.
The article is not entirely clear on whether the plants simply absorb the chemicals, becoming contaminated by them in turn, or whether they actually break them down. In the former case, they might be useful for concentrating air, water, and soil contaminants into plant matter than can then be disposed of as hazardous waste. In the latter case, they could perform remediation without the need for such careful treatment of their remains. Another question is how the plants would deal with combinations of chemicals, such as might be found in actual contaminated sites.
All told, it seems a promising potential use for biotechnology. The world is certainly well saturated with contaminated sites and having more cost effective means of reclaiming them could be a boon to both nature and human health. It remains to be seen whether these limited trials can be scaled up and made cost-effective for commercial or governmental use.