Bioremediation in action

Bioremediation uses microbes to remove toxic pesticides and other pollutants, or change them into harmless forms. Bacteria such as Pseudomonas, Acinetobacter, Sphingomonas and Flavobacterium do this with enzymes: cytochrome P450 (oxidation), esterases (hydrolysis), oxidases, peroxidases and transferases. In Pseudomonas, a set of genes (AtzA-F) breaks down the weedkiller atrazine all the way to ammonia and CO₂.

In situ bioremediation cleans the site where it is:

• Intrinsic: the native microbes slowly break down the toxins on their own. It is cheap and causes little disturbance, but it is slow and may be incomplete.
• Engineered: oxygen, nitrogen and nutrients are pumped through wells into the ground to boost the microbes.

Ex situ bioremediation, for heavily contaminated soil, which is dug out and treated elsewhere:

• Slurry bioreactors: the soil is stirred with water and nutrients (mobile units exist).
• Land farming: the soil is spread out and tilled.
• Composting, with straw or corncobs.
• Biopiles: heaps of soil, aerated and fed with nutrients.

Ananda Mohan Chakrabarty, an Indian-born scientist, built a Pseudomonas 'superbug' carrying plasmids that let it break down camphor, octane, xylene and naphthalene, all components of oil. In the case Diamond v. Chakrabarty (1980), the US Supreme Court allowed him to patent it, the first patent on a living microbe.

India has its own oil-eating product, Oilzapper, developed by TERI with the Department of Biotechnology and made by ONGC TERI Biotech Ltd. It uses five bacterial strains on powdered corncob to clean up oil sludge.

Phytoremediation uses plants. Plants such as Brassica napus and sunflower (Helianthus) take up mercury and lead. Microbes around their roots help, by binding metals, adding methyl groups, and changing the pH. Nitrogen-fixing bacteria (Azotobacter, Rhizobium) also make plant growth hormones and help remove lead, zinc and nickel. Water plants such as Hydrilla and the water lily (Nymphaea) reduce chromium.