Breaking down and making green

Plastics and fluorinated carbons take hundreds of years to break down. Bacteria have been found that can eat plastics, and scientists are working to make them faster.

Bioplastics are made from natural materials: disposable plates and cups from leaves, bamboo, corn starch or seaweed, and plastics from biological polymers. PHB, a biodegradable plastic, is made by fermentation with the bacterium Alcaligenes eutrophus. Its three genes have also been put into the plant Arabidopsis, which then makes granules of PHB in its chloroplasts. The main limit is cost.

Paper. Making pulp normally means cooking wood chips with caustic soda and sulphur to remove lignin, the tough material that binds wood fibres, which uses a lot of energy and chemicals. Biotechnology helps:

• Biopulping: fungi that digest lignin do part of the job, saving energy and chemicals.
• GM trees with less lignin are easier to pulp.
• Biobleaching with the enzyme xylanase reduces the need for chlorine.
• Non-wood materials such as bagasse (sugarcane waste), bamboo and jute save forests.

Oil. After the usual methods have pumped out what they can, a lot of oil is left in the ground. Microbes help get more of this residual oil out (enhanced oil recovery), and help clean up oil spills. An engineered Pseudomonas 'superbug' can eat oil.

Heavy metals such as arsenic, chromium, mercury, cadmium and zinc can also be bioremediated. Three questions decide whether it will work: can the pollutant be changed into a less toxic form? Is it available to the organisms (bioavailable)? And is their activity efficient enough?