In the second of two programmes about nanotechnology, Richard Hollingham concentrates on the environmental uses for nanotechnology, especially water and energy generation. Professor Eugene Cloete from Stellenbosch University has developed a water filter that looks like a teabag and which uses nanofibres to filter out contaminants. Researchers at the University of Brighton are developing ways of purifying large amounts of water at source. Scientists at the University of Cambridge are developing thin films of nanocrystals that capture sunlight and turn it into electrical energy. As nanoparticles become more widely used, there’s growing concern about their safety. Richard talks to Professor Ian Colbeck from Essex University and Richard Denison from the Environmental Defence Fund about the potential risks posed by nanoparticles if they escape into the environment.