The Fukushima nuclear disaster delivered an unprecedented amount of radioactivity into the sea over a relatively brief time. How did that pulse of cesium and other radioisotopes make its way through the marine food chain?
How is the changing global population affecting people's daily lives? With the UN set to announce that there are now seven billion people on the planet, BBC News reporters spoke to seven people from around the world to hear their stories. Production: Anna-Marie Lever, Fiona Crack, John Galliver, Emily Jones.