Leon Barron monitors pollution in our rivers, keeping tabs on chemicals that could be harmful to the environment and to our health. He’s also gathered intelligence on the behaviour of millions of Londoners by studying the water we flush down the loo. His analysis of sewage revealed, for example, just how much cocaine is consumed in London every day. And he’s helped the Metropolitan Police to crack crimes in other ways too, inventing new chemistry tools that can be used by forensic scientists to uncover clues. At school he had no idea he wanted to be an analytical chemist but a short work experience placement at the fertiliser factory convinced him that this kind of detective work was fun. Producer: Anna Buckley