‘I see cocaine in wild shrimp in Suffolk’: meet the

Water detective Dr Leon Barron studies London’s wastewater, analysing it in all its chemical, narcotic, polluted glory, before and after treatment. Amazingly, he still drinks the stuff from the tap

If you live in London, Dr Leon Barron knows what you’re up to. He knows what prescribed drugs you’re on – painkillers, antidepressants, antipsychotics or beta blockers – and what illicit ones you’re taking for fun. He knows if you’ve been drinking and when (“Friday and Saturday are the main ones”); perhaps even if you’re worried about your dog getting fleas.

Of course, I only mean the collective “you”, the city. Barron, who leads the Emerging Chemical Contaminants team at Imperial College, has no idea what any individual is taking or doing; he explains that very clearly and carefully. He has a research scientist’s precision plus the slight wariness of someone whose research has grabbed headlines, with the inaccuracies and misinterpretations that brings (I wonder what he thought about “Prawn to be wild”, reporting his research on cocaine residue in wild river shrimps.) But he’s also infectiously enthusiastic and generous with his time, spending a whole morning taking me round his lab and through his groundbreaking work.