The inhabitants of Montchavin in the French Alps knew something was killing them. They just didn't know what. Some wondered whether lead from a disused mine in the village had leaked into the water supply. Others thought mobile phone masts were to blame. One woman believed the area was cursed. Between 1991 and 2019, 16 people – almost a tenth of the area's 200-strong population – were diagnosed with amyotrophic lateral sclerosis, a fatal condition more commonly known as motor neurone disease (MND). In other words, if you lived in Montchavin, you were 20 times more likely to contract MND...