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Syria, Salisbury, Malaysia Airport – all sites of nerve agent attacks carried out in the past couple of years. Yet hundreds of countries have supposedly destroyed their stockpiles of chemical weapons. It’s also illegal to produce and use them.

We look to four of the world’s most experienced chemists and researchers to tell us more about the nerve agents used in these recent attacks, how they are regulated and the ongoing problems of getting rid of them.

(Photo: Members of the emergency services in green biohazard encapsulated suits. Credit: Ben Stansall/AFP/Getty Images)