Mercury (Hg)

Mercury is beautiful, yet deadly poisonous. Known as quicksilver, the Minamata international treaty aims to phase its use out completely. But how will the ban on element 80 affect artisanal gold miners? Or coal-fired power stations? And why does so much of this liquid metal end up in tuna and swordfish? (Picture: Ghanaian artisanal miner holds mercury in his hand; Credit: Matt Davies/BBC)