In 2017, a new global treaty was meant to bring mercury pollution under control. But three decades of data from UK harbor porpoises show mercury is still increasing, and is linked to a higher risk of dying from infectious disease. When the Minamata convention came into force eight years ago, it was hailed as a turning point. The global treaty on mercury commits countries to reducing mercury from coal-fired power plants, industry and products, like batteries and dental fillings.