When British environmental geochemist Jon Hawkings arrived in Greenland for the first time in 2012, he was impressed. “It’s mind-blowing: You look onto the horizon and it’s just ice and it goes on for 150, 200 kilometers at least.” He went to the Arctic with a group of international scientists. Their goal was to investigate the relationship between nutrients entering coastal ecosystems from glacial meltwater. But the group’s research took an unexpected turn. The scientists analyzed samples from meltwater rivers and fjords and found concentrations of dissolved mercury among the highest ever recorded. Despite it being a pristine and remote...