Samples from the Arctic track rising and falling levels of lead over two millennia.

A detailed history of lead pollution’s drift into the Arctic is written in the region’s ice, which records spikes of contamination during periods of intense silver mining, and lower levels during plagues and famines.

Industrial activities such as mining and fossil-fuel burning inject lead into the atmosphere. From there, it can eventually drift down onto polar ice. Joseph McConnell at the Desert Research Institute in Reno, Nevada, and his team hunted for lead in 13 ice cores that were extracted from Greenland and the Russian Arctic and spanned the years between 200 BC and AD 2010.

Arctic lead levels rose by as much as a factor of 300 between the start of the Middle Ages (around AD 500) and the 1970s. After North American and European countries began regulating pollution in the 1970s, lead levels dropped by more than 80% — but are still substantially higher than they were at the outset of the Middle Ages.

The cores provide one of the most extensive records of lead pollution across the Arctic.