We know that lead is a dangerous metal that accumulates in the body, and that it's particularly harmful to the young. Yet 800 years ago, so much lead was mined that traces of the toxic metal have been found in the bodies of medieval farmers and miners. A new study of an ice core from a Swiss glacier has provided a clearer picture of medieval lead production.
One important mine was in the High Peak district of Derbyshire, roughly in the middle of England. Lead and silver are often found in the same ore, so lead pollution can indicate silver production too. Winds from the northwest delivered lead dust from England to the Colle Gnifetti glacier in the northwest Swiss-Italian Alps more 930 miles away.
Scientists took an ice core from a north-facing slope of the glacier near the town of Monte Rosa. The ice core is about 79 yards long and records about 2,000 years of events like volcanic eruptions, Saharan dust storms and manmade lead pollution. Scientists used a laser to take 0.004-inch slices of the ice core, each representing a few days or weeks of snowfall. They analyzed 50,000 slices for about a dozen elements, including lead.
The Romans smelted silver and other ores and accumulated lead in their bodies. The heyday for lead pollution was the Industrial Revolution between 1790 and 1870, when lead was found in paints, pipes and ceramics. Lead acetate was even used to sweeten wines after long voyages from Italy and Spain.
The scientists found tracking lead pollution in the ice core provided insight into the medieval English economy. The cores from the years between 1170 and 1219 had the highest lead levels measured before the Industrial Revolution. Another peak appeared in the 1970s, corresponding to the use of leaded gasoline.
The scientists studied the English Pipe rolls, a record of taxes paid by miners for one-ton cartloads of lead. Elevations in lead levels coincided with significant events in history. A drop in lead levels in 1170 correlated with King Henry II sending assassins to kill Thomas Becket, the archbishop of Canterbury, when the king was at odds with the pope. Mining slowed and tax collections declined.
Ten years later, the king and pope came to an arrangement, and Henry funded the rebuilding of the Cistercian Abbeys, leading to large orders of lead to build roofs, gutters and cisterns. Declines in lead production occurred during the civil war with Scotland in 1173-1174 and in 1193 when the Holy Roman Emperor imprisoned and ransomed Richard the Lionheart in Germany.
Peaks in taxes and lead production also occurred during major construction projects including the Clairvaux Abbey (1179-1188), Winchester Palace (1172), Woodstock Palace (1176) and during years when new coins were minted.
The history of England can be read in the lead pollution it generated and deposited in the Swiss glacier. It also shows how much people throughout history were exposed to lead, which we're thankfully much better at controlling today.