12th-century lead pollution visible in Alpine ice

Lead pollution produced by 12th-century mines in Britain can be seen in Alpine ice cores, new research reports – directly mirroring historical records and demonstrating the impact of political events of the time.

Lead-silver ores have been mined for centuries, for use in the production of diverse objects such as coins, roofs, water pipes, and even paint. Echoes of this industry can still be seen today: in a study recently published in the journal Antiquity (https://doi.org/10.15184/aqy.2019.202), analysis of an ice core taken from the Colle Gnifetti (CG) glacier in Switzerland has revealed layers containing chemical elements such as lead, deposited by winds coming from the north-west, carrying dust and pollution from the UK. The pollution levels offer yearly insights into historical production levels and the political, social, and economic situation in Britain at the time.

PHOTO: © Nicole Spaulding.
The ice core was drilled from the Colle Gnifetti glacier in the Monte Rosa Massif on the Swiss-Italian border in 2013. PHOTO: © Nicole Spaulding.

Previous research has looked at pollution levels in the 14th century and the impact of the Black Death on lead and silver production, as well as the change to a silver monetary system in mid-7th-century western Europe (see CA 347). In this new study, experts from the Universities of Nottingham, Harvard, and Maine investigated what the CG core can tell us about annual production levels in England in the 12th century, and how this reflects the wars, buildings projects, and other political events that occurred under the Angevin kings: Henry II, Richard I, and John.

This time period was chosen because the lead pollution signal was at its highest level prior to the modern era (AD 1650), in the period between c.1170 and 1220. Additionally, English taxation records known as the Pipe rolls, which documented annual production levels, were kept in great detail from 1167 onwards, allowing measurements from the ice core to be directly matched with historical records.

The project’s analysis highlighted the association between lead and silver production levels and the workings of governments. For example, it is possible to identify the deaths of Henry II, Richard I, and John in the ice core because lead production plummeted in these periods. The pollution levels also reflect other times of political crisis or royal absence, with lead deposition falling in 1170 during Henry II’s dispute with the Church (leading to the murder of Thomas Becket), and in 1191–1192, when Richard I was absent from the kingdom co-leading the Third Crusade.