Lead pollution resulting from Roman gold extraction in northwestern Spain

Abstract

Roman mining and metallurgy left a detectable signal of lead pollution throughout Europe, northern Africa, and the Middle East. Las Médulas, in Northwestern Iberia, was the largest Roman gold mine and fundamentally altered the local landscape. To document the environmental consequences of this activity, we present a 4000-year record of lake sediment geochemistry from Laguna Roya, 35 km south of Las Médulas. Using the concentrations of trace metals weakly bound to sediment including lead, antimony, bismuth, and arsenic, we find increased levels of these metals from 300 BC to AD 120, during the Roman Republic/Empire. We attribute these increases to the atmospheric deposition of heavy metals arising from the regional extraction, processing, and/or smelting of gold ores. Lead pollution at the peak of this activity (15 BC) is twice as high as modern-day concentrations, suggesting that the amount of pollution generated by pre-Industrial civilizations and the associated environmental impacts are much larger than previously estimated. We find additional increases in antimony and bismuth from AD 1500 to 1700, possibly associated with post-medieval mining activity. Concentrations of lead begin to increase again ~AD 1860 during the start of the Industrial Revolution and reach a peak in AD 1990. Declining modern-day levels of lead can be attributed to the phase out of leaded gasoline. This is one of only a handful of studies to document pre-industrial pollution levels substantially higher than present-day, adding to a growing body of evidence that anthropogenic environmental degradation has been taking place for several thousands of years.