Pan-European atmospheric lead pollution, enhanced blood lead levels, and cognitive decline from Roman-era mining and smelting

Abstract

Ancient texts and archaeological evidence indicate substantial lead exposure during antiquity that potentially impacted human health. Although lead exposure routes were many and included the use of glazed tablewares, paints, cosmetics, and even intentional ingestion, the most significant for the nonelite, rural majority of the population may have been through background air pollution from mining and smelting of silver and lead ores that underpinned the Roman economy. Here, we determined potential health effects of this air pollution using Arctic ice core measurements of Roman-era lead pollution, atmospheric modeling, and modern epidemiology-based relationships between air concentrations, blood lead levels (BLLs), and cognitive decline. Findings suggest air lead concentrations exceeded 150 ng/m³ near metallurgical emission sources, with average enhancements of >1.0 ng/m³ over Europe during the Pax Romana apogee of the Roman Empire. The result was blood lead enhancements in young children of about 2.4 µg/dl above an estimated Neolithic background of 1.0 µg/dl, leading to widespread cognitive decline including a 2.5-to-3 point reduction in intelligence quotient throughout the Roman Empire.

Keywords: human health; intelligence quotient; lead poisoning; lead pollution; roman antiquity.

Fig. 1.

Changes in Arctic lead pollution from 500 BCE to 600 CE and silver content in Roman coinage. Annual (gray) and 11-y median-filtered (black) average of normalized nonbackground lead (nbPb) fluxes from three Arctic ice cores (SI Appendix, Fig. S1), with major historical events and changes in silver bullion content in Roman coinage identified (29). The inset shows the outline of the extent of the Roman Empire in 14 CE and locations of ice cores (crosses) and Roman-era silver and lead mining sites (blue dots).

Fig. 2.

Simulated annually averaged nonbackground lead (nbPb) concentrations in air, blood lead level (BLL) enhancements in young children with associated cognitive deficits, and average annual nbPb deposition during the Pax Romana. (A–C) Scenario 1 with emissions only from Rio Tinto (white dot). (D–F) Scenario 2 with emissions distributed equally among known Roman-era silver and lead mining sites (white dots). Blue contours in B and E show estimated IQ point changes resulting from enhanced BLLs. Crosses identify tooth enamel study sites. The dotted line shows the high-resolution FLEXPART model domain. The heavy black line delineates the extent of the Roman Empire in 14 CE.

Fig. 3.

Lead isotopic ratios in Greenland ice during and following the Pax Romana. Included are prior GRIP (18) and new NGRIP2 total and Holocene background-corrected measurements (Materials and Methods). Ellipses represent typical source compositions from Roman-era mining sites (Materials and Methods).