Even in Roman times, human activity altered atmospheric composition

Greenland ice cap reveals a record of large-scale lead air pollution


he chemical analysis of a 9,000-foot core taken from the Greenland ice sheet has now uncovered unequivocal evidence of large-scale atmospheric lead pollution in the Northern Hemisphere dating to 300 A.D. The source has been traced to ancient Carthaginian and Roman mines in Spain, according to Dr. Kevin J. Rosman of the Curtin University of Technology in Perth, Australia. Rosman's group, along with colleagues from the Domaine Universitaire in France, reported their results in the December issue of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.

Using sophisticated techniques, Rosman's team measured the amount of four different lead isotopes in the 2,000 year-old ice. "The work is difficult," Rosman notes, "because it must be performed in extremely clean laboratories using ultraclean procedures." These measures were necessary because the lead concentrations were as low as one picogram per gram of ice, where one picogram is about one trillionth the weight of a paper clip. The result is a unique lead isotope "fingerprint" that can be related to the original sources.

"The history of pollution of the earth resulting from human activity is contained in the Greenland ice sheet," says Rosman. While others have used lead isotopes to identify trade routes and establish the authenticity of ancient artifacts, Rosman's group has taken the work one step further to identify the origin of pollution in the ancient atmosphere. Analysis of the lead isotope ratios in the ice shows that the mining areas in Spain were the dominant sources of this lead. The results provide quantitative evidence of the importance of these mining districts to the Carthaginians, who controlled the area from 535 - 205 B.C., and the Romans, who followed until 410 A.D. Rosman has also identified the specific mining region, stating that about 70 percent of the lead in the Greenland ice between 150 B.C. and 50 A.D. came from the Rio Tinto mining district in southwestern Spain.

"Our work," Rosman relates, "proves that human activity and not natural phenomena significantly altered the composition of the atmosphere, even as far back as Roman times. Vast quantities of lead were produced as a by-product of smelting sulfide ores for silver. However, lead found extensive use in Roman times and is sometimes referred to as Roman metal for that reason. Because it is a corrosion-resistant metal and is easily worked, it found use in plumbing, architecture and shipbuilding. It was also used as a preservative for food, and was added to wine to stop fermentation. In the later application, its high toxicity was a health hazard and there is evidence that lead may have contributed to the fall of the Roman Empire."

For further information, contact Jim Bohning, email: j_bohningacs.org