 |
 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."  |
acs.org