If only the Romans had an EPA
Scientists, working with core samples taken from the depths of Greenland's ice, say they have found "unequivocal evidence of early large-scale atmospheric pollution" by lead. Moreover, instruments capable of detecting parts per trillion quantities of four lead isotopes incriminated the Carthaginians's and Romans's working the silver mines in southern Spain between 600 B.C. and 300 A.D.
These and other results were reported in the December 1997 issue of Environmental Science & Technology. They were presented by Dr. Kevin J. R. Rosman of Curtin University in Perth, Australia, and his colleagues there and at the Laboratory of Glaciology and Geophysics of the Environment in Grenoble, France.
The scientists focused on the ratio of two stable isotopes of lead at points within a mile-and-a-half-long ice-core sample. The sample formed over millennia from precipitation carrying particles from the air. They found the ratio of lead-206 and lead-207 in 8000-year-old ice to be 1.201. They took this as the ratio existing before people began smelting ores.
All lead-bearing ores have distinctive isotopic-ratio signatures. The ratio for lead-206 to lead-207 from the silver-mining and smelting district of Rio Tinto (near the modern city of Nerva in southwestern Spain) is 1.164. Calculations by the Australian-French scientists showed that 70 percent of the global atmospheric lead pollution came from the Roman-operated Rio Tinto mines during the period that the Roman Empire was at its peak.
Archeologists are reported to recognize the Rio Tinto mining region as having been one of the richest sources of silver in the ancient world. The Romans reportedly have left some 6.6-million tons of slag from their smelting operations at Rio Tinto.
Silver was but one of the metals extracted from Rio Tinto's ore. The Romans also harvested the lead because it is easily shaped, melted, and molded. Lead was widely used by the Romans for plumbing, stapling masonry, casting statues, and manufacturing many kinds of utensils. All these uses presumably contributed to the chronic poisoning of Rome's populace. The Romans also used lead vessels to boil and concentrate fruit juices and preserves. Fruits contain acetic acid, which reacts with metallic lead to form lead acetate. Lead acetate sweetens food--it once was called "sugar of lead"--but causes lead poisoning. The ailment is often fatal and, even in mild cases, debilitates and reduces cognition.
More recent representations of the Greenland ice core suggest that smelting of lead-bearing ore declined sharply after the fall of the Roman Empire. However it had a renaissance during the Renaissance. By 1523, the last year for which the scientists conducted their Greenland ice analysis, atmospheric lead pollution had reached nearly the same level recorded for the peak period of Roman mining.
The previous article was adapted from a report by Malcomb W. Browne, appearing in the science section of the December 9, 1997, issue of The New York Times.