Fouling the air: not just a modern problem.

Greece gave the world philosophers and timeless tragedies. Rome bequeathed Latin and enduring architecture. But that's not all that came out of these ancient societies. Lake sediments in Sweden contain evidence of air pollution that drifted over the skies of Europe even as Socrates and Seneca paced through marble halls.

"Most people believe that there was no air pollution in preindustrial times," says Ingemar Renberg, an environmental scientist at the University of Umea in Sweden. Yet he and his colleagues detected signs of lead pollution in Swedish lakes going back at least 2,600 years. "This is the clearest evidence so far presented for preindustrial airborne pollution," says Renberg.

The Swedish researchers measured concentrations of lead in sediment cores pulled from 19 lakes. Using radiocarbon dating, they pinpointed important changes, which they describe in the March 24 NATURE.

Lead amounts remained low and showed little variation between 10,000 and 3,000 years ago. Around 2,600 years ago, they started to rise, reaching a small peak 2,000 years ago at five times the natural amount of lead. Concentrations then dropped but began to rise steeply 1,000 years ago. They jumped even more during the 1800s and crested in 1970.

The rise and fall of lead concentrations in the sediments appear to parallel the history of lead production in the ancient world, according to Claire Patterson, a geochemist at the California Institute of Technology in Pasadena who studies preindustrial use of metals. Patterson notes that lead pollution started to appear in Swedish lakes at roughly the time when Greece began coining silver, which was obtained by melting down lead ores.

Lead mining increased until approximately 2,000 years ago, when the Roman Empire exhausted its principal deposits in Spain. During Roman times, people used lead for water pipes, cisterns, and even as an additive for wine, says Patterson. Such heavy reliance on lead by the Romans has prompted some to speculate that lead poisoning contributed to the empire's fall.

The lead increase 1,000 years ago correlates with rising silver production and lead use in Germany.

Renberg's team argues that lead in the lakes came from air pollution because the changes in lead concentration occurred at the same time all over Sweden, ruling out the possibility that local fires caused the spikes in lead values. The lakes also show a gradient, with the smallest amounts of lead in the north and the largest in the south - the region closest to early Roman cities in England and northern Europe.

By today's standards, ancient air pollution was modest: Lead concentrations 1,000 years ago only reached a tenth of modern values in the sediments, says geochemist Stephen Norton of the University of Maine in Orono. But because lead use has such a long history, pollution added at least as much lead to the environment during ancient times as it has since the industrial revolution, says Renberg. He believes preindustrial air pollution also contained other heavy metals.