GLOBAL atmospheric pollution dates back to Roman and Greek times - long before the Industrial Revolution - according to scientists who have detected lead fallout in samples of ancient Greenland ice.
The researchers have detected small but significant quantities of lead particles in ice cores drilled to a depth of more than a kilometre - covering a timespan of nearly 8,000 years.
They detected surges in the amount of lead - a by-product of the process of extracting silver from lead ore - at depths corresponding to the rise of Athens and Rome. They also found lead pollution from medieval and Renaissance silver mines.
Finding lead in ice cores represents the oldest report of international atmospheric pollution, scientists say in today's issue of the journal Science. 'Analysis of the Greenland ice core covering the period from 3,000 to 500 years ago - the Greek, Roman, Medieval and Renaissance times - shows that lead is present at concentrations four times as great as natural values from about 2,500 to 1,700 years ago (500BC to AD300).'
The researchers, led by Claude Boutron, a geologist at the Domaine University at Grenoble in France, estimate that about 400 tons of lead fell on the Greenland ice cap during the 800 years of the Roman Empire. This is about 15 per cent of the lead that has fallen on the area in the past 60 years of using lead additives in petrol, they say.
Professor Clair Patterson, a geochemist at the California Institute of Technology, in Pasadena, said the pollution came from the ancient tradition of smelting lead ore in open furnaces in order to extract the valuable silver. Although the process - known as cupellation - was invented about 5,000 years ago, it was the Greeks who first exploited it on a large scale, notably at the silver mines of Laurium on the Aegean Sea, which financed the Greek naval victory over the Persians.
Lead smelting during Roman times was done on an even larger scale for a much longer period. At its peak, the Romans produced airborne lead emissions equivalent to the pollution produced at the beginning of the Industrial Revolution 1,700 years later, Professor Patterson said.
'What we see from the ice record of the Greenland cores is that we have been poisoning the Earth's atmosphere with lead for 2,000 years.' At around the birth of Christ, silver mines were producing about 80,000 tons of lead slag a year and at least 1 per cent of this went into the air, he said.
The scientists analysed 22 ice cores drilled to depths from between about 300 metres to 1.3 kilometres. The deepest core corresponded to a period 7,760 years ago, long before lead ore was smelted for silver, which acted as a measure of background levels of lead.
Professor Patterson said that the eventual depletion of the lead and silver mines - resulting in a shortage of silver coins - led to the decline and fall of the Roman Empire. Lead poisoning, which results in mental deterioration, played only a minor role, he said.
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