Molecule of the Month: Plumb line to a grisly death: Lead pollution has been a threat for thousands of years, says John Emsley

Atmospheric pollution by lead existed long before the industrial revolution.

That was the surprising conclusion reached earlier this year by Dr Ingemar Renberg, of the University of Umea in Sweden. He made his discovery after studying levels of lead in layers of lake sediment.

This month Dr Claude Boutron and colleagues at Domaine University in Grenoble, France, confirmed Renberg's finding by analysing the snow that fell on Greenland during Roman times. They found that the lead level rose over 3,000 years from a 'natural' background of 0.5 parts per trillion (ppt), which comes from dust in the atmosphere, to 2ppt.

At its height, Roman lead production was 80,000 tons a year, much of it mined in Britain. Professor Iain Thornton and Dr John Maskall, of Imperial College, London, have been researching lead pollution around smelting works in Derbyshire and North Wales that were in use from Roman times to the Middle Ages.

'Britain is unique in that we are able to monitor lead pollution over such long periods of time,' Thornton says. They discovered that despite heavy surface contamination around the sites, there was little evidence of lead leaching into surrounding soils or contaminating ground water.

Rome flourished from about 350BC to AD400, and lead was commonly used in roofs, pipes, cisterns and pewter. The Romans also made white lead paint and used sugar of lead (lead acetate) syrup to sweeten sauces - thus poisoning large numbers of the populace.

After the Dark Ages, lead mining began again and people found new outlets for it, such as pottery glazes, bullets and printing type. The Victorians even used lead acetate as a medicine for diarrhoea and as hair dye.

They also soldered tins with lead, a practice that explained the mysterious disappearance of Sir John Franklin's expedition, which set off in 1848 to search for the North West Passage to the Pacific. After perfectly preserved bodies of crew members were uncovered in frozen graves on Beechey and King William Islands in the Eighties, analysis showed they had died of lead poisoning. The cause was proved to be the lead solder of their tinned food, confirmed by the ratio of lead - 206 to 204 - isotopes in their bodies, which matched the ratio of the tins found nearby.

In 1921, Thomas Midgley found that adding tetraethyl lead (TEL) to petrol boosted its performance, and by the Sixties cars were running on four-star leaded petrol. Lead in the snow of the Arctic reached a maximum 300ppt by the late Seventies, although levels are now declining thanks to the introduction of unleaded petrol.

This summer Dr Richard Lobinski, of the University of Antwerp, analysed the lead content of Chateau Neuf du Pape from a vineyard at the junction of the A7 and A9 motorways in the Rhone region of France. His group's findings even reflected the changes of compound used to make leaded petrol. TEL residues in the wine declined from the Fifties onwards, while TML (tetramethyl lead) derivatives increased, together reaching a maximum 0.5 micrograms per litre by 1978. They concluded that if the 1978 wine was drunk regularly, it could cause mild lead poisoning. Curiously, this is one of the best vintages and can cost up to pounds 25 a bottle. Since 1980 the levels of lead in Chateau Neuf du Pape have fallen and are now only a 10th of that found in earlier years.

This is not the first time that wine has been contaminated with lead. The ancient Greeks used it to 'sweeten' wine, and although their wine was popular, it was also reputed to cause miscarriages.

In the Middle Ages, vintners adulterated cheap wine with lead, sometimes resulting in mysterious local outbreaks of stomach cramps, constipation, weariness, anaemia, insanity and lingering death. These are the symptoms of severe lead poisoning. Old wine, also, may still be contaminated by the lead/tin seals around the necks of bottles - these were not phased out until the Eighties.

Lead is element number 82 and has the chemical symbol Pb, which comes from the Latin plumbum, the same word that gave us 'plumber' and 'plumb bob'.

Lead weights used by fishermen were responsible for the deaths of many swans which scooped up lost sinkers as they fed in the mud along the bottom of rivers. These have now been replaced by non-toxic sinkers.

Yet almost as soon as one form of lead pollution is cleared up another appears. This month saw an outbreak of lead poisoning in Hungary, due to red lead being used to colour paprika, the spicy flavouring made from dried red peppers. Red lead is an oxide which was used for hundreds of years as a pigment.

Why is lead so harmful to health? Most of the lead in our diet passes straight through us, but a little is absorbed into the bloodstream and this is taken up by the enzymes that make haemoglobin and poisons them. The result is that a precursor to haemoglobin, a toxin called aminolevulinic acid, then builds up in the body, and this is what causes the symptoms.

The gut is paralysed, hence the stomach cramps and constipation; excess fluid in the brain causes headaches and loss of sleep; and it affects the reproductive system, which may lead to a miscarriage or birth deformities.

Anaemia is also a long-term effect.

Children who live in the inner cities are thought to be most at risk from lead poisoning, and in the UK some researchers blame lead-laden traffic fumes for learning difficulties and violent behaviour. In the United States, lead paint from old housing is blamed, and inner-city children there are automatically given a blood test for lead before they start school.

John Emsley is the author of 'The Consumer's Good Chemical Guide', published by W H Freeman ( pounds 18.99).

(Photograph omitted)