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17 January 2004
Peat bog reveals mining pollution through the ages

Scientists have reconstructed the environmental history of a Celtic mining town by digging through a peat bog near Dijon in France in search of lead residues and pollen grains. Their results confirm some historical theories about the settlement says Fabrice Monna from the University of Bourgogne in Dijon, who led the study. "Archaeologists suspected that there had been mining there before the first century CE, but there was no direct proof until now."
     But the results also serve as a sobering reminder about how long pollution lasts. "Any lead pollution we create today will persist for thousands of years into the future," says Monna. The finding isn't particularly surprising to environmental chemists. Once lead is locked up in organic material such as peat, it tends to stay put rather than being washed away by water. But the study emphasizes that researchers should pay more attention to where pollution comes from, says Monna.
     The peat bog the researchers analysed is in the modern day region of Morvan in France, about 100 km south west of Dijon. The team found no evidence of mining activity from before about 1300 BCE, providing a 'natural' level of lead pollution that could prove important for future clean-up efforts at the site. Pollen records show that the area was covered in hazel, beech and oak trees, along with a few cereal crops. But around 1300 BCE, the first lead mine opened. In those days, lead was a valuable resource as it was used to help smelt other ores. Adding lead lowered the melting point of the metal mixture to temperatures that a charcoal furnace could reach - about 700 C. Lead was also later used for water pipes and other vessels.
     The opening of the mine is marked by a sharp rise in the lead levels in the peat, along with a drop in pollen from local trees, which were probably chopped down as fuel for the smelting ovens. Lead pollution peaked in the first century BCE, after a Celtic tribe settled the area to exploit the rich deposits of lead, silver and zinc in the surrounding hills, and once again in the nineteenth century at the height of the Industrial Revolution.

Source: Nature (13 January 2004)

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