Geologists led by Aubrey L. Hillman of the University of
Pittsburgh used sediment cores from Erhai Lake to examine levels of
heavy metal pollution in southwestern China over the past 4,500 years.
According to a report in
Science,
they found a rise in copper contaminants at the start of China’s Bronze
Age, but those levels remained stable until the Mongols conquered China
in the late thirteenth century A.D. The sediment cores show that heavy
metal pollution during the reign of Kublai Khan and the Mongols, who
mined and processed silver for coins, jewelry, art, and taxes, was three
to four times higher than modern industrialized mining. To read about a
similar study, see "
Colonial-Era Air Quality Recorded in Andean Ice."
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