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Pollution From Ancient Metallurgy is Still Affecting the Environment Today

Traces of dangerous heavy metals in soil and water suggest the anthropocene may extend thousands of years before the present.

by Monica Blaylock
Mar 23 2015, 4:15pm

​It's easy to think that the ​anthropocene—the unofficial new epoch in which humans are causing drastic environmental change on a global scale—began with the industrial revolution. Or, if not the industrial revolution, a more recent study suggests that it may have begun in the early 16​00s. But a growing group of researchers are beginning to believe that human society has significantly impacted its natural surroundings for almost as long as we've been around.

"We're suggesting the anthropogenic era is extending thousands of years before the present," said David Pompeani, PhD candidate in Geology and Planetary Science at University of Pittsburgh.

PhD candidate Aubrey Hillman, also from the University of Pittsburgh, recently published a paper in the journal of Environmental Science and Technology, in which she examined core samples of sediment from Lake Erhai in the southwestern Chinese province of Yunnan. Hillman discovered extremely large quantities of lead, silver, zinc and cadmium, and her team traced the source of these pollutants to the production of copper and silver starting in 1500 BC and continuing through the reign of the Mongol Yuan Dynasty (1271-1368 AD).

"This study is the first to show that pollution was greater in the past than today. It shows that people may have been seriously impacting the environment for much longer than we thought," Hillman wrote.

According to their research, ancient metallurgy in the area created three to four times more lead pollutants than modern metal working techniques. Though it may not be the only example, it is certainly the first example, according to Hillman, of a Chinese society polluting more than their modern equivalents.

"Through the process of silver smelting, many pollutants [...] made their way into the lake sediments, but they also would have been deposited on the surrounding landscape. As land use change occurs and soils are lost, these heavy metals may be mobilized and cause contamination issues," Hillman wrote.

During the reign of Emperor Kublai Khan (1260-1294 AD) the Mongols ruled about one-fifth of the world's inhabited land, and their main currency was silver coin. Not surprisingly, this precious metal was in high demand. Silver smelting—in which impurities are burned away from silver ore to make it more pure—was conducted on a massive scale. Hillman's research team studied pollution near the mines of the Yunnan Province because they were responsible for producing more than 50 percent of the Empire's silver during this time.

"We speculate that the peak in lead pollution 700 years ago may, in part, be contributing to modern-day pollution in the lake," Hillman noted. "We think it's important that people are aware of these potential complications arising from land use change."

University of Pittsburgh researchers with a sediment sample from Lake Erhai. Image: Aubrey Hillman

Research found the lake sediment had a concentration of lead of about 120 parts per million. Sediment quality guidelines for freshwater find that harmful effects from lead pollution can impact aquatic organisms at about 128 parts per million. In other words, run-off from ancient smelting was not only dangerous to the lake's environment—it remains potentially harmful, even today.

While research is still ongoing, it's worth noting that these ancient smelting processes could have had an impact on agriculture too, as one-sixth of China's cultivable land is affected by excessive accumulation of​ heavy metals.

In the past archaeologists had fewer ways to study ancient civilizations and the effects they had on their environments. Records were pieced together by studying man-made items such as tools and weaponry, but this was only scratching the surface. Using geochemistry—the study of chemical changes and composition of the Earth—scientists can examine particulates not seen by the naked eye and piece together a more complete picture of ancient cultures and their environmental impacts.

In North America, off the shores of southern Ontario's five Great Lakes, David Pompeani of the University of Pittsburgh and his team have used such techniques to study the environmental impact of 8000 year old copper​ mines. Others have documented the widespread and lasting effects of Inca gold a​nd silver industry on the environments of South America, while still other teams have discovered that Ancient Roman metallurgy polluted on a global scal​e over two-thousand years ago.

"The geochemistry has social implications. Its a mechanism to get information about social change," he continued, adding that "it offers a brand new perspective into the past that was previously limited to artifacts. With this work we're actually measuring the dust to infer processes that are happening, the timing, the magnitude, and the spatial location."

"When we look at the particulates we're looking at things used during metalworking, like mercury and lead, because they usually only show up during human activity," Pompeani said.

Of course, more research is needed before ancient environmental data can be formally included in global models of climate change. But this is what researchers such as Hillman and Pompeani are aiming for. It would strengthen their case that the anthropocene may have indeed begun many millennia before the industrial revolution.

"My opinion is we're going to find out [these records] are very important," said Pompeani. "The nature of human society is to modify their environment. Human agency itself is such a powerful force, it might have been a force of nature thousands of years ago too."

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