Ancient soil pollution, contemporary consequences

Published 30 May 2017

Some of the world’s first known man-made soil pollution is showing that contaminated soils may be compromised for millennia.

University of New England (UNE) researcher Dr Matt Tighe has been measuring the long-term effects of copper smelting at archaeological sites in central Thailand that date back 3000-4000 years.

His early findings pose troubling questions about the longevity of soil pollutants and how they threaten future food security.

“Some sites were grossly contaminated, containing concentrations of copper 150 times what we would expect in Thai soils, and there is evidence that some of the copper is mobile,” Dr Tighe said. “Mobile copper is capable of moving with water, being taken up by plants and thus made available to animals. Some of the levels we measured were well above what’s recommended for stock intake and could also pose a risk to humans eating agricultural produce.”

Trace elements like copper occur naturally in soils to varying degrees, but Dr Tighe’s work lends support to the theory that once added to the environment they can endure far longer than we imagined.

Copper at the Thailand sites is the result of early industrial activity in villages, where metal workers heated crushed rock in small crucibles over open fires to produce tools, small ornaments and jewellery. Some of this copper contaminated the area’s soils.

Using a portable X-ray fluorescence spectrometer resembling a Star Trek gun, researchers can shoot X-rays into a soil sample and gain a relative reading of the elements it contains. Dr Tighe has measured copper levels in archived soil samples taken as part of the Thailand Archaeological Project and has made two visits to Lopburi, in central Thailand, to collaborate with archaeologists from UNE, the University of Pennsylvania, the University of Santa Clara and the Thailand Federal Government. He is one of the few researchers in the world studying the soil extracted during such digs.

“Most archaeological sites are now in areas with rapidly expanding populations, so it is important to understand how long pollution remains a problem and what risks it poses as it ages,” said Dr Tighe, who co-leads the Pollution Science Research Group at UNE with Dr. Sue Wilson.”We are also interested in studying whether the ancient contaminants have moved into the agricultural crops grown in the soil. These sites require more investigation from an agricultural, environmental and human health perspective.”

Such smelting sites are scattered throughout similar locations in Cambodia, Laos, Burma and China, as well as the Middle East, Wales and Spain. Understanding their impact on the surrounding soil has implications for communities wrestling with pollution the world over.

“Learning how long pollution remains a problem is important in terms of the pollution we are creating now, including that at mining sites,” Dr Tighe said. “If we visit these sites 3000 years later and find high concentrations of a trace element, then people are possibly going to be dealing with any contamination we cause today hundreds of years later.”

IMAGE: University of New England scientist Dr Matthew Tighe uses a portable X-ray fluorescence spectrometer to analyse soil samples in the lab.