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Mine workers are often exposed directly to stibnite ore (antimony sulfide) and to airborne antimony via inhalation and skin exposure. Used in small quantities, antimony has a wide variety of applications—from hardening the lead in bullets to combating malaria. Little is known about antimony’s toxicity, in part because the metalloid element is usually found at low, parts-per-billion concentrations in natural environments. (Credit: Chen Zhu)

INDIANA U. (US)—Waters around the Xikuangshan mine in southwest China contain levels of antimony that are two to four orders of magnitude higher than normal, making it a unique laboratory to study the contaminant’s environmental impact.

Land within and around the mining area is used for farming. The drinking water plant for local residents is also in the mining area, and health problems are common.

“Antimony is an emergent contaminant,” says Faye Liu, a doctoral student at Indiana University. “People have not paid enough attention to it.”

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Heaps of ore tailings are exposed directly to the open air at Xikuangshan. (Credit: Chen Zhu)

Details of the report appear online in Environmental Geochemistry and Health.

Used in small quantities, antimony has a wide variety of applications—from hardening the lead in bullets to combating malaria.

Little is known about antimony’s toxicity, in part because the metalloid element is usually found at low, parts-per-billion concentrations in natural environments.

Aqueous antimony concentrations at Xikuangshan were found to be as high 11 parts per million—1,000 times the antimony levels found in uncontaminated water—presenting an opportunity to understand what happens to antimony, geologically and chemically, when large quantities of it are introduced to the environment.

That knowledge may be useful to investigations of antimony contamination near factories and military bases around the world.

The U.S. Environmental Protection Agency and similar regulatory agencies in Europe operate under the assumption that antimony’s properties are similar to those of arsenic, another element in antimony’s chemical group.

“That will need to change,” says geologist Chen Zhu, Liu’s advisor and the project’s principal investigator.

“We saw that antimony behaves very differently from arsenic—antimony oxidizes much more quickly than arsenic when exposed.”

The vast majority of antimony the scientists isolated at Xikuangshan was of the “V” type, an oxidation state in which the metal has given up five electrons.

It is believed V is the least toxic of the three oxidation states of which antimony is capable (I, III, and V). It is not known whether antimony-V’s relatively diminished toxicity is upended at Xikuangshan by its overwhelming presence.
Zhu says he is discussing a possible collaboration with IU School of Medicine toxicologist Jim Klaunig.

Researchers would return to Xikuangshan to determine whether the elevated antimony can be tied to acute and chronic health problems among those who live in the vicinity. Another possible study group might be those Chinese who live downstream of Xikuangshan along the Qing River.

As part of their study, Zhu and scientists from the Chinese Academy of Sciences conducted field work at Xikuangshan in 2007, drawing multiple water samples from 18 different sample sites.

Samples were shipped back to Indiana University for atomic fluorescence spectroscopic analysis and to Alberta for inductively coupled plasma mass spectroscopy analysis.

The scientists learned antimony-III was rare, beyond detection or present at trace levels. The near totality of antimony in each water sample was antimony-V.

Researchers from the University of Alberta and the Chinese Academy of Sciences contributed to the study, which was supported by the China Scholarship Council and Indiana University.

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