Environmental Protection

Indiana Study Finds Antimony Properties Not Similar to Arsenic

antimony 

Mine workers are often exposed directly to stibnite ore (antimony sulfide) and to airborne antimony via inhalation and skin exposure.

The world's largest antimony mine in Xikuangshan, China, has become the world's largest laboratory for studying the environmental consequences of escaped antimony ─ an element whose environmental and biological properties are still largely a mystery.

"Antimony is an emergent contaminant," said Faye Liu, Indiana University Bloomington Ph.D. student and lead author of the paper on. "Antimony speciation and contamination of waters in the Xikuangshan antimony mining and smelting area, China." "People have not paid enough attention to it," she added.

In small quantities, antimony is used to harden lead in bullets, improve battery performance, and combat malaria. Little is known about its toxicity, in part because the metalloid element is usually found at low, parts-per-billion concentrations in natural environments. At Xikuangshan, Liu and her colleagues found that aqueous antimony concentrations could be as high 11 parts per million, 1,000 times the antimony levels found in uncontaminated water.

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," said IU Bloomington geologist Chen Zhu, Liu's adviser 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.

Land within and around the mining area is used for farming. The drinking water plant for local residents was built in the mining area. Zhu says health problems are common at Xikuangshan, possibly the result of antimony intoxication.

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 Bloomington 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.

The Xikuangshan antimony mine is the world's largest. Since antimony mining began there more than 200 years ago, mine production has increased steadily to the present day. Today, Xikuangshan produces 60 percent of the world's antimony.

Liu also was advised by IU Bloomington biogeochemist and inaugural Provost's Professor Lisa Pratt. Zhu and Pratt recently began a joint project to learn more about the biogeochemistry of antimony. The scientists' antimony research complements their concurrent NSF-funded research on arsenic.

The research was supported by the China Scholarship Council and Indiana University. It was authored by Liu, X. Chris Le, Anthony McKnight-Whitford, Yunlong Xia, Fengchang Wu, Erika Elswick, Claudia C. Johnson, and Zhu.

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