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11 November 2005

Increasing global atmospheric antimony contamination: should we put on the brakes?

Measurements of antimony (Sb) in samples of snow and ice from a remote region of the Canadian high arctic show that enrichments of this potentially toxic element in aerosols has increased 50% during the past three decades — At the Institute of Environmental Geochemistry, University of Heidelberg, scientists find surprising results

Measurements of antimony (Sb) in samples of snow and ice from a remote region of the Canadian high arctic show that enrichments of this potentially toxic element in aerosols has increased 50% during the past three decades. The effects of human activities on Sb in the environment are comparable in extent to those of lead (Pb). Antimony is a global atmospheric contaminant.

Which element is fifty times less abundant at the surface of the earth than lead, has also been used by mankind for thousands of years, is thought to have poisoned Mozart, and is used to make PET bottles for the drinks industry? If you guessed antimony (Sb), you're right.

Although it is mainly used today as a flame retardant in plastics, it has numerous other industrial applications, including in alloys with lead to harden car batteries as well as bullets, and in brake shoe pads. Imagine this next time you are driving your car: each time you use your brakes, sub-microscopic particles rich in Sb are abraded from the brake pads and released to the air. In urban aerosols today, Sb is more enriched than any other trace element. Compared to other potentially toxic metals such as lead, cadmium, mercury or arsenic, much less is known about the sources, behaviour, and ultimate fate of antimony in the environment. At the Institute of Environmental Geochemistry, University of Heidelberg, scientists are addressing these issues, with some surprising results.

Using specialised equipment to withdraw long cores of peat from bogs in Switzerland, Dr. Michael Krachler has developed analytical methods and procedures for measuring Sb in the oldest, most pristine, ancient peat samples. Samples which are between six and nine thousand years old have the lowest concentrations of Sb and these are considered to represent the natural "background" abundance of Sb in dust particles which were deposited from the air to the surface of the bog so long ago. The first evidence of atmospheric Sb contamination — when Sb was first enriched in the air, relative to natural values — appeared in the samples dating from the Roman Period, a time in human history when lead ores were extensively mined and smelted.

Lead ores are commonly very rich in Sb, and the peat bogs show that the history of environmental Sb contamination has run in parallel to that of lead. For comparison with ancient contamination, peat samples near the surface of the bog and representing the past few centuries of peat accumulation, have far greater Sb enrichments. In fact, the natural abundance of Sb in these samples is dwarfed by the atmospheric inputs of Sb which were supplied from mining, smelting, and refining of base metals, as well as coal burning, since the Industrial Revolution. The impacts of Sb contamination from human activities is clearly seen even in the peat cores collected from the most remote bogs from Scotland, the Shetland Islands, and the Faroe Islands. Atmospheric Sb contamination not only has a very long history, but it extends even to the most remote regions of Europe. Taken together, these new results show that the impacts which humans have had on the emissions of Sb to the environment are comparable to those we have had on lead.

How extensive is atmospheric Sb contamination? To answer this question, Dr. Krachler joined forces with James Zheng, a glaciologist with the Geological Survey of Canada in Ottawa. Mr. Zheng had been analysing radioactive fallout from atomic bomb testing using snow and ice cores from the high arctic. For this new collaborative study of Sb and other trace metals, Mr. Zheng travelled to Devon Island in the high arctic of Canada. On top of a glacier 1800 m above sea level, Mr. Zheng carefully dug a 5 metre snow pit by hand, using a series of stringent precautions to avoid contamination. To obtain older material from deeper snow and ice layers, Mr. Zheng drilled a 65 m long ice core using special equipment made of titanium. Last year, he brought hundreds of samples, representing 160 years of snow accumulation, to the University of Heidelberg, in Germany, for chemical analyses.

Reliable measurements of Sb in snow and ice from the arctic is a tremendous challenge, partly because the concentrations in the samples are so low, but also because the risks of contamination are so great. At the Institute of Environmental Geochemistry, University of Heidelberg, Dr. Michael Krachler is responsible for what may well be the cleanest of the clean labs: a unique lab with specialised instrumentation and facilities which allows Dr. Krachler to measure trace metals down to concentrations lower than any other lab on earth. The lower limit of detection for antimony (Sb) which he has achieved, for example, is 30 femtograms per gram: this is roughly equivalent to one ice cube taken from a glacier weighing one hundred million tonnes. But Dr. Krachler can also measure scandium (Sc), a rare metal which has never before been measured in polar ice. Scandium is a useful element for comparison with Sb, as there are no industrial uses of Sc, and all of the Sc in the snow is derived exclusively from atmospheric soil dust particles.

Compared to the natural abundance of Sb in soil dust particles, all of the samples, from 1842 to 2004, are enriched in Sb by 25 to 125 times. In other words, natural sources of Sb can account for only a tiny fraction of the Sb contained in these samples. Perhaps even more important, the enrichment of Sb in the arctic aerosols has actually increased approximately 50% during the past three decades. The snow pit samples had been collected and studied very carefully, and represent approximately 10 years of snow accumulation, with distinct summer-winter layers clearly visible. By fastidiously collecting the samples layer by layer, the scientists found that Sb concentrations are far greater during the winter months when air masses arrive primarily from northern Europe and Asia. In contrast, snow layers from the summer months, when air masses to this region of the arctic originate mainly from Canada, contain much less Sb. The findings have broad implications for air quality worldwide as they show that the economic boom currently being experienced in Asia has ramifications not only locally and regionally, but globally.

Contact Information:
Dr. Michael Krachler
Institute of Environmental Geochemistry
University of Heidelberg
Im Neuenheimer Feld 236, D-69120 Heidelberg
phone +49 6221 544848, fax 545228
krachler@ugc.uni-heidelberg.de

Dr. Michael Schwarz
Press Officer of the University of Heidelberg
phone: 06221/542310, fax: 54317
michael.schwarz@rektorat.uni-heidelberg.de
http://www.uni-heidelberg.de/presse/index.html

REFERENCES
Shotyk, W., Chen, B., and Krachler, M. Lithogenic, oceanic, and anthropogenic sources of Sb to a maritime blanket bog, Myrarnar, Faroe Islands. Journal of Environmental Monitoring, 2005, Special Issue "Antimony in the Environment" DOI:10.1039/b509928p.

Krachler, M., Zheng, J., Zdanowicz, C., Koerner, R., Fisher, D. and Shotyk, W. Increasing enrichments of antimony in the Arctic Atmosphere. Journal of Environmental Monitoring, Special Issue "Antimony in the Environment". DOI:10.1039/b509373b.

Both articles are published on the web:
http://www.rsc.org/Publishing/Journals/em/sb_SI.asp

NOTE
Maps and graphics available upon request


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