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28 November 2005

Ongoing global atmospheric lead contamination

A new study published by the Institute of Environmental Geochemistry, University of Heidelberg in Geophysical Research Letters, shows that 95 to 99 % of the lead in the air of the Canadian High Arctic is still from industrial sources

Measurements of lead in snow and ice samples from a remote region of the Canadian High Arctic show that, even in the most recent samples, 95 to 99 % of the lead is still industrial in origin. The greatest inputs of this lead are supplied during the winter months, when the air masses are predominately from Eurasia (northern Europe and northern Asia). These findings are the result of a collaborative study between the Institute of Environmental Geochemistry, University of Heidelberg, and the Geological Survey of Canada.

Three thousand five hundred kilometres north of Ottawa, the capital of Canada, James Zheng of the Geological Survey of Canada stood on the top of a glacier 1800 metres above sea level, and proceeded to dig a 5 metre snow pit, by hand. With outside air temperatures well below zero, James was on Devon Island in the High Arctic, dressed in special clothing usually worn only in "clean" laboratories for the production of electronic equipment and pharmaceuticals. Using a plastic shovel and bags which had been carefully cleaned in high purity acids, his goal was to collect the most recent layers of fresh arctic snow without contaminating them, and to bring them back to the University of Heidelberg, in Germany, for analyses of trace metals.

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 lead (Pb) which he has achieved, for example, is 60 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 Pb, as there are no industrial uses of Sc, and all of the Sc in the snow is derived exclusively from atmospheric soil dust particles.

Although the natural ratio of Pb to Sc in soil dust particles is 1:1, the recent snow samples typically contain 100 times more Pb than Sc. These results, just published in Geophysical Research Letters, show unambiguously that 95% to 99% of the Pb in the air in this remote part of the world is still industrial in origin.

The pit represents 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 Pb concentrations are far greater during the winter months when air masses arrive primarily from northern Europe and northern 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 Pb.

Analyses of a 65 m long ice core collected from the same glacier and representing snow accumulation since 1842, shows that there was extensive atmospheric Pb contamination in the arctic, even before leaded gasoline was introduced. Although the samples from the past few decades show declining Pb concentrations due to the phase-out of leaded gasoline in the U.S. and Canada, in western Europe as well as Japan, this decline has taken place from levels which were very high, compared to the natural values.

Clearly, the ban on gasoline additives was positive and successful, but this action alone will not solve the global environmental Pb problem. Efforts are still needed to continue to reduce atmospheric Pb emissions worldwide.

Not far from Devon Island, Captain Franklin and his entire crew perished in 1847, during their search for a northwest passage from Europe to Asia. Autopsies of some of the frozen bodies of the seamen recently discovered that, in addition to the obvious problem of their ship having become stranded in pack ice, they had become fatally poisoned by the lead used to seal the cans containing their food reserves. Ironically, the most recent snow and ice layers from Devon Island analysed by Krachler and Zheng, show that modern society has not lost its affinity for this industrially useful but also potentially toxic trace metal.

REFERENCE
Shotyk, W., Zheng, J., Krachler, M., Zdanowicz, C., Koerner, R. and Fisher, D. Predominance of industrial Pb in recent snow from Devon Island, Arctic Canada. Geophysical Research Letters 32, L21814, doi:10.1029/2005GL023860.

Contact Information:
Prof. Dr. William Shotyk
Institute of Environmental Geochemistry
University of Heidelberg
INF 236, D-69120
tel (06221) 54 4803
fax (06221) 54 5228
shotyk@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


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