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Fresh Out of Arsenic-73

15 November 2000 7:00 pm
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Hot commodity. Purifying a radioisotope at Los Alamos, where a shortage of one isotope has sparked an outcry from scientists.

Researchers trying to gauge the dangers of arsenic have run into a roadblock: They need an arsenic isotope for their studies, and the only place in the world that makes it has run out. It could take until mid-2001 before enough is produced to restock the two dozen labs around the world that need the isotope.

The shortage comes at a particularly bad time. In May, the U.S. Environmental Protection Agency (EPA) proposed a costly reduction of arsenic levels, a natural contaminant, in drinking water. EPA is also funding a burst of research on how arsenic causes cancer, because pinning down this elusive mechanism could reveal whether the limit needs to be so stringent. To understand the mechanism, researchers are using arsenic-73 to find genes that metabolize arsenic and to explore how these metabolites enter cells and damage DNA.

But the Department of Energy's Los Alamos National Laboratory in New Mexico hasn't produced any arsenic-73 since early 1999. They made the isotope by smashing protons from an accelerator into a rubidium bromide target, but their source of these protons--a tritium production program--shut down. A new isotope production facility was slated to open early next year, but the massive fires that swept through the region this spring have pushed back the scheduled completion date to mid-2002. Los Alamos ran out of its arsenic-73 inventory around July.

"None of us knew about it until it was too late" to make other plans, says Marc Mass, an EPA toxicologist. There are alternative tracers, he says, but they're costly and too insensitive for some experiments. Los Alamos officials say they can make arsenic-73 at another accelerator, possibly in Canada--but it may be another 6 months before any arsenic-73 comes available, says Gene Peterson, manager of the lab's Isotope Production and Distribution Program.

That's little comfort to arsenic researchers, who are at their wits' end. Toxicologist Vas Aposhian of the University of Arizona in Tucson, who bought up the last few millicuries of arsenic-73 this summer, says that he and his colleagues are "going to scream bloody murder" when their lab's supply runs out in a few weeks. Miroslav Styblo, a biochemist at the University of North Carolina, Chapel Hill, is trying to persuade colleagues at an accelerator in his native Prague to make a batch of arsenic-73. But "so far," he says, "we don't have realistic promises."

Related sites

Los Alamos Isotope Production and Distribution Program

EPA proposed arsenic drinking water rule

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