Chemical & Chemical Engineering News (80th Anniversary Issue), Vol. 81, No. 36, 2003, Sept. Edited by X. Lu Introduction

Biological harm can also be caused by Sr-90 from outside the body. When -particles it emits are stopped in air, liquids, or solids, the frictional or braking energy that slows down the electrons is emitted in the form of X-rays called brehmstrahlung (German for braking) radiation. This radiation, like the dentist's X-rays, can penetrate the body and cause the ionizing of molecules and increased cancer risk.

Pollution from Sr-90 first attracted international attention during the atmospheric tests of nuclear weapons carried out in the 1950s by the U.S., the Soviet Union, and England. It was present as an important component of the fallout that was deposited all over the world. After a serious incident of fallout on Rongelap Atoll and on a Japanese fishing boat because of a U.S. hydrogen bomb test at Bikini on March 1, 1954, a worldwide call to stop nuclear weapons testing was issued. That demand centered on Sr-90 contamination of milk.

In the U.S., the Greater St. Louis Citizens Committee for Nuclear Information issued a call for people to send in baby teeth, where Sr-90 accumulation was expected. Positive results seemed to clinch the matter. In 1963, the U.S., the Soviet Union, and Great Britain signed a treaty banning atmospheric testing.

Sr-90 also pollutes soil and water at some reprocessing plants, such as those at the Savannah River Site in South Carolina, the Hanford Site in Washington, and the Mayak plant in Russia's southern Urals. At Mayak, an explosion of a tank containing high-level wastes in 1957 released 20 million curies of radioactive fission products into the environment. About 2 million curies of this was deposited over an area of 15,000 to 23,000 km², necessitating the evacuation of more than 30 towns and villages. About 5% of this was Sr-90 and yttrium-90.

Sr-90 has been used to make radioisotope thermoelectric generators (RTGs). The energy of the -particles is captured as heat, some of which is converted to electricity using thermocouples. RTGs have been used as power sources in space missions both by the U.S. and the Soviet Union. They were deployed as power sources for powering remote seismic stations in Alaska and, far more commonly, in remote areas of the former Soviet Union. RTGs using plutonium-238, with a half-life of 87 years, are now preferred, since these devices can be made more compact because they need less shielding.

After the disintegration of the Soviet Union, the system for keeping track of Sr-90 power sources fell into some disarray. They are now a source of danger to the local population. (Hunters in the Republic of Georgia have been accidentally irradiated, for instance.) There is also the risk that they could be discovered by or sold to terrorists for use in radiological weapons. Each RTG typically contains tens of thousands of curies--several hundred grams--of Sr-90.

A little over 10 µg of Sr-90, if inhaled in insoluble form, would give a sufficient dose to cause cancer with high probability. The risk is mitigated by the fact that it would be difficult to make radioactive dispersal weapons using Sr-90, given the potentially severe radiation risk to those who might want to fabricate such devices without expert help or considerable experience. A considerable effort to locate and secure Sr-90 RTGs is now under way. Ironically, the use of radiological weapons was first conceptualized by the U.S. during World War II as part of the Manhattan Project. Fortunately, the idea was never implemented.

Despite the crimson brilliance of stable strontium, its radioactive variety has given element 38 an air of risk and notoriety.

Arjun Makhijani is president of the Institute for Energy & Environmental Research. He has a Ph.D. from the University of California, Berkeley, where he specialized in nuclear fusion. He is principal editor of "Nuclear Wastelands," MIT Press, 1995 and 2000, which was nominated for the Pulitzer Prize.

STRONTIUM AT A GLANCE

Name: Named for Strontian, the town in Scotland where it was discovered.

Atomic mass: 87.62.

History: Discovered by Irish scientist Adair Crawford in 1790.

Occurrence: Primarily obtained from the ores celestite and strontianite.

Appearance: Silvery yellow metal.

Behavior: Sr-90, a by-product of nuclear explosions, can replace calcium in bone tissue, causing radiation damage.

Uses: Strontium is used to make color television picture tubes.

BARIUM

LOUISA WRAY DALTON, C&EN WASHINGTON

My gut response to the mention of barium is resentment. "This might be a little uncomfortable," the technician told me when she said they wanted to do a test to find out what might be causing my appetite to plummet and my stomach to hurt. I don't think the word "enema" was ever brought up. But even enema is an understatement. The lower gastrointestinal exam, also known as the barium enema, entails inserting a milky suspension of barium sulfate into "the back passage," as the English say, of your large intestine until it has entirely filled your colon--with more liquid than you ever thought could fit in there--and then placing you on a cold X-ray table and asking you to hold it ... and continue to hold it ... and hold it a little longer ... you're doing great ... and we're getting there ... for what, under the circumstances, is a very long time.

I'm sorry to get into the details, but it must be understood that "uncomfortable" just doesn't adequately describe the sensation of keeping all of that dense white fluid inside of you. Ancient reflexes well honed by evolution launch all their weight against this modern medical procedure.

REVEALED A colored barium X-ray showing a healthy large intestine (in red).

At least mine did, although I must grant that I was 10 years old and under a certain amount of stress already. After one bad night two months earlier, I had been struggling with frequent stomachaches, a low-grade fever, high white blood cell count, no desire to eat, and general malaise. My mother knew something was terribly wrong, because my appetite usually took care of all of my siblings' leftovers. But I had no sharp pain, and our family doctor was perplexed: thus the hospital tests. The barium enema did the trick. It outlined my inflamed and half-burst appendix covered up with scar tissue.

That meant that when I came out from the loo, I was promptly told that I would now be going into surgery--a word that scared the bejeebers out of me. I think that's when I lost it, begging my mom to not let them take me, right up until they put me under.

I once told my doctor friend about my traumatic barium enema experience, and with a surprised and unrepentant look, she said, "Gee, we order those all the time." I now grudgingly admit she has good reason. Despite my reflex resentment toward barium, it seems I owe it my life.

Barium sulfate has been entering gastrointestinal tracts for nearly 100 years because the stuff works [Science, 300, 936 (2003)]. Most of the human midsection is invisible to X-rays, which pass right through soft tissue, yet particles of heavy barium sulfate block X-rays. The film of a barium enema shows in sharp relief all gastrointestinal curves and abnormalities. (For the small intestine, there's a similar test, except that the barium sulfate is made into a palatable "barium meal," and it gets sent down the hatch.)

It works so well for perhaps the same reason I wanted it out of me: Barium sulfate is uncommonly dense. The substance is found naturally in Earth's crust as a mineral called barite, which the oil industry found was heavy enough to use as a "weighting agent." About 98% of the barite in the world is put to use by petroleum firms, which grind it up and add it to drilling muds to help counteract the high pressures found at oil-drilling depths.

Besides being heavy, barium sulfate does little else--which is yet another boon. Both doctors and oil-well diggers love it because it just sits there, impeding X-rays or counteracting pressure. The compound is insoluble in water and loath to react in other ways. Even in an intestine designed to digest, barium sulfate goes in and comes right back out.

Other barium compounds aren't so harmless. Potters like to use barium carbonate to lower the melting point of a glaze, but are advised to wear a mask and gloves because even the dust is soluble and toxic. And the barium chlorate that makes green fireworks is rather unstable (C&EN, July 2, 2001, page 30).

Yet barium sulfate is approachable. It may be dense and more than uncomfortable to have inside my colon. But give me a minute to swallow my childhood trauma, and I'll raise a grateful toast to the element that lights up intestines.

Louisa Dalton is an assistant editor in the science, technology, and education group at C&EN. To this day, she regards eating someone else's leftovers as a sign of good health.

BARIUM AT A GLANCE

Name: From the Greek barys, heavy.

Atomic mass: 137.33.

History: Swedish chemist Karl Wilhelm Scheele distinguished baryta (a barium alkali) from lime in 1774, but the pure element was discovered by British chemist Sir Humphrey Davy in 1808.

Occurrence: Found most often as barium carbonate and barite. The pure form must be derived through electrolysis of barium chloride.

Appearance: Silvery white, soft metal.

Behavior: Oxidizes quite easily and must be stored under petroleum or oil to exclude air. Extremely toxic when soluble. Barium chloride, a soluble salt, causes heart problems, but insoluble barite is used as a tracer for X-raying the human intestinal tract because it is extremely dense and opaque to X-rays.

Uses: Used as a "getter" in vacuum tubes. The sulfate is used in paint, in X-ray imaging, and glassmaking. Barite is used in drilling fluids for oil and gas exploration. Barium carbonate has been used as rat poison. Barium nitrate and chlorate are used in green-colored fireworks. Barium is also used to make spark plugs.

RADIUM

DONALD P. AMES, FLUOTECH

In 1942, Gen. Leslie R. Groves purchased Belgian Congo pitchblende for the uranium required by the newly formed Manhattan Project. This ore was owned by the Belgium-owned U. S. Radium Corp. When refined, the ore was the radium source for hospital - and - sources. Radon, the daughter generated by radium -disintegration, was condensed in capillaries for personal irradiation sources. Uranium for the Manhattan Project, as U₃O₈, was purified by diethyl ether extraction by Mallinckrodt Chemical, St. Louis, and the radium was returned to U. S. Radium. The company wanted to ascertain that it got all the radium back.

The aqueous solution analyses following radium separation were assigned to the Chemistry Section C-I of the Metallurgical Laboratories at the University of Chicago in June 1945. A control analysis group containing four of the nine members of the Special Engineering Detachment, U.S. Army Corps of Engineers, was formed in July 1945 to develop analyses for aqueous solutions suspected of containing radium. (For more on this project, see Seaborg, Katz, and Manning, editors, "Plutonium Project Record: National Nuclear Energy Series 14B." New York: McGraw-Hill Book Co., 1949.)

BANG! Colored images of the radioactive emission of a-particles from radium.