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.

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.

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


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