Barium: rat poison or radio-contrast agent?

Barium: rat poison or radio-contrast agent?

The element barium (Ba) has the atomic number 56 and is classified as a heavy metal. Barium metal is highly reactive and therefore no elemental barium exists in nature. Natural sources of barium are the water-insoluble minerals barite (barium sulfate) and whiterite (barium carbonate). In order to obtain pure barium compounds, the mineral barite is reacted with carbon, and barium sulfide is formed. Barium sulfide is, in contrast to barium sulfate, water soluble. Subsequently, the pure barium sulfide is treated with sulfuric acid and pure barium sulfate can be obtained.

BaSO₄ + 4C → BaS + 4CO

BaS + H₂SO₄ → BaSO₄ + H₂S

Barium salts can be highly toxic even at low concentrations. Barium carbonate is highly toxic and can be used as rat poison as it readily dissolves in the stomach acid. Barium sulfate is the least toxic barium compound mainly because of its insolubility. Barium sulfate is used in a variety of applications ranging from white paint to X-ray contrast agent.

The clinical use of barium sulfate suspension is well known under the term barium meal. Patients are given a suspension of barium sulfate to swallow. Using X-ray imaging, the whole oesophagus, the stomach and the intestines can be visualised. Barium sulfate lines the tissue whilst travelling through the digestive tract. The heavy barium ions absorb X-rays readily and therefore these structures become visible in an X-ray screening. Barium sulfate is a well-used and tolerated oral radio-contrast agent. It is also used as radio-contrast agent in enemas (Figure 3.14) .