Iodine and radiation protection

Following the recent (2011) tsunami in Japan, and the damage it caused to the Fukushima nuclear plant, there has been much discussion about using iodine as a protection against radiation exposure.

Iodine was discovered accidentally by the French chemist, Bernard Courtois, in 1811 during the manufacture of saltpetre for use in gunpowder by Napoleon’s army. He accidentally added too much sulphuric acid to seaweed ash during the purification process, and a violet coloured cloud erupted from the mass, which condensed on metal objects as solid iodine (named from iodes, the Greek word for violet).

Today, iodine is chiefly obtained from deposits of sodium iodate in Chile and from the purification of brine in gas and oil fields, mainly in Japan and the US.

Trace amounts of iodine are required by the human body, and its role as a constituent of thyroid hormones and effect on body metabolism is well known.

Traditional uses of iodine in solution were as an indicator in the detection of polysaccharides and as an antiseptic.

In the wake of the damage to the Fukushima nuclear plant, the Japanese government distributed some 300,000 units of potassium iodide tablets as a precautionary measure against radiation exposure. The iodide is taken up by the thyroid gland until saturated, blocking the uptake of the radioactive isotope, which is excreted in the urine.

Radioactive caesium and iodine tend to be the major hazards to health following nuclear accidents, and a recent United Nations report into the 1986 disaster at Chernobyl revealed that, among disease conditions directly attributable to the leak, thyroid cancer showed the greatest increase, with three times as many cases than normal. No iodide treatment was offered in the area around Chernobyl.

Treatment only works if  taken before exposure, and the Japanese authorities have been criticised because it was not until three days after the Fukushima reactors were damaged that tablets were made available.