Strontium-90 is not good news. It emits ionizing radiation, which means you want to keep it out of our body. Unfortunately, your body has other ideas. The body’s own mechanisms welcome this isotope in, and store it away.

Strontium-90 was one of the many isotopes the world got acquainted with after the invention of the atomic bomb. Pure strontium is a silver metal, but you’re unlikely to see it that way. It’s highly reactive, so if you put it in air, it will react with the oxygen to form a yellowish “rust.” In nature, it’s mostly found in compounds. Most isotopes of the element don’t do much harm, but strontium-90, with 38 protons and 52 neutrons, is the black sheep of the bunch.

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Strontium-90 isn’t too radioactive. It has a half-life of nearly 29 years. It decays by climbing the periodic table. One of its neutrons turns into a proton and the entire element turns into yttrium-90. To make the change, the neutron emits a beta particle—in this case a high-speed electron. Outside of the body, beta particles are no big deal. They can be stopped by solid objects, including clothing. The slow down if they travel too far through the air.

Once Strontium-90 gets inside the body. It’s sequestered in bones, in marrow, and especially in teeth. The body itself is what’s bringing the strontium in and keeping it stored up. Strontium-90 is, chemically speaking, a mimic of calcium. The cells in the body can’t tell the difference, so if people ingest any of the strontium-90 isotope, the body sees it as nutrition, and uses it the same way it would use calcium from a glass of milk. Children who were born in the 1950s and 1960s, the era of above-ground nuclear testing, had a relatively high level of strontium-90 in their bones. This is one of the reasons why above-ground testing was banned.

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Today, not too much of the atomic test strontium-90 is left. Most of the strontium-90 pollution comes from nuclear waste, with the occasional leak from medical or agricultural testing facilities, which use the isotope as a tracer for tests. It’s still nasty stuff, but you’re less likely to get a mouthful of it.

Top Image: DOE, Second Image: Matthias Zepper