Strontium is a soft, silvery metal with a number of uses: it blocks X-rays emitted by TV picture tubes; it causes paint to glow in the dark; and it is responsible for the brilliant reds in fireworks. Strontium also plays an important role in figuring out the origins of species: Anthropologists measure the levels of strontium ions in bones and teeth to help determine the geographic origins of ancient humans and animals. While natural strontium is harmless, one of its isotopes, Sr-90, carries a more sinister reputation: it is a dangerous byproduct of nuclear fallout. And yes, you do not want it in your drinking water.
Strontium occurs naturally in the environment. Air, dust, soil, foods and drinking water all contain small amounts of strontium. Ingestion of small amounts of strontium is not harmful. However, high levels of strontium can occur in water drawn from bedrock aquifers that are rich in strontium minerals. Strontium occurrence is also linked to other sources such as air contamination from milling processes, coal burning and phosphate fertilizers. In some cases, low levels of strontium have been administered to osteoporosis patients as a treatment of their condition.
Like other alkali metals, strontium is highly reactive chemically and reacts with both air and water. When exposed to air, it burns with a bright red flame. When combined with water, strontium gives off hydrogen gas and strontium hydroxide — a strong irritant.
The risk posed by strontium depends on the concentration ingested and on the exposure conditions and the U.S. environmental Protection Agency’s current reference concentration indicates that ongoing exposure to strontium at levels of more than 4000 parts per billion per day may lead to negative health effects. There is no evidence that drinking water with trace amounts of naturally-occurring strontium is harmful.
However, exposure to high levels of naturally-occurring strontium during infancy and childhood can affect bone growth and cause dental changes, and there is some evidence that strontium increases bone density in adults. The isotope strontium-90 has been linked to bone cancers and leukemia.
There is not a federal drinking water standard for strontium at this time. The EPA has set a health reference level for strontium. As of October 2014 the health reference level for strontium was listed as 1.5 milligrams per liter (mg/L).