While strontium citrate, the popular over-the-counter supplement is not
supposed to contain any of the dangerously radioactive strontium-90 isotope,
it does beg the question as to what testing is done by the manufacturer of
strontium citrate, as well as strontium renalate, to verify that no
detectable strontium-90 is present.

The raw material for pharmaceutical use of strontium is the mineral,
stronianite (strontium carbonate), which is mined mainly in China.  Since
this mineral is mined subsurface, and was formed long before the development
of nuclear weapons, its believed by most chemists to be free of significant
strontium-90. And, we do know that most strontium-90 is of concern to milk
and water, and both are tested for its presence.

However, China did conduct numerous nuclear bomb tests so it's not
completely clear on how much, if any, strontium-90 percolated through the
ground-water and into the stronianite mines in China.  We can only hope that
the manufacturers of strontium preparations are testing their raw material
for the presence of strontium-90.

Wolfy, PhD Chemistry (retired)