OK I just spent a bit of time on the web, looking up Strontium (chemical symbol Sr). Here is what I found:
Strontium is a natural mineral (a metal), present in all soils and water. The natural type is not radioactive. Radioactive Strontium is produced by nuclear bombs and nuclear plants, it has a half-life of 29 years, and can be a serious problem. It has been found contaminating soils/water from Chernobyl Nuclear Reactor Meltdown, Fukushima Meltdown, even "normal" activity of nuclear reactors have contaminated nearby soils (Vermont Yankee Nuclear Power Plant), and it is of course found near the troubled Hanford Nuclear Reservation in my own Washington State. We do not have to worry about the radioactive type in Azomite.
There is a huge variability in natural levels of Sr in soils and water. There used to be Sr mines in TX and CA, but nobody mines it in the U.S. anymore, We use a lot of it in our TV screens, to absorb and REDUCE radioactivity.
The lowest levels in our water are found in the Pacific Northwest, Northeast, and Gulf Coast (leached soils in areas of high rainfall), with the highest levels in North and West TX, and southern AZ an New Mexico (arid enviornments where there is little leaching). There are increased amounts of Strontium in soils near coal and oil burning power plants. This is not radioactive either. There are a lot of metals and other toxic elements produced by burning coal and oil, this causes pollution we worried a lot about, long before we worried about global warming, and there has been a lot of technology to try and reduce these toxic emissions, partly successful.
There are no harmful effects of stable Sr in humans at levels typical in the environment. If you ate the stuff (maybe kids who lived and played by the mines) it will cause rickets and even death.
Back to Azomite. It is ground up volcanic rock from Utah. It has been tested, and has , on average, about 380 ppm Sr (that is parts per million, which is approximately mg/kg). Worldwide, average Sr in soils is about 240 mg/kg. Some are much much much higher than this, and we eat food grown on these fertile soils.
My decision- I am not going to worry about causing Strontium toxicity by spreading a bag of Azomite in my garden.
