Natural occurring strontium is harmless and not radioactive. It fine to have it in toothpaste. The reason you often hear about is strontium as something radioa

Natural occurring strontium is harmless and not radioactive. It fine to have it in toothpaste. The reason you often hear about is strontium as something radioactive is because of Strontium-90, which is one of the longer lived products of nuclear fission, with 30 year half-life. Thus radioactive strontium-90 is always present after a nuclear accident or explosion.