Cesium and strontium are nasty customers too. Cesium tends to destroy bone marrow and I believe strontium accretes in the liver.
That said, I find this whole article full of vague alarmism and pseudoscientific hyperbole.
Strontium is chemically like calcium, so it collects in bones, where it causes bone cancer and leukemia. Cesium is chemically like sodium, which means it goes everywhere in your body but also washes out pretty easily. Cesium 137 is a nasty gamma emitter, so it can irradiate stuff at a distance. Strontium 90 is a beta emitter, so you have to eat it, breathe it, or park it on your skin for it to cause trouble.
Strontium is in the same family as calcium, and thus behaves chemically similar to calcium. That means it deposits in bones and other tissues that have high calcium content.
And yes, this article is heavy on the vague fear-mongering.