(The body sometimes confuses Lead and Strontium-90 for calcium, so this Osteoblast [the cell type that makes bones] takes them and puts them inside the bones.)

Lead doesn't just stick around poisoning your brain, some will get put in your bones and eventually will fall out of your bones years or decades later, then poison your brain.

Strontium-90 is a radioisotope found in nuclear bomb fallout, a ton of it got put into the atmosphere back when testing nuclear bombs was still a thing, so everyone who so much as breathed back then still has some little Strontiumballs in them, continuously irradiating their bones. Fun!