[nkmnz]

There is a natural level of radioactivity which the body is used to compensate. Small additional doses of radioactivity can therefor be neglected. This is not true for stuff like abestos.

[jojobas]

There is even the "hormesis hypothesis" which posits that low levels above background might be beneficial for human health.

[userbinator]

There are actually naturally occurring asbestos fibers in the air, caused by weathering of asbestos-containing rocks.