DLC: Attack of the Sentient Nirnroots.

you heard it here first.

It wasn't until I got to about 40 hours playtime I realised it wasn't some strange bell getting my attention it was these blasted things! I'd get right to where the noise was loudest and still not realise what it was. D'oh!

Fun fact: radiation decreases with time.

Fun fact 2: the radioactive isotopes with the longest half-lives are much less radioactive.

Fun fact 3: Nuclear weapons produce mostly fairly short-lived (but initially highly radioactive) isotopes - the radiation from a nuclear weapon is gone after 300 years.

Conclusion: After thousands of years, there'd be essentially nothing left except small quantities of not-very-radioactive isotopes with long half-lives.

(In fact, Fallout 3 gets this terribly wrong - 300 years after a nuclear war, the capitol wasteland should have been lush with vegetation and animal life, with basically no radiation left.)

At least they don't continue to play the sound when they are in your inventory - could you imagine if you picked up a nirn root, and started getting that wind-chime sound non-stop until you dropped the nirn root, ate it, or created a potion? lol