So steel in every smelter on earth can become so contaminated solely via the atmosphere from explosions decades ago it is measurably radioactive, but labs can't be contaminated via the atmosphere with tiny crystals that change nucleation? Walk me through your thought process here.

The crystals (a) weren't deliberately dispersed into the jetstream with hundreds of multi-megaton explosions, and (b) are not radioactive or otherwise capable of affecting unrelated substances from a distance.

Other than that, yeah, I guess it's exactly the same.

Isn't crystal nucleation exactly the kind of process that _is_ affected by impossibly small impurities? One good conference could spread crystal residue over a whole industry.