Can anyone tell whether these exposures occurred through the camera lens (from fallout particles in the sky of the depicted scenes) or in post- (or pre-) exposure handling of the film from hot dust carried by the photographer?
So this just happened somewhere between arrival to and departure from the zone.
The optics would just be a slight attenuation much like the rest of the camera housing, film reel, operator, etc. So really a summation of all the exposure types you can imagine.