film – Pinholes in 35 mm slides

While scanning many 35 mm slides (mostly Kodachrome and its successors), I noticed what appear to be pinholes in the emulsion, perhaps on the order of 10 or 100 microns. The defects are mostly from some slides, taken in the U.S. Southwest in the late 1980’s, such as that below, cropped from a photo in Bryce Canyon National Park in Utah.

Bryce Canyon with pinholes

Though I can think of alternative causes, such as electrostatic discharge (unlikely, as it was in summer, and there are no accompanying streaks) or scratches (however, they’re points, not linear), I thought (the defects might be due to radiation from past nuclear weapons testing upwind from that area, either alpha particles, or judging by the comparatively size, even fission fragments. Contaminated dust certainly could have entered the camera while changing lenses or film.

Does anyone have insight into what may have caused the pinholes? Is nuclear radiation damage an actual likelihood, or is that farfetched?