Silver on edge of film

I just developed some old film and see what looks like metallic silver along one of the edges. Is this just due to the age of the film? Film is 8x10 Tri-X from 1972.

I would guess, "yes", as the same effect was on some Plux-X 126 I processed from the 1960s.

Wonder what the environmental variable is to cause this?

I used to see it a LOT in motion picture film printed prior to the 1920s...