If we’re just looking at the grinding of the metal wheels against the rails, it’s very little. Some metallic particles are produced in the normal wear but ferrous metals easily react and oxidize into more inert and normal forms for life.

Reverse threads on gas cylinders are (as far as I know) only used for flammables.

It’s always been a big deal, it just died down as Photoshop as a tool became normalized and people became accustomed to it as a tool.