I guess you are pretty young and don't know what a slide carousel is. I am old and instantly knew what was inside. They are slide holders that fit on top of a slide projector. Each one would hold 80 or 140 color slides. As far as I know color slides do not contain any PMs.How is anyone supposed to know without - at least - photos of the material?
Photographs (photographic paper) should have even more.Black and white negatives (& also x-rays) are loaded with silver.