You don't understand what tanning is.  It is a reaction to inflammation caused by UV rays hitting your skin.  The melanocytes release melanin to act as an antioxidant *against* this inflammation.  The ability of the melanin to perform this function is limited and when enough UV light is absorbed melanin becomes pro-oxidant.  The same is true of metals, this is from your own reference:
https://image.nostr.build/75518313614a99dc2bd9a47d0001e2b62156633e8214456c22a6ebbd7412cabe.png
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2533804/

Tanning doesn't increase your bodies ability to utilise melanin for metal detoxification, if anything it decreases it.

In contrast melatonin can be supplemented and is not dangerous or deleterious in immediate release form.