Industrial copper could be loaded with contaminants.
No, not 'loaded with'. There are standards for house wiring (and other wires) which specifies the minimum purity level, because that strongly affects conductivity. The value I saw was 99.90%. I got the impression that a large portion of the impurities is oxygen, which means that what's left can only be trace amounts. If there are only micrograms of impurities in a bracelet, then the amount that would be absorbed with the tiny amount of copper that you absorb would be picograms or less. Compared to your typical daily intake of toxins from breathing, wearing clothes, etc, it should be insignificant, even if the copper was from a Chinese supplier who bribed the inspectors. Remember: copper is actually fairly toxic to humans (we need only trace amounts), so if you absorbed enough heavy metals from a bad copper bracelet to be even measurable, you'd probably have absorbed enough copper to have killed your flesh.
BTW, do you really believe that the sellers of copper bracelets are buying super-ultra-pure, carefully inspected copper, rather than buying a sheet of copper at the local industrial supplier? My guess is that typical copper sheeting used by bracelet makers has lower purity standards than house wiring, since impurities in wiring could cause fires, while no one cares much about the purity of roofing or eavestroughing.
If you can't find copper dermal patches, you could make your own. Stuck some copper (super-ultra-amazingly-pure if you prefer) in some vinegar, wait a few days until the vinegar turns blue/green, and bush it on your skin (somewhere where it won't be embarrassing), or soak a patch with it and apply to your skin. I did the copper/vinegar bit to treat a skin fungal infection. Worked great, though I'm glad I didn't have to explain why my toes were green.
Just sanity checking: RDA for copper is 900 mcg/day (and typical diet provides a bit more than that). That's about a 1 mm cube of pure copper, if my math is right. Given that you can wear a copper bracelet for years (decades?) without wearing it away noticeably, I'm not sure how much copper you'd actually absorb that way. Since your gut is already dealing with more than 1 mg of copper a day anyway, I don't think that the slightly higher level of what you could absorb from a bracelet would make a difference if you swallowed that amount as an oral supplement, so your microbiome shouldn't notice it.
Simple experiment: try taking copper supplement tablets. See whether you notice a benefit or an increase in gut issues. If you don't notice a benefit, you don't need an expensive copper bracelet. If you don't notice any increased gut issues, the tablets are safe, but if you don't notice a benefit, you don't need to take tablets either.
