One Sunday, I made coffee sorbet for the wait-staff. Sunday lunches were hard, so everyone was glad to take a break after the rush and recover before dinner. Being a nice sort of guy, I made a sugar syrup, added some coffee left over from the lunch and turned it in the ice cream machine. Trouble is, I used an unlined copper pan, and the coffee chelated or complexed the copper salts coating the pan’s interior surface. This shined up the pan really nicely, but it totally overwhelmed 12 livers, causing the owners of those livers to spend the afternoon in the bathrooms.
Copper is a micronutrient. The key word here is micro, not macro.