Just read that too much copper can cause unwanted yeast mutation and/or death as well as lend a hand in haze. Copper is readily used in breweries, however when does it become too much? What kind of mutations can be caused by copper?
I haven’t seen much copper being used post-pitching in breweries. If there’s no contact with the yeast, then that should take care of the concerns with mutation.
I did my PhD in a yeast DNA repair and mutagenesis lab. I’m pretty sure that copper in and of itself is not mutagenic. Some copper complexes, sure, but I don’t think copper ions are (at least not directly that I know of).
Even if it did cause mutations, unless the mutation was advantageous, the rest of the culture would presumably out-compete the mutant yeast just based on shear number of cells. Maybe you would notice something with serial repitching, but I wouldn’t really worry about this.
If using a little bit of copper (say in chilling) released enough copper ions into wort to be cytotoxic to yeast, I wouldn’t be drinking beer.
Very little copper used in breweries now a days(save for say old German and Belgian breweries), the Copper kettles you see are more likely just copper lined SS kettles.
So there is no confusion my friend! 
Can it cause issues with Lacto starter? I held my WLP677 in a copper tea kettle on a candle warmer for 18 days before pitching to a sour almost 4 months ago. I was worried about the Copper mutation issues along with possibly causing an issue with the amount of copper leaked into the starter and causing an issue with the yeast. Trying to build a solid “house sour” I am wondering what I could see/notice/taste if the strain mutates to something to be worried about in the future.
I don’t think mutation is necessarily a concern but copper is absorbed by LAB and particularly with lactobacillus strains commonly used in brewing it reduces cell viability which may have a deleterious effect on the souring ability of your culture.
On the other hand, many traditional lambic producers have copper kettles, grants and coolships. So in practice it has no effect, unless you’re making a Berliner Weiss maybe, although many traditional German breweries also used copper.
Todd is correct. If a mutation occurs after the logarithmic phase, one will not see a major change until the culture has been propagated a few times due to the fact the non-mutated cells vastly outnumber the mutated cells. Petite mutation is example of a mutation that occurs over time. It is result of damage to mitochondrial DNA.
http://onlinelibrary.wiley.com/doi/10.1111/j.1472-765X.2008.02360.x/pdf