By Capt. Paul (Eclogite) on Saturday, January 2, 2010 - 04:52 pm:
Indeed; C&H had to remove the arsenic from the copper during smelting for many reasons, one of the most important is that arsenic destroys the conductivity of copper so removing as much as possible increases its capability to conduct eletricity. However, that I know of, arsenic was never added to copper in the Keweenaw; that would have been done at places like Wolverine Tube in Detroit where specialty materials were developed. In addition, the only real industrial use for arsenical copper is the fabrication of copper locomotive fireboxes, long used in Britain from a distrust of steel in this application. Today, cadmium has replaced arsenic for most applications that required the addition of arsenic to copper.
As far as drinking water in the Keweenaw, the link I provided earlier in this thread is a very good read about the quality of the water. The maximum contaminant level for arsenic in Michigan drinking water is 50 parts per billion (ppb). While there is arsenic in the water, it is only 0-2 ppb, well below the MCL for drinking water. Arsenic is a natural by-product of the native copper found in the Keweenaw. It is soluble as it enters the ecosystem though the erosion of natural deposits, runoff from orchards, etc...
There were indeed many other chemicals used besides arsenic in the processing of native coppers. Some of the chemicals include cupric ammonium carbonate, lime, pyridine oil, coal-tar and wood creosotes, pine oil, xanthates, beryllium, and many aromatic hydrocarbons to name a few. Some of these pose no threat to humans, while others are known to cause cancer if exposed over a long period of time.