I didn’t think that sounded right, but that was what I was reading. It is definitely a poison, though, and the locals, here did win a huge law suit for the contamination, and it does cause symptoms similar to lead poisoning. It crippled the local cows and caused some problems with the deer, too.
The problem in Whatcom County was so acute, that the department of ecology had to come in and manage the area around the smelter.
Almost anything is a poison (or rather, is toxic) in sufficient doses.