Simply answer this question. When you open the tumbler and pour the brass through a strainer or some other separating tool, what happens to the media? If you do it like most folks it falls through into another container and in doing so clouds of dust are created. Breath it in and the toxins come with it.
Keith
No clouds of dust. If this was the case, I'd be wearing something over my face. I own a business in the industry, that requires some breathing protection sometimes.