Chlorine Dioxide breaks down in the body into salt, and some hypochlorous acid...it does not leave Chlorine. There are tons of studies on this subject produced for the water purification industry, the FDA and the EPA which demonstrate this. Hypochlorous acid is a naturally occurring compound in the body.
The main reason for using Chlorine Dioxide is specifically that it does NOT yield chlorine when used in the body. Chlorine tends to form organic chlorine compounds in the body, which are toxic...this problem is completely avoided when using Chlorine Dioxide.