Actually, chlorine dioxide works well over a broad PH range. I believe it is most effective in the 4 - 10 PH range, but can be used in the 2 - 12 PH range.
I believe the PH of the colon ranges from around 6.8 - 7.2.
A better statement would be that chlorine dioxide kills all bacteria in the body provided the concentration is high enough and the contact time long enough.
The testing that we did with pinworms and their eggs revealed a PH that was basically neutral, but that was for the whole solution. I don't know what the actual PH of the pinworm or egg is. A chlorine dioxide solution is effective at killing pinworms and their eggs in test tubes. I don't believe it has been formally studied in the body.