There is a series of complex formulas and several rounds of discussions involving leading medical experts that enable a MRL for humans to be determined from studies done on animals. I don't know what the exact process is, but I have noticed that they experts involved pay close attention to the clinical studies to make sure there were adequate controls and to make sure that the targets of the study were well defined and met.
I am sure you can appreciate the fact that there are no 68 kg rats around, and that the observations from studying rats may need to be adjusted when applying them to humans.
Once again I must point out that there is not a lot of information on what these chemicals do in humans. The majority of the information on humans was based on the concentrations used for water purification and the residuals anticipated from this process. Since the concentrations of these chemicals used in water treatment are much lower than those used in the Miracle-Mineral-Supplement protocol, we are in the dark as far as knowing what risks are associated with these higher concentrations of sodium chlorite and chlorine dioxide.