The docment to replace the 1990 recommendations does not contain emerging information about the other radon, i.e., 220Rn (thoron). The research now shows that although the lung dose from thoron decay products is negligible compared with that from radon decay products, the measurement of radon gas is almost universally contaminated by thoron. This means that radon risk is associated with a ficticiously high radon concentration. Tokonami et al., for example, have shown with follow up measurements of both radon and thoron in China, that the China Gansu epidemiologic study had significant thoron concentrations in the original exposure assessments. The published risk estimates per unit radon exposure for this study are in error. The topic should be included in the upcoming report with suggestion for additional research.