[en] Past experience has indicated that radioiodine in ventilation effluents from light water reactors aged from the point of emanation within the plant to the point of plant effluent release. As used in the context of this report, ''aging'' implies that there was a greater reduction in the concentrations of the isotopes with shorter half-lives compared to what would be expected from normal ventilation air flow rates, and that there was a change in the chemical form from the more reactive elemental form to the less reactive organic form. This study was conducted to determine if the interaction of airborne radioiodine with surfaces could have been the cause of this occurrence. Various surface materials common to nuclear power plants, such as concrete, galvanized steel, aluminum, and paints, were applied. The results indicated that surface interactions do shift the chemical forms of radioiodine from the more reactive elemental form to the less reactive organic form, and that the iodine can be retained for a sufficient length of time to affect the concentration ratios of long-lived isotopes relative to those with shorter half-lives. Concrete and painted surfaces were found to be most effective