In this paper, the behavior of TEDA and KI impregnated activated carbons (AC) towards the capture of methyl iodide (CH3I) is investigated using complementary methodologies. On the one hand, radioactive CH3I decontamination factors (DF) were determined at different water vapor contents for various commercial activated carbons. A combination between the retention performances and the physicochemical properties is performed to gain insights about the AC influencing parameters on Y-labelled CH3I capture. On the other hand, new experimental methodologies are developed in order to measure both stable and Y-labelled CH3I breakthrough curves (BTC) for KI or TEDA impregnated AC {T = 20 - 30 °C, dry conditions}. These works improve the knowledge about the role played by KI and TEDA. Indeed, TEDA is found to enhance CH3I retention especially under humid conditions and, for the first time, the KI contribution is isolated and quantified: the KI action towards 131I is highlighted after the breakthrough phase through an isotopic redistribution mechanism.