Aged anthropogenic iodine in a boreal peat bog

This in situ study assesses the long term sorption of I in a natural peat bog, a matter that is scarcely addressed but required for safety studies such as for radioactive waste disposal. Fifteen years after the artificial contamination of a boreal peat bog, the groundwater (piezometers), the peat and the vegetation were resampled to determine I distribution with comparison to the initial situation (1989). Spectroscopic analyses (SS-NMR, electronic microscopy and EDX spectroscopy) were carried out on the peat solids to identify the sorption processes. Over the past 15 a the I has been spreading mostly outwards and possibly upwards in the groundwater. Sorption of I is higher at the surface of the bog ( K d = 37.6 L kg −1) than at the bottom ( K d = 5.1 L kg −1), and this is attributed to the oxic/anoxic conditions of the peat layers. The average surface K d values showed more than a 2-fold increase after 15 a. TEM–EDX analyses of the surface peat showed here for the first time that I was only associated with natural polyphenolic substances contained in humified plant tissues. Plants growing in the bog have not taken up much I with the exception of sedge species ([I] sedge leaves is up to 283 mg kg −1).