Migration of iodine in diatomaceous and siliceous shales based on speciation and I/I analysis I/I

Shimamoto, Yoko*; Takahashi, Yoshio*; Amano, Yuki   ; Matsuzaki, Hiroyuki*; Muramatsu, Yasuyuki*; Iwatsuki, Teruki  

We determined iodine distribution, speciation, and isotope ratio (I/I), to investigate long-term migration of iodine in diatomaceous and siliceous shales, using core and groundwater samples collected at JAEA Horonobe underground research center. Iodine in core samples dramatically decreased near the boundary between Wk and Kt Formations. Iodine exists as I in groundwater, while that in shales is a mixture of organic and inorganic I. Iodine isotope ratio (I/I) is slightly higher in siliceous shale compared with that of groundwater. According to these results, migration of iodine in this area can be expected as follows; (1) iodine accumulated as organic iodine in siliceous sediment. (2) Iodine was released from Wk Formation during diagenetic process as I to form iodine-rich groundwater. (3) Iodine-rich groundwater was distributed to Wk and Kt Formations due to the compaction of the layers. (4) Both iodine and chlorine were diluted by freshwater from the surface.