Study on transport of radionuclides in watershed environment

Nakanishi, Takahiro   ; Tsuruta, Tadahiko  ; Funaki, Hironori ; Sakuma, Kazuyuki   ; Miura, Tomisato*; Yoshida, Mitsuaki*

To elucidate the mechanism of transport of dissolved radiocesium to masu trout, a feeding experiment was conducted in a culture pond introduced with mountain stream water (dissolved Cs concentration: 0.1 - 0.2 Bq/L) using a non-contaminated bait. The Cs concentration in the muscle of the adult masu trout (n = 10) was relatively high, showing individual differences (30 - 200 Bq/kg-wet). Pond bottom gravel was found in their stomach, suggesting a source of Cs other than bait and stream water. As a result of dietary analysis using stable isotope ratios, the contribution of aquatic organisms was higher in masu trout with higher Cs concentration in the muscle. This suggests that the Cs concentration in masu trout does not exceed the Japanese limit of 100 Bq/kg for general foodstuffs by transport only from the dissolved Cs.