Evaluating the accumulation potential of organically bound tritium in edible seaweed under dark and light conditions through a deuterium tracer experiment.

To estimate the accumulation potential of organically bound tritium (OBT) by seaweed from tritiated water in the coastal area beside Fukushima Daiichi Nuclear Power Plant (FDNPP), the organically bound deuterium (OBD) accumulation in seaweed was examined in incubation experiments using artificial seawater with addition of ²H₂O. In this experiment, two species (Ulva prolifera, Gracilaria vermiculophylla) were investigated at 15 and 25 °C under dark and light, respectively. OBD accumulation rates were higher under light than dark. OBD accumulation rates were higher at 25 °C or under light in U. prolifera, while these trends were not seen in G. vermiculophylla. Using the obtained data, a maximum OBT concentration in seaweed was calculated from seawater with upper permissible tritium concentration from FDNPP, as proposed by TEPCO. OBT result was 0.11 Bq g^-1 per wet weight, far smaller than the upper limit value in foods (10 Bq g^-1) proposed by WHO/FAO.