Fate of radiocesium in freshwater aquatic plants and algae in the vicinity of the Fukushima Daiichi nuclear power plant

The behavior of radiocesium (137Cs) in aquatic plants (five species) and algae (three genera) grown in either a river (one sampling point) or pond (four sampling points) in the vicinity of the Fukushima Daiichi nuclear power plant was investigated. The 137Cs concentration of <0.45-μm fractions of water taken from the river and ponds was between 5.01 × 10−1 and 2.98 Bq/L, while that of sediment was between 4.85 × 103 and 5.72 × 104 Bq/kg dry weight. The ratio of 137Cs concentration of sediment/water in ponds was ~104. The sediment-to-plant transfer factor (TF) [(137Cs concentration Bq/kg dry weightplant) × (137Cs concentration Bq/kg dry weightsediment)−1] was also measured. For aquatic plants, the highest value was 5.55 for Potamogeton crispus from the river, while the lowest was 3.34 × 10−2 for P. distinctus from a pond. There were significant differences in values between aquatic plants belonging to the same genus. The water-to-plant TF [(137Cs concentration Bq/kg dry weightplant) × (137Cs concentration Bq/Lwater)−1] of filamentous algae (Spirogyra sp.) and cyanobacteria (coexisting Anabaena sp. and Microcystis sp.) were 2.39 × 103 and 1.26 × 103, respectively. The 137Cs concentration of cyanobacteria in pond water was 4.87 × 10−1 Bq/L, which was the same order of magnitude as the 137Cs concentration of pond water. Enrichment of 137Cs in cyanobacteria was not observed.