Radiocesium transfer into freshwater planktonic Chlamydomonas spp. microalgae in a pond near the Fukushima Dai-ichi Nuclear Power Plant

We investigated the transfer of radiocesium and its behavior in living cells and cellular debris in a Chlamydomonas spp. bloom in a pond located approximately 5 km from the Fukushima Dai-ichi Nuclear Power Plant. A microalgal bloom in the pond was the dominant factor in determining the radiocesium concentration (Bq/L) of the > 0.45 μm pond water fraction. The water-to-algae transfer factor [( 137 Cs concentration Bq/kg >0.45 μm fraction ) × ( 137 Cs concentration Bq/L <0.45 μm water ) −1 ] was 1.6 × 10 3 . The transfer factor was similar for filamentous algae attached to the wall of the pond, and suggesting that radiocesium transfer to algae was through water, not directly from sediment. Intact microalgal cells and cellular debris displayed nearly equal 137 Cs concentrations, and radiocesium was also transferred in cellular debris as well as living algal cells. The water-to-algae transfer factor in this study is two to three orders of magnitude lower than previously reported radiocesium concentration ratio of suspended solid (> 0.45 μm) and water in rivers in Fukushima [( 137 Cs concentration Bq/kg >0.45 μm fraction ) × ( 137 Cs concentration Bq/L <0.45 μm water ) −1 ].