Fukushima 137Cs at the base of planktonic food webs off Japan

The potential bioaccumulation of Cs in marine food webs off Japan became a concern following the release of radioactive contaminants from the damaged Fukushima nuclear power plant into the coastal ocean. Previous studies suggest that Cs activities increase with trophic level in pelagic food webs, however, the bioaccumulation of Cs from seawater to primary producers, to zooplankton has not been evaluated in the field. Since phytoplankton are frequently the largest component of suspended particulate matter (SPM) we used SPM concentrations and particle-associated Cs to understand bioaccumulation of Cs in through trophic pathways in the field. We determined particle-associated Cs for samples collected at 20 m depth from six stations off Japan three months after the initial release from the Fukushima nuclear power plant. At 20 m SPM ranged from 0.65 to 1.60 mg L 1 and rapidly declined with depth. The ratios of particulate organic carbon to chlorophyll a suggested that phytoplankton comprised much of the SPM in these samples. Cs activities on particles accounted for on average 0.04% of the total Cs in seawater samples, and measured concentration factors of Cs on small suspended particles were comparatively low (∼10). However, when Cs in crustacean zooplankton was derived based only on modeling dietary Cs uptake, we found predicted and measured Cs concentrations in good agreement. We therefore postulate the possibility that the dietary route of Cs bioaccumulation (i.e., phytoplankton ingestion) could be largely responsible for the measured levels in the copepod-dominated (%) zooplankton assemblages in Japanese coastal waters. Finally, our data did not support the notion that zooplankton grazing on phytoplankton results in a biomagnification of Cs. & 2015 Elsevier Ltd. All rights reserved.