Spatiotemporal change of cesium-137 in the Pacific coast of Tohoku, Japan: The mussel watch approach

Highlights: • Mussel ¹³⁷Cs concentration collected from the Tohoku coast, Japan affected by the FDNPP accident • Mussel ¹³⁷Cs distribution was higher in the south and lower in the north same as the other environmental data. • Spatiotemporal pattern is consistent with seabed sediment rather than seawater. • ¹³⁷Cs in mussel reflects the ¹³⁷Cs in suspended matter. • Mussel watch approach is a valuable monitoring tool for ¹³⁷Cs in suspended matter in coastal areas. We measured radiocesium in mussel tissue collected from the Pacific coast of Tohoku from 2011 to 2015 to investigate the temporal and spatial dynamics of radiocesium in the coastal area. Radioactive ¹³⁷Cs was detected in all the samples collected in 2011, but it was not found in samples from localities north of Sendai after 2012. In contrast, ¹³⁷Cs was detected in many sites in the Fukushima area even from 2012 to 2015. The fluctuation of ¹³⁷Cs concentration in mussel tissue seems to reflect the ¹³⁷Cs concentration in suspended particles in the seawater, suggesting that there was an influx of soil deposition and resuspension of seabed sediment. These results suggest that the ¹³⁷Cs concentration in mussel tissue sensitively indicates the ¹³⁷Cs concentration in the environment, and that the "mussel watch" approach is an effective way to understand the dynamics of radiocesium concentrations in coastal areas.