Activity concentrations of ¹³⁷Caesium and ²¹⁰Polonium in seafood from fishing regions of New Zealand and the dose assessment for seafood consumers

A study was undertaken to determine activity concentrations for ¹³⁴Caesium, ¹³⁷Caesium and ²¹⁰Polonium in New Zealand seafood, and establish if activity concentrations varied with respect to species/ecological niche and coastal region. Thirty seafood samples were obtained from six fishing regions of New Zealand along with a further six samples of two commercially important species (hoki and arrow squid) with well-defined fisheries. ¹³⁴Caesium was not detected in any sample. ¹³⁷Caesium was detected in 47% of samples, predominantly in pelagic fish species, with most activities at a trace level. Detections of ¹³⁷Caesium were evenly distributed across all regions. Activity concentrations were consistent with those expected from the oceanic inventory representing residual fallout from global nuclear testing. ²¹⁰Polonium was detected above the minimum detectable concentration in 33 (92%) of the analysed samples. Molluscs displayed significantly elevated activity concentrations relative to all other species groups. No significant regional variation in activity concentrations were determined. Two dose assessment models for high seafood consumers were undertaken. Dose contribution from ¹³⁷Caesium was minimal and far below the dose exemption limit of 1 mSv/year. Exposure to ²¹⁰Polonium was significant in high seafood consumers at 0.44-0.77 mSv/year (5th-95th percentile). ¹³⁷Caesium is concluded to be a valuable sentinel radionuclide for monitoring anthropogenic releases, such as global fallout and reactor releases, in the marine environment. ²¹⁰Polonium is of importance as a natural radionuclide sentinel due to its high contribution to dietary committed dose in seafood consumers.