Spatial variability in Polonium-210 and Lead-210 activity concentration in New Zealand shellfish and dose assessment.

The activity concentrations of Polonium-210 (210Po) and Lead-210 (210Pb) were determined in shellfish (Perna canaliculus and Paphies subtriangulata) sampled bimonthly from March 2018 to February 2019 from 14 sites around New Zealand. Activity concentrations of 210Po ranged from 4.7 ±â€¯1.1 to 324 ±â€¯17 Bq. kg-1 with a mean value of 57 ±â€¯72 Bq. kg-1 (wet weight). The activity concentrations of 210Pb were lower than those for 210Po (0.1 ±â€¯0.4 and 1.9 ±â€¯0.4 Bq. kg-1, with a mean value of 0.7 ±â€¯0.4 Bq. kg-1, wet weight). The calculated 210Po/210Pb activity concentration ratios were higher than unity in all samples indicating that radionuclides are not in equilibrium in shellfish and most of the 210Po was unsupported by its grandparent 210Pb. No significant difference was noted in 210Po activity concentration between different seasons, species or shellfish condition index. Significant spatial variability in 210Po activity concentration was observed with elevated 210Po activity concentration in two sampling sites: Ninety Mile Beach (mean 257 ±â€¯47 Bq. kg-1) and Maunganui Bluff (mean 127 ±â€¯22 Bq. kg-1). Elevated 210Po is hypothesised to be related to an increase of 210Po accumulation through diet. Individuals who consume large quantities of shellfish (10 g per day or more) from areas affected by elevated 210Po activity concentration may be exposed to an annual committed effective dose from 210Po in shellfish in excess of 1 mSv.