Transfer of 65Zn from sediments by marine polychaete worms

Silty marine sediments spiked with ⁶⁵Zn lose only small fractions of their radioactivity when exposed to slowly flowing seawater for several weeks. However, polychaete worms (Nereis diversicolor), burrowing through the sediment, cause ⁶⁵Zn losses 3 to 7 times higher than in sediment without worms. Long-term experiments on the uptake and loss of ⁶⁵Zn by the polychaete Hermione hystrix indicate that 60 or more days exposure are required for this worm to approach steady state with ⁶⁵Zn in the sediment. Biological half-life estimates for ⁶⁵Zn accumulated from sediment by H. hystrix are extremely variable (52 to 197 days), depending on the loss-time interval chosen for the calculation. Following 5 days exposure to 16 cm³ of radioactive sediment, N. diversicolor individuals contained an average of 0.2% of the total ⁶⁵Zn in the sediment. When these worms were transferred to non-radioactive sediment, estimates of biological half-life for ⁶⁵Zn averaged 14 to 17 days during the loss period Day 3 to Day 15. Based on these experimental results, it is estimated that a population of N. diversicolor could cause an annual loss of 3% or more of the ⁶⁵Zn in the upper 2 cm of the sediment of a hypothetical radioactive estuary.