Transfer of 65Zn from sediments by marine polychaete worms

Abstract

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.