Time-dependent transfer of 137Cs, 85Sr and 65Zn to earthworms in highly contaminated soils

The transfer characteristics of 137Cs, 85Sr and 65Zn to earthworms (Eisenia andrei) in soils with different amounts of the radionuclides have been investigated. The time-dependent whole-body concentration ratios (CR) were derived for worms in artificially contaminated soils with three different activity concentrations. Two parameters of a first order kinetic model, the equilibrium concentration ratio (CReq) and the effective loss rate constant (k), were estimated by a comparison of experimental CR results with model predictions. The estimated CReq (Bq/kg fresh worm per Bq/kg dry soil) ranged from 3.9 × 10−4 to 4.1 × 10−3 for 137Cs, 1.39 × 10−3 to 2.94 × 10−2 for 85Sr, and 1.39 × 10−3 to 5.0 × 10−2 for 65Zn, and consistently decreased with increasing soil activity concentration but the trend was not statistically significant. The CReq for 137Cs was one to two orders of magnitude lower than previously reported CRwo-soil values (based on field data with much less contaminated soil), that for 85Sr was comparable with other reported values and for 65Zn was less two to three orders of magnitude lower than CRwo-soil values for stable zinc. The estimated k (d−1) values ranged from 9 × 10−2 to 1.4 × 10−1 for 137Cs, 7 × 10−2 to 2 × 10−1 for 85Sr, and 6 × 10−2 to 1.8 × 10−1 for 65Zn, and did not show a relationship with soil activity concentration. The effect of CReq on the total dose rate was insignificant for 137Cs or 65Zn because external dose rates to the soil dwelling earthworms due to these radionuclides were much greater than the internal dose rate. In contrast, the total dose from 90Sr was determined by the internal dose rate and therefore proportional to the CReq.