Rapid screening of 90Sr activity in water and milk samples using Cherenkov radiation.

A method for screening 90Sr in milk samples is proposed. This method is based on a liquid scintillation technique taking advantage of Cherenkov radiation, which is produced in a liquid medium and then detected by the photomultipliers of a Liquid Scintillation Counter (LSC). Twenty millilitres of water and milk samples spiked with various concentrations of 90Sr/90Y in equilibrium were added in plastic vials and then were measured with an LSC (TriCarb 3170 TR/SL). The derived efficiencies were 49% for water samples and 14% for milk samples. The detection limit was 470 mBq L(-1)(90)Sr for water, without any pretreatment. Milk contains potassium, which also produces Cherenkov radiation due to the presence of 40K. For this reason, the interference of 40K in the measurements of 90Sr in milk samples was also investigated. The detection limit for milk was 1.7 Bq L(-1)90Sr.

Radiocaesium transfer to sheep's milk as a result of soil ingestion.

Soil ingestion as a source of radiocaesium contamination to ruminants was studied by measuring the transfer coefficient to sheep milk. Eight lactating ewes, housed in individual metabolism cages, were used. Fifty grams per day of heavily contaminated sandy topsoil, collected in 1990 from the Chernobyl area, were administered orally to the animals for a period of 1 week. The daily dose intake in 137Cs was 1835 Bq day-1. During this contamination period, daily milk production and excreta output were measured. The ewes were monitored for an additional 7 day decontamination period, while they fed on uncontaminated feed. Transfer coefficients were obtained through a best fit (minimum chi 2) of the data to predictions of a linear compartment model. The values obtained were fm = (2.6 +/- 0.7) x 10(-2) and f mu = (5 +/- 2) x 10(-2) days kg-1 for radiocaesium transport to milk and urine, respectively. These results suggest that soil ingestion can be a major source of radiocontamination for sheep and other free-grazing ruminants. Comparison of our results with soil-to-milk transfer coefficient values derived in two recent independent experiments suggests that there might be a strong dependence of radiocaesium availability on soil composition.

Reduction of cesium concentration in ovine tissues following treatment with Prussian Blue labeled with 59Fe.

The effectiveness of Prussian Blue in reducing the radiocesium contamination in ovine tissues was investigated. Five ewes were fed 137Cs-contaminated wheat for 30 d. When the 137Cs concentration in milk had reached equilibrium, one animal, serving as the control, was slaughtered and the activity in its tissues was measured. Two ewes were offered daily 1 g of Prussian Blue labeled with 59Fe in the Fe(III) position, outside the complex anion. One week after the administration of Prussian Blue, these animals were slaughtered, 1 wk apart, and the level of 137Cs in their tissues was measured. Comparing the concentration of 137Cs in the blood and tissues of the Prussian Blue treated animals to the corresponding concentrations measured in the control, a considerable reduction in the radiocesium activity concentration is observed. However, 137Cs concentrations are maintained at non-zero (about 20%) values in the first 2 wk after the administration of Prussian Blue. This observation can be attributed to the fact that most of 137Cs binds to Prussian Blue in the animals' digestive tracts and the measured activity concentrations follow the elimination of cesium from tissues. Using a two-compartment mathematical model, we can predict the level of 137Cs in tissue, following the administration of Prussian Blue. Labeling Prussian Blue in the Fe(III)-position resulted in the measurement of a (2.4 +/- 0.02) % retention of Fe(III) in sheep.

Kinetics of radiocesium sorption in lake sediments.

The sorption of radiocesium (137Cs) in sediments sampled from Lake Pamvotis of Ioannina was studied in a laboratory simulation. In a series of experiments, the kinetics of 137Cs sorption and 137Cs distribution profiles in sediment cores were investigated. The results have shown that a significant percentage of 137Cs (35%) is adsorbed in the sediments during the first 3 d, at a rate of 0.41 +/- 0.05 d-1. The rest of 137Cs is adsorbed with the slower rate of 0.024 +/- 0.004 d-1. 137Cs rapidly reaches (< 5 d) a depth that does not exceed 3.5 cm. The sorption of 137Cs was found to follow Freundlich's empirical law, which describes the adsorption of most substances in solution to solids.