Transport of radiocaesium from a sheep's diet to its tissues.

Transfer coefficients for radiocaesium transport from a sheep's diet to blood, muscle, lung, liver, kidney, spleen heart, brain, rumen, intestines and fat were measured in a controlled experiment involving 50 adult ewes. The animals were fed dry grass and wheat, both contaminated with Chernobyl fallout debris, for a period of 60 days. During this period half of the animals were killed at regular intervals and samples of their blood and tissues were measured for radiocaesium concentration. The rest of the animals were returned to uncontaminated food and were monitored for radiocaesium concentration through periodic slaughtering for an additional 60 days. Transfer coefficients were extracted from the plateau reached at the end of the contamination phase. The data were also analyzed by means of a recently proposed linear multiple compartment model and transport rate parameters for each compartment were extracted. Transfer coefficients computed through the model's transport rate parameters show remarkable agreement with the experimentally obtained values.

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

Soil ingestion as a source of radiostrontium contamination of ruminant milk products was studied by measuring the transfer coefficient to ovine milk. This is a follow-up report from a previous experiment (Assimakopoulos et al., 1993), which investigated radiocaesium transfer to sheep's milk as a result of soil ingestion. Milk samples from three lactating ewes, housed in individual metabolism cages, were used. Fifty grams per day of heavily contaminated sandy topsoil, collected in the Chernobyl area, were administered orally to the animals for a period of 1 week. The daily intake of 90Sr was 78 Bq day-1. During this contamination period, daily milk production and excreta output were measured. Excreta and milk was collected for an additional 7-day decontamination period, while they were fed on uncontaminated feed. The transfer coefficient was obtained through a best fit (minimum chi 2) of the data to predictions of a linear compartment model. The value obtained was fm = 0.041 +/- 0.016 d kg-1 for radiostrontium transport to milk. This result suggests that soil ingestion can be a major source of radiostrontium contamination in sheep and other free-grazing ruminants.

A study of radiocesium contamination and decontamination of sheep's milk.

The radiocesium contamination and decontamination of sheep's milk were studied under a constant level of activity concentration in the sheep's diet. Two sets of experiments were performed: one at the end of the animal's lactating period and one during the main lactating period. The data were in satisfactory agreement with the predictions of a simple two-compartment model. At the stage of equilibrium the data yielded the transfer coefficient fm with an average value of fm = 0.063 +/- 0.005 d L-1. In the second experiment a detailed study of the decontamination phase revealed a two-component decay with amplitudes 53% and 43% and half-lives 1.5 d and 6.9 d, respectively. A small 4% long-lived (T1/2 = 170 d) third component could not be distinguished from an overall background decay, measured in control animals.

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.

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.

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.

Processes that contribute to radiocesium decontamination of feta cheese.

In a series of experiments, the transfer of radiocesium from ovine milk to feta cheese was investigated through modifications of the standard cheese making procedure. All variations explored showed no significant change in the percentage of radiocesium transfer and the milk-to-cheese transfer coefficient was determined as f=.79 plus/minus .04 L.kg-1. It is concluded that cesium, like the rest of the alkali metals, remains in the water phase and thus follows very closely the distribution of moisture into the products of cheese making. The possibility of radiocesium decontamination of mature feta during the customary storage of the product in brine was also explored in a second series of experiments. The theoretical model employed in the analysis of cesium transport from feta to brine is presented in the Appendix to this paper. Predictions of the model were validated by experiments. A procedure is thus proposed for decontaminating mature feta during storage through successive replacements of the storage medium. Nomograms are presented for the determination of the optimum time interval between changes of the brine and the radiocesium concentration remaining in the feta. Changes in the properties of the product induced by the proposed treatment were also investigated with respect to composition, taste, and overall quality.