The transfer of radionuclides from saltmarsh vegetation to sheep tissues and milk.

Radionuclides released into the Irish Sea by the Sellafield reprocessing plant are deposited onto tide-washed pastures along the western coast of the United Kingdom. Many of these pastures are grazed by sheep or cattle. This paper describes a controlled feeding study, in which saltmarsh vegetation harvested from close to the Sellafield plant, was fed to lambs and adult female sheep for a period of 8 weeks. Activity concentrations of (60)Co, (95)Nb, (106)Ru, (134)Cs, (137)Cs, (238)Pu, (239,240)Pu and (241)Am were determined in edible tissues and transfer parameters estimated. The activity concentrations of some of the radionuclides will not have been in equilibrium with those in the diet. Nevertheless, the study was reasonably realistic in terms of agricultural management as the period of the study was similar to that for which lambs graze on the saltmarshes. A field study to determine the activity concentrations of (137)Cs and (239,240)Pu in the milk of ewes grazing a saltmarsh close to Sellafield is also described.

The transfer of different forms of 35S to goat milk.

Sulphur-35 is released during the routine operation of UK gas-cooled reactors. An experiment to determine the rates of transfer of different forms of (35)S to goat milk is described. Lactating goats received (35)S orally as single administrations of sulphate, L-methionine, or grass contaminated either through root uptake of (35)S as sulphate or through aerial deposition of (35)S as carbonyl sulphide onto the grass. Transfer was higher for (35)S administered as methionine compared with (35)S administered as sulphate. Changes in activity concentrations in milk for all sources of (35)S demonstrated two components of loss. The first component had a half-life of circa 1 d for all sources, the second was longer in goats administered carbonyl sulphide (44 d) than in all of the other treatments (circa 10 d). The rate of transfer of (35)S to milk of a further group of goats receiving (35)S-sulphate daily appeared to reach equilibrium within 30 d. Extrapolation of transfer parameters derived to other dairy ruminants is discussed.

A model of radioiodine transfer to goat milk incorporating the influence of stable iodine.

Previously reported models for radioiodine in ruminants cannot account for the effect of variations in stable iodine intake including large countermeasure doses of stable iodine on the transfer of radioiodine to goat milk. A metabolically based model of radioiodine transfer in goats has been parameterised using new experimental data on the effect of countermeasure doses of stable iodine on radioiodine transfer to milk. To account for the effect of dietary stable iodine levels, the model represents the transfer of iodine from the extracellular fluid to milk with Michaelis-Menten kinetics. The model shows good agreement with the experimental data, and the estimated parameters compare favourably with values which can be estimated from the literature. The parameterised model accounts for 95% of the variation in the observed data for milk, faeces, urine and thyroid (n=199). The model has been used to predict the effects of variation in stable iodine intake and the extent of consequent chemical contamination of milk by stable iodine. The time taken for radio-iodine to reach peak concentrations in milk following a deposition event is predicted to vary significantly (ca. 2 days) over a range of expected stable iodine intakes. Doses of stable iodine sufficient to reduce the radioiodine transfer to milk will result in stable iodine concentrations in milk greatly in excess of internationally advised limits. Therefore, we recommend that stable iodine supplementation not be used as a countermeasure to reduce radioiodine transfer to milk. Indeed, model predictions suggest that reductions in stable iodine intake would be a more effective countermeasure. However, this is unlikely to be feasible since the short physical half-life of 131I may not allow adequate time to implement changes in feed manufacture. The model described in this paper is freely available in ModelMaker 3.0 format (http://www.notingham.ac.uk/environmentalmodelling+ ++/).

A metabolic approach to simulating the dynamics of C-14, H-3 and S-35 in sheep tissues.

The results of a study in which groups of sheep were given single oral administrations of 14C, 3H and 35S and then slaughtered over a period of 1 year are reported. The experimental data were used to investigate the potential of metabolically based models for describing the transfer of the three radionuclides to sheep tissues. The structure of these models is based upon a simplified understanding of the transfer of the macro-elements C, H and S by processes such as respiration and protein synthesis/degradation. A consequence of this approach is that the three models have many common parameters. The models reproduced the general trends of the observations, accounting for 74%, 66%, and 58% of the observed variation in the 14C, 3H and 35S data, respectively, suggesting that they may provide a useful alternative approach to modelling the transfer of these radionuclides. The models presented are limited to the particular experimental situation for which they were developed, and further experimental work would be required to extend them. However, such metabolically based models have great potential: for example, they should be able to account for the influence of dietary intake, physiological status or the form of the radionuclide in the animals diet (e.g. tritiated water or organically bound tritium).

Novel approaches to the estimation of intake and bioavailability of radiocaesium in ruminants grazing forested areas.

It is difficult to measure transfer of radiocaesium to the tissues of forest ruminants because they can potentially ingest a wide range of plant types. Measurements on undomesticated forest ruminants incur further difficulties. Existing techniques of estimating radiocaesium intake are imprecise when applied to forest systems. New approaches to measure this parameter are discussed. Two methods of intake estimation are described and evaluated. In the first method, radiocaesium intake is estimated from the radiocaesium activity concentrations of plants, combined with estimates of dry-matter (DM) intake and plant species composition of the diet, using plant and orally-dosed hydrocarbons (n-alkanes) as markers. The second approach estimates the total radiocaesium intake of an animal from the rate of excretion of radiocaesium in the faeces and an assumed value for the apparent absorption coefficient. Estimates of radiocaesium intake, using these approaches, in lactating goats and adult sheep were used to calculate transfer coefficients for milk and muscle; these compared favourably with transfer coefficients previously obtained under controlled experimental conditions. Potential variations in bioavailability of dietary radiocaesium sources to forest ruminants have rarely been considered. Approaches that can be used to describe bioavailability, including the true absorption coefficient and in vitro extractability, are outlined.

Teaching professional ethics to undergraduate counseling students.

Teaching ethics to undergraduates is a topic of increasing interest among mental health professionals; knowledge of ethics is particularly important to students who seek employment in agencies after graduation. This article describes methods of presenting ethics of practice both in a separate ethics course and as part of an undergraduate counseling practicum. Sources of materials used for course readings are presented.

Transfer of radiocesium from different environmental sources to ewes and suckling lambs.

Indoor experiments are described that compare the transfer of radiocesium to ewe and lamb tissues from different sources. Lactating ewes were fed either perennial ryegrass contaminated by Chernobyl fallout, or saltmarsh vegetation contaminated by marine discharges from the Sellafield reprocessing plant. The transfer to ewe tissues and milk was greater from the Chernobyl contaminated herbage than from saltmarsh vegetation. Lambs receiving a mixture of vegetation and milk were given radiocesium from one of the two vegetation sources or from milk obtained from the experimental ewes. Transfer to lamb tissues declined in the order milk greater than Chernobyl fallout greater than Sellafield discharge. The radiocesium transfer to lamb tissues exceeded that to ewe tissues. Transfer coefficients for 137Cs in the Chernobyl fallout were higher than most previously published figures at 0.12 d kg-1 for ewe muscle and 0.50 d kg-1 for lamb muscle. The transfer coefficient for 137Cs from ewe milk to lamb muscle was 1.20 d kg-1.

A possible method for estimating the true absorption coefficient for radiocaesium in ruminants.

A method has been described for estimating the true absorption coefficient for radiocaesium. The ratio of the excretion of 137Cs in the faeces to that excreted in the urine was estimated in housed ewes and lambs offered a radiocaesium-free diet for 16-22 days, after previously grazing a pasture contaminated with Chernobyl fall-out. There was a two-fold range in the faeces:urine excretion ratio. The ratios obtained were used to estimate the the faecal 137Cs of endogenous origin from the urinary excretion rates of ewes given diets contaminated with radiocaesium from Chernobyl or from marine effluent from BNFL, Sellafield, and hence the true absorption coefficient could be determined. The observed variations in faeces:urine excretion ratios had little effect upon the estimates of true absorption coefficient.

Circadian variation in abomasal digesta flow in grazing ewes during lactation.

1. Lactating grazing ewes, fistulated at the rumen and abomasum were either not supplemented or offered, individually, 600 g/d of either pelleted, molassed sugar-beet pulp ('energy' supplement) or a pelleted 1:1 (w/w) mixture of this feed and formaldehyde-treated soya-bean meal ('protein' supplement). Digesta flows at the abomasum were estimated from the concentrations of the markers CrEDTA and ruthenium phenanthroline complex, during their administration by continuous intra-rumen infusion. Digesta samples were taken at 09.00 hours and at six further times at 4 h intervals. This was repeated 2 d later. 2. No significant difference in flow between days was noted. Daily flows of dry matter (DM) and non-ammonia-nitrogen (NAN) (g/d) in supplemented ewes were significantly higher than in unsupplemented ewes, both in total digesta and its particulate phase. However, there were significant differences between sampling times or significant interactions between sampling time and supplement treatment. The results were therefore examined by Fourier analysis for possible circadian variation in digesta flow. As there was marked between-animal variability in flow-rate, the digesta-flow values for each sampling time were re-expressed as percentages of the flows calculated from daily mean marker concentrations. 3. In unsupplemented animals, marked and significant circadian variation was then identified in the flow of DM, total N and NAN in both whole digesta and the particulate phase. There was also significant circadian variation in the flow of DM, total N and NAN in the digesta of the supplemented ewes. Curves were of the same general shape as those for unsupplemented animals, but some significant differences were found, principally for digesta NAN flow. In both supplemented and unsupplemented animals, peak flows occurred in the period 20.00-01.00 hours. The proportion of DM and NAN flowing in the particulate phase was relatively constant through the day for unsupplemented ewes, but significant circadian variation occurred for supplemented ewes. 4. The possible mechanisms generating the circadian variation in digesta flow, such as grazing behaviour and the rumen digestion of supplements, are discussed. Values are also presented to indicate the extent of the likely errors if digesta flows were estimated from samples which did not represent all stages of the circadian pattern.

Threonine metabolism in sheep. I. Threonine catabolism and gluconeogenesis in mature Blackface wethers given poor quality hill herbage.

In three experiments, mature Blackface wethers were given freeze-stored Agrostis festuca herbage by continuous feeder. In Expt 1, on separate occasions [U-14C]threonine, [U-14C]glucose and NaH14CO3 were infused over 12 h periods to obtain estimates of irreversible loss rate (ILR) of threonine, glucose and carbon dioxide in the plasma and of the exchange of C between these metabolites. In Expts 2 and 3, during periods when glucose and threonine metabolism were examined, glucose loss across the kidneys (23-29 g/d) was induced by infusion of phloridzin. Results from the four sheep used in Expts 1 and 3 are presented as three-pool models. They indicate that threonine ILR (7.8 g/d; 3.1 g C/d) was approximately three times the estimated rate of absorption of exogenous threonine (1 g C/d). Glucose ILR was approximately 76 g/d (mean +/- SE; 30.3 +/- 0.57 g C/d). Only 0.3% of the glucose-C (0.09 g/d) was derived directly from threonine-C (i.e. 3% of the threonine-C ILR). Bicarbonate ILR was 170 +/- 7.3 g C/d, and glucose contributed 11.1 +/- 3.52 g C/d to this, accounting for 51 +/- 4.4% of glucose-C ILR. Threonine contributed 0.20 +/- 0.026 g C/d to the bicarbonate-C ILR, accounting for only 6.4 +/- 0.87% of the threonine-C ILR. When, in Expts 2 and 3, phloridzin was infused, glucose ILR was increased by 28 +/- 1.5% and bicarbonate ILR was increased by 13 +/- 2.4%. Threonine ILR (3.1 g C/d) was not increased, but the metabolic distribution of threonine-C was altered. The transfer of threonine-C into glucose and CO2 was increased by 39 and 69% respectively to 0.125 and 0.45 g C/d, accounting for 4 and 13% of the threonine ILR respectively. Both technical and metabolic considerations which affect interpretation of these results in terms of rates of catabolism of threonine and of quantitative estimates of gluconeogenesis from threonine are discussed.