Biomedical subjects

N M Crout

Publications and source records attributed to N M Crout.

15 recordsLinked to original sources

PubMed2001

A metabolic derivation of tritium transfer coefficients in animal products.

Tritium is a potentially important environmental contaminant originating from the nuclear industry, and its behaviour in the environment is controlled by that of hydrogen. Animal food products represent a potentially important source of tritium in the human diet and a number of transfer coefficient values for tritium transfer to a limited number of animal products are available. In this paper we present an approach for the derivation of tritium transfer coefficients which is based on the metabolism of hydrogen in animals. The derived transfer coefficients separately account for transfer to and from free (i.e. water) and organically bound tritium. A novel aspect of the approach is that tritium transfer can be predicted for any animal product for which the required metabolic input parameters are available. The predicted transfer coefficients are compared to available independent data. Agreement is good (R2=0.97) with the exception of the transfer coefficient for transfer from tritiated water to organically bound tritium in ruminants. This may be attributable to the particular characteristics of ruminant digestion. We show that tritium transfer coefficients will vary in response to the metabolic status of an animal (e.g. stage of lactation, diet digestibility etc.) and that the use of a single transfer coefficient from diet to animal product is inappropriate. It is possible to derive concentration ratio values from the estimated transfer coefficients which relate the concentration of tritiated water and organically bound tritium in an animal product to their respective concentrations in the animals diet. These concentration ratios are shown to be less subject to metabolic variation and may be more useful radioecological parameters than transfer coefficients. For tritiated water the concentration ratio shows little variation between animal products ranging from 0.59 to 0.82. In the case of organically bound tritium the concentration ratios vary between animal products from 0.15 (goat milk) to 0.67 (eggs).

Animals↗

PubMed2001

Temporal and spatial prediction of radiocaesium transfer to food products.

A recently developed semi-mechanistic temporal model is used to predict food product radiocaesium activity concentrations using soil characteristics available from spatial soil databases (exchangeable K, pH, percentage clay and percentage organic matter content). A raster database of soil characteristics, radiocaesium deposition, and crop production data has been developed for England and Wales and used to predict the spatial and temporal pattern of food product radiocaesium activity concentrations (Bq/kg). By combining these predictions with spatial data for agricultural production, an area's output of radiocaesium can also be estimated, we term this flux (Bq/year per unit area). Model predictions have been compared to observed data for radiocaesium contamination of cow milk in regions of England and Wales which received relatively high levels of fallout from the 1986 Chernobyl accident (Gwynedd and Cumbria). The model accounts for 56% and 80% of the observed variation in cow milk activity concentration for Gwynedd and Cumbria, respectively. Illustrative spatial results are presented and suggest that in terms of food product contamination areas in the North and West of England and Wales are those most vulnerable to radiocaesium deposition. When vulnerability is assessed using flux the spatial pattern is more complex and depends upon food product.

Cesium Radioisotopes↗

PubMed2001

Predicting the transfer of radiocaesium from organic soils to plants using soil characteristics.

A model predicting plant uptake of radiocaesium based on soil characteristics is described. Three soil parameters required to determine radiocaesium bioavailability in soils are estimated in the model: the labile caesium distribution coefficient (kd1), K+ concentration in the soil solution [mK] and the soil solution-->plant radiocaesium concentration factor (CF, Bq kg-1 plant/Bq dm-3). These were determined as functions of soil clay content, exchangeable K+ status, pH, NH4+ concentration and organic matter content. The effect of time on radiocaesium fixation was described using a previously published double exponential equation, modified for the effect of soil organic matter as a non-fixing adsorbent. The model was parameterised using radiocaesium uptake data from two pot trials conducted separately using ryegrass (Lolium perenne) on mineral soils and bent grass (Agrostis capillaris) on organic soils. This resulted in a significant fit to the observed transfer factor (TF, Bq kg-1 plant/Bq kg-1 whole soil) (P < 0.001, n = 58) and soil solution K+ concentration (mK, mol dm-3) (P < 0.001, n = 58). Without further parameterisation the model was tested against independent radiocaesium uptake data for barley (n = 71) using a database of published and unpublished information covering contamination time periods of 1.2-10 years (transfer factors ranged from 0.001 to 0.1). The model accounted for 52% (n = 71, P < 0.001) of the observed variation in log transfer factor.

Absorption↗

PubMed2000

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+ ++/).

Animals↗

PubMed1998

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).

Administration, Oral↗

PubMed1998

Generic relationship between calcium intake and radiostrontium transfer to the milk of dairy ruminants.

The hypothesis is tested that there is a generic relationship between the calcium intake and the transfer of radiostrontium to milk which can be used for all dairy ruminants. In addition to the daily calcium intake, the relationship also requires values for the strontium to calcium observed ratio, which describes the discrimination in transfer of the two elements to milk (a value of 0.11 is used), and the calcium concentration in milk. The relationship had previously only been validated for dairy cattle as there were insufficient data for other ruminant species. Here, we present recently available data for dairy goats, and also a limited amount of data for sheep derived from the literature. From the comparison between these data and predicted values, we conclude that it is possible to derive a generic model of the transfer of radiostrontium to the milk of dairy ruminants.

Animals↗

PubMed1998

Variation in the metabolism of radiocaesium between individual sheep.

Considerable variability has been recorded in the radiocaesium activity concentration of muscle between individual sheep in the same flocks in upland areas that received fallout from the Chernobyl accident. In a previous paper we demonstrated that there is a propensity for certain sheep within a flock to be always amongst the most contaminated and others to be consistently the least contaminated. Here we report a study to determine the extent to which variation in the metabolism of radiocaesium by individual sheep may contribute to the observed variability within sheep flocks. The transfer coefficient and biological half-life of orally administered ionic radiocaesium in muscle were determined under controlled conditions in 22 ewes from an upland farm in an area of the UK which received comparatively high levels of Chernobyl fallout. There was considerable variation between individuals in both the transfer coefficient (0.19-0.56 day x kg(-1); mean 0.34 day x kg(-1)) and biological half-life in muscle (5.2-18.7 days; mean 9.8 days). Changes in liveweight during the study and feed intake together accounted for 72% of the variation in the derived transfer coefficients; liveweight change also accounted for 56% of the observed variation in biological half-life. In a subsequent study, the true absorption coefficient of radiocaesium was determined in 12 of the ewes. There was a positive correlation between transfer and true absorption coefficients (R = 0.57). We conclude that differences in the metabolism of radiocaesium will contribute to the observed variability in radiocaesium activity concentrations within sheep flocks in areas which were contaminated by Chernobyl fallout. We also suggest that for growing animals, the influence of liveweight change and feed intake on radiocaesium transfer may be greater than observed here. Similarly, in dairy cattle, for which feed intake changes considerably during the course of a lactation, large temporal variation in radiocaesium transfer to milk could be expected.

Animals↗

PubMed1998

A model of radiostrontium transfer in dairy goats based on calcium metabolism.

A model for the transfer of radiostrontium (90Sr) in dairy goats is presented. The novel feature of the model is that it is based on the current understanding of Ca metabolism and assumes that the transfer of radiostrontium is driven by Ca transfer. Previously published models of radiostrontium transfer in animals have ignored the influence of Ca metabolism. Unknown model parameters were obtained by fitting the model to data from a study of radiostrontium and Ca transfer in goats. The model accounted for 95 and 97% of the observed variation in the data for Ca (n = 22) and radiostrontium (n = 43), respectively. Unlike previously reported models, the model presented here could be applied to simulate the effect of additional dietary Ca as a countermeasure to the contamination of milk by radiostrontium under different circumstances.

Absorption↗

PubMed1997

The use of dietary calcium intake of dairy ruminants to predict the transfer coefficient of radiostrontium to milk.

Transfer coefficients (the equilibrium ratio between radionuclide activity concentration in milk or meat and the daily intake of radionuclide) are widely used to predict the contamination of animal products following the release of radionuclides into the environment. For a transfer coefficient to be generally applicable, its value must be constant for a range of circumstances. However, this is not the case for radiostrontium, the behaviour of which is strongly influenced by that of the homeostatically controlled nutrient, calcium. In this study, a relationship is derived between radiostrontium transfer coefficients and dietary calcium intake which takes into account the observed ratio for strontium:calcium transfer to milk. This relationship is tested against a range of observed data collated from the literature (n = 30) and found to account for 93% of the variability in transfer coefficient values. Model calculations show that a reduction in Fm of at least 40%-60% would be expected if dairy cattle, fed rations typical for well-managed herds, were supplemented with 100-200 g per day. Larger reductions would be predicted when dietary calcium intake is low.

Animal Feed↗

PubMed1996

Radiocaesium variability within sheep flocks: relationships between the 137Cs activity concentrations of individual ewes within a flock and between ewes and their progeny.

As a consequence of radiocaesium deposition following the Chernobyl accident the movement and slaughter of sheep were restricted within some upland areas of the United Kingdom. Considerable variability in the radiocaesium activity concentrations between individual sheep within flocks has been recorded. This paper reports studies conducted to investigate the reasons for this within flock variability on three farms in the restricted area of west Cumbria. On each farm, study sheep were selected and live-monitored over the period 1991-93. Results from all three study farms showed a correlation in the 137Cs activity concentration of individual sheep on different monitoring occasions. This observation suggested that a few sheep on each farm are likely to be responsible for the continuation of restrictions on many of the affected holdings. Comparisons between monitoring data obtained in summer and autumn months were better correlated than those involving data collected in the winter and spring. Prior to weaning there was a linear relationship between the 137Cs levels in the muscle of a lamb and that in the muscle of its dam. Given these observations it is suggested that, in successive years, ewes identified as consistently having high radiocaesium levels in their muscle will produce lambs which will also have comparatively high levels of radiocaesium; the limited data available support this hypothesis. However, no relationship between the 137Cs activity concentration of a ewe and its lamb was evident post-weaning, thereby discounting any possibility of an inherited effect. On one of the farms a significant difference was found between the 137Cs activity concentration of different breeds of sheep.

Animals↗

PubMed1996

Development and testing of a revised dynamic model of radiocaesium transfer to sheep tissues.

The model of radiocaesium transfer to sheep presented by Galer et al. provides reliable predictions only for sheep of a similar body weight to those used in the development of the model (approximately 30 kg). To extend the applicability of the model, it was necessary to re-parameterise it in terms of activity concentrations in tissues rather than total activities within them (although for gut compartments the use of activity has been retained). The rate coefficients for the new model have been estimated by fitting the model to the data used by Galer et al. which was derived from a single "calibration" experiment. The new model was found to account for 94% of the observed variation in the data (n = 42), a result similar to that obtained by Galer et al. The model has also been tested against data not used in its development but obtained from four separate experiments undertaken by three different laboratories. Good agreement between the predictions of the new model and observations was found for most circumstances and for several breeds of sheep with different body weights. It is concluded that the new model provides a useful dynamic description of radiocaesium transfers to the tissues of sheep of different breeds and under different contamination scenarios.

Administration, Oral↗

PubMed1996

Modeling the dynamics of radioiodine in dairy cows.

A metabolically based model of radioiodine transfer in cows was applied to previously collected data. The model required some modification and reparameterization before it could describe the measured data satisfactorily. In particular, significant fecal excretion of radioiodine needed to be considered. The model was used to predict the effect of dietary intake of stable iodine on the transfer of radioiodine to milk. Increased dietary intake asymptotically increased the proportion of radioiodine excreted via milk.

Animals↗

PubMed1994

Dynamic behavior of 110mAg in sheep tissues.

The transfer coefficient of 110mAg to a range of sheep tissues and its biological half-life in these tissues has been determined. Liver was shown to be the major site of 110mAg deposition and retention, with a transfer coefficient of Ff 7.1 d kg-1 and a biological half-life of 79 d. These results also suggest that previous estimates of the transfer of silver to muscle were too high, although further work would be required to confirm this. There is a need for accurate data which can be used to predict the transfer of 110mAg to food-producing animals.

Animals↗

PubMed1991

The radioecological consequences for lowland pastures used to fatten upland sheep contaminated with radiocaesium.

Current farming practice in upland areas of Cumbria, England, affected by Chernobyl fallout is to remove lambs to lowland pastures for fattening prior to slaughter. The radiocaesium (137Cs and 134Cs) burden of lambs is rapidly lost via excreta deposited on the pasture. This may increase the radiocaesium activities in vegetation of these pastures. Studies were performed to assess the radioecological consequences of this practice. Results obtained from experiments were used to calibrate a soil/vegetation model which was used to predict long-term radiocaesium behavior.

Accidents↗

PubMed1991

In situ neutron spectrometry to 60 MeV in a water phantom exposed to a cancer therapy beam.

In-air and in-phantom neutron spectra have been measured between 10 and 60 MeV for two field sizes on the Clatterbridge cyclotron by unfolding the response of a specially built NE213 scintillator. The in-phantom measurements show distinct spectral hardening with depth, which is reflected in changes in the spectrum-averaged mean neutron energy. These findings are confirmed using Monte Carlo calculations.

Fast Neutrons↗