Evaluation of radiocerium as a nonabsorbed reference material for determining gastrointestinal sites of nutrient absorption and excretion in cattle

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4

The 2007 Recommendations (ICRP, 2007) introduced changes that affect the calculation of effective dose, and implied a revision of the dose coefficients for internal exposure, published previously in the Publication 30 series (ICRP, 1979a,b, 1980a, 1981, 1988) and Publication 68 (ICRP, 1994b). In addition, new data are now available that support an update of the radionuclide-specific information given in Publications 54 and 78 (ICRP, 1989a, 1997) for the design of monitoring programmes and retrospective assessment of occupational internal doses. Provision of new biokinetic models, dose coefficients, monitoring methods, and bioassay data was performed by Committee 2 and its task groups. A new series, the Occupational Intakes of Radionuclides (OIR) series, will replace the Publication 30 series and Publications 54, 68, and 78. OIR Part 1 (ICRP, 2015) describes the assessment of internal occupational exposure to radionuclides, biokinetic and dosimetric models, methods of individual and workplace monitoring, and general aspects of retrospective dose assessment. OIR Part 2 (ICRP, 2016), OIR Part 3 (ICRP, 2017), this current publication, and the final publication in the OIR series (OIR Part 5) provide data on individual elements and their radioisotopes, including information on chemical forms encountered in the workplace; a list of principal radioisotopes and their physical half-lives and decay modes; the parameter values of the reference biokinetic models; and data on monitoring techniques for the radioisotopes most commonly encountered in workplaces. Reviews of data on inhalation, ingestion, and systemic biokinetics are also provided for most of the elements. Dosimetric data provided in the printed publications of the OIR series include tables of committed effective dose per intake (Sv per Bq intake) for inhalation and ingestion, tables of committed effective dose per content (Sv per Bq measurement) for inhalation, and graphs of retention and excretion data per Bq intake for inhalation. These data are provided for all absorption types and for the most common isotope(s) of each element. The online electronic files that accompany the OIR series of publications contains a comprehensive set of committed effective and equivalent dose coefficients, committed effective dose per content functions, and reference bioassay functions. Data are provided for inhalation, ingestion, and direct input to blood. This fourth publication in the OIR series provides the above data for the following elements: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), actinium (Ac), protactinium (Pa), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), and fermium (Fm).

Rate of passage of digesta in sheep. 6. The effect of level of food intake on mathematical predictions of the kinetics of digesta in the reticulorumen and intestines

1.Five sheep were given 400, 625, 850, 1075 and 1300 g lucerne chaff/d according to a 5 × 5 Latin square design to perturbate a mathematical model describing the rate of passage of digesta in terms of rate constants for the reticulo-rumen (k1) and caecum and proximal

2.colon (k2), and a transit time (TT) for the intestines. These values were obtained from the concentration curves of51Cr EDTA and144Ce-144Pr (144Pr) excretion in faeces for comparison with similar measurements obtained directly.

3.The retention times of markers in the reticulo-rumen, caecum and proximal colon and intestines all decreased by approximately 50% as intakes were increased from 400 to 1300 g/d. For both markers, the direct and indirect measures of half-time in the reticulo-rumen were essentially identical. The predicted (indirect) values for half times in the caecum and proximal colon were smaller than the direct values (P< 0.005) but the correlations between them were significant (P< 0.01) for51Cr EDTA (r0.66) and144Pr (r0.78). The direct measures of transit time were smaller (P< 0.025) by 5–10% than the predicted values but correlations between them were significant (P< 0.01) for51Cr EDTA (r0.91) and for144Pr (r0.93). Thus the model predicted the changes produced in the rate of passage of digesta and its usefulness and limitations are discussed.

3.With144Pr1/2k1for the reticulo-rumen andT1/2k2for the caecum and proximal colon were both positively correlated (P< 0.025) with the organic matter digestibilities.T1/2k2decreased at half the rate ofT1/2k1with increasing intakes. This would have favoured compensatory digestion in the large intestine.

Rate of passage of digesta in sheep. 4. Passage of marker through the alimentary tract and the biological relevance of rate-constants derived from the changes in concentration of marker in faeces

1. The rates of passage of markers of fluid and particulate digesta through the sheep alimentary tract have been described mathematically in single-injection experiments by analysing the concentration curves of marker excretion in faecal dry matter and then predicting these concentrations by means of an equation containing two exponential terms. Three components related to this equation are a transit time for digesta in the intestines, a half-time of marker in the reticulo-rumen and a half-time tentatively associated with the passage of marker through the caecum and proximal colon. With this approach no surgical interference with an animal is required to obtain meaningful information about gut function.

2. Abomasal cannulation did not affect the rate of passage of 51Cr EDTA through the gut.

3. The mean half-times (T1/2) for 51Cr EDTA in the reticulo-rumen and hind-gut, respectively, were 646 and 236 min for a roughage diet and 890 and 607 min for a diet consisting mainly of wheat grain, both diets providing approximately the same amounts of digestible dry matter. These results indicated that the changes in half-times were proportionately much greater in the caecum and proximal colon than in the reticulo-rumen. The mean transit time of marker through the digestive tract also increased from 721 to 1345 min when the concentrate diet was given.

4. The complex of chromium-51 with EDTA was excreted faster in faeces than cerium-144–praseodymium-144 when both were given together as a single injection into the reticulorumen. This was caused mainly by differential rates of elimination of water and particulate matter from the reticulo-rumen.

Rate of passage of digesta in sheep. 3. Differential rates of passage of water and dry matter from the reticulo-rumen, abomasum and caecum and proximal colon

1. Three groups of sheep receiving 400, 800 and 1200 g lucerne chaff/d in equal hourly meals were killed. The large intestines were removed and divided into segments 15 cm long to provide information on the amounts and dry-matter contents of digesta and on the rates of passage of digesta and absorption of water along the large intestine.

2. With increasing intakes of food, increases were observed along the entire large intestine in the amounts of wet digesta present, in the transit rates of digesta and in the rates of absorption of water. The mean retention time of digesta in the large intestine decreased with increasing food intake, being 1737, 1056 and 692 min respectively.

3. Four patterns of sodium and potassium concentrations in digesta water along the large intestine were found.