Environmental Radiochemical Analysis II
By Peter WarwickThe Royal Society of Chemistry
Copyright © 2003 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85404-618-8Contents
Development of an In-Vitro Procedure to Measure the Availability of Soil-Associated Radionuclides for Uptake After Inadvertent Ingestion by Humans S. Shaw and N. Green, 1,
Separation of Iron-55/59 From Fisson and Activation Products Using Di Isobutylketone-Based Extraction Chromatographic Materials P. E. Warwick and I. W. Croudace, 8,
Synthesis of a Novel Ion Exchanger, Zirconium Vanadate, For Immobilising 134,137Cs Radionuclides R. Kamalika, D. K. Pal, S. Basu, D. Nayak, A. De and S. Lahiri, 17,
Investigation of a Method for Measuring Radon in Irish Domestic Groundwater Supplies S. Sequeira, L. McKittrick, T. P. Ryan and P. A. Colgan, 21,
A Comparison of Three Methodologies for the Determination of Gross Alpha Activity in Water Samples C. Zhou, R. Zhou, S. Lin, Z. Cheng, S. Feng, K. Zhao, 31,
Efficiency and Resolution of Germanium Detectors as a Function of Energy and Incident Geometry R. M. Keyser, 38,
New Method for Determination of Transplutonium Isotopes by Using a PM-143 Tracer A. Ermakov, T. Kuprishova, L. Velichko, Yu Maslov, S. Malinovsky, A. Sobolev and A. Novgorodov, 45,
Ultra Low-Background Gamma Spectrometry for the Monitoring of Environmental Neutrons K. Komura, 53,
Estimation of Uncertainty in Radiochemical Analysis from Sub-sampling Solid Matrices G. J. Ham and M. J. Youngman, 60,
A Rapid Determination of RA-226 and RA-224 Using Extraction Chromatography A. H. Thakkur, M. J. Fern and D. McCurdy, 69,
Construction of an Uncertainty Budget for Alpha Spectrometry: A Case Study (The Determination of Uranium Isotopic Activity Levels in Vegetation Samples Using Extraction Chromatography) T. Gingell and M. Harwood, 76,
Spatial and Temporal Variation of Tritium Activities in Coastal Marine Sediments of the Severn Estuary (UK) P. E. Warwick, I. W. Croudace, A. G. Howard, A. B. Cundy, J. Morris and K. Doucette, 92,
High Precision PU Isotope Ratio Measurements Using Multi-Collector ICP-MS I, W. Croudace, T. Warneke, P. E. Warwick, R. N. Taylor and J. A. Milton, 104,
Measurement of Gross Alpha and Gross Beta Activity in Sediment: An Analysts' Intercomparison J. Toole, 113,
The Radiological Significance of Foods Collected from the Wild N. Green, 120,
Natural Radionuclides Measurements in Drinking Water by Liquid Scintillation Counting. Methods and Results M. Forte, R. Rusconi, E. Di Caprio, S. Bellinzona and G. Sgorbati, 128,
Po Concentrations in UK Seafood A. K. Young, D. McCubbin, K. Thomas, W. C. Camplin, K. S. Leonard and N. Wood, 143,
A Study of Colloids in the Near-Field Waters at the Low-Level Waste Repository Site at Drigg P. Warwick, S. J. Allison, A. Eilbeck, 150,
Low Level Liquid Scintillation Counting in a Deep Underground Laboratory: Background Reduction Aspects F. Verrezen and C. Hurtgen, 160,
Complete Dissolution of Soil Samples by Fusion A. V. Harms, 167,
LSC: From the Routine Counter to the Real Spectrometer I. A. Kashirin, A. I. Ermakov, S. V. Malinovskiy and K. M. Efimov, 174,
Simultaneous Determination of Long-Lived Radionuclides in Environmental Samples N. Vajda, Zs. Molnar, É. Kabi and Sz. Osvath, 185,
Analysis of Am, Pu and Th in Large Volume Water Samples in the Presence of High Concentrations of Iron M. Schultz, W. Burnett, T. Hinton, J. Alberts and M. Takacs, 197,
In-Situ Radionuclide Retardation in Groundwater Conducting Systems – Overview of the Research Carried out at Nagra's Grimsel Test Site, Central Switzerland C. Biggin, A. Möri, W. R. Alexander, K. Ota, B. Frieg, W. Kickmaier and I. McKinley, 207,
Elution Behaviour of Technetium and Rhenium Through a Tc-Selective Chromatographic Resin Column S. Uchida and K. Tagami, 229,
The Use of Fucus Vesiculosus to Monitor the Transport of 129I in The English Channel S. J. Parry and A. Davies, 237,
Determination of 237Np by Neutron Activation Analysis and Alpha Sepctrometry L. Benedik and U. Repinc, 245,
Man-Made Radionuclides in Age-Dated Sediment Cores from the Black Sea R. A. Aliev, St. N. Kalmykov and Y. A. Sapozhnikov, 254,
Determination of Plutonium in the Air by Isotopic Dilution ICP-MS After TNOA Extraction Chromatographic Separation Y-R. Jin, J-F. Gao, J-F. Bai, G-Q. Zhou, L. Li, J-C. Zie, J-F Wu, X-H. Wang and F-R Zhu, 263,
Simple Method for C-14 Analysis in Organic Material and its Distribution in Forest and Cultivated Field M. Atarashi-Andoh and H. Amano, 273,
F-Labelling of Humic Substances K. Franke, J. T. Patt, M. Patt, D. Rößler and H. Kupsch, 280,
Chemical and Radiological Characterisation of Santos Estuary Sediments P. S. C. Silva, B. P. Mazilli and D. I. T. Favaro, 285,
Thermochromatographic Studies on the Separation of Plutonium from Soil Samples U. G. Schneider, U. Krähenbühl and S. Röllin, 291,
Partitioning of Plutonium Isotopes in Lake Bottom Sediments R. Gvozdaite, R. Druteikiene, B. Luksiene, N. Tarasiuk and N. Spirkauskaite, 296,
Radioanalytical Method for the Determination of Sr In Soil Samples by Yttrium Solvent Extraction and Cerenkov Counting D. Pérez Sánchez, A. Martin Sánchez, M. R. Garcia Sanz and A. Fernández Timón, 307,
Investigation of Inorganic Contaminants in Packaging Made From Recycled Paper and Board S. J. Parry and D. S. J. Aston, 313,
Equilibrium Factor F and Effective Dose Equivalent with Solid State Nuclear Track Detectors A. Chávez, M. Balcázar and M. E. Camacho, 328,
Biological Monitoring of Radioactivity and Metal Pollution in Edible Eggs of Liometopurn apiculatum (Ants) From a Radioactive Waste Site in Central Mexico M. I. Gaso, N. Segovia, O. Morton and M. A. Armienta, 334,
Preparation of Environmental Samples for Radioanalytical Assay: An Overview S. M. Coganand K. S. Leonard, 340,
Comparative Investigations on Hydrophilicity and Mobility of Humic Substances Using Radiolabelling Techniques H. Lippold, D. Roessler and H. Kupsch, 349,
Determination of Gross Alpha in Drinking Water and Nuclear Waste Water Using Actinide Resin™ and LSC P. J. M. Kwakman and M. Witte, 354,
Chromium Speciation in Acidic Solutions Using Radiochromtographic Methods S. H. Pezzin, J. F. Lugo Rivera, K. E. Collins and C. H. Collins, 360,
Influence of Geochemical Parameters on the Mobility of Metal-Humate Complexes A. Mansel and H. Kupsch, 368,
Ultra Sensitive Measurements of Gamma-Ray Emitting Radionuclides Using HPGE-Detectors in the Underground Laboratory Hades M. Hult, J. Gasparro, L. Johansson, P. N. Johnston and R. Vasselli, 375,
Sedimentation Rates and Metals in Sediments from the Reservoir Rio Grande – Săo Paulo/Brazil S. R. D. Moreira. D. I. T. Fávaro. F. Campagnoli and B. P. Mazzilli, 383,
Operational Speciation of Ra and U-Isotopes in Sediments Affected by Non-Nuclear Industry Wastes J. L. Aguado, J. P. Bolivar, E. G. SanMiguel and R. Garcia-Tenorio, 391,
Radiochronology of Sediment Cores Collected in an Estuary Strongly Affected by Fertilizer Plants Releases E. G. San Miguel, J. L. Aguado, J. P. Bolivar and R. Garcia-Tenorio, 401,
Chemical Fractionation of Iodine-129 and Cesium-137 in Chernobyl Contaminated Soil and Irish Sea Sediment X. L. Hou, C. L. Fogh, J. Kucera, K. G. Andersson, H. Dahlgaard and S. P. Nielsen, 410,
Isotope Index, 418,
Subject Index, 419,
CHAPTER 1
DEVELOPMENT OF AN IN-VITRO PROCEDURE TO MEASURE THE AVAILABILITY OF SOIL-ASSOCIATED RADIONUCLIDES FOR UPTAKE AFTER INADVERTENT INGESTION BY HUMANS
S. Shaw and N. Green
National Radiological Protection Board, Chilton, Didcot, Oxon OX11 ORQ, UK
1 INTRODUCTION
The ingestion of soil by humans is relatively common and can be inadvertent or purposeful. Inadvertent ingestion of soil generally occurs through primitive living conditions or professions that have close and continual contact with soil. For example, dust may adhere to hands or plants and be subsequently transferred to the mouth and ingested. Inadvertent ingestion is of particular importance to children because they may be less meticulous about hygiene than adults. Purposeful ingestion of soil can occur as a result of pica (an eating disorder manifested by a craving to ingest any material not fit for food) or geophagy, a special case of pica where substances such as chalk, clay or earth are ingested.
Radiological assessments of the impact of routine and accidental releases of radionuclides into the environment generally take into account the dose from inadvertent ingestion of radionuclides associated with soil or sediment. However, a lack of relevant data has meant that radionuclides associated with soil or sediment are assumed to have the same availability for gut uptake as those incorporated into food. Studies investigating the availability of soil-associated radionuclides after ingestion have been mainly conducted on ruminant animals. The ruminant digestive tract is totally different to that of man, and so data from animal experiments may not be valid in the case of humans. The importance of inadvertent ingestion in radiological assessments can be illustrated using a recent study on the potential incursion of marine sediment inland in Northwest England. The results indicated that inadvertent ingestion of deposited material could account for a substantial fraction of the estimated dose, especially for children.
Studies to investigate the availability and the possible absorption of soil-associated radionuclides in humans have to be carried out in vitro. The digestive system in humans is difficult to simulate because of the complex processes involved. Many experiments designed to simulate human digestion have been carried out to determine the availability/absorption of trace elements and heavy metals in nutritional studies. These studies either used expensive complex equipment or were simple acid extractions carried out on a small scale.
This paper summarises the development of a relatively simple inexpensive in vitro digestion procedure (enzymolysis) that would be able to simulate in vivo conditions as closely as possible. The enzymolysis procedure was then used to determine the availability of specific radionuclides, for potential absorption across the gut, in a range of soil types. A full report is available at NRPB's web site.
2 MATERIALS
2.1 Soil Types and Radionuclides of Interest
Loam, peat and sand soils were chosen for this study to cover a broad spectrum of cultivated soils found in the UK. The soils were collected from NRPB's established lysimeter facility, set up in 1983 and containing elevated levels of 137Cs, 90Sr, 239Pu and 241Am. Collected soil was stored in a field moist condition at 4 °C until required; sub-samples of soil were air-dried before use.
2.2 Reagents
The porcine enzymes pepsin (catalogue number P-7000), pancreatin (catalogue number P-1750), α-amylase (catalogue number A-1376) and bile salts (catalogue number B-8756) were purchased from Sigma Chemicals. The enzymes are available from the manufacturer in different strengths and therefore the catalogue numbers have been given here for clarification. All other reagents used were Analytical Reagent grade or equivalent.
2.3 Equipment
The vessel used to carry out the digestion was a 2 litre magnetic culture vessel. The vessel had two access ports and contained a magnetic stirrer and baffles to aid mixing. A magnetic hotplate stirrer connected to an electronic contact thermometer was used to keep the solution well mixed and at a constant temperature of 37 °C (body temperature).
3 ANALYTICAL METHODS
3.1 Sample Preparation
The liquid and solid phases of a sample were separated by centrifugation immediately after completion of the enzymolysis procedure described in Section 4. The liquid phase was then decanted through a series of cellulose nitrate membrane filters (5.0, 0.65 and 0.45µm). The membrane filters were dissolved in acetone and evaporated to dryness for analysis with the solid phase.
3.1.1 Liquid Phase. The sample volume was reduced, the solution was acidified with 8 M nitric acid and poured into a suitable container for 137Cs determination, if required. After 137Cs measurement the solution was evaporated to dryness and ashed at 500°C. The ash was dissolved in the minimum volume of 8 M nitric acid. Any undissolved residue was separated from solution and treated with small amounts of a 3:1 hydrofluoric acid: nitric acid mixture, to ensure total dissolution, before re-dissolving in 8 M nitric acid and combining with the bulk sample.
3.1.2 Solid Phase. After separation from the liquid phase, the residue was evaporated to dryness and then dried at 105°C. The dried residue was lightly ground and packed into a suitable container for 137Cs determination, if required. After 137Cs determination the sample was then combined with the membrane filters and carefully ashed at 500°C. Dissolution of the ash was carried out as described in Section 3.1.1. If after the hydrofluoric acid: nitric treatment solids still remained, then a caustic fusion was carried out to obtain total dissolution. The caustic fusion procedure was a modification of the method originally described by Bock, the full method is given in NRPB W-17.
3.2 Sample Analysis
Caesium-137 was measured by gamma-ray spectrometry using hyperpure Ge detectors, housed in a purpose built facility and appropriately calibrated. The separation and purification of 90Sr was carried out using Sr resin (EIChroM Industries, Inc.) and based on a method developed by Shaw and Green. After a suitable period of ingrowth followed by separation, 90Sr was determined by beta counting of its 90Y daughter on a low background gas flow beta counter. The analytical methods used for 239Pu and 241Am were based on those described by Krey and Beck" and Ham' respectively. All of the analytical methods employed are in regular operational use at WB's laboratories and are carried out within formal agreement with the United Kingdom Accreditation Service (UKAS).
4 ENZYMOLYSIS PROCEDURE DEVELOPMENT
After evaluation of several published methods, two phase enzymolysis procedure was designed based on a method developed by McKay and Memmott. The first phase of the procedure simulated the conditions found in the stomach and the second phase those found in the small intestines. The full detailed enzymolysis procedure is given in NRPB W-17. Briefly, the stomach phase consisted of pepsin dissolved in a saline hydrochloric solution which was heated to 37°C and then air-dried soil added. The stomach phase was then incubated for 1 h. After 1 h, the simulated intestinal fluid (intestinal enzymes dissolved in a sodium bicarbonate solution) heated to 37°C was added to the stomach phase and the pH adjusted to 7.5 with sodium hydroxide. The intestinal phase was then incubated for 2 h. When the digestion was complete the solid and liquid phases were separated by centrifugation.
The experimental protocol was developed by carrying out various studies to ensure that parameters which could possibly affect the extraction of radionuclides from the soil were optimised. The incubation times were chosen to reflect retention times of food in the stomach and small intestines and were investigated to see if longer incubation times increased the amount of activity extracted from the soil. It was found that longer incubation times had little effect on the extraction of the soil-associated radionuclides. The extraction of the radionuclides in the different phases was also studied. These experiments showed that a two phase procedure was necessary to simulate in vivo conditions.
Whilst evaluating the enzymolysis procedure, problems with soil ageing were also discovered. It is common practice to collect a bulk sample of soil and store in a refrigerator when sub-samples are required for a series of experiments. The storage of soil was found to have an indirect effect on the amount of activity extracted from the soil, especially for 239Pu. Therefore, subsequent experiments used freshly sampled soil is used for experiments. The detailed enzymolysis procedure development is given in NRPB W-17.
5 AVAILABILITY OF SPECIFIC RADIONUCLIDES FOR UPTAKE
The enzymolysis procedure was used to determine the availability of 137Cs, 239Pu, 241Am and 90Sr in loam, peat and sand soils. Each experiment was carried out in quadruplicate to ensure reproducibility of the results. The results are given in Table 1.
The soil type did not have a marked effect on the amount of 137Cs and 241Am that was extracted, the range being between 1% and 3%. However, the amount of 239Pu and 90Sr extracted was dependent on soil type. For 239Pu, approximately 6% was extracted from loam and peat soils, whereas 11 % was extracted from sand soil. The effect of soil type was even greater for 90Sr, approximately 20% being extracted from peat soil compared to around 50% extracted from loam and sand soil. If the soil type is unknown it is recommended that the generalised availability factors 3%, 3%, 10% and 50% for 137Cs, 241Am, 239Pu and 90Sr respectively are used. There was little variation between the results of the quadruplicate samples indicating that the procedure gave reproducible data.
Excerpted from Environmental Radiochemical Analysis II by Peter Warwick. Copyright © 2003 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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