Review of methods to measure internal contamination in an emergency.

In the event of a radiation emergency, people close to the site of the incident may be exposed to radiation by external exposure, or as a result of intakes of radioactive material. For these incidents it may be necessary to monitor members of the public both for external and internal contamination. This work reviews currently available equipment for the assessment of internal exposure following an emergency. It concentrates on incidents involving the spread of radioactive material and on contamination by radionuclides which emit penetrating radiation. It is essential that this monitoring is carried out as soon as possible so that people who have been exposed at a level which could have an effect on health can be identified and receive prompt medical assessment. Proposed action levels to identify people who need medical attention are reviewed to determine the required sensitivity of monitoring equipment. For releases containing gamma-ray emitting radionuclides the best means of measuring internal contamination is to use detectors placed close to the body (whole body or partial body monitoring). Laboratory based whole body monitors could be used but these may well be inconveniently located and so equipment which can be deployed to the site of an incident has been developed and these are described. The need for rapid selection and prioritisation of people for monitoring, methods to deal with potentially high numbers of contaminated people and the requirement for a means of rapidly interpreting monitoring information are also discussed.It has been found that for many types of incidents and scenarios, systems based on unshielded high-resolution detectors and hand-held instruments do have the required sensitivity to identify people who require medical assessment.

An experimental study of clearance of inhaled particles from the human nose.

Retention in the extrathoracic airways, and clearance by nose blowing, of monodisperse indium-111-labeled polystyrene particles were followed for at least 2 days after inhalation by healthy volunteers. Nine volunteers inhaled 3-µm aerodynamic diameter particles while sitting at rest, whereas subgroups of 3 or 4 inhaled 1.5-µm or 6-µm particles at rest, and 3-µm or 6-µm particles while performing light exercise. Retention of the initial extrathoracic deposit (IETD) in the extrathoracic airways was described by 4 components: on average 19% IETD cleared by nose blowing; 15% was swallowed before the first measurement, a few minutes after inhalation; 21% cleared by mucociliary action between the first measurement and about an hour later; and 45% subsequently cleared by mucociliary action. Geometric mean times in which 50% and 90% of IETD cleared were 2.5 and 22 hours. The geometric mean retention fractions at 24 and 48 hours were 7% and 2.4% IETD, respectively. No clear trends were found between parameters describing retention and any related to deposition (e.g., particle size). However, the fraction cleared by nose blowing was related to the frequency of nose blowing and therefore appears to be a characteristic of the individual.

Effect of particle size on slow particle clearance from the bronchial tree.

The Human Respiratory Tract Model of the International Commission on Radiological Protection assumes that a fraction of particles deposited in the bronchial tree clears slowly, this fraction decreasing with increasing particle geometric diameter. To test this assumption, volunteers inhaled 5-microm aerodynamic diameter 111In-polystyrene and 198Au-gold particles simultaneously, as a 'bolus' at the end of each breath to minimize alveolar deposition. Because of the different densities (1.05 versus 19.3 g cm3), geometric diameters were about 5 and 1.2 microm, respectively, and corresponding predicted slowly cleared fractions were about 10% and 50%. However, lung retention of the 2 particles was similar in each subject. Retention at 24 hours, as a percentage of initial lung deposit (mean +/- SD) was 34 +/- 12 for polystyrene and 31 +/- 11 for the gold particles.

ERIDAS, a computer program for rapid calculation of internal doses from measurements of people in an emergency.

In an emergency involving the deliberate or accidental release of radioactive materials, there could potentially be a large number of people who require monitoring for internal contamination. Doses from these measurements will need to be calculated as quickly as possible. Emergency Response Internal Dose Assessment Software (ERIDAS) has been designed for this purpose.

Further study of the effect of particle size on slow particle clearance from the bronchial tree.

The ICRP human respiratory tract model (HRTM) assumes that the 'slow-cleared fraction' fs in the bronchial (BB) and bronchiolar (bb) regions decreases with increasing particle geometric diameter dp. To test this assumption, five volunteers inhaled 8-microm aerodynamic diameter, dae, (111)In-polystyrene (PSL) and (198)Au particles simultaneously. The particles were administered at the end of each breath to maximise deposition in BB and bb. Because of the difference in densities (1.05 vs. 19.3 g cm(-3)), corresponding dp values are approximately 8 and 1.8 microm, and fs values are approximately 2 and 50%, respectively. However, lung retention was somewhat greater for PSL than for gold, contrary to the HRTM prediction. Other recent human experimental studies found no difference in retention for particles with the same dae but different dp values. It is concluded that the HRTM model of particle clearance from BB and bb needs revision.

Microwave-assisted extraction of C60 and C70 from fullerene soot.

Microwave-assisted extraction (MAE) was examined as an alternative to the traditional Soxhlet method of extracting C(60) and C(70) from fullerene soot. MAE of 0.20 g of fullerene soot with 95:5 toluene-acetonitrile yielded greater than 7.8 mg of C(60) and greater than 0.54 mg of C(70) in 4 min with no further increase in yield after 30 min of irradiation. By comparison, exhaustive Soxhlet extraction of the same size sample with the same solvent yielded 7.1 mg of C(60) and 0.58 mg of C(70) in 340 min. Re-extraction by MAE of soot initially extracted by Soxhlet increased the yield of Soxhlet alone. Although MAE was limited to less than 0.5-g sample per extraction vessel, multiple samples were extracted with minimal increased extraction time and no reduction in the amount of material recovered.

Calibration and evaluation of a transportable in vivo monitoring system for accident monitoring of internal contamination.

A transportable in vivo monitoring system has been constructed and calibrated. The system uses two hyper pure germanium detectors--one for measuring whole body activities, by measuring activity in the torso, and the second for determining activities of radioiodine in the thyroid. The optimum counting geometries have been determined and the system has been calibrated for subjects of different ages and builds. The complete system is transported in two trailers which are pulled by ordinary motor vehicles. The minimum detectable activity (MDA) for 137Cs in whole body for a 10 min counting interval at the 95% confidence level is 200 Bq. The MDA for a count of 131I in thyroid is 20 Bq. The system is capable of detecting activities that are equivalent to a dose of 1 mSv for a wide range of radionuclides.

A feasibility study for transportable 241Am-in-lung and 241Am-in-nose-blow monitoring systems for use following a weapons accident.

In a nuclear weapon accident involving fire or conventional explosion, most of the radiation dose received by people in the immediate vicinity would result from inhalation of 239Pu. This is accompanied by the nuclide 241Am, which is much easier to determine by external counting because of the 60 keV gamma ray emission. In the event of an accident, a priority would be to identify any people who have had intakes of 239Pu which were so large that decorporation therapy should be considered. Direct measurement of lung content provides the most rapid and convenient method for assessing intakes by inhalation. A transportable system has been considered as this could be deployed close to the site of the accident and would allow rapid measurements to be made. The feasibility of a transportable 241Am-in-nose-blow and nasal swab measurement system has also been considered. This would be used to help select people for 241Am-in-lung measurements.

Biokinetics and assessment of intake of thorium dioxide.

The aim of this work was to investigate the biokinetics of thorium dioxide in animals for the purpose of assessing intakes of the compound by workers and the resulting doses. The results imply that measurements of the decay products in the chest or extrapolations from urine analysis data are unlikely to be of value for doses below 20 mSv. Even higher doses should be interpreted with caution as a consequence of uncertainties in particle size distribution and variations in dietary excretion.

Comparison of predicted with observed biokinetics of inhaled plutonium nitrate and gadolinium oxide in humans.

The absorption kinetics to blood of plutonium and gadolinium after inhalation as nitrate and oxide in humans and animals has been studied. For each material, values describing the time dependence of absorption were derived from the studies in animals and used with the ICRP human respiratory tract model to predict lung retention and cumulative amounts to blood for the volunteers inhaling the same materials. Comparison with the observed behaviour in the volunteers suggests that absorption of plutonium and gadolinium is reasonably species independent, and that data obtained from animal studies can be used to assess their biokinetic behaviour in humans.

Triage, monitoring and dose assessment for people exposed to ionising radiation following a malevolent act.

The part played by individual monitoring within the context of the overall response to incidents involving the malevolent use of radiation or radioactive material is discussed. The main objectives of an individual monitoring programme are outlined, and types of malevolent use scenario briefly described. Some major challenges facing those with responsibilities for planning the monitoring response to such an incident are identified and discussed. These include the need for rapid selection and prioritisation of people for individual monitoring by means of an effective triage system; the need for rapid initiation of individual monitoring; problems associated with monitoring large numbers of people; the particular difficulties associated with incidents involving pure-beta and alpha-emitting radionuclides; the need for techniques that can provide retrospective estimates of external radiation exposures rapidly and the need for rapid interpretation of contamination monitoring data. The paper concludes with a brief review of assistance networks and relevant international projects planned or currently underway.

A review of measurements of radionuclides in members of the public in the UK.

This paper summarises a comprehensive review of radio-analytical data from autopsy, whole or partial body monitoring and the assay of teeth, foetuses and urine for non-occupationally exposed members of the public in the UK between 1957 and 2003. Most attention has been given to measurements of artificial radionuclides formed in the nuclear fuel cycle, uranium and thorium. The review concentrates on measurements on people in the UK who live or have lived in the vicinity of nuclear power sites. When UK data are unavailable, or for the purposes of comparison, information has been included from studies in other countries. Highlights of key findings of the document are listed: The concentrations of strontium-90 in bone and teeth have reflected changes in the amounts present in the environment due to fallout from nuclear testing. There are higher concentration levels of 239+240Pu in samples from West Cumbria compared with the rest of the UK. However, the levels are so low that any increase in risk of induced skeletal tumours (including leukaemia) would be very small compared with those arising from the intake of natural radionuclides. As expected there have been only a few published autopsy studies. Both tissue sample mass and radionuclide concentrations were low, leading to relatively large measurement uncertainties. Whole body measurements of 137Cs in residents in Berkshire and Oxfordshire clearly show the effect of atmospheric testing of nuclear weapons and of the Chernobyl accident. A survey of whole body 137Cs and 134Cs content following the Chernobyl accident showed that residents of Central Scotland, North-West England and North Wales had twice the radiocaesium content of residents in the rest of England and Wales. Measurements of 131I in the thyroid have been reported following the accidents at Windscale and Chernobyl for most regions of the UK. Few excretion studies have been reported although this does not diminish their importance. One study on the urinary excretion rate of 90Sr in adults and children living in the Dounreay area suggested that the results did not support this radionuclide as being the cause of increased childhood leukaemia. Similar conclusions were drawn from another study involving the assay of 239Pu. It is suggested that a national database of measurements made on members of the public should be initiated. The database would provide a means for identifying future trends.