The work of Committee 2 of ICRP on internal dosimetry.

Over the last few years Committee 2 of ICRP has been responsible for preparing a series of publications giving dose coefficients for intakes of radionuclides by members of the public. The last report in this series covers doses to the offspring in mothers' milk and should be issued in 2005. The emphasis of work on internal dosimetry is now concerned with occupational exposure. It is intended to replace Publications 30 and 68 that give biokinetic data and dose coefficients for intakes of radionuclides and Publications 54 and 78 that give information for bioassay interpretation, with a single series of publications. The first report of the series is expected to cover radionuclides of the elements addressed in the publications on dose coefficients for members of the public. It will also take into account new recommendations from the Commission. Subsequent publications will cover additional elements. A supporting Guidance Document is also being developed that will give more comprehensive advice on the interpretation of bioassay data. The need for this document was identified following recent interlaboratory comparisons that have shown wide variations in the way monitoring data can be interpreted in different laboratories.

The work of committee 2 of ICRP on internal dosimetry.

Following publication of new recommendations by ICRP, a series of publications on Occupational Intakes of Radionuclides (OIR) will give both dose coefficients for intakes of radionuclides and data for the interpretation of bioassay information. Account will be taken of revised tissue weighting factors given in the new recommendations and a number of additional developments. These include new human phantoms based upon medical imaging data for calculating doses to body tissues and the new Human Alimentary Tract Model. In addition, parameter values for the Human Respiratory Tract Model are being reviewed, radionuclide decay data are being updated and systemic models for a number of elements revised to take account of more recent data and to provide models that are appropriate for both dosimetry and for bioassay interpretation. The OIR series of publications will be accompanied by a supporting Guidance Document that will give advice on the interpretation of bioassay data.

Dose coefficients for the embryo and fetus following intakes of radionuclides by the mother.

The International Commission on Radiological Protection has recently issued Publication 88, giving dose coefficients for the embryo, fetus and newborn child from intakes of selected radionuclides of 31 elements by the mother, either before or during pregnancy. The biokinetic models used for calculating these doses were based upon the available human data and the results of animal experiments. This paper summarises the approach used for the development of biokinetic and dosimetric models. It also compares the estimates of dose received by the offspring with those received by the reference adult. The main findings are that, in general, doses to the offspring are similar to or lower than those to the reference adult. For a few radionuclides, however, the dose to the offspring can exceed that to the adult. The reasons for these variations in comparative doses are examined.

Dose coefficients for the embryo and foetus following intakes of radionuclides by the mother.

Committee 2 of the International Commission on Radiological Protection (ICRP) has the responsibility for calculating radiation doses from intakes of radionuclides for all age groups in the population. Publication 88 of the ICRP, which has recently been published, describes the development of models used for calculating radiation doses to the embryo and foetus following intakes of radionuclides by the mother. It also gives radiation doses to the offspring for intakes of radionuclides by the mother either before or during pregnancy. The approaches used in the development of the biokinetic and dosimetric models are summarised here together with a comparison of the doses to the offspring with those to the reference adult.

The assessment of doses and effects from intakes of radioactive particles.

The behaviour of radionuclides after entry into the body and the radiation doses received by individual tissues depend on the chemical nature of the element, the physicochemical form of the intake, the radioactive half-life of the isotope and the type and energy of the emissions. Ingestion of radionuclides in insoluble particles will result in radiation doses being delivered to tissues of the gastrointestinal (GI) tract; other tissues will also be irradiated by nuclides with penetrating photons emissions (gamma) but doses may be largely confined to the GI tract for charged particle emissions (alpha, beta). Ingestion of more soluble forms will lead to greater absorption to blood and deposition in other tissues and therefore may result in greater doses to other tissues. Similar considerations apply to inhaled material and to the entry of radionuclides through cuts or wounds. For ingested materials, including particles, more information is needed on uptake and retention in intestinal tissues and consequent doses to sensitive cells, particularly for alpha emitters. There has been concern that the pattern of distribution of activity throughout irradiated tissues may influence the extent of damage, particularly for alpha emitters because of the localised deposition of energy and their greater relative biological effectiveness compared with beta/gamma emitters. Aggregation of activity has the potential to result in greater acute tissue damage and has been shown, for example, to result in focalised pneumonitis and fibrosis in the lung and ulceration of the skin. The main long-term effect of irradiation of tissues is the induction of malignant change, although hereditary disease may also be of concern following irradiation of the gonads. There are only limited data available to compare the effect on cancer induction of heterogeneous and homogeneous irradiation of tissues. However, the available information, for irradiation of the lung, skin or liver, indicates that in general nonuniform alpha irradiation from radioactive particles is no more hazardous, and may be less hazardous, than if the same activity is uniformly distributed.

The gastrointestinal absorption of plutonium and americium in rats and guinea pigs after ingestion of dusts from the former nuclear weapons site at Maralinga: implications for human exposure.

The gastrointestinal absorption of plutonium and americium present in dusts from the Maralinga test sites in South Australia has been measured as an input to dose assessments. The materials studied were from three different areas, designated Taranaki (Q380II), TM100 (10/2) and N. Plume (26). The three dusts were fed to groups of rats, mixed with their normal food. The Taranaki and TM100 dusts were also fed to guinea pigs, as a suspension in water. Expressed as fractional absorption from the gastrointestinal tract (f1), the values obtained for plutonium were 2 x 10(-6) and 8 x 10(-6) for Taranaki dust in rats and guinea pigs, respectively, 3 x 10(-6) and 10(-5) for TM100 dust in rats and guinea pigs, respectively, and 2 x 10(-6) for N. Plume dust in rats. The f1 values obtained for americium were 3 x 10(-6) and 2 x 10(-5) for Taranaki dust in rats and guinea pigs, respectively, 10(-5) and 5 x 10(-5) for Taranaki dust in rats and guinea pigs, respectively, and 10(-5) for N. Plume dust in rats. On the basis of these results, rounded f1 values used in the dose assessments were 10(-5) for plutonium and 10(-4) for americium, applying to all intakes of dust. These values compare with the International Commission on Radiological Protection recommendations of 10(-3) for unspecified chemical forms of both elements, 10(-4) for plutonium nitrate and 10(-5) for plutonium oxides. The effect of changes in f1 values on doses from 239Pu and 241Am is considered.

The biokinetics of plutonium-239 and americium-241 in the rat after subcutaneous deposition of contaminated particles from the former nuclear weapons site at Maralinga: implications for human exposure.

As an input to dose assessments, measurements have been made of the clearance of Pu and Am after subcutaneous implantation in rats for six particulate materials and one dust from the Maralinga test sites. The tissue distribution of Pu and Am were measured in groups of six animals at one month and 6 months after implantation. In addition, in vitro solubility tests were carried out on eight different particulate materials. Histological examination of the subcutaneous implantation site was undertaken after one year for selected materials. Autoradiographs of tissue sections showed that particles were surrounded by fibrotic tissue with macrophage and polymorphonuclear cell infiltration, the normal tissue response to foreign materials. The clearance data have been used to make estimates of the likely range in potential radiation doses in humans. To calculate the dose from dissolved 239Pu and 241Am, four different situations have been considered. For the dust, the results suggest that dissolution essentially ceases after the removal of Pu and Am from the surfaces of dust particles. From the values obtained, the acute release of a fraction of 10(-2) of both nuclides from a dust contaminated wound was assumed. For a number of particles the results suggested continued dissolution and the clearance of 10(-3) per year of both nuclides, continuing for a number of years, has therefore been considered. For the least soluble particles, there was no clear evidence of continued clearance and the acute release of 10(-4) has therefore been taken as a lower estimate for dose calculations.(ABSTRACT TRUNCATED AT 250 WORDS)

Implementation of the 1990 recommendations of ICRP in the countries of the European Community.

The International Commission on Radiological Protection (ICRP) has published new Recommendations in ICRP Publication 60. These 1990 Recommendations provide a System of Radiological Protection that takes account of the most recent information on the effects on health of exposure to ionising radiation and trends in the setting of safety standards. Within the European Community the Recommendations of the ICRP are implemented through a Euratom Directive which is binding on member states, a draft of which has been accepted by the Article 31 Group and must eventually be ratified by the Council of Ministers. It is expected that the new directive will broadly endorse the principles of protection given in the 1990 Recommendations together with the dose limits for both workers and members of the public. There are likely to be some modifications to the 1990 Recommendations that are mainly related to their practical application. As it will be some time before the directive is incorporated into national regulations, a number of member states have taken independent initiatives. The development of dose constraints for occupational, medical and public exposure is being seen by national organisations in many countries as a significant new approach to improving standards of radiation protection.

Radiological implications of inhaled 239Pu and 241Am in dusts at the former nuclear test site in Maralinga.

The biokinetics of 239Pu and 241Am present in three dust samples obtained from Maralinga were investigated after their deposition in the rat lung. Results were used as an experimental basis for assessing the radiological implications for human exposure. The transfer rates of these actinides to blood in the various dusts differed by 50-fold. The most transportable forms were compatible with a material that had 25% class W and 75% class Y characteristics. The doses per unit intake for adults, children, and infants exposed to an aerosol of 5 microns AMAD were calculated to be, respectively, 0.059, 0.076, and 0.140 mSv Bq-1. The corresponding doses for the least transportable forms were the same as those calculated for a class Y compound, namely 0.036, 0.049, and 0.096 mSv Bq-1. The behavior of the actinides in humans was predicted by combining the transfer rates to blood with mechanical clearance data obtained after volunteers had inhaled 85Sr or 88Y labeled fused aluminosilicate particles. The results suggested that monitoring of 241Am in the chest could be used to advantage for assessing intakes incurred by workers involved with any further decontamination procedures but would be of little practical value for assessing inadvertent public exposure. The paper includes comments on the relevance of the 1990 ICRP recommendations and the proposed new dosimetric model for the respiratory tract.

Estimates of embryonic and fetal doses from 239Pu.

Previously reported studies on the transfer of 238Pu from the maternal circulation to the developing embryo and fetus in rats and guinea pigs have provided data for developing dosimetric models. The highest concentrations of 238Pu were measured in the yolk sac. In late gestation, preferential uptake of 238Pu in liver and bone was observed. The data obtained, together with other published information, have been used to estimate in utero doses to hemopoietic tissues, taking account of transfer to the blastocyst/egg cylinder, yolk sac, liver, and bone marrow. From animal data, the concentration ratios relative to maternal liver for these tissues were taken to be 0.1, 2, 0.01, and 0.02, respectively, and were applied to periods of human gestation of 0-2.5 wk, 2.5-6 wk, 6-12 wk, and 12-38 wk, respectively. Doses to fetal tissues from 239Pu were calculated for chronic ingestion by the mother for a total of 1.8 kBq 239Pu during the year of pregnancy, giving a committed effective dose to the mother of 1 mSv. On this basis, the total in utero dose to hemopoietic tissue was about 2 microSv compared with red bone marrow doses of 34 microSv to the mother for the year. The yolk sac and bone marrow dominated in utero doses. The total dose to hemopoietic tissue in the offspring to age 70 y, taking into account the activity present at birth and including in utero doses, was estimated as 24 microSv compared with a maternal dose to red bone marrow of 2.5 mSv. An acute maternal intake of 1.8 kBq by ingestion during the period of yolk sac hemopoiesis would result in the highest in utero dose, estimated at about 36 microSv. However, activity at birth would be lower, giving only a small additional dose.

The efficacies of pure LICAM(C) and DTPA on the retention of plutonium-238 and americium-241 in rats after their inhalation as nitrate and intravenous injection as citrate.

The pure carboxylated catechoyl amide LICAM(C) and the calcium and zinc salts of diethylenetriaminepenta-acetic acid (DTPA), were tested for efficacy for removing 238Pu and 241Am from rats after inhalation of the nitrate or intravenous injection of the citrate. The results were compared with the efficacy of methylated LICAM(C) used in previous experiments. It was shown that: (1) after inhalation of 238Pu nitrate, DTPA was far superior to pure LICAM(C); (2) after intravenous injection of 238Pu citrate, the infusion of DTPA plus LICAM(C) was only marginally more effective than DTPA alone; and (3) after inhalation or intravenous injection of 238Pu plus 241Am, the efficacy of pure LICAM(C) was only marginally more effective than the methylated form and neither form was effective for the decorporation of 241Am. It was concluded that DTPA, at present, remains the chelating agent of choice for treating persons accidentally contaminated with transportable forms of Pu and Am.

The use of animal experiments for assessing annual limits on intake and interpreting chest-monitoring data for workers exposed to industrial actinide-bearing dusts.

The metabolic behavior of 239Pu and 241Am present in three industrial dusts has been studied after their inhalation by the rat. A comparative experiment has also been carried out with a mixture of these actinides, inhaled as their nitrates. The aim of this work was to provide an experimental basis for assessing limits on intake and to establish whether the 239Pu content in the lungs could be interpolated from measurements of 241Am. The results (1) demonstrate the wide differences in the lung retention kinetics of the actinides and in the absolute and relative amounts which translocate to the blood that can occur for industrially produced materials; (2) show that the annual limits on intake (ALI) for the different materials vary between those postulated for class W and Y compounds by the International Commission on Radiological Protection; (3) indicate that, depending on the nature of the dust, acute intakes of 239Pu equivalent to the ALI can be estimated from 241Am chest-monitoring data at times from a few days up to about 3 y after exposure.

A new small animal inhalation facility: design and performance.

A new inhalation facility is described which allows any combination of up to 72 rodents ranging in size from the mouse to the guinea pig to be exposed simultaneously. Typically for aerosols of MMD 1.5 microns the initial lung deposit in the rat is 0.05 to 0.07% of the total amount of material used and the coefficient of variation between animals is 15 to 20%.