Internal dosimetry: towards harmonisation and coordination of research.

The CONRAD Project is a Coordinated Network for Radiation Dosimetry funded by the European Commission 6th Framework Programme. The activities developed within CONRAD Work Package 5 ('Coordination of Research on Internal Dosimetry') have contributed to improve the harmonisation and reliability in the assessment of internal doses. The tasks carried out included a study of uncertainties and the refinement of the IDEAS Guidelines associated with the evaluation of doses after intakes of radionuclides. The implementation and quality assurance of new biokinetic models for dose assessment and the first attempt to develop a generic dosimetric model for DTPA therapy are important WP5 achievements. Applications of voxel phantoms and Monte Carlo simulations for the assessment of intakes from in vivo measurements were also considered. A Nuclear Emergency Monitoring Network (EUREMON) has been established for the interpretation of monitoring data after accidental or deliberate releases of radionuclides. Finally, WP5 group has worked on the update of the existing IDEAS bibliographic, internal contamination and case evaluation databases. A summary of CONRAD WP5 objectives and results is presented here.

Coordination of research on internal dosimetry in Europe: the CONRAD project.

The EUropean RAdiation DOSimetry Group (EURADOS) initiated in 2005 the CONRAD Project, a Coordinated Network for Radiation Dosimetry funded by the European Commission (EC), within the 6th Framework Programme (FP). The main purpose of CONRAD is to generate a European Network in the field of Radiation Dosimetry and to promote both research activities and dissemination of knowledge. The objective of CONRAD Work Package 5 (WP5) is the coordination of research on assessment and evaluation of internal exposures. Nineteen institutes from 14 countries participate in this action. Some of the activities to be developed are continuations of former European projects supported by the EC in the 5th FP (OMINEX and IDEAS). Other tasks are linked with ICRP activities, and there are new actions never considered before. A collaboration is established with CONRAD Work Package 4, dealing with Computational Dosimetry, to organise an intercomparison on Monte Carlo modelling for in vivo measurements of (241)Am deposited in a knee phantom. Preliminary results associated with CONRAD WP5 tasks are presented here.

Improvement of the measuring equipment used in the assessment of internal doses in emergency situations.

Emergency response plans have long been focused on accidents at nuclear power plants. Recently, the malevolent use of radiation aimed at creating disruption in the society has been considered as a possible threat. In this kind of emergency situations casualties will most likely be members of the public and the number of affected people can vary from a few to mass casualties. There is an evident need for rapid measurements of large groups of internally contaminated people. Radiation and Nuclear Safety Authority (STUK) in Finland has obtained new monitors for thyroid and simple whole-body measurements in field conditions as a part of the continuous improving of emergency preparedness. The new monitors consist of a NaI(Tl) detector and a control unit. The monitors work as spectrometers allowing real-time spectrum analysis in the field.

Assessment of occupational exposure to uranium by indirect methods needs information on natural background variations.

Urine monitoring is the preferred method to determine exposure to soluble compounds of uranium in workplaces. The interpretation of uranium contents in workers bioassay samples requires knowledge on uranium excretion and its dependence on intake by diet. Exceptionally high concentrations of natural uranium in private drinking water sources have been measured in the granite areas of Southern Finland. Consequently, high concentrations of natural uranium have been observed in the urine and hair samples of people using water from their own drilled wells. Natural uranium content in urine and hair samples of family members, who use uranium-rich household water, have been analyzed by using ICP-MS. The uranium concentrations both in urine and hair samples of the study subjects were significantly higher than the world-wide average values. In addition, gammaspectrometric methods have been tested for determining uranium in hair samples. This method can be used only for samples with highly elevated uranium concentrations.

OMINEX: survey of internal dose monitoring programmes for radiation workers.

Monitoring of the workforce in the nuclear industries is carried out primarily in order to demonstrate compliance with European Union (EU) legislation and the Basic Safety Standards for the protection of the health of workers against the dangers arising from ionizing radiation recommended by the International Atomic Energy Agency (IAEA). There is, however, no common strategy for internal dose monitoring programmes currently in use in the EU countries. Surveys have been carried out in which organisations were asked to provide information on the design of their internal dose monitoring programmes and on the costs of these programmes. Information was requested from both EU countries and Associated States. Databases for storage and reporting of all gained information were constructed, and results from the surveys have been compiled. This work was carried out within the EC 5th Framework Programme project, OMINEX, which aims to provide advice and guidance on designing and implementing internal dose monitoring programmes in the workplace in such a way that best use is made of available resources, while minimising costs.

Estimation of human exposure to natural radionuclides using in vivo skull measurements.

In a preliminary study, in vivo skull measurements and in vitro urine measurements of 210Pb and nulU have been performed to find out the individual, chronic exposure to waterborne natural radionuclides of a small group of Finnish people. For their domestic water, the studied individuals use water from drilled wells containing elevated concentrations of natural uranium and its daughter nuclides ((234,235,238)U, 222Rn, (226,228)Ra, 210Po, 210Pb). Enhanced 210Pb and 235U activities were observed in several people. A positive correlation is observed between the U concentration in urine (microg d(-1)) and the number of counts (cpm) in the gamma ray energy peaks originating from the decay of 235U and 234Th respectively. Calibration of the detector set-up and the determination of background sources are in progress.

Design and implementation of monitoring programmes for internal exposure (project OMINEX).

The costs of monitoring for internal exposure in the workplace are usually significantly greater than the equivalent costs for external exposure. Therefore, there is a need to ensure that resources are employed with maximum effectiveness. The EC-funded OMINEX (optimisation of monitoring for internal exposure) project is developing methods for optimising the design and implementation of internal exposure monitoring programmes. Current monitoring programmes are being critically reviewed, the major sources of uncertainty in assessed internal dose investigated, and guidance formulated on factors such as programme design, choice of method/techniques, monitoring intervals, and monitoring frequency. OMINEX will promote a common, harmonised approach to the design and implementation of internal dose monitoring programmes throughout the EU.

Levels of 90Sr and 137Cs in the urine of Finnish people.

The aim of this study was to estimate the current concentrations of 90Sr and 137Cs in the urine of Finnish people and to estimate the doses. Two to three daily urine samples were collected from 18 adult Finnish volunteers in connection with studies of 137Cs body burdens in 1999-2001. The 90Sr activities in urine varied between 1.4 and 11 mBq l(-1). The 137Cs activity in urine varied between 0.36 and 56 Bq l(-1). The daily urinary excretion was found to be 4.8-17 mBq for 90Sr and 0.81-68 Bq for 137Cs. Assuming that the daily 90Sr intake was constant and that 18% of the ingested activity was excreted in urine, the mean intake in the investigated group would vary between 27 and 96 mBq d(-1). Based on these estimated intake values, the respective annual effective internal doses from 90Sr and 90Y varied from 0.3 to 1.0 microSv and from 137Cs from 4 to 350 microSv during the sampling period.

Intercomparison of whole-body counters by using a subject who had incorporated 137Cs into the body.

During the years 1996-2000, eight whole-body counting facilities (WBC) from Finland, Germany, Japan and Russia took part in an intercomparison using a resident of the Russian town of Novozybkov who had been seriously contaminated as a result of the Chernobyl accident. The subject R (adult male, height 172 cm average body mass 64 kg; and 137Cs body burden within the range of 1-15 kBq) was investigated in the participating institutions during his business trips. The experimentally obtained data for his 137Cs body burden were compared with the predicted values, which had been deduced from the measurements of subject R using the reference WBC (St Petersburg Institute of Radiation Hygiene) and from his effective half-time of 137Cs in the body (68 days). The obtained results did not deviate more than 20% from reference activities. Four facilities were able to quantity the 40K in the subject's body. The differences between reported values of potassium did not exceed 10%. For subject R, the average annual effective dose from radiocaesium was 0.25 mSv and it was 0.18 mSv from 40K in the years 1996/97. The reliability of using a subject with naturally incorporated artificial radionuclides ('walking standard') instead of an anthropomorphous phantom for calibration and intercomparison of whole-body counters in a large-scale nuclear accident is discussed.

Contribution of different foodstuffs to the internal exposure of rural inhabitants in Russia after the Chernobyl accident.

In a large village, Veprin of the Bryansk region of Russia contaminated with radionuclides as a result of the Chernobyl accident, 137Cs concentration in food products of agricultural produce and natural origin was regularly measured, local inhabitants were polled on the composition of their diet, and the 137Cs content in their bodies was measured at the same time. These results were used as the basis for calculation of annual effective doses of internal exposure to inhabitants and for reconstruction of the dose during the entire period after the accident (1986-1996). The efficiency of countermeasures performed for reduction of the internal dose was assessed. The internal dose in inhabitants during the 10 years after the accident was shown to be reduced by countermeasures by a factor of 2, namely down to 35 mSv instead of the expected 70 mSv. The dose of external gamma radiation during the same time period is close to the obtained dose of internal exposure. The presence of peat and water-meadow soils in the vicinity of this village that are characterised by high transfer factors for radionuclides from soil to vegetation causes a high contribution of internal exposure to the total dose of population exposure. The contribution of natural products to the internal dose increased from 6% in 1987 increased to 25% in 1996. The individual content of 137Cs in the body of inhabitants reliably correlates with consumption of milk in the initial period after the accident and with consumption of forest mushrooms in the subsequent period.

Chernobyl fallout and outcome of pregnancy in Finland.

Possible effects of Chernobyl fallout on outcome of pregnancy in Finland were evaluated in a nationwide follow-up study. The outcomes were the rate of live births and stillbirths, pregnancy loss, and induced abortions by municipality. Exposure was assessed based on nationwide surveys of radiation dose rate from the Chernobyl fallout, from both external and internal exposures. Using these measurements, we estimated the monthly dose rate for each of the 455 Finnish municipalities. On average, the dose rate from Chernobyl fallout reached 50 microSv per month in May 1986--a doubling of the natural background radiation. In the most heavily affected area, 4 times the normal background dose rates were recorded. Given the underlying regional differences in live birth, stillbirth, and abortion rates, we used longitudinal analysis comparing changes over time within municipalities. A temporary decline in the live birth rate had already begun before 1986, with no clear relationship to the level of fallout. A statistically significant increase in spontaneous abortions with dose of radiation was observed. No marked changes in induced abortions or stillbirths were observed. The decrease in the live birth rate is probably not a biological effect of radiation, but more likely related to public concerns of the fallout. The effect on spontaneous abortions should be interpreted with caution, because of potential bias or confounding. Further, there is little support in the epidemiologic literature on effects of very low doses of radiation on pregnancy outcome.

Soil to plant uptake of fallout 137Cs by plants from boreal areas polluted by industrial emissions from smelters.

To study the impact of industrial pollution on the soil-to-plant uptake of fallout-radiocesium in a boreal forest ecosystem, four study sites were selected at distances of 7, 16, 21 and 28 km from the large copper-nickel smelter at Monchegorsk on the Kola Peninsula (Russia). At each site, soil and selected plant species were sampled from five plots and analysed separately for 137Cs and 40K. The data show that the root-uptake of 137Cs, as characterised by the median aggregated transfer-factor T(ag), decreased significantly (P < 0.05) with decreasing distance from the smelter for the plants Vaccinium myrtillus (from 0.023 to 0.007 m2 kg-1) and Empetrum nigrum (from 0.015 to 0.007 m2 kg-1), but increased for Deschampsia flexuosa (from 0.013 to 0.031 m2 kg-1). For Vaccinium vitis-idaea a significant trend for the T(ag) was not observed. The median 40K activity concentrations in these plants also decreased significantly (P < 0.001) with decreasing distance from the smelter for Vaccinium myrtillus (from approx. 140 to 20 Bq kg-1 dry wt.), Empetrum nigrum (from approx. 90 to 40 Bq kg-1 dry wt.), and also for Deschampsia flexuosa (from approx. 270 to 40 Bq kg-1 dry wt.). For Vaccinium vitis-idaea such a continuous significant trend was not observed. The results for the Cu-Ni polluted soils thus show: (1) that the soil-to-plant transfer of radiocesium can be significantly modified; (2) that these modifications are quite specific; and (3) that modifications of the uptake of potassium do not always correspond to those of radiocesium.

Fallout from Chernobyl and incidence of childhood leukaemia in Finland, 1976-92.

OBJECTIVE: To assess effects of fallout from Chernobyl on incidence of childhood leukaemia in Finland. DESIGN: Nationwide cohort study. External exposure measured for 455 Finnish municipalities with instruments driven 19,000 km throughout the country. Values specific to municipalities corrected for shielding due to houses and fallout from A bomb testing. Internal exposure estimated from whole body measurements on a random sample of 81 children. Mean effective dose for two years after incident calculated from these measurements. Data on childhood leukaemia obtained from Finnish cancer registry and verified through hospitals treating childhood cancers. SETTING: Finland, one of the countries most heavily contaminated by the Chernobyl accident; the population was divided into fifths by exposure. SUBJECTS: Children aged 0-14 years in 1976-92. MAIN OUTCOME MEASURES: Standardised incidence ratio of childhood leukaemia and relative excess risk of childhood leukaemia per mSv. From incidence data of Finnish cancer registry for 1976-85, expected numbers specific to sex and age group (0-4, 5-9, and 10-14 years) were calculated for each municipality for three periods (1976-85, 1986-8, and 1989-92) and pooled as exposure fifths. Dose response was estimated as regression slope of standardised incidence ratios on mean doses for fifths for each period. RESULTS: Population weighted mean effective doses for first two years after the accident were 410 microSv for the whole country and 970 microSv for the population fifth with the highest dose. In all Finland the incidence of childhood leukaemia did not increase 1976-92. The relative excess risk 1989-92 was not significantly different from zero (7% per mSv; 95% confidence interval -27% to 41%). CONCLUSIONS: An important increase in childhood leukaemia can be excluded. Any effect is smaller than eight extra cases per million children per year in Finland. The results are consistent with the magnitude of effect expected.

PIP: The objective of a nationwide cohort study was to assess the effects of fallout from Chernobyl on the incidence of childhood leukemia in Finland, one of the countries most heavily contaminated by the Chernobyl accident. External exposure was measured with instruments driven by car 19,000 km throughout 455 Finnish municipalities, where the population was divided into fifths by exposure. Values specific to municipalities were corrected for shielding due to houses and fallout from A-bomb testing. Internal exposure estimated from whole body measurements on a random sample of 81 children aged 0-14 years during 1976-1992 and 5-15 in June, 1986, and April, 1988. Mean effective doses from cesium-134 and cesium-137 for 2 years after the incident were calculated from these measurements. Data on childhood leukemia cases that had occurred in children aged 0-14 years during 1975-1992 were obtained from the Finnish cancer registry and verified through each of the 5 university hospitals treating childhood leukemia. Standardized incidence ratio of childhood leukemia and relative excess risk of childhood leukemia per milli sievert (mSv) was measured. From incidence data of the Finnish cancer registry for 1976-1985, expected numbers specific to sex and age group (0-4, 5-9, and 10-14 years) were calculated for each municipality for 3 periods (1976-85, 1986-8, and 1989-92) and pooled as exposure fifths. Dose response was estimated as regression slope of standardized incidence ratios on mean doses for fifths for each period. Population-weighted mean effective doses for first 2 years after the accident were 410 micro Sv for the whole country and 970 micro Sv for the population fifth with the highest dose. In all Finland, the incidence of childhood leukemia did not increase during 1976-1992. The relative excess risk 1989-1992 was not significantly different from zero (7% per mSv; 95% confidence interval -27% to 41%). An important increase in childhood leukemia can be excluded. Any effect is smaller than 8 extra cases per million children per year in Finland.

Pregnancy outcome in Finland after the Chernobyl accident.

The explosion at the Chernobyl nuclear power plant caused radioactive fallout in Finland in April-May 1986. The fallout was unevenly distributed geographically, and, accordingly, the country was divided into 3 fallout zones. Whole-body radioactivity measurements of randomly chosen persons showed that the regional differences prevailed throughout the following 2 years. Data for legal abortions, registered congenital malformations as well as preterm births and stillbirths of malformed children were collected. The corresponding expected figures were obtained from statistics from 1984 and 1985. No differences in the expected/observed rates of the above parameters were detected.

PIP: The effects of the 1986 Chernobyl accident on Finland are reported. Legal abortions, registered congenital malformations, preterm births, and stillbirths showed no differences in observed vs. expected rates after the accident. The limitations are that the population base is small, the detection system is incomplete, no reliable data are available on early abortions, and germinal mutations were not presently analyzed. Measurement of radiocesium (Cs 134 and 137) was accomplished by the Research Institute for Social Security with a stratified random sample of 380 people. 5 fallout zones differentiated groups, which were then collapsed into 3 groups. Regional differences in levels persisted into 1988. The Finnish Register of Congenital Malformations provided the compulsory data on congenital malformations. The 3 groups (children born before the accident in 1984-85, in the latter half of 1986, and in 1987) were analyzed in the 3 zones during 2 study periods (August-December 1986 and January-December 1987). Monthly analysis of induced abortions showed no increase following the accident. There was a slight decrease in births between January and March 1987, which is believed to be related to anxiety reinforced by public advice. There were no differences between expected and observed congenital defects in the 2 study periods. Preterm and stillbirths followed a similar pattern. The analysis showed no association between the temporal and spatial variations in radioactivity and variable incidence of congenital malformations.

Cs-137 concentration in reindeer and its fodder plants.

Radionuclides, especially the long-lived 137Cs (physical half-life 30 years), are accumulated efficiently in the northern, subarctic, lichen-reindeer-man foodchain. Until the Chernobyl accident the fallout nuclides studied originated from nuclear weapons tests. After this accident some fresh fallout was deposited in Finnish Lapland. Lichens grow very slowly and collect nutrients very efficiently from air, rain and snow. During winter the basic fodder plants for reindeer are lichens and some winter-green plants, shrubs and dry leaves. During the bare-ground season, the reindeer eat various grasses, herbs and leaves etc. Lichens constitute 30-50 per cent of the entire vegetable mass consumed by the reindeer in a year. The highest 137Cs-concentration 2500 Bq/kg dry weight was found in lichen in the middle of the 1960s. In 1985 the concentration had decreased to about 240 Bq/kg dry weight. After the Chernobyl accident the 137Cs-concentration in lichen varied from 200 to 2000 Bq/kg dry weight in Finnish Lapland. In reindeer fodder plant samples collected in the 1980s before the Chernobyl accident the 137Cs-concentration varied from 5 to 970 Bq/kg dry weight. The highest 137Cs-concentration in reindeer meat, about 2500 Bq/kg fresh weight, was found in 1965 and thereafter decreased to about 300 Bq/kg fresh weight in the winter before the Chernobyl accident. After the accident the mean 137Cs-concentration in reindeer meat from the 1986-87 slaughtering period was 720 Bq/kg fresh weight and in 1987-88, 630 Bq/kg fresh weight.

On biological half-life of potassium in man.

The highly sensitive whole-body counting technique makes quantitative determinations of nanocurie amounts of gamma-emitters within the body possible. So such counters are especially suitable for the long-term measurement of tracer retention and excretion rates. In the present study, the biological half-life of body potassium in ten male volunteers was determined using 42K as tracer. The group was measured using two different types of whole-body counters. A 43-cm standard chair technique was used with counter A and a multidetector linear scanning technique with counter B. The oral tracer dose of 12-15 muCi 42K to volunteers made it possible to estimate the biological half-life of potassium, which varied from 10 to 28 days, the mean being 16 days. The total body potassium determinations were carried out with the 42K- and 40K-methods. The results of the parallel determinations performed with Counter A agreed well with those of Counter B. A good consistency was also found in the body potassium values of individual subjects, obtained using both the methods separately for each counter.

The distribution and biological half-time of 203Hg in the human body according to a modified whole-body counting technique.

The distribution and biological half-life of 203Hg in the human body was investigated using 203Hg-labeled compounds and a regional whole-body counting technique. Fifteen volunteers were administered methylmercury as a labeled fish proteinate. A single serving of the proteinate contained an average of 1.8 uCi of 203Hg-activity and 22 mug of total mercury. Inorganic mercury was given to eight volunteers as labeled calf liver paste containing 4-8 muCi of inorganic 203Hg-activity and 6 mug of total mercury. The radiomercury determinations were performed in a steel room equipped with the standard chair geometry and one 4 inch x 8 inch NaI(Tl) crystal. For determinations of 203Hg-activity in the head a 3 inch x 3 inch NaI(Tl) crystal was used. A lead collar was utilized as a shield in order to absorb any disturbing radiation that might originate in the stomach region. The effectiveness of the Pb collar was determined using phantoms. The activities in the whole-body, the head, the legs and the liver were determined. About 20% of the methylmercury activity in the whole-body was found to be localized in the head 30 d after administration. No significant amounts of 203Hg-activity were found in the head during the first 58 d after administration of inorganic mercury. An average value of 10-15% methylmercury activity was found in the legs 30 d after administration. A control mean value of 13% was determined by measuring five of the same volunteers the next day in Sweden. Not more than 1% of inorganic mercury was found in leg muscle after 39 d in one male volunteer. The biological half-life of protein-bound inorganic mercury in the liver region, studied in one male volunteer, was estimated at 53 +/- 15 d.