The quantity of the long lived (half-life 15.7 million years) radioactive isotope 129I in the pre-nuclear age ocean was approximately 100 kg. Various nuclear related activities, including weapons testing, nuclear fuel reprocessing, Chernobyl and other authorized or non-authorized dumping of radioactive waste have increased the ocean inventory of 129I by more than one order of magnitude. The most important of these sources are the direct marine discharges from the commercial reprocessing facilities at La Hague (France) and Sellafield (UK) which have discharged approximately 1640 kg in the English Channel, and approximately 720 kg in the Irish Sea, respectively. We discuss how this 129I can be used as both a 'pathway' and 'transit time' tracer in the North Atlantic and Arctic oceans, as well as a parameter for distinguishing between reprocessed and non-reprocessed nuclear waste in the ocean, and as a proxy for the transport and dilution of other soluble pollutants input to the North Sea.
The method of processing and the results of measurements of 131I content in the thyroids of Russian people performed in May-June 1986 are presented. The contribution of radiation from Cs radionuclides in the human body was taken into account in the processing of measurement data with an SRP-68-01 device. The greatest individual 131I content was found in the thyroids of inhabitants of the Bryansk region, up to 250-350 kBq, and in the Tula and Orel regions, up to 100 kBq. The average 131I thyroid activity in the middle of May 1986 reached 80 kBq for inhabitants of some settlements in the Bryansk region, 5-8 kBq in the Tula region and 5 kBq in the Orel region.
The age- and sex-dependence of the 131I induced count rates is determined for the measurements performed in Ukraine after the Chernobyl accident on the thyroids of over 60,000 persons. For this, the individual measurements are scaled in such a way that the mean values over age and sex on one side and the mean values over measurement series on the other side are normalized to one. The resulting distribution of all scaled measurements is roughly log-normal. Half of them lie within a factor 1.6 of the median. 131I induced count rates have a minimum at birth year 1986, about half the value of adults. The maximum count rates with about 30% above adults are reached for males around age 16 y. The count rates are up to about 40% (at age 14-17 y) higher for males than for females. The results are within statistical uncertainties independent of the geographical area and the urban or rural nature of the settlements. Starting from the relative count rates, the age- and sex-dependence is calculated for the thyroid activities 1 mo after the accident for the integrated activities and for the doses. The dose of young children is a factor of about 6.5 higher than that of adults. Uncertainties are estimated throughout.
A numerical model simulation has been used to predict extent and variability in the anthropogenic (129)I pollution in the Arctic Ocean and Nordic Seas region over a period of 100 years. The source function of (129)I used in the model is represented by a well-known history of discharges from the Sellafield and La Hague nuclear reprocessing facilities. The simulations suggest a fast transport and large inventory of the anthropogenic (129)I in the Arctic and North Atlantic Oceans. In a fictitious case of abrupt stop of the discharges, a rapid decline of inventories is observed in all compartments except the North Atlantic Ocean, the deep Nordic Seas and the deep Arctic Ocean. Within 15 years after the stop of releases, the model prediction indicates that near-equilibrium conditions are reached in all compartments.
The Human Monitoring Laboratory, which acts as the Canadian National Calibration Reference Center for In Vivo monitoring, has constructed a robust neck-thyroid phantom for use in the Canadian Thyroid Intercomparison Program. The phantom is rugged and capable of being distributed through the mail with no expectation of a leak of radioactive materials; it is anthropomorphic; the thyroid inserts simulate 125I and 131I; the phantom can be used to mimic different layers of adipose tissue over the thyroid insert; and it is cost effective. This paper describes the design criteria and the manufacturing process; the performance characteristics have been described in an earlier publication.
Time-dependent thyroid doses were reconstructed for over 29,000 Techa River Cohort members living near the Mayak production facilities from 131I released to the atmosphere for all relevant exposure pathways. The calculational approach uses four general steps: 1) construct estimates of releases of 131I to the air from production facilities; 2) model the transport of 131I in the air and subsequent deposition on the ground and vegetation; 3) model the accumulation of 131I in environmental media; and 4) calculate individualized doses. The dose calculations are implemented in a Monte Carlo framework that produces best estimates and confidence intervals of dose time-histories. Other radionuclide contributors to thyroid dose were evaluated. The 131I contribution was 75-99% of the thyroid dose. The mean total thyroid dose for cohort members was 193 mGy and the median was 53 mGy. Thyroid doses for about 3% of cohort members were larger than 1 Gy. About 7% of children born in 1940-1950 had doses larger than 1 Gy. The uncertainty in the 131I dose estimates is low enough for this approach to be used in regional epidemiological studies.
The pathways of 131I, 134Cs and 137Cs from the Chernobyl fallout to man were followed in the county of VÃ¤sterbotten, Sweden. Reported airplane measurements had shown that the ground deposition of 137Cs was 3-40 kBq/m2 with hot spots with more than 80 kBq/m2. Multiplying with a factor of 0.6 gave the 134Cs deposition and an approximate factor of 20 the 131I ground deposition. The effective dose equivalent from 131I became low, less than 0.1 mSv, as the cows were stabled. The 137Cs activity concentration in different types of food was measured in approximately 8,000 samples. The most important sources of Cs intake in man were lake fish, elk (European moose) and reindeer. Variations with time was studied in detail for four types of lake fish. Whole-body measurements on more than 250 persons showed that no group of people on average received more than 1 mSv from food during the first year after the Chernobyl accident. However, single persons eating large amounts of reindeer meat received up to 2.5 mSv. People buying all their food in ordinary provision-shops got less than 0.1 mSv from the food during the first year. The present level of 90Sr activity concentration in man will only give an effective dose equivalent of 0.004 mSv/year, most of it being a result of the atmospheric nuclear bomb tests.
On 26 April 1986, an accident at a Ukrainian nuclear reactor at Chernobyl triggered the release of large quantities of fission products into the atmosphere. After 7 May 1986 measurable quantities of ruthenium-103, iodine-131, cesium-134, and cesium-137 were detected in environmental sampling carried out in all regions of Canada. Maximum airborne concentrations for each radionuclide were of the order of a few mBq.m-3 and contaminated milk samples on average contained less than 1Bq.L-1 of iodine-131 and cesium-137. The mean value of the effective dose equivalent for an adult Canadian in the two months following the accident is calculated to be 0.28 microSv. As this total radiation dose is about 10(-33) of the dose from natural background during the same period, the resultant radiological detriment is concluded to be negligible.
A worldwide monitoring system for radioactive aerosols is being implemented for verification of the Comprehensive Test Ban Treaty. These 80 stations will detect airborne radioactivity not only from nuclear explosions but also from other anthropogenic and natural sources. A prototype unit has been in operation since April 1996 in Vancouver, British Columbia, Canada. It is a very sensitive system and reports clear signals for natural radioactivity, including cosmogenic 7Be, and the decay products from soil exhalation of 220Rn (thoron). In addition, there have been frequent detections of anthropogenic nuclides, probably coming from three distinct facilities-a medical isotope production center, a major university hospital, and a particle accelerator laboratory--all between 1 and 2 km away from the monitoring station. This experience is discussed to sensitize health physicists to the potential uses of this publicly available information.