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PubMed1964

RADIATION PROTECTION IN CANADA. I.

The current status of radiation protection in Canada has been summarized in the present paper, the first of a three-part series. Particular emphasis has been placed on the role of the Radiation Protection Division of the Department of National Health and Welfare. Somatic and hereditary effects of radiation exposure are briefly discussed as a basis for an understanding of the radiation protection standards which have been developed at national and international levels. The rapid increase in use of radioactive materials and x-ray apparatus in medicine, industry and research, and the extensive atmosphere testing of nuclear weapons have led to the development of comprehensive radiation protection activities in Canada, especially in the Department of National Health and Welfare. Well-established lines of communication and liaison exist among the various agencies responsible for these activities.

Atmosphere↗
PubMed1997

Long-term effective decrease of cesium concentration in foodstuffs after nuclear fallout.

The long-term decrease in activity concentrations in various foodstuffs relevant for the long-term ingestion dose after a nuclear fallout is reviewed. The effective decrease observed in various countries of Central Europe after the Chernobyl accident are compared to the effective decrease observed after the atmospheric nuclear weapons testing. The presentation also includes the short-term decline immediately after fallout and the time course in the first year, which are relevant to the first year ingestion dose. The initial effective decrease is dominantly controlled by plant growth and follows an approximate half-life of 4.2 d in lettuce and spinach, and 10.5 d in grass during the growing season, resulting in an effective half-life of 33 d in milk. In order to avoid artifacts due to local fallout or plant variations or differences in the metabolism of single animals, the sampling of each foodstuff was spread over very large areas of production and a large number of samples including investigations in several individual provinces. The long-term decrease over the following years, which is vital for the long-term internal exposure, is slower but still follows an effective half-life for different foodstuffs: milk = 1.4-2.2 y, vegetables = 1.4-2.7 y, potatoes = 2.0-2.6 y, cereals = 3.0-3.4 y, and fruit = 1.2-1.6 y. Differences observed between the different products and areas are discussed. Half-lives in milk vary between three central-European countries from 708 d (Austria), to 663 d (Germany), to 538 d (Czechia). The observed effective half-life is much shorter than observed after nuclear weapons testing where a half-life of approximately 4.5-4.9 y was observed, which is explained by the weapons tests' fallout lasting for several years compared to the single short-term fallout after the Chernobyl accident.

Animals↗
PubMed1992

Uptake and transfer factors of 137Cs by mushrooms.

The 137Cs content of 118 species (668 samples) of higher fungi collected in the period from August 1984 to October 1989 at three different locations in Styria, Austria, was determined by gamma-spectrometry. The Cs-content of most mushrooms has been increasing since September 1986. In order to find out which factors determine the 137Cs-contamination of mushrooms and the transfer-value soil to mushroom, the concentration of total and plant-available radiocesium in soils as well as the pH-value, the content of humus, clay, silt, sand, exchangeable cations, the composition of the clay minerals, and the particle size distribution of the soils of two different locations were examined. The higher the 137Cs contamination of the soil, the thicker the layer of humus and the higher the content of humus, the lower the pH-value, and the lower the amount of essential cations, especially of K+, the higher the amount of 137Cs plant-available will be. Therefore, the contamination of the mushrooms in the coniferous forest of Koralpenblick (1000 m) is higher than in the mixed forest at the Rosenberg around Graz at approx. 500 m height. Of 26 different species of mushrooms measured at both sites, only 61% show the highest TF-values soil to mushrooms also at the Koralpenblick. In the spruce forest at Koralpenblick there are many species of mushrooms with high 137Cs-contamination which were not found at the Rosenberg. However, the properties of the species to which a mushroom belongs are more important than environmental conditions and soil properties. The transfer values of 40K stay within narrow bounds, whereas those of 137Cs differ widely.

Accidents↗
PubMed1993

Deposition of radiocesium to the soil by stemflow, throughfall and leaf-fall from beech trees.

The amount of Chernobyl-derived 137Cs transferred to the soil by stemflow, throughfall (precipitation under the tree crown), and leaf-fall from three beeches was investigated as a function of time in the growing seasons of 1991 and 1992. Up to 70 Bq/week was deposited with the stemflow, mainly in dissolved form (< 0.45 micron) rather than in particulate form (> 0.45 micron). The ratio of dissolved radiocesium to particulate radiocesium was about 10 in the stemflow. It varied considerably with time, but since these variations followed the same pattern for all three trees, they indicated a common cause to be responsible for the fractionation of radiocesium (e.g. meterological conditions for bark weathering). A significant correlation was observed for the amount of dissolved 137Cs (in Bq) and the amount of stemflow (in liters). The 137Cs concentration in the stemflow (in Bq/1), however, decreased with increasing stemflow intensity (in Bq/week). For particulate radiocesium such correlations were not detected. Up to 5 Bq/m2 per week was deposited with the throughfall from the canopy, mainly in particulate form (ratio dissolved radiocesium to particulate radiocesium = 0.34). The mean total annual amounts of 137Cs deposited to the ground (dissolved+particulate) for the three trees were: stemflow: 1991 600 Bq; 1992 460 Bq; throughfall: 1991 and 1992 approximately 100 Bq/m2 each; leaffall: 1992 approximately 10 Bq/m2. The data indicate that at present a substantial amount of the radiocesium in the leaves derives already from root uptake.

Accidents↗
PubMed2004

Bioavailability of 239+240Pu and 137Cs in aerosols and deposited dusts: a comparative study by fractional extraction.

The bioavailability of (137)Cs and (239+240)Pu in soil, dust and aerosols has been determined by applying a fractional extraction procedure. In aerosols, 47-57% of (137)Cs was found to be easily exchangeable. This differs significantly from soil and deposited dust samples collected on a nearby street as well as on grassland where (137)Cs was quantitatively found in the acid-soluble fraction and the residue. A similar difference was observed for (239+240)Pu: 47% of (239+240)Pu in aerosols was associated with the organic fraction, while in soil and deposited dust from grassland 63-75% of (239+240)Pu was found in the acid-soluble fraction. In deposited street dust, 53% of (239+240)Pu was associated with the oxide fraction.

Aerosols↗
PubMed1989

The influence of the feeding practice and the season on the contamination of animal food products after a single deposition of radionuclides.

After accidental releases of radionuclides to the atmosphere, the activity concentration in animal food products are dependent on the month in which the release occurs. In most cases the highest contamination of milk or meat can be expected in that month in which the main feedstuff of the ration is harvested. The integral activity concentrations due to foliar uptake in the first year are much greater than the integral activity concentrations over 50 years root uptake.

Animal Feed↗
PubMed1989

Assessment of milk transfer coefficients for use in prediction models of radioactivity transport.

The transfer coefficient (Fm) which is widely used to predict the fraction of ingested radionuclides found in milk is an important parameter for modelling. The accuracy of estimates can be improved by considering the following factors that influence the Fm; (1) the physical-chemical form of the radionuclide in the feed of cows, (2) the hay to concentrate ratio of cows diets and (3) correcting for a steady state situation for feed intake and milk concentrations. Factors such as stable element intake, soil intake, milk production rate, metabolic rate and inhalation do not appear to have significant effects upon the transfer coefficient.

Accidents↗
PubMed1992

Influence of combined alpha, beta and gamma radionuclide contamination on the frequency of waxy-reversions in barley pollen.

The mutagenic effectiveness of chronic, combined alpha-, beta-, and gamma-irradiation caused by radionuclide contamination of the biogeocenosis was studied in comparison with chronic gamma-irradiation from an external 60Co source. The waxy-test on barley pollen proved to be sufficiently sensitive to evaluate the increase in waxy-reversion frequencies in plants exposed to a 3 mSv dose. A dose of 50-200 mSv from external irradiation was needed to double the mutation rate in barley pollen. Moreover, the smaller doses (dose rates) were more harmful than the higher doses if measured as the increase in mutation frequency per unit of irradiation. Higher genotoxicity was observed from combined irradiation due to radionuclide contamination than from similar doses from an external gamma source. We concluded that mutagenic effects in plant cells, in the case of radionuclide contamination of the biogeocenosis, could not be extrapolated only on the basis of measured dose, but separate investigations should be carried out to establish the genotoxicity of specific radionuclide mixtures and possible toxic chemical synergisms.

Accidents↗