The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has published a substantive series of reports concerning sources, effects, and risks of ionizing radiation. This article summarizes the highlights and conclusions from the most recent 1986 and 1988 reports. The present annual per person effective dose equivalent for the world's population is about 3 mSv. The majority of this (2.4 mSv) comes from natural background, and 0.4 to 1 mSv is from medical exposures. Other sources contribute less than 0.02 mSv annually. The worldwide collective effective dose equivalent annually is between 13 and 16 million person-Sv. The Committee assessed the collective effective dose equivalent to the population of the northern hemisphere from the reactor accident at Chernobyl and concluded that this is about 600,000 person-Sv. The Committee also reviewed risk estimates for radiation carcinogenesis which included the new Japanese dosimetry at Hiroshima and Nagasaki. These data indicate that risk coefficient estimates for high doses and high dose rate low-LET radiation in the Japanese population are approximately 3-10% Sv-1, depending on the projection model utilized. The Committee also indicated that, in calculation of such risks at low doses and low dose rates, a risk-reduction factor in the range of 2-10 may be considered.
The age dependence of the natural concentration of uranium and thorium in the skeleton was investigated using human vertebrae bone collected from two Canadian locations (Winnipeg, Manitoba, and Regina, Saskatchewan). The concentration of both radioelements in digested ashed bone samples was determined using sector-field inductively coupled plasma mass spectrometry. The geometric means for uranium level in bones showed a significant statistical difference between the two locations studied. Similarly for thorium, a statistical difference was observed, although this difference was considered marginal. The thorium concentration differed only marginally with respect to age group, indicating that its behavior in the body could be age-independent. Conversely, the uranium level in bones was found to change for the age groups tested, an indication of age-specific deposition. The age profile for uranium was comparable to the calcium turn-over rate, indicating that uranium deposition is probably, in part, dictated by this metabolic process, showing the role of present uptake into the uranium concentration in bones for populations exposed to significant uranium intake.
The children living in 4 regions of Russia contaminated as a result of the Chernobyl catastrophe were investigated. The control group consisted of the children of 2 regions which did not undergo this influence. The investigations were made 1-3 years after the catastrophe took place. An increase of etiologically non-clear asthenic-vegetative disorders was determined in the regions of radiation contamination. They were observed mainly among the children who had light residual organic cerebral deficiency. The authors cannot exclude the impact of the psychogenic factors.
A review and analysis of published information combined with the results of recent gamma ray surveys were used to determine the annual effective dose to Canadians from natural sources of radiation. The dose due to external radiation was determined from ground gamma ray surveys carried out in the cities of Toronto, Ottawa, Montreal and Winnipeg and was calculated to be 219 microSv. A compilation of airborne gamma ray data from Canada and the United States shows that there are large variations in external radiation with the highest annual outdoor level of 1424 microSv being found in northern Canada. The annual effective inhalation dose of 926 microSv from 222Rn and 220Rn was calculated from approximately 14,000 measurements across Canada. This value includes a contribution of 128 microSv from 222Rn in the outdoor air together with 6 microSv from long-lived uranium and thorium series radionuclides in dust particles. Based on published information, the annual effective dose due to internal radioactivity is 306 microSv. A program developed by the Federal Aviation Administration was used to calculate a population-weighted annual effective dose from cosmic radiation of 318 microSv. The total population-weighted average annual effective dose to Canadians from all sources of natural background radiation was calculated to be 1769 microSv but varies significantly from city to city, largely due to differences in the inhalation dose from 222Rn.
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.
High doses of ionizing radiation are an established cause of childhood leukemia. However, substantial uncertainty remains about the effect of low doses of radiation, including background radiation and potential differences between genetic subgroups of leukemia have rarely been explored. We investigated the effect of the background gamma radiation on childhood leukemia using a nationwide register-based case-control study. For each of the 1,093 cases, three age- and gender matched controls were selected (N?=?3,279). Conditional logistic regression analyses were adjusted for confounding by Down syndrome, birth weight (large for gestational age), and maternal smoking. Complete residential histories and previously collected survey data of the background gamma radiation in Finland were used to assess the exposure of the study subjects to indoor and outdoor gamma radiation. Overall, background gamma radiation showed a non-significant association with the OR of childhood leukemia (OR 1.01, 95% CI 0.97, 1.05 for 10 nSv/h increase in average equivalent dose rate to red bone marrow). In subgroup analyses, age group 2-