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 Chernobyl nuclear accident on 26th April, 1986, led to a massive release of radionuclides into the environment. Although vast areas of Europe were affected by Chernobyl-related ionising radiation, the accident had the greatest impact in Belarus, Ukraine, and the Russian Federation. Epidemiological studies that have investigated the link between the Chernobyl accident and cancer have largely focused on malignant diseases in children, specifically thyroid cancer and leukaemia. There is good evidence to suggest that rates of thyroid cancer in children from the countries that were formally part of the Soviet Union have risen as a consequence of the Chernobyl accident. The findings for childhood leukaemia are less conclusive. Overall rates for this disease do not seem to have been affected by the Chernobyl-related ionising radiation, but there may be a larger risk of infant leukaemia in contaminated areas of Europe. Among adult populations, there is no strong evidence to suggest that risk of thyroid cancer, leukaemia, or other malignant disease has increased as a result of the Chernobyl accident.
Cytogenetic analysis of chromosomal aberrations (CA) in 175,229 cells from 1113 individuals, both unexposed and occupationally or environmentally exposed to heavy metals (mercury and lead), organic (styrene, formaldehyde, phenol and benzo(a)pyrene) and inorganic (sulfur and nitrogen oxides, hydrogen and ammonium fluorides) volatile substances and/or ionizing radiation was performed. In addition, 11,250 cells from 225 individuals were scored for the frequency of sister-chromatid exchanges (SCE). Increased frequencies of CA were found in all occupationally exposed groups. A principal difference between the exposure to heavy metals and organic substances was found: increase in the CA frequency was dependent on duration of exposure to mercury but not dependent on duration of exposure to styrene, formaldehyde and phenol. A higher CA incidence was found in lymphocytes of children living in the vicinity of a plant manufacturing phosphate fertilizers. This indicates that children are a sensitive study group for the assessment of environmental exposure. However, the results of SCE analysis in these children were inconclusive. Exposure to ionizing radiation was found to cause chromosome breaks and chromatid exchanges in Chernobyl clean-up workers and chromatid breaks, chromatid exchanges, dicentric chromosomes and chromosome translocations in workers from the Ignalina Nuclear Power Plant. The increased frequency of chromatid exchanges in individuals exposed to ionizing radiation was quite unexpected. This may be attributed to the action of some unrecognized life-style or occupational factors, or to be a result of radiation-induced genomic instability. Also an increased SCE frequency was found in lymphocytes of Chernobyl clean-up workers.
BACKGROUND: The hazards of acute radiation exposure are well known. Bone marrow failure from total body gamma or neutron irradiation is the most clinically relevant aspect of acute radiation disease. With nonhomogeneous exposure, as is characteristic in accidents, other organ systems, such as the skin, may be more important in determining clinical prognosis. This became obvious in the two worst radiation accidents since 1945, the Chernobyl accident in April 1986 and the Goiania accident in September 1987. OBJECTIVE: Our purpose was to describe the characteristic chronic sequelae of accidental cutaneous radiation in a group of patients who survived the Chernobyl nuclear power plant accident. METHODS: Fifteen patients with the delayed type of the cutaneous radiation syndrome were examined between September 1991 and January 1992. All patients had a history of acute radiation disease. The exposure pattern was characterized by partial body exposure with high doses of beta and gamma irradiation from radioactive water, steam, or dust. RESULTS: Radiation-induced lesions were confined primarily to the legs and distal arms, but sometimes involved up to 50% of the total body surface. In addition to telangiectases, radiation keratoses, and radiation ulcers, hemangiomas, hematolymphangiomas, splinter hemorrhages in the distal nail bed, lentiginous hyperpigmentation, and severe subcutaneous fibrosis were noted. No malignant transformation could be detected. Associated diseases included cataracts, chronic hepatitis, and recalcitrant bacterial and herpesvirus infections. CONCLUSION: After accidental partial body exposure to high doses of beta and gamma irradiation, the predominant involvement of the skin, described as the cutaneous radiation syndrome, can become the characteristic feature. This causes longlasting, serious diagnostic and therapeutic problems.
Long-lived, sensitive, and specific biomarkers of particular mutagenic agents are much sought after and potentially have broad applications in the fields of cancer biology, epidemiology, and prevention. Many clastogens induce a spectrum of chromosome aberrations, and some of them can be exploited as biomarkers of exposure. Densely ionizing radiation, for example, alpha particle radiation (from radon or plutonium) and neutron radiation, preferentially induces complex chromosome aberrations, which can be detected by the 24-color multifluor fluorescence in situ hybridization (mFISH) technique. We report the detection and quantification of stable complex chromosome aberrations in lymphocytes of healthy former nuclear-weapons workers, who were exposed many years ago to plutonium, gamma rays, or both, at the Mayak weapons complex in Russia. We analyzed peripheral-blood lymphocytes from these individuals for the presence of persistent complex chromosome aberrations. A significantly elevated frequency of complex chromosome translocations was detected in the highly exposed plutonium workers but not in the group exposed only to high doses of gamma radiation. No such differences were found for simple chromosomal aberrations. The results suggest that stable complex chromosomal translocations represent a long-lived, quantitative, low-background biomarker of densely ionizing radiation for human populations exposed many years ago.
Literature data during 1980-1989 and own studies carried out at the Institute of Experimental Radiology, All-Union Research Center of Radiation Medicine, USSR AMS, summarized in the paper, describe three types of biological responses (increase, decrease and no response) to low-level ionizing radiation up to 100 Rem. It is shown that pathological changes in the biosystems exposed to radiation are detectable with sensitive techniques, the responses are phasic in nature and depend on the input information signal that causes energy redistribution and changes in the living system response.