Health Effects of Exposure to Low Levels of Ionizing Radiation BEIR V (1990) / Chapter Skim
Currently Skimming:
6 Other Somatic and Fetal Effects
6 Other Somatic and Fetal Effects
Pages 352-370
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 352... ...
also showed an excess of cancers among those exposed to diagnostic x rays in utero. In this study, cases were compared with age- and sex-matched nonirradiated controls.
|
From page 353... ...
Because of the comparatively small magnitude of the average radiation dose to the fetus from diagnostic radiography, which has been estimated as 5-50 mGy, the data imply that susceptibility to radiation carcinogenesis is relatively high during prenatal life (NRC72, NRC80, UN77, Mogul. Such an interpretation is complicated, however, by the fact that little increase in susceptibility has been evident in prenatally x-irradiated experimental animals and there is no known biological basis for such an increase in susceptibility or for the suggested equivalence in magnitude of the leukemia excess with that of other childhood cancers (Might.
|
From page 354... ...
recent estimate from the Oxford survey, 217 cases/104 person Gy, falls within this range. The epidemiologic studies also suggest that an association exists between In utero exposure to diagnostic x rays and carcinogenic effects in adult life; however, the magnitude of the risk remains uncertain.
|
From page 355... ...
Severe Mental Retardation Injurious effects of ionizing radiation on the developing human brain have been documented in Japanese A-bomb survivors who were exposed in utero (B173, B175, IC86, Mi76, Ot83, Sc86a, Sc86b, UN86, Wo67) , in whom the prevalence of mental retardation and small head size increases with increasing exposure.
|
From page 356... ...
Among atomic-bomb survivors exposed in utero, a dose-dependent increase in the incidence of severe mental retardation occurred in the gestational age group 8-15 weeks after conception and, to a lesser extent, in the gestational age group 16-25 weeks after conception (Figure 6-1~. No subjects exposed to radiation at less than 8 weeks or >26 weeks of gestational age were observed to be mentally retarded.
|
From page 357... ...
{ / ~._-' 8-15 wee/ 1 ~gestational / ages I/ A,' ,,,' , ,""'\ ' ,' 16-25 weeks 1 0 0.10 0.20 0.30 0.50 1.00 1.50 FETAL DOSE (Gy) FIGURE 6-2 The percentage of severe mental retardation among those exposed in utero by dose and gestational age in Hiroshima and Nagasaki.
|
From page 358... ...
During the period at 8-15 weeks, the period of maximum sensitivity, the dose-response relationship appeared to be different from that at subsequent gestational ages, indicating that radiation effects on cerebral growth and development vary with gestational age at exposure. This period of maximum radiation sensitivity is the time of the most rapid cell proliferation and migration of immature neurons from the ventricular and subventricular proliferative layers to the cerebral cortex (Do73, Ra75, Ramp.
|
From page 359... ...
Intelligence Test Scores Intelligence test (Koga) scores of individuals of 10-11 years of age who were exposed prenatally to the Hiroshima and Nagasaki atomic bombs have been analyzed, using estimates of the uterine absorbed dose based on the DS86 system of dosimetry (Scaly.
|
From page 360... ...
These results parallel those obtained for prenatally exposed atomic-bomb survivors with regard to achievement on standard intelligence tests in childhood as discussed above (Scaly. Summary Japanese Results: The DS86 in utero sample consisted
|
From page 361... ...
There is some indication of a threshold for severe mental retardation, but this is difficult to assess because there is a continuous diminution of intelligence with increasing dose. Using a 95% confidence interval, the grouped dose data suggest a lower bound on the threshold dose of about 0.1 Gy, whereas regressions using individual doses yield a lower bound of about 0.2 Gy.
|
From page 362... ...
The irradiated children had lower examination scores on scholastic aptitude, intelligence quotient, and psychological tests; completed fewer school grades; had increased admissions to mental hospitals for certain neuropsychiatric diseases; and had a slightly higher frequency of mental retardation. Childhood Leukemia Patients: Meadows et al.
|
From page 363... ...
, whereas similar occupational exposure to comparable doses of x rays or gamma rays has not (ICRP84~. Although it is clear from the foregoing that detectable injury of the lens can result from a dose of as low as 1 Gy, depending on the dose rate and LET of the radiation, the threshold for a vision-impairing cataract under conditions of highly fractionated or protracted exposure is thought to be no less than 8 Sv (ICRP84~.
|
From page 364... ...
Even if such an effect of low-level irradiation were reproducible, which is uncertain, its biological significance and its relevance to human populations living under contemporary conditions of nutrition and sanitation are questionable (Sa62, UNTO. Relatively low doses of ionizing radiation can produce certain other types of effects which might be interpreted as beneficial (Sash.
|
From page 365... ...
Conclusions The estimated threshold dose equivalent for induction of temporary sterility in the adult human testis is 0.15 Sv; for permanent sterility it is 3.5 Sv when received as a single exposure. The corresponding threshold dose equivalent for permanent sterility in the adult ovary is 2.5-6.0 Sv received
|
From page 366... ...
1957. Accelerated aging: Long term effect of exposure to ionizing radiations.
|
From page 367... ...
1982. Physiological benefits from low levels of ionizing radiation.
|
From page 368... ...
1987. Severe Mental Retardation among the Prenatally Exposed Survivors of the Atomic Bombing of Hiroshima and Nagasaki: A Comparison of the Old and New Dosimet~y Systems.
|
From page 369... ...
1988. Effect on Intelligence Test Score of Prenatal Exposure to Ionizing Radiation in Hiroshima and Nagasaki: A Comparison of the Old and New Dosimetry Systems.
|
From page 370... ...
1962. Behavioral and histological effects of head i~radiation in new born rats In Response of the Ne~vous System to Ionizing Radiation, T
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.