Mutation and cancer in relation to the atomic-bomb radiation effects

The linear No-Threshold (LNT) dose response model: A comprehensive assessment of its historical and scientific foundations

The linear no-threshold (LNT) single-hit (SH) dose response model for cancer risk assessment is comprehensively assessed with respect to its historical foundations. This paper also examines how mistakes, ideological biases, and scientific misconduct by key scientists affected the acceptance, validity, and applications of the LNT model for cancer risk assessment. In addition, the analysis demonstrates that the LNT single-hit model was inappropriately adopted for governmental risk assessment, regulatory policy, practices, and for risk communication.

Radiation-induced malformations after exposure of murine germ cells in various stages of spermatogenesis

We studied radiation effects in day 19 fetuses of the mouse strain 'Heiligenberger' after exposure (2.8 Gy, 137 Cs gamma rays, dose rate 0.28 Gy/h) of their fathers. We observed an increased lethality (exclusively due to preimplantation death and early resorptions) after exposure of all stages of spermatogenesis with the exception of early spermatogonia. In addition, there was a significant increase in the frequency of malformed fetuses (gastroschises only); this increase was observed primarily after exposure of the meiotic stages.

Biological and biophysical techniques to assess radiation exposure: a perspective

Biological dosimeters measure biologically relevant effects of radiation exposure that are in some sense an estimate of effective dose, whereas biophysical indicators serve as surrogates of absorbed dose in a manner analogous to conventional thermoluminescent dosimeters (TLD). The biological and biophysical dosimeters have the potential to play an important role in assessing unanticipated or occupational radiation exposures. For example, where the exposure is large and uncertain (i.e. radiation accidents), accurate dose information can help in deciding the most appropriate therapy and medical treatment. Another useful area is that of lifetime accumulated dose determination, and the ability to distinguish between and integrate the exposures from natural and anthropogenic (medical X-rays, indoor radon, natural background radiation, occupational and non-occupational exposures). Also, the possibility to monitor individual response and differences in inherent or induced radiation sensitivity may have important implications for radiation protection. More commonly, this type of dosimetry could be used for routine monitoring to detect and quantify unsuspected exposure, for regulatory purposes or for epidemiological studies of the long-term effects of radiation exposure (e.g. in Japanese A-bomb survivors or in the population surrounding Chernobyl). This review is a comparative study of the existing techniques and their future prospects. It summarizes the sensitivity, reproducibility, limiting dose, dose-rate, energy, LET response, sources of variability and uncertainty, and other practical aspects of each bio-indicator. The strengths and weaknesses of each approach are evaluated on the basis of common criteria for particular applications, and are summarized for each assay both in the text and in tabular form, for convenience. It is clear that no single indicator qualifies to reliably measure occupational exposures at the current levels of sensitivity conventional dosimetry services provide. Most of the bio-techniques are applicable to the detection of relatively high radiation exposures at relatively short times after exposure. Some of the bio-indicators have been identified that are, or offer future prospects for becoming, appropriate bio-indicators for dosimetry needs. However, all methods are subject to biological and other variables that are presently uncontrolled, and represent a major source of uncertainty. These include variations in background signals not directly associated with radiation exposure, inter- and intra-individual variability of radiation response, and genetic and environmental effects. Although these factors contribute to the lack of confidence in biological dosimetry, promising bio-indicators may be applied to large populations to establish the inherent variability and confounding factors that limit quantitative data collection and analysis, and reduce reliability and reproducibility.

Apparently beneficial effect of low to intermediate doses of A-bomb radiation on human lifespan

Among about 100,000 A-bomb survivors registered at Nagasaki University School of Medicine, 290 male subjects exposed to 50-149 cGy showed significantly lower mortality from non-cancerous diseases than age-matched unexposed males. This was deduced from the fitting of a U-shaped dose-response relationship. Reasons for this effect in males, but not in females, are discussed with reference to selection of individuals and to hormesis.

Induced rates of mitotic crossing over and possible mitotic gene conversion per wing anlage cell in Drosophila melanogaster by X rays and fission neutrons

As a model for chromosome aberrations, radiation-induced mitotic recombination of mwh and flr genes in Drosophila melanogaster strain (mwh +/+ flr) was quantitatively studied. Fission neutrons were five to six times more effective than X rays per unit dose in producing either crossover-mwh/flr twins and mwh singles-or flr singles, indicating that common processes are involved in the production of crossover and flr singles. The X-ray-induced rate/wing anlage cell/Gy for flr singles was 1 X 10(-5), whereas that of crossover was 2 x 10(-4); the former and the latter rate are of the same order of magnitude as those of gene conversion and crossover in yeast, respectively. Thus, we conclude that proximal-marker "flr" singles induced in the transheterozygote are gene convertants. Using the model based on yeast that recombination events result from repair of double-strand breaks or gaps, we propose that mitotic recombination in the fly is a secondary result of recombinational DNA repair. Evidence for recombinational misrepair in the fly is given. The relative ratio of radiation-induced mitotic crossover to spontaneous meiotic crossover is one order of magnitude higher in the fly than in yeast and humans.

Dietary carcinogens, environmental pollution, and cancer: some misconceptions

Various misconceptions about dietary carcinogens, pesticide residues, and cancer causation are discussed. The pesticides in our diet are 99.99% natural, since plants make an enormous variety of toxins against fungi, insects, and animal predators. Although only 50 of these natural pesticides have been tested in animal cancer tests, about half of them are carcinogens. About half of all chemicals tested in animal cancer tests are positive. The proportion of natural pesticides positive in animal tests of clastogenicity is also the same as for synthetic chemicals. It is argued that testing chemicals in animals at the maximum tolerated dose primarily measures chronic cell proliferation, a threshold process. Cell proliferation is mutagenic in several ways, including inducing mitotic recombination, and therefore chronic induction of cell proliferation is a risk factor for cancer.