Ionizing radiation, carcinogenicity

Other factors associated with the risk of NMSC include exposure to ionizing radiation and arsenic, which is connected with BCC. Chemical carcinogens that give rise to NMSC include industrial hydrocarbons that are found in coal tars, soot, asphalt, paraffin waxes, and tobacco.21 Exposure to the human papilloma virus (HPV-6, -11, -16, and -18) has been linked to SCC.31 Lastly, a personal history of previous melanoma is a risk factor for developing another primary melanoma. 

Radiation is carcinogenic. The frequency of death from cancer of the thyroid, breast, lung, esophagus, stomach, and bladder was higher in Japanese survivors of the atomic bomb than in nonexposed individuals, and carcinogenesis seems to be the primary latent effect of ionizing radiation. The minimal latent period of most cancers was <15 years and depended on an individual s age at exposure and site of cancer. The relation of radiation-induced cancers to low doses and the shape of the dose-response curve (linear or nonlinear), the existence of a threshold, and the influence of dose rate and exposure period have to be determined (Hobbs and McClellan 1986). 

Woloschak, G.E., P. Shearin-Jones, and C.M. Chang-Liu. 1990b. Effects of ionizing radiation on expression of genes encoding cytoskeletal elements kinetics and dose effects. Molec. Carcinogen. 3 374-378. 

Relative biological effectiveness (RBE) The biological effectiveness of any type of ionizing radiation in producing a specific damage (i.e., leukemia, anemia, carcinogenicity). See Radiation dose. 

The biochemical mechanism of ozone toxicity appears to have many similarities with those of other agents, particularly ionizing radiation, that ate known human carcinogens. 

The problem is that nuclear wastes contain radioactive isotopes that release life-threatening ionizing radiation that may pose a threat to humans and the environment for hundreds, thousands, or even millions of years. This radiation can cause carcinogenic, teratogenic, and mutagenic effects in small amounts and can result in radiation sickness and death in larger amounts. 

Differential sensitivity of target organs and tissues to the carcinogenic potency of ionizing radiation... 

Host factors age-at-exposure The magnitude and temporal distribution of radiogenic cancers clearly depend on age-at-exposure, but in no simple, uniform fashion. The dependence probably varies by tumor site. Of particular interest is the question whether e embryo or fetus is very much more sensitive to the carcinogenic action of ionizing radiation than the infant or the young child. Also of interest is the dependence of the temporal distribution of the ag at-exposure effect on the age-specific pattern of natural incidence. 

Other host factors What other host factors may modify the carcinogenic response to ionizing radiation remains unclear, but it seems plain that hormonal factors, at least, play such a role in breast cancer. Immime competence and genetic characteristics, e.g., those governing DNA repair capabilities, are also possibilities. 

The existing evidence does not exclude the existence of a threshold for some (perhaps even aU) forms of cancer, but the available epidemiological and laboratory data do not favor such a possibility. Hence, the interpolation models used by national and international experts for estimating the carcinogenic risks of low-level ionizing radiation are generally based on the assumption of a non-threshold dose-incidence relationship (ICRP, 1977 UNSCEAR, 1977 NAS/NRC, 1980 NCRP, 1980 Sinclair, 1981 Rail eta/., 1985). 

The models developed by the BEIR Committee (NAS/NRC, 1980) for assessing the risks of low-level ionizing radiation include consideration of differences in the duration of the latent period for different types of cancer and ages at irradiation, in accordance with the available epidemiological data. Salient features of the models are illustrated in Figure 8.6. Models for assessing the carcinogenic risks of chemicals... 

This Report has considered the extent to which the principles and methods that have been developed fw use in assessing the carcinogenic risks of ionizing radiation are applicable in assessing the carcinogenic risks of chemicals. Conclusions are as follows ... 

In spite of the aforementioned differences among carcinogens, the principles for risk assessment that have proven to be useful with ionizing radiation appear to be applicable, within limits, to chemicals, particularly those chemicals that resemble radiation in genotoxicity, cytotoxicity, and in the stages of carcinogenesis affected. 

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