Radiation human exposure studies

Available information from human exposures indicates that airborne americium-containing particles are deposited in the respiratory tract, cleared to some extent via mucociliary action, and swallowed or expelled (Edvardsson and Lindgren 1976 Fry 1976 Newton et al. 1983 Sanders 1974 Toohey and Essling 1980). Descriptions of human respiratory tract models that can be used for radiation protection also include relevant information regarding biokinetics of inhaled particles (ICRP 1994b, 1995 NCRP 1997). Quantitative data are not available, however. Supporting animal studies include inhalation exposure to aerosols of americium (Buldakov et al. 1972 DOE 1978 Gillett et al. 1985 Sanders and Mahaffey 1983 Talbot et al. 1989 Thomas et al. 1972) or intratracheal instillation of americium compounds (Moushatova et al. 1996). 

Epidemiological and Human Dosimetry Studies. Epidemiological studies of radiation dose typically involve estimates of exposure that are based on whole-body measurements of internally-deposited americium. A need remains for epidemiological data that can provide quantitative human dose-response information while supplying additional information on the health effects of exposure to ionizing radiation and americium in particular, for cases of known internal exposure. 

Continuance of protracted exposure studies to measure carcinogenesis in animal and human cell lines and the role of secondary factors — especially chemical agents — in radiation carcinogenesis (Little 1990)... 

Although this has been shown to occur in experimental animals after exposure of males to foreign compounds such as cyclophosphamide, there is only inconclusive evidence that this occurs in humans. Thus, studies of exposure of human males to vinyl chloride, dibromo-chloropropane, and anesthetic gases, for example, have revealed only equivocal evidence of developmental toxicity in the offspring. There now seems to be some evidence that the leukemia occurring in children, which appears to be clustered around nuclear fuel-reprocessing plants such as Sellafield in the United Kingdom, may be due to paternal exposure to radiation. 

Additionally, before the first study with radiolabeled test substance in man can be started, a risk assessment of a human radiokinetic study is mandatory. The estimation of the radiation exposure in humans given a radiolabeled dose is based on exposure data obtained typically from QWBA studies in animals. 

The lethal effects of inhalation exposure to uranium have been investigated in humans in epidemiological studies and in animal studies under controlled conditions. Epidemiological studies indicate that routine exposure of humans (in the worlq)lace and the environment at large) to airborne uranium is not associated with increased mortality. Brief accidental exposures to very high concentrations of uranium hexafluoride have caused fatalities in humans. Laboratory studies in animals indicate that inhalation exposure to certain uranium compounds can be fatal. These deaths are believed to result from renal failure caused by absorbed uranium. The low specific activity of uranium precludes the possibility of absorbing enough uranium to deliver a lethal dose of radiation. 

Because there are few data on the results of human exposure to actinides, the health effects of these radioelements are more uncertain than those discussed above for ionizing radiation, radon, and fission products. Americium accumulates in bones and will likely cause bone cancer due to its radioactive decay. Animal studies suggest that plutonium will cause effects in the blood, liver, bone, lung, and immune systems. Other potential mechanisms of chemical toxicity and carcinogenicity of the actinides are similar to those of heavy metals and include (i) disruption of transport pathways for nutrients and ions (ii) displacement of essential metals such as Cu, Zn, and Ni ... 

Human exposures to RF radiation arise from military use, industrial use, broadcasting, and cellular phone use. These exposures have been linked to increased numbers of spontaneous abortion, neurological effects, altered red and white blood cell counts, increased somatic mutation rates in lymphocytes, cardiovascular effects, increased cancer risk, and increased childhood cancers/28 311 Other studies.however, have refuted these findings) 27,32 As stated in the introduction, only a relatively few studies addressed the combined effects of toxic chemical and RF exposure. A thorough search of the literature shows that such studies have not been refuted. The following are illustrative examples of these mixture studies. 

Radioactive Strontium. No studies were located regarding death in humans following inhalation exposure to radioactive strontium. Information on the lethality of inhaled radioactive strontium is limited to acute exposure studies. Because of the bone-seeking behavior of strontium, an acute exposure to airborne 90Sr results in chronic exposure to radiation from 90Sr incorporated into bone. If insoluble radiostrontium compounds are inhaled, there could be long-term lung exposure (see discussion of the study by Willard and Snyder (1966) in Section 3.4.1.1). 

Radon ( Rn) is the dominant source of human exposure to ionizing radiation in every country of the world. It is dominant in most circumstances at home and at work, for individual persons and for whole populations. The worst characteristic of radon, apart from its carcinogenicity, is its ubiquity. Before radon became a matter of concern for human exposure, it was studied and measured for many purposes. It was an inert tracer for air masses, it was a geological indicator for radium and uranium, and it was a shortlived source of y-radiation for cancer treatment. Radon plus beryllium was used as neutron source by Fermi for the discovery of neutron-induced fission reactions. 

The toxic effects of the intake of uranium are based purely on its characteristics as a heavy element. There are no reports of radiation-induced effects in humans from the inhalation or ingestion of uranium. Inferential material on radiation effects has been gathered through animal experiments and comparison with human exposures to radium isotopes. Extensive reviews of the uranium literature concerning experimental studies in animals and humans are available [3,9,10]. 

As part of the investigation of integrated human exposure to natural radiation, external penetrating radiation absorbed dose rates in air were determined both indoors and outdoors in communities where previous geological and geochemical studies indicated the elevated uranium and thorium content of the local rocks (Table 8) [73]. In the comparison to world averages, the estimated total (gamma + cosmic)... 

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