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Radiation homeostasis



Radiation Homeostasis is a controversial idea that exposure to radiation renders an organism more able to resist radiation and/or enjoy a better state of health than that of the unirradated organism. This idea is one which is directly opposed to the second event theory which is favoured by Dr Chris Busby (of the NGO known as the The Low Level Radiation Campaign)

Additional recommended knowledge

Some studies have suggested that preexposure to radiation exerts a protective effect upon cells [1] and whole animals[2]. In mice it has been shown that a 200 mGy X-ray dose protects mice against both further X-ray exposure and ozone gas.[3] Furthermore it has been shown in a rodent study that low level (1 mGy hr-1) gamma irradiation prevents the development of cancer (induced by chemical means, injection of methylcholanthrene).[4] Also it has been shown that irradation with gamma rays increases the concentration of glutathione (an antioxidant) found within cells, this is likely to lead to an adaptive response.[5]

While it is clear that a large single exposure to plutonium dioxide powder is able to cause a fatal lung cancer in monkeys (and thus it is likely that PuO2 powder is carcinogenic in humans),[6] some studies have shown that moderate internal exposure to plutonium results in a reduction of the risk of getting cancer,[7]. Other studied have suggested that a small dose of radiation may be good for you.[8] However one explanation for this effect is the fact that the majority of radiation workers are subject to greater number of health checks than the general population, and thus as a result any sign of disease is more likely to be seen at an early (curable) stage. Also see the "healthy worker hypothesis". In plants radiation hormesis has been observed[9] However the existence of radiation hormesis in humans has been questioned, it is reasonable to state that for late effects (such as cancer) that the scientific community has not come to an agreement regarding this matter.[4] But in one recent case it was claimed (In Journal of American Physicians and Surgeons) that the persons living in a apartment block in Taiwan which was constructed using concrete which contained rebar contaminated with cobalt-60 experience a better state of health than the average person.[10]

It would be the case that if radiation homeostasis occurred that if an organism was exposed at a low dose rate that it would be more likely to have the time to adapt to the effect of the radiation and thus acquire some greater resistance to radiation.

Mainstream science is divided on the question of does division of a radiation dose into smaller doses reduce or increase the likelihood of the induction of cancer. In a recent paper[11] a dose of 1 Gy was delivered to the cells (at constant rate from a radioactive source) over a series of lengths of time. These were between 8.77 and 87.7 hours, the abstract stated for a dose delivered over 35 hours or more (low dose rate) no transformation of the cells occurred. Also for the 1 Gy dose delivered over 8.77 to 18.3 hours that the biological effect (neoplastic transformation) was about 1.5 times smaller than that which that had been observed using a single high dose rate of X-ray photons of similar energy. Likewise it has been reported that [12] that fractionation of gamma irradation reduces the likelihood of a neoplastic transformation. It is clear that the findings in these two papers do not agree with the hypothesis of the second event theroy. But in a further paper[13] it is reported that for both fast neutron and gamma rays from Cs-137 that preexposure can increase the ability of a second dose to induce a neoplastic transformation.

References

  1. ^ Azzam, E.I., Radiation Research, 1994, 138(1), S28-S31
  2. ^ Kensuke Otsuka, Takao Koana, Hiroshi Tauchi and Kazuo Sakai, "Activation of Antioxidative Enzymes Induced by Low-Dose-Rate Whole-Body γ Irradiation: Adaptive Response in Terms of Initial DNA Damage", Radiation Research, 2006, 166(3), 474-478
  3. ^ Y Miyachi, The British Journal of Radiology, 2000, 73, 298-304.
  4. ^ Sakai, Kazuo; Iwasaki, Toshiyasu; Hoshi, Yuko; Nomura, Takaharu; Oda, Takeshi; Fujita, Kazuko; Yamada, Takeshi; Tanooka, Hiroshi, International Congress Series (2002), 1236 (Radiation and Homeostasis), 487-490.
  5. ^ Sonia M. de Toledo, Nesrin Asaad, Perumal Venkatachalam, Ling Li, Roger W. Howell, Douglas R. Spitz and Edouard I. Azzam, Radiation Research, 2006, 166(6), 849-857
  6. ^ Hahn, F.F. ; Brooks, A.L. ; Mewhinney, J.A., Radiation Research, 1987, 112(2), 391-397
  7. ^ Kendall GM et al. Mortality and occupational exposure to radiation; First analysis of the National Registry for Radiation Workers. Brit Med Jour 1992; 304: 220
  8. ^ [1]
  9. ^ Atkinson, G.F., 1898. Report upon some preliminary experiments with Roentgen rays in plants. Science, 7: 7.
  10. ^ [2],[3]
  11. ^ Elmore, E.; Lao, X.-Y.; Kapadia, R.; Redpath, J. L., The effect of dose rate on radiation- induced neoplastic transformation in vitro by low doses of low-LET radiation, Radiation Research, 2006, 166(6), 832-838
  12. ^ C.K. Hill, A. Han, F. Buonaguro and M.M. Elkind, Multifractionation Of Co-60 Gamma-Rays Reduces Neoplastic Transformation in vitro, Carcinogenesis, 1984, 5, 193
  13. ^ J. Cao, R.I. Wells and M.M. Elkind, Enhanced Sensitivity To Neoplastic Transformation By Cs-137 Gamma-Rays Of Cells In The G2-/M-Phase Age Interval, International Journal of Radiation Biology, 1992, 62, 191
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Radiation_homeostasis". A list of authors is available in Wikipedia.
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