Health effects background radiation

Harley, N.H., 2008. Health effects of radiation and radioactive materials. In Klaassen, C.D. (Ed.), Cassarrett and Doull s "Toxicology The Basic Science of Poisons", seventh ed. McGraw Hill Medical, New York, NY, pp. 1,053-1,082. Hendry, J.H., Simon, S.L., Wojcik, A., et al., 2009. Human exposure to high natural background radiation what can it teach us about radiation risks J. Radiol. Prot. 29 (2A), A29-A42. 

Most of the data on radiation health effects have come from medical monitoring of Japanese atomic bomb survivors. For survivors who received radiation exposures up to 0.10 Sv, the iacidence of cancer is no greater than ia the geaeral populatioa of Japanese citizens. For the approximately 1000 survivors who received the highest radiation doses, ie, >2 Sv, there have been 162 cases of cancer. About 70 cases would have been expected ia that populatioa from aatural causes. Of the approximately 76,000 survivors, as of 1995 there have beea a total of about 6,000 cases of cancer, only about 340 more cases than would be expected ia a group of 76,000 Japanese citizens who received only background radiation exposure (59). 

For comparison, we have calculated the health effects for typical residential properties (4 occupants each) based on 1) the naturally occurring background radiation levels and radionuclide concentrations in four cities across the U.S. (see Table V) and 2) the EPA (CFR, 1981) guideline values (20 yR/h, 0.02 WL, 5 pCi Ra-226/g of soil) for cleanup at inactive uranium processing sites (see Table VI). 

Table V. Lifetime Health Effects Estimates at Background Radiation Levels for a Typical Residential Property in Several U.S. Cities...

For comparison, the health effects calculated from exposure to natural background radiation levels for typical residential properties were all about 0.01 per property, with radon daughters accounting for more than 50% of the total health effects estimated. 

The human body is equipped to deal with nominal levels of radiation doses. Background (natural) radiation from radon gas, cosmic sources, soil, and water produces an average dose of about 0.3 rem (0.003 Sv) per year.4 However, large doses of radiation generated after a terrorist attack can overwhelm the body s ability to repair damage, leading to stochastic or acute health effects. 

Stochastic radiation effects are typically associated with those that occur over many months or years (i.e., are typically chronic instead of acute). Chronic doses are typically on the order of background doses (0.3 rem [0.003 Sv] or less) and are not necessarily associated with larger doses that could result from a terrorist attack with radiological weapons. However, stochastic health effects are defined here as effects that occur many years after chronic or acute exposure to radiological contaminants. Stochastic effects are categorized as cancers and hereditary effects. Because no case of hereditary effects (e.g., mutation of future generations) has been documented, this discussion focuses on cancer risk. 

The National Coimcil for Radiation Protection (NCRP) has identified a negligible individual risk level (NIRL) as a level of annual excess risk of health effects attributable to irradiation below which further effort to reduce radiation to the individual is unwarranted. The NCRP emphasized that this level should not be confused with an acceptable risk level, a level of significance or a standard. The NCRP recommended a level around half the natural background radiation level the final recommended NIRL level is 1 mrem this level is now called negligible individual dose (NID) level (Harley, 2001, 2008). 

How is the actual incidence of cancer caused by radiation exposure actually related to the total incidence of cancer, and can it be reduced One study (235) showed that of the total number of cancer fatalities in the United States in 1975 resulting from radiation, only 2.7 percent of the ongoing exposures would result in low-level radiation-induced cancer fatalities. Most arise from natural background radiation or medical exposures. The only significant change that could be made to alter this number is to attempt to modify the incidence of medical exposure. Since most exposures to medical radiation are undertaken to benefit the individual, and presumably other adverse health effects would result as a consequence of withholding the exposure, limiting medical exposures would probably not reduce the total overall mortality. 

The National Academy issued its report on 12 June 1956. In some ways its findings were reassuring. Contrary to widely circulated speculation, it denied that nudear-bomb tests had caused discernible changes in climate or weather conditions. In its assessment of the effects of radioactive fallout, the study concluded that the amount of radiation produced by weapons tests to that time did not present a major health hazard. Compared with the exposure the U.S. population received firom X rays and from natural background radiation that comes from cosmic rays and radioactive substances in rocks and the soil, the doses from fallout were small. The report also declared "It appears that radiation problems, if... 

The creation of our world occurred in intense radiation Helds and, consequently, we have inherited an Earth drenched in radiation from cosmic sources and the minerals in the groimd (Ch. S, 10 and 17). Though the intensity of these radiation sources is much smaller than produced by human techniques, no human can avoid these natural sources. Therefore, the effects of the natural radiation background has become an important health issue, particularly radon levels in houses. Closely related to this problem is the effects of man-made sources of similarly low levels, such as the storage of nuclear waste. Much research is presently devoted to the effects of low-level radiation. 

---