Natural background risks radiation

Tb a considerable extent, these risk estimates and risk comparisons are merely exposure comparisons. Their interpretation is aided by comparing them with natural background radiation exposure and its variations or comparison to the other risks of a particular activity or to the risks associated with safe industry . 

The acceptable risks for substances that induce stochastic responses discussed in this Section are values in excess of unavoidable risks from exposure to the undisturbed background of naturally occurring agents that cause stochastic responses, such as many sources of natural background radiation and carcinogenic compounds produced by plants that are consumed by humans. This distinction is based on the assumption of a linear, nonthreshold dose-response relationship for substances that cause stochastic responses and the inability to control many sources of exposure. Risk management can address exposures to naturally occurring substances that induce stochastic responses, but only when exposures are enhanced by human activities or can be reduced by reasonable means. 

In contrast, risk management for substances that cause deterministic effects must consider unavoidable exposures to the background of naturally occurring substances that cause such effects. Based on the assumption of a threshold dose-response relationship, the risk from man-made sources is not independent of the risk from undisturbed natural sources, and the total dose from all sources must be considered in evaluating deterministic risks. In the case of ionizing radiation, thresholds for deterministic responses are well above average doses from natural background radiation (see Section 3.2.2.1)... 

NCRP has recommended that annual effective doses to individuals from any practice or source of 10 p.Sv or less are negligible (see Section 4.1.2.5.3). This dose is one percent of the dose limit for continuous exposure to all man-made sources combined discussed in the previous section, and it also is about one percent of the dose from natural background radiation, excluding radon (NCRP, 1987b). The recommended negligible individual dose corresponds to an estimated lifetime fatal cancer risk of about 4 X 10 5. 

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). 

Current opinion is that there is a small risk to human health from even low levels of exposure to ionizing radiation, but there is also a known quantity of natural background radiation that the human species has always encountered. In 1984, an employee at a nuclear power plant began to set off radiation alarms while walking into the plant. An investigation found that his home contained high levels of radon gas from natural minerals. Radon tests are now routinely performed in many homes. 

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. 

Figures 18.6, 18.7, and 18.8 show that it is impossible to assess the risk at the 1 — 5 mSv level, which is the range of natural radiation background. As epidemiological investigations seem to fall short, it has been suggested (Sondhaus, Yalow, Sagan, Cohen etc) that the only way to resolve this question is through in vivo radiation studies at the molecular level.

Natural resources account for most radiation exposure. Attempts to determine if there are subtle effects from background irradiation have only begun to yield information about these widely dispersed effects. Advent of new techniques for such estimation has increased the sensitivity and reliability of detection. The objectives of this chapter are to describe common types of ionizing radiation, discuss radiation toxicity in humans, and provide information on the possible benefits and risks associated with ionizing radiation. 

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