Another air sampling detail deals with the actual quantity of the contaminant. For example, OSHA's PEL for airborne lead is 0.05 mg m−3. For 1 μm mass median aerodynamic diameter (MMAD) particles, the PEL corresponds to 3.13 × 108 particles m−3. NRC's DAC for lead‐210 is 1 × 10−4 μCi m−3, which corresponds to a 1‐μm‐sized particle concentration of 8 particles m−3. If the 210Pb were uniformly dispersed throughout the air, and if one wished to determine 50% of the DAC, that is, 5 × 10−5 μCi m−3, and if the lower limit of detection of the counting system is 5 × 10−6 μCi, the required sample volume would be calculated as
However, because the radioactive lead is not continuously dispersed throughout the air, but is randomly distributed as a very small number of discrete particles, we must consider the probability of catching a particle in our sample. If one wishes to detect 50% of a DAC, or 4 particles m−3 within ±25% at the 95% CI (confidence interval), the required sample size is 16 m3, calculated as follows:
According to Poisson statistics
13 ASSESSMENT OF INTERNAL RADIOACTIVITY
A bioassay program internally monitors the deposited radionuclides. Two different, complementary bioassay techniques are employed to determine the internally deposited radioactivity. In vivo bioassay means direct determination of internal radionuclides by scanning the whole body, or a selected part of the body, with a sensitive detector. This method is useful only for gamma‐emitting radionuclides or high‐energy beta emitters that generate bremsstrahlung within the body. In vitro bioassay involves the analysis of body fluids, excreta, and exhaled air for the purpose of estimating the original intake. Although a single measurement may suffice for determining whether or not radioactivity is present in the body, generally, repeated measurements are necessary if one wishes to achieve the best estimate of the intake and of the dose.
The rationale underlying the practice of in vitro bioassay is that a quantitative relationship exists among inhalation or ingestion of a radionuclide, the resulting body burden, and the rate at which the radionuclide is eliminated. From measurements of radioactivity in urine or feces, therefore, one should be able to infer the body burden, and thus estimate the radiation dose. Unfortunately, the kinetics of metabolism in any particular person is influenced by many factors, resulting in a great deal of uncertainty about the exact quantitative relationships among elimination rates, body burden, and radiation dose. In most instances, therefore, bioassay data allows only a reasonable estimate of the intake and dose.
14 CONCLUSIONS
Ionizing radiation and radioisotopes are used safely today in industry, science, and medicine because of the vast amount of knowledge about radiation physics and biology that has been gained since the discovery about a century ago. Occupationally and medically exposed populations have been observed: 270 000 survivors of the nuclear bombings in Japan,2 those who had been exposed to fallout from nuclear weapons tests and from nuclear reactor accidents in England in 1956 and Chernobyl in 1986 (there was no exposure to the public during the Three Mile Island accident), and populations living in environments with high levels of naturally occurring radiation. Investigations into effects of radiation from the Fukushima accident in 2011 are ongoing. The following statements have been made by UNSCEAR (2013)3 and reaffirmed by UNSCEAR (2015)4 regarding the Fukushima accident:
1 “No radiation‐related deaths or acute diseases have been observed among the workers and general public exposed to radiation from the accident.”
2 “No discernible increased incidence of radiation‐related health effects are expected among exposed members of the public or their descendants.”
3 “The most important health effect is on mental and social well‐being, related to the enormous impact of the earthquake, tsunami and nuclear accident, and the fear and stigma related to the perceived risk of exposure to ionizing radiation.”
4 “Exposures of both marine and terrestrial non‐human biota following the accident were, in general, too low for acute effects to be observed, though there may have been some exceptions because of local variability…”
More is known about radiation bioeffects than is known for most other environmental stressing agents. Coincident with the expansion of knowledge about radiation bioeffects was the development of sensitive radiation measuring instruments that enabled us to accurately measure radiation fields and quantities of radioactive materials at a level far below that at which harmful radiation effects are seen. This vast amount of dose–response data enables health physicists and industrial hygienists to control the radiation environment in the workplace so that no harmful radiation effects are seen. Thus, medical, scientific, and industrial applications of radiation technology continue at levels of risk no greater than, and often less than, those associated with other applications of science and technology that are generally considered by society to be safe.
Note
†Deceased.
ENDNOTES
1See NCRP Report 174, Preconception and Prenatal Radiation Exposure: Health Effects and Protective Guidance (2013).2The Incidence of Leukemia, Lymphoma and Multiple Myeloma among Atomic Bomb Survivors: 1950–2001, Wan‐Ling Hsu, Dale L. Preston, Midori Soda, Hiromi Sugiyama, Sachiyo Funamoto, Kazunori Kodama, Akiro Kimura, Nanao Kamada, Hiroo Dohy, Masao Tomonaga, Masako Iwanaga, Yasushi Miyazaki, Harry M. Cullings, Akihiko Suyama, Kotaro Ozasa, Roy E. Shore and Kiyohiko Mabuchi, Radiation Research 179(3): 361–382(2013).3Sources, Effects and Risks of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 2013 Report to the General Assembly with Scientific Annexes, VOLUME I, Scientific Annex A. Available online at https://www.unscear.org/unscear/en/publications/2013_1.html.