The answer to this question in large part depends on the specifics of an individual's life. Our bodies are well adapted to some degree of exposure; humans evolved in the presence of radiation and have well developed mechanisms for repairing cell damage from it.
Knowing the annual dose received by an "average" person provides some perspective. The most recent data on the average annual dose in the U.S. come from a 1987 study by the National Commission on Radiation Protection and Measurement. At the time of the study, people in the U.S. received an average annual radiation dose of about 360 milli rem (one thousandth of a rem) per year.
Background Radiation
Most (82 percent) of the average annual dose in the 1987 study originated from "background" radiation. "Background" radiation includes naturally-occurring radiation:
- Radon in soil and water 55%
- Cosmic radiation 8%
- Terrestrial radiation from minerals such as uranium and radium in rock and soil 8%
- Radionuclides, primarily potassium-40, in living tissue 11%
The average is calculated from a range of doses that depend in part on where people live. Background levels in a particular geographic region depend on multiple factors:
- altitude (cosmic radiation increases with altitude)
- the content of soils (some areas have higher natural levels radon gas)
- local geology (e.g., geologic deposits of uranium and other radioactive elements)
Radiation from Man-Made Sources
The remaining 18% of the average annual dose was found to come from man-made sources:
- Medical x-rays, 11%
- Nuclear medicine 4%
- Consumer products 3%
- Other <1%
- Occupational 0.3%
- Fallout <0.3%
- Nuclear fuel cycle 0.1%
- Miscellaneous 0.1%
The average included individual variations related to several factors:
- exposure from medical procedures (e.g. x-rays, nuclear medicine), which accounted for the majority of man-made exposure
- occupation (e.g. uranium miners' greater exposure to radon, uranium, and other radionuclides)
- use of consumer products (e.g., smokers' inhalation of the radionuclides that tobacco leaves, radium watches, ceramics).
- other man-made factors (e.g., fallout from nuclear testing, proximity to abandoned uranium mines or areas contaminated by radioactive materials from manufacturing)
New NCRP Study
Since the completion of the NCRP studies in 1987, new medical technologies such as CT scans and MRIs have been developed and become widely used. Also, awareness, testing, and remediation of radon in homes and other buildings has increased. Because of these changes, the proportion of the U.S. population exposure represented by these two categories of sources has likely shifted. Current studies being conducted by the NCRP will show the degree of the shift.
NCRP is currently updating the study to account for a number of factors:
- increased use of medical procedures involving radiation (e.g., CT scans and MRIs)
- increased awareness and remediation of radon in homes, schools, and other buildings
- decay of radionuclides from nuclear weapons testing which ended in the 1970s
- atmospheric changes.
Source: EPA
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