Information about Radiation and Food & Water Safety
Website Sources of Information Regarding Radioactivity and Food and Water Safety:
National
Institute of Radiation Science (NIRS): (PDF 204KB)
Very Useful: Includes a series of "Basic facts regarding radiation exposure
resulting from the nuclear plant accident caused by the Tohoku area earthquake,"
including "Radioactivity 101," explanations of terms and measurement units, and FAQ:
Ministry
of Education, Culture, Sports, Science and Technology (MEXT):
The English-language website includes information on daily atmospheric radiation
readings by prefecture around the country, and in drinking water.
Yahoo Japan
Emergency Information:
Includes environmental radiation readings by prefecture and detailed monitoring readings
in the vicinity of the Fukushima nuclear power plants; also drinking water readings.
Ministry of Land,
Infrastructure, Transportation, and Tourism (MLIT):
The English-language website includes a page on the Tohoku Earthquake with sections on
measurement of radiation doses around the Metropolitan Airports, and measurement of
radiation doses around the Port of Tokyo, Yokohama, Kawasaki and Chiba, as well as
transportation-related policies and information.
Ministry of
Health, Labor, and Welfare (MHLW):
The English-language website, under “topics,” has a listing for “Food Safety Information
” that includes two notices regarding Japanese policy and regulations on the handling of
food possibly contaminated by radioactive substances.
Food and Safety Commission (FSC): (PDF 234KB)
Includes information on radiation and food safety “nuclear emergency” page of its
Japanese-language section (not included in the English-language section).
Information Regarding Measurement of Radiation Exposure
(adapted from the Centers for Disease Control and Prevention website)
Measuring Radiation Dose
When a person is exposed to radiation, energy is deposited in the tissues of the body.
The amount of energy deposited per unit of weight of human tissue is called the absorbed
dose. Absorbed dose is measured using the conventional unit of measurement rad, which
stands for radiation absorbed dose.
Measuring Biological Risk
A person's biological risk (that is, the risk that a person will suffer health effects
from an exposure to radiation) is measured using the conventional unit rem or the newer
unit Sv. To determine a person’s biological risk, scientists have assigned a number to
each type of ionizing radiation (alpha and beta particles, gamma rays, and x-rays)
depending on that type’s ability to transfer energy to the cells of the body. This
number is known as the Quality Factor (Q). When a person is exposed to radiation,
scientists can multiply the dose in rad by the quality factor for the type of radiation
present and estimate a person’s biological risk in rems. Thus, risk in rem = rad X Q.
The rem is now commonly replaced by the sievert (Sv). One Sv is equal to 100 rem.
Common Radiation Exposures
People are exposed to radiation daily from different sources, such as naturally
occurring radioactive materials in the soil and cosmic rays from outer space (of which
we receive more when we fly in an airplane). Some common ways that people are exposed
to radiation and the associated doses are shown in the table below.
| Source of exposure | Dose in rem | Dose in sievert (mSv/(µSv)) |
|---|---|---|
| Exposure to cosmic rays during a roundtrip airplane flight from New York to Los Angeles | 3 mrem | 0.03 mSv (30 µSv) |
| One dental x-ray | 4–15 mrem | .04–.15 mSv (40-140 µSv) |
| One chest x-ray | 10 mrem | 0.1 mSv (100 µSv) |
| One mammogram | 70 mrem | 0.7 mSv (700 µSv) |
| One year of exposure to natural radiation (from soil, cosmic rays, etc.) | 300 mrem | 3 mSv (3000 µSv) |
1 mrem (millirem) = .001 rem (1 X 10-3); 1 mSv (millisievert) = .001 Sv (1 X 10-
3).
1 µSv (microsievert) = .001 mSv (1 X 10-3) = 0.000001 Sv (1 X 10-6).