Risks in Perspective - hdbk11300216

DOE-HDBK-1130-98

slightly smaller head size, lower average birth weight, and increased incidence of mental

retardation. Some later showed lower IQ test scores and slower scholastic development,

smaller physical size, and increased incidence of behavioral problems.

1. Sensitivity of the fetus

Embryo/fetal cells are rapidly dividing, which makes them sensitive to many

environmental factors including ionizing radiation. The embryo/fetus is most susceptible

to developing adverse health effects if exposed during the time period of 8 - 15 weeks

after conception.

2. Factors for potential effects associated with prenatal exposures

Many chemical and physical (environmental) factors are suspected of causing or known

to have caused damage to a fetus, especially early in the pregnancy. Radiation, alcohol

consumption, exposure to lead, and heat, such as from hot tubs, are only a few such

factors.

E. Risks in Perspective

Current radiation protection standards and practices are based on the premise that any

radiation dose, no matter how small, can result in health effects such as cancer. Further, it is

assumed that these effects are produced in direct proportion to the dose received (i.e.,

doubling the radiation dose results in a doubling of the risk of the effect). These two

assumptions lead to a dose-response relationship, often referred to as the linear, no-

threshold model, for limiting health effects at very low radiation dose levels.

However, it should be noted that this is a conservative assumption made in the absence of

more conclusive evidence. Health effects (primarily cancer) have been observed in humans

only at doses in excess of 10 rem delivered at high dose rates. Below this dose, estimation

of adverse health effects is speculative. Risk estimates that are used to predict health effects

in exposed individuals or populations are based on epidemiological studies of well-defined

populations (e.g., the Japanese survivors of the atomic bombings in 1945 and medical

patients) exposed to relatively high doses delivered at high dose rates. It is generally

accepted that studies have not demonstrated adverse health effects in individuals exposed to

small doses (less than 10 rem) delivered over a period of many years.

1. Risk from exposures to ionizing radiation

a. No increases in cancer have been observed in individuals who receive a dose of

ionizing radiation at occupational levels. The possibility of cancer induction cannot

be dismissed even though an increase in cancers has not been observed. Risk

estimates have been derived from studies of individuals who have been exposed to

high levels of radiation.