Module 2 Biological Effects
Factors for potential effects associated with prenatal
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.
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.
Risk from exposures to ionizing radiation
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.