Examine Radiation Exposures

As noted in the EPCs and Exposure Calculations section of this e-manual, there are differences in the process for evaluating radiological exposures compared to chemical exposures. ATSDR has developed a basic guidance document to introduce health assessors to the science of radiological dose assessment. But because it can be difficult to ascertain the effects resulting from radiation exposure, health assessors should consult a health physicist before conducting a public health evaluation.

People can be exposed to radiation either externally or internally. External exposure occurs when a person is exposed to a source of penetrating radiation (beta particles of specific energies and gamma radiation). Internal exposure occurs when a person inhales or ingests radioactive materials or they are absorbed through the skin or taken in through wounds. The potential for health effects depends on the radiation dose delivered, rate of delivery, and where radionuclides concentrate in the body.

All radionuclides are partly absorbed from the lungs and intestinal tract into the bloodstream where they circulate through the body and either redeposit in organs or are cleared by the kidneys for urinary excretion. In general, most radionuclides taken into the body by ingestion are excreted in feces. Some radionuclides accumulate in specific tissues. Generally, cells that divide most rapidly are most sensitive to ionizing radiation.

Also recognize that uranium can pose significant chemical toxicity not related to its radiotoxicity. For example, the most sensitive health endpoint for uranium exposure is its chemical toxicity to the kidney rather than its radiotoxicity.

There are models to estimate the radiation dose to specific organs and tissues, as well as total body dose. However, interpretation of these model results will require specialized knowledge of dose assessment and the integration period of the radiological decay. Like chemical exposures, ionizing radiation can produce many different effects, depending on (1) the type of radiation, (2) the radionuclide and its decay products, and (3) the dose received by the critical or most sensitive organ.