Each of the different routes, or
pathways, by which people can be exposed to radiation result
in exposure to different parts of the body. Health physicists
must analyze the potential for and effects of exposure via each
of the three basic pathways, inhalation,
ingestion, and direct
exposure, when calculating exposures or estimating the effects
of exposures.
Inhalation
Exposure by the inhalation pathway occurs when people breathe
radioactive materials into the lungs. The chief concerns are
radioactively contaminated dust, smoke, or gaseous radionuclides
such as radon.
What happens to inhaled radioactive materials?
Radioactive particles can lodge in the lungs and remain for
a long time. As long as it remains and continues to decay,
the exposure continues. For radionuclides that decay
slowly, the exposure continues over a very long time.
Inhalation is of most concern for radionuclides that are alpha
or beta particle emitters.
Alpha and beta particles can transfer large amounts of energy
to surrounding tissue, damaging DNA or other cellular material.
This damage can eventually lead to cancer or other diseases
and mutations.
How does EPA protect people from inhalation exposure?
EPA first determines the risk for inhalation from various
sources of radionuclides and then determines protective emission
limits. In estimating the risk and effects of exposure
for a given situation, EPA's health physicists consider several
factors:
potential for soil to be disturbed and suspended into
the air
potential for radon generation
presence of other volatile radionuclides (e.g., tritium,
carbon-14)
industrial processes, such as incineration, that could
release radionuclides to the air or generate residues, such
as ash
Exposure by the ingestion pathway occurs when someone swallows
radioactive materials. Alpha and beta emitting radionuclides
are of most concern for ingested radioactive materials. They
release large amounts of energy directly to tissue, causing
DNA and other cell damage.
What happens to ingested radioactive materials?
Ingested radionuclides can expose the entire digestive system.
Some radionuclides can also be absorbed and expose the kidneys
and other organs, as well as the bones. Radionuclides
that are eliminated by the body fairly quickly are of limited
concern. These radionuclides have a short biological
half-life.
How does EPA protect people from ingestion exposure?
EPA first considers the potential for radionuclides
from various sources to enter water, the food chain, or get
into peoples' mouths in day to day activities. We also look
at the percentage of peoples' diet--food and drink--that comes
from radioactive sources. Factors that can lead to ingestion
include the following:
radioactively contaminated drinking water, for example, polluted
ground water
working closely with radioactively contaminated soil, for
example farming
locally grown food plants that take up certain soil radioactivity
use of radioactively contaminated water to irrigate crops
local livestock operations, when radionuclides that accumulate
in animal tissue are present
consumption of fish with radioactivity from local bodies of
water
people bathing, swimming, or otherwise using radioactive
water sources
EPA then takes appropriate measures to reduce the potential for
exposure through ingestion of radioactivity. The measures
often include setting limits on emissions from a source, radioactive
contaminant levels in water resources, consumption of radioactivity
from locally grown food.
The third pathway of concern is direct or external exposure from
radioactive material. The concern about exposure to different
kinds of radiation varies:
Limited concern about alpha particles. They cannot penetrate
the outer layer of skin, but if you have any open wounds you
may be at risk.
Greater concern about beta particles. They can burn the skin
in some cases, or damage eyes.
Greatest concern is about gamma radiation. Different radionuclides
emit gamma rays of different strength, but gamma rays can travel
long distances and penetrate entirely through the body.
Gamma rays can be slowed by dense material (shielding), such
as lead, and can be stopped if the material is thick enough. Examples
of shielding are containers; protective clothing, such as a lead
apron; and soil covering buried radioactive materials.
How does EPA protect people from direct exposure?
We rely on the fundamental radiation protection principles of
time, distance, and shielding to protect people who work directly
with radioactive materials. In assessing potential direct
exposure, we ask three basic questions:
How long is the person exposed (time)?
How close is the person to the source of exposure (distance)?
Is there something between the person and the source of exposure
that can absorb some of the radiation (shielding)?
The amount of exposure also depends on how the source is arranged.
For example, whether the source is concentrated in one place,
or more evenly distributed.
Health Effects 
