2.3 Evaluating Exposures for Possible Health Effects
The health assessor reviews scientific literature to find studies with
exposure conditions similar to the exposure being evaluated. The health
assessor focuses on toxicologic and epidemiologic studies that provide
information on exposure to the selected chemicals.
Studies in which specific amounts of a chemical are observed to cause
identifiable health effects in animals or humans.
Studies that compare an exposed population to a similar population that
is not exposed in order to determine the possibility of an association
between the exposure and any increased rate of a specific illness in the
Purpose. The goal of the evaluation is to fully consider site-specific
exposure doses relative to available chemical-specific information in
the scientific literature.
Some information that a health assessor considers in the weight-of-evidence
approach includes the following:
Sensitive populations are those people in a community who are unusually
susceptible to exposure to a chemical. Sensitive populations may include
children, older adults, people with various types of health problems,
and those who are exposed to a chemical for a longer period of time than
the general population (for example, people who are exposed to chemicals
in their workplace).
Route of exposure
The route of exposure is the way in which the chemical enters the body.
Studies reviewed should be carefully selected so that the route of exposure
for the study population is similar to that of the people in the community
Bioavailability is the percentage of the total amount of a chemical that
is absorbed into the bloodstream. Only the absorbed amount of the chemical
is available to cause harm. For example, people who are gardening might
get soil that contains a pesticide on their hands. When they are eating,
they might accidentally eat some of the soil containing the pesticide.
Only a portion of the pesticide will be absorbed into the bloodstream
because some amount of the chemical will remain attached to the soil and
will pass through their bodies without being absorbed.
Chemicals often exist in different forms. Slight differences in the form
can affect how a chemical moves in the environment, its bioavailability,
and how it can affect a person's health. For example, one form of chromium,
chromium III, is an essential nutrient, needed in the human diet. Another
form of chromium, chromium VI, has been associated with cancer when it
Toxicokinetics describe how a chemical, once contacted, enters the body
(absorption), moves around the body (distribution), changes within the
body (metabolism), and is removed from the body (excretion). Chemicals,
once metabolized, might become more or less toxic.
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