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10. GLOSSARY
Case Series—
Describes the experience of a small number of individuals
with the same disease or
exposure. These may suggest potential topics for scientific research, but are not actual research studies.
Ceiling Value—
A concentration of a substance that should not be exceeded, even instantaneously.
Chronic Exposure—
Exposure to a chemical for 365 days or more, as specified in the Toxicological
Profiles.
Cohort Study—
A type of epidemiological study of a specific group or groups of people who have had a
common insult (e.g., exposure to an agent suspected of causing disease or a common disease) and are
followed forward from exposure to outcome. At least one exposed group
is compared to one unexposed
group.
Cross-sectional Study—
A type of epidemiological study of a group or groups of people that examines
the relationship between exposure and outcome to a chemical or to chemicals at one point in time.
Data Needs—
Substance-specific informational needs that if met would reduce the uncertainties of human
health assessment.
Developmental Toxicity—
The occurrence of adverse effects on the developing organism that may result
from exposure to a chemical prior to conception (either parent), during prenatal development, or
postnatally to the time of sexual maturation. Adverse developmental effects may be detected at any point
in the life span of the organism.
Dose Equivalent—
A quantity used in radiation protection to place all radiation on a common scale for
calculating tissue damage. Dose equivalent is the absorbed dose in grays
multiplied by a radiation
weighting factor. The radiation weighting factor accounts for differences in radiation effects caused by
different types of ionizing radiation. Some radiation, including alpha particles, causes a greater amount of
damage per unit of absorbed dose than other radiation. The sievert (Sv) is the unit used to measure dose
equivalent.
Dose-Response Relationship—
The quantitative relationship between
the amount of exposure to a
toxicant and the incidence of the adverse effects.
Effective Dose—
A dosimetric quantity useful for comparing the overall health effects of irradiation of
the whole body. It takes into account the absorbed doses received by various organs and tissues and
weighs them according to present knowledge of the sensitivity of each organ to radiation. It also accounts
for the type of radiation and the potential for each type to inflict biologic damage. The effective dose is
used, for example, to compare the overall health detriments of different radionuclides in a given mix. The
unit of effective dose is the sievert (Sv); 1 Sv = 1 J/kg.
Embryotoxicity and Fetotoxicity—
Any toxic effect on the concepts as a result of prenatal exposure to a
chemical; the distinguishing feature between the two terms is the stage of development during which the
insult occurs.
The terms, as used here, include malformations and variations, altered growth, and
in utero
death.
Environmental Protection Agency (EPA) Health Advisory—
An estimate of acceptable drinking water
levels for a chemical substance based on health effects information. A health advisory is
not a legally
enforceable federal standard, but serves as technical guidance to assist federal, state, and local officials.
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10. GLOSSARY
Epidemiology—
Refers to the investigation of factors that determine the frequency and distribution of
disease or other health-related conditions within a defined human population during a specified period.
Equivalent Dose—
The absorbed dose in an organ or tissue multiplied by the relevant radiation weighting
factor
w
R
.
Genotoxicity—
A specific adverse effect on the genome of living cells that,
upon the duplication of
affected cells, can be expressed as a mutagenic, clastogenic, or carcinogenic event because of specific
alteration of the molecular structure of the genome.
Half-life—
A measure of rate for the time required to eliminate one half of a quantity of a chemical from
the body or environmental media.
Immediately Dangerous to Life or Health (IDLH)—
The maximum environmental concentration of a
contaminant from which one could escape within 30 minutes without any escape-impairing symptoms or
irreversible health effects.
Immunologic Toxicity—
The occurrence of adverse effects on the immune system that may result from
exposure to environmental agents such as chemicals.
Immunological Effects—
Functional changes in the immune response.
Incidence—
The ratio of individuals in a population who develop a specified
condition to the total
number of individuals in that population who could have developed that condition in a specified time
period.
Intermediate Exposure—
Exposure to a chemical for a duration of 15–364 days, as specified in the
Toxicological Profiles.
In Vitro—
Isolated from the living organism and artificially maintained, as in a test tube.
In Vivo—
Occurring within the living organism.
Lethal Concentration
(LO)
(LC
LO
)—
The lowest concentration of a chemical in air that has been reported
to have caused death in humans or animals.
Lethal Concentration
(50)
(LC
50
)—
A calculated concentration of a chemical in
air to which exposure for
a specific length of time is expected to cause death in 50% of a defined experimental animal population.
Lethal Dose
(LO)
(LD
Lo
)—
The lowest dose of a chemical introduced by a route other than inhalation that
has been reported to have caused death in humans or animals.
Lethal Dose
(50)
(LD
50
)—
The dose of a chemical that has been calculated to cause death in 50% of a
defined experimental animal population.
Lethal Time
(50)
(LT
50
)—
A calculated period of time within which a specific concentration of a chemical
is expected to cause death in 50% of a defined experimental animal population.
Lowest-Observed-Adverse-Effect Level (LOAEL)—
The lowest exposure level of chemical in a study,
or group of studies, that produces statistically or biologically significant increases in frequency or severity
of adverse effects between the exposed population and its appropriate control.
