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Agency for Toxic Substances and Disease Registry
 1. Agency for Toxic Substances and Disease Registry




GLOSSARY OF TERMS

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Glossary of Terms
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Table of Contents


The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public
health agency with headquarters in Atlanta, Georgia, and 10 regional offices in
the United States. ATSDR’s mission is to serve the public by using the best
science, taking responsive public health actions, and providing trusted health
information to prevent harmful exposures and diseases related to toxic
substances. ATSDR is not a regulatory agency, unlike the U.S. Environmental
Protection Agency (EPA), which is the federal agency that develops and enforces
environmental laws to protect the environment and human health.

This glossary defines words used by ATSDR in communications with the public. It
is not a complete dictionary of environmental health terms. If you have
questions or comments, call ATSDR’s toll-free telephone number, 1-800-CDC-INFO
(232-4636).

En Español
 

A B C | D E F | G H I | J K L | M N O | P Q R S | T U V | W X Y Z

Absorption
The process of taking in. For a person or an animal, absorption is the process
of a substance getting into the body through the eyes, skin, stomach,
intestines, or lungs.

Acute
Occurring over a short time [compare with chronic].

Acute exposure
Contact with a substance that occurs once or for only a short time (up to 14
days) [compare with intermediate duration exposure and chronic exposure].

Additive effect
A biologic response to exposure to multiple substances that equals the sum of
responses of all the individual substances added together [compare with
antagonistic effect and synergistic effect].

Adverse health effect
A change in body function or cell structure that might lead to disease or health
problems

Aerobic
Requiring oxygen [compare with anaerobic].

Ambient
Surrounding (for example, ambient air).

Anaerobic
Requiring the absence of oxygen [compare with aerobic].

Analyte
A substance measured in the laboratory. A chemical for which a sample (such as
water, air, or blood) is tested in a laboratory. For example, if the analyte is
mercury, the laboratory test will determine the amount of mercury in the sample.

Analytic epidemiologic study
A study that evaluates the association between exposure to hazardous substances
and disease by testing scientific hypotheses.

Antagonistic effect
A biologic response to exposure to multiple substances that is less than would
be expected if the known effects of the individual substances were added
together [compare with additive effect and synergistic effect].

Background level
An average or expected amount of a substance or radioactive material in a
specific environment, or typical amounts of substances that occur naturally in
an environment.

Biodegradation
Decomposition or breakdown of a substance through the action of microorganisms
(such as bacteria or fungi) or other natural physical processes (such as
sunlight).

Biologic indicators of exposure study
A study that uses (a) biomedical testing or (b) the measurement of a substance
[an analyte], its metabolite, or another marker of exposure in human body fluids
or tissues to confirm human exposure to a hazardous substance [also see exposure
investigation].

Biologic monitoring
Measuring hazardous substances in biologic materials (such as blood, hair,
urine, or breath) to determine whether exposure has occurred. A blood test for
lead is an example of biologic monitoring.

Biologic uptake 
The transfer of substances from the environment to plants, animals, and humans.

Biomedical testing
Testing of persons to find out whether a change in a body function might have
occurred because of exposure to a hazardous substance.

Biota
Plants and animals in an environment. Some of these plants and animals might be
sources of food, clothing, or medicines for people.

Body burden
The total amount of a substance in the body. Some substances build up in the
body because they are stored in fat or bone or because they leave the body very
slowly.

CAP [see Community Assistance Panel.]

Cancer
Any one of a group of diseases that occur when cells in the body become abnormal
and grow or multiply out of control.

Cancer risk
A theoretical risk for getting cancer if exposed to a substance every day for 70
years (a lifetime exposure). The true risk might be lower.

Carcinogen
A substance that causes cancer.

Case study
A medical or epidemiologic evaluation of one person or a small group of people
to gather information about specific health conditions and past exposures.

Case-control study
A study that compares exposures of people who have a disease or condition
(cases) with people who do not have the disease or condition (controls).
Exposures that are more common among the cases may be considered as possible
risk factors for the disease.

CAS registry number
A unique number assigned to a substance or mixture by the American Chemical
Society Abstracts ServiceExternal [external link].

Central nervous system
The part of the nervous system that consists of the brain and the spinal cord.

CERCLA [see Comprehensive Environmental Response, Compensation, and Liability
Act of 1980]

Chronic
Occurring over a long time [compare with acute].

Chronic exposure
Contact with a substance that occurs over a long time (more than 1 year)
[compare with acute exposure and intermediate duration exposure]

Cluster investigation
A review of an unusual number, real or perceived, of health events (for example,
reports of cancer) grouped together in time and location. Cluster investigations
are designed to confirm case reports; determine whether they represent an
unusual disease occurrence; and, if possible, explore possible causes and
contributing environmental factors.

Community Assistance Panel (CAP)
A group of people from a community and from health and environmental agencies
who work with ATSDR to resolve issues and problems related to hazardous
substances in the community. CAP members work with ATSDR to gather and review
community health concerns, provide information on how people might have been or
might now be exposed to hazardous substances, and inform ATSDR on ways to
involve the community in its activities.

Comparison value (CV)
Calculated concentration of a substance in air, water, food, or soil that is
unlikely to cause harmful (adverse) health effects in exposed people. The CV is
used as a screening level during the public health assessment process.
Substances found in amounts greater than their CVs might be selected for further
evaluation in the public health assessment process.

Completed exposure pathway [see exposure pathway].

Comprehensive Environmental Response, Compensation, and Liability Act of 1980
(CERCLA)
CERCLA, also known as Superfund, is the federal law that concerns the removal or
cleanup of hazardous substances in the environment and at hazardous waste sites.
ATSDR, which was created by CERCLA, is responsible for assessing health issues
and supporting public health activities related to hazardous waste sites or
other environmental releases of hazardous substances. This law was later amended
by the Superfund Amendments and Reauthorization Act (SARA).
 

Concentration
The amount of a substance present in a certain amount of soil, water, air, food,
blood, hair, urine, breath, or any other media.

Contaminant
A substance that is either present in an environment where it does not belong or
is present at levels that might cause harmful (adverse) health effects.

 

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Delayed health effect
A disease or an injury that happens as a result of exposures that might have
occurred in the past.

Dermal
Referring to the skin. For example, dermal absorption means passing through the
skin.

Dermal contact
Contact with (touching) the skin [see route of exposure].

Descriptive epidemiology
The study of the amount and distribution of a disease in a specified population
by person, place, and time.

Detection limit
The lowest concentration of a chemical that can reliably be distinguished from a
zero concentration.

Disease prevention
Measures used to prevent a disease or reduce its severity.

Disease registry
A system of ongoing registration of all cases of a particular disease or health
condition in a defined population.

DOD
United States Department of Defense.

DOE
United States Department of Energy.

Dose (for chemicals that are not radioactive)
The amount of a substance to which a person is exposed over some time period.
Dose is a measurement of exposure. Dose is often expressed as milligram (amount)
per kilogram (a measure of body weight) per day (a measure of time) when people
eat or drink contaminated water, food, or soil. In general, the greater the
dose, the greater the likelihood of an effect. An “exposure dose” is how much of
a substance is encountered in the environment. An “absorbed dose” is the amount
of a substance that actually got into the body through the eyes, skin, stomach,
intestines, or lungs.

Dose (for radioactive chemicals)
The radiation dose is the amount of energy from radiation that is actually
absorbed by the body. This is not the same as measurements of the amount of
radiation in the environment.

Dose-response relationship
The relationship between the amount of exposure [dose] to a substance and the
resulting changes in body function or health (response).

Environmental media
Soil, water, air, biota (plants and animals), or any other parts of the
environment that can contain contaminants.

Environmental media and transport mechanism
Environmental media include water, air, soil, and biota (plants and animals).
Transport mechanisms move contaminants from the source to points where human
exposure can occur. The environmental media and transport mechanism is the
second part of an exposure pathway.

EPA
United States Environmental Protection Agency.

Epidemiologic surveillance [see Public health surveillance].

Epidemiology
The study of the distribution and determinants of disease or health status in a
population; the study of the occurrence and causes of health effects in humans.

Exposure
Contact with a substance by swallowing, breathing, or touching the skin or eyes.
Exposure may be short-term [acute exposure], of intermediate duration, or
long-term [chronic exposure].

Exposure assessment
The process of finding out how people come into contact with a hazardous
substance, how often and for how long they are in contact with the substance,
and how much of the substance they are in contact with.

Exposure-dose reconstruction
A method of estimating the amount of people’s past exposure to hazardous
substances. Computer and approximation methods are used when past information is
limited, not available, or missing.

Exposure investigation
The collection and analysis of site-specific information and biologic tests
(when appropriate) to determine whether people have been exposed to hazardous
substances.

Exposure pathway
The route a substance takes from its source (where it began) to its end point
(where it ends), and how people can come into contact with (or get exposed to)
it. An exposure pathway has five parts: a source of contamination (such as an
abandoned business); an environmental media and transport mechanism (such as
movement through groundwater); a point of exposure (such as a private well); a
route of exposure (eating, drinking, breathing, or touching), and a receptor
population (people potentially or actually exposed). When all five parts are
present, the exposure pathway is termed a completed exposure pathway.

Exposure registry
A system of ongoing followup of people who have had documented environmental
exposures.

Feasibility study
A study by EPA to determine the best way to clean up environmental
contamination. A number of factors are considered, including health risk, costs,
and what methods will work well.

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Geographic information system (GIS)
A mapping system that uses computers to collect, store, manipulate, analyze, and
display data. For example, GIS can show the concentration of a contaminant
within a community in relation to points of reference such as streets and homes.

Grand rounds
Training sessions for physicians and other health care providers about health
topics.

Groundwater
Water beneath the earth’s surface in the spaces between soil particles and
between rock surfaces [compare with surface water].

Half-life (t½)
The time it takes for half the original amount of a substance to disappear. In
the environment, the half-life is the time it takes for half the original amount
of a substance to disappear when it is changed to another chemical by bacteria,
fungi, sunlight, or other chemical processes. In the human body, the half-life
is the time it takes for half the original amount of the substance to disappear,
either by being changed to another substance or by leaving the body. In the case
of radioactive material, the half life is the amount of time necessary for one
half the initial number of radioactive atoms to change or transform into another
atom (that is normally not radioactive). After two half lives, 25% of the
original number of radioactive atoms remain.

Hazard
A source of potential harm from past, current, or future exposures.

Hazardous Substance Release and Health Effects Database (HazDat)
The scientific and administrative database system developed by ATSDR to manage
data collection, retrieval, and analysis of site-specific information on
hazardous substances, community health concerns, and public health activities.

Hazardous waste
Potentially harmful substances that have been released or discarded into the
environment.

Health consultation
A review of available information or collection of new data to respond to a
specific health question or request for information about a potential
environmental hazard. Health consultations are focused on a specific exposure
issue. Health consultations are therefore more limited than a public health
assessment, which reviews the exposure potential of each pathway and chemical
[compare with public health assessment].

Health education
Programs designed with a community to help it know about health risks and how to
reduce these risks.

Health investigation
The collection and evaluation of information about the health of community
residents. This information is used to describe or count the occurrence of a
disease, symptom, or clinical measure and to evaluate the possible association
between the occurrence and exposure to hazardous substances.

Health promotion
The process of enabling people to increase control over, and to improve, their
health.

Health statistics review
The analysis of existing health information (i.e., from death certificates,
birth defects registries, and cancer registries) to determine if there is excess
disease in a specific population, geographic area, and time period. A health
statistics review is a descriptive epidemiologic study.

Indeterminate public health hazard
The category used in ATSDR’s public health assessment documents when a
professional judgment about the level of health hazard cannot be made because
information critical to such a decision is lacking.

Incidence
The number of new cases of disease in a defined population over a specific time
period [contrast with prevalence].

Ingestion
The act of swallowing something through eating, drinking, or mouthing objects. A
hazardous substance can enter the body this way [see route of exposure].

Inhalation
The act of breathing. A hazardous substance can enter the body this way [see
route of exposure].

Intermediate duration exposure
Contact with a substance that occurs for more than 14 days and less than a year
[compare with acute exposure and chronic exposure].

In vitro
In an artificial environment outside a living organism or body. For example,
some toxicity testing is done on cell cultures or slices of tissue grown in the
laboratory, rather than on a living animal [compare with in vivo].

In vivo
Within a living organism or body. For example, some toxicity testing is done on
whole animals, such as rats or mice [compare with in vitro].

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Lowest-observed-adverse-effect level (LOAEL)
The lowest tested dose of a substance that has been reported to cause harmful
(adverse) health effects in people or animals.

 

Medical monitoring
A set of medical tests and physical exams specifically designed to evaluate
whether an individual’s exposure could negatively affect that person’s health.

Metabolism
The conversion or breakdown of a substance from one form to another by a living
organism.

Metabolite
Any product of metabolism.

mg/kg
Milligram per kilogram.

mg/cm2
Milligram per square centimeter (of a surface).

mg/m3
Milligram per cubic meter; a measure of the concentration of a chemical in a
known volume (a cubic meter) of air, soil, or water.

Migration
Moving from one location to another.

Minimal risk level (MRL)
An ATSDR estimate of daily human exposure to a hazardous substance at or below
which that substance is unlikely to pose a measurable risk of harmful (adverse),
noncancerous effects. MRLs are calculated for a route of exposure (inhalation or
oral) over a specified time period (acute, intermediate, or chronic). MRLs
should not be used as predictors of harmful (adverse) health effects [see
reference dose].

Morbidity
State of being ill or diseased. Morbidity is the occurrence of a disease or
condition that alters health and quality of life.

Mortality
Death. Usually the cause (a specific disease, a condition, or an injury) is
stated.

Mutagen
A substance that causes mutations (genetic damage).

Mutation
A change (damage) to the DNA, genes, or chromosomes of living organisms.

National Priorities List for Uncontrolled Hazardous Waste Sites (National
Priorities List or NPL)
EPA’s list of the most serious uncontrolled or abandoned hazardous waste sites
in the United States. The NPL is updated on a regular basis.

National Toxicology Program (NTP)
Part of the Department of Health and Human Services. NTP develops and carries
out tests to predict whether a chemical will cause harm to humans.

No apparent public health hazard
A category used in ATSDR’s public health assessments for sites where human
exposure to contaminated media might be occurring, might have occurred in the
past, or might occur in the future, but where the exposure is not expected to
cause any harmful health effects.

No-observed-adverse-effect level (NOAEL)
The highest tested dose of a substance that has been reported to have no harmful
(adverse) health effects on people or animals.

No public health hazard
A category used in ATSDR’s public health assessment documents for sites where
people have never and will never come into contact with harmful amounts of
site-related substances.

NPL [see National Priorities List for Uncontrolled Hazardous Waste Sites]

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Physiologically based pharmacokinetic model (PBPK model)
A computer model that describes what happens to a chemical in the body. This
model describes how the chemical gets into the body, where it goes in the body,
how it is changed by the body, and how it leaves the body.

Pica
A craving to eat nonfood items, such as dirt, paint chips, and clay. Some
children exhibit pica-related behavior.

Plume
A volume of a substance that moves from its source to places farther away from
the source. Plumes can be described by the volume of air or water they occupy
and the direction they move. For example, a plume can be a column of smoke from
a chimney or a substance moving with groundwater.

Point of exposure
The place where someone can come into contact with a substance present in the
environment [see exposure pathway].

Population
A group or number of people living within a specified area or sharing similar
characteristics (such as occupation or age).

Potentially responsible party (PRP)
A company, government, or person legally responsible for cleaning up the
pollution at a hazardous waste site under Superfund. There may be more than one
PRP for a particular site.

ppb
Parts per billion.

ppm
Parts per million.

Prevalence
The number of existing disease cases in a defined population during a specific
time period [contrast with incidence].

Prevalence survey
The measure of the current level of disease(s) or symptoms and exposures through
a questionnaire that collects self-reported information from a defined
population.

Prevention
Actions that reduce exposure or other risks, keep people from getting sick, or
keep disease from getting worse.

Public availability session
An informal, drop-by meeting at which community members can meet one-on-one with
ATSDR staff members to discuss health and site-related concerns.

Public comment period
An opportunity for the public to comment on agency findings or proposed
activities contained in draft reports or documents. The public comment period is
a limited time period during which comments will be accepted.

Public health action
A list of steps to protect public health.

Public health advisory
A statement made by ATSDR to EPA or a state regulatory agency that a release of
hazardous substances poses an immediate threat to human health. The advisory
includes recommended measures to reduce exposure and reduce the threat to human
health.

Public health assessment (PHA)
An ATSDR document that examines hazardous substances, health outcomes, and
community concerns at a hazardous waste site to determine whether people could
be harmed from coming into contact with those substances. The PHA also lists
actions that need to be taken to protect public health [compare with health
consultation].

Public health hazard
A category used in ATSDR’s public health assessments for sites that pose a
public health hazard because of long-term exposures (greater than 1 year) to
sufficiently high levels of hazardous substances or radionuclides that could
result in harmful health effects.

Public health hazard categories
Public health hazard categories are statements about whether people could be
harmed by conditions present at the site in the past, present, or future. One or
more hazard categories might be appropriate for each site. The five public
health hazard categories are no public health hazard, no apparent public health
hazard, indeterminate public health hazard, public health hazard, and urgent
public health hazard.

Public health statement
The first chapter of an ATSDR toxicological profile. The public health statement
is a summary written in words that are easy to understand. The public health
statement explains how people might be exposed to a specific substance and
describes the known health effects of that substance.

Public health surveillance
The ongoing, systematic collection, analysis, and interpretation of health data.
This activity also involves timely dissemination of the data and use for public
health programs.

Public meeting
A public forum with community members for communication about a site.

Radioisotope
An unstable or radioactive isotope (form) of an element that can change into
another element by giving off radiation.

Radionuclide
Any radioactive isotope (form) of any element.

RCRA [see Resource Conservation and Recovery Act (1976, 1984)]

Receptor population
People who could come into contact with hazardous substances [see exposure
pathway].

Reference dose (RfD)
An EPA estimate, with uncertainty or safety factors built in, of the daily
lifetime dose of a substance that is unlikely to cause harm in humans.

Registry
A systematic collection of information on persons exposed to a specific
substance or having specific diseases [see exposure registry and disease
registry].

Remedial investigation
The CERCLA process of determining the type and extent of hazardous material
contamination at a site.

Resource Conservation and Recovery Act (1976, 1984) (RCRA)
This Act regulates management and disposal of hazardous wastes currently
generated, treated, stored, disposed of, or distributed.

RFA
RCRA Facility Assessment. An assessment required by RCRA to identify potential
and actual releases of hazardous chemicals.

RfD [see reference dose]

Risk
The probability that something will cause injury or harm.

Risk reduction
Actions that can decrease the likelihood that individuals, groups, or
communities will experience disease or other health conditions.

Risk communication
The exchange of information to increase understanding of health risks.

Route of exposure
The way people come into contact with a hazardous substance. Three routes of
exposure are breathing [inhalation], eating or drinking [ingestion], or contact
with the skin [dermal contact].

Safety factor [see uncertainty factor]

SARA [see Superfund Amendments and Reauthorization Act]

Sample
A portion or piece of a whole. A selected subset of a population or subset of
whatever is being studied. For example, in a study of people the sample is a
number of people chosen from a larger population [see population]. An
environmental sample (for example, a small amount of soil or water) might be
collected to measure contamination in the environment at a specific location.

Sample size
The number of units chosen from a population or an environment.

Solvent
A liquid capable of dissolving or dispersing another substance (for example,
acetone or mineral spirits).

Source of contamination
The place where a hazardous substance comes from, such as a landfill, waste
pond, incinerator, storage tank, or drum. A source of contamination is the first
part of an exposure pathway.

Special populations
People who might be more sensitive or susceptible to exposure to hazardous
substances because of factors such as age, occupation, sex, or behaviors (for
example, cigarette smoking). Children, pregnant women, and older people are
often considered special populations.

Stakeholder
A person, group, or community who has an interest in activities at a hazardous
waste site.

Statistics
A branch of mathematics that deals with collecting, reviewing, summarizing, and
interpreting data or information. Statistics are used to determine whether
differences between study groups are meaningful.

Substance
A chemical.

Substance-specific applied research
A program of research designed to fill important data needs for specific
hazardous substances identified in ATSDR’s toxicological profiles. Filling these
data needs would allow more accurate assessment of human risks from specific
substances contaminating the environment. This research might include human
studies or laboratory experiments to determine health effects resulting from
exposure to a given hazardous substance.

Superfund [see Comprehensive Environmental Response, Compensation, and Liability
Act of 1980 (CERCLA) and Superfund Amendments and Reauthorization Act (SARA)

Superfund Amendments and Reauthorization Act (SARA)
In 1986, SARA amended the Comprehensive Environmental Response, Compensation,
and Liability Act of 1980 (CERCLA) and expanded the health-related
responsibilities of ATSDR. CERCLA and SARA direct ATSDR to look into the health
effects from substance exposures at hazardous waste sites and to perform
activities including health education, health studies, surveillance, health
consultations, and toxicological profiles.

Surface water
Water on the surface of the earth, such as in lakes, rivers, streams, ponds, and
springs [compare with groundwater].

Surveillance [see public health surveillance]

Survey
A systematic collection of information or data. A survey can be conducted to
collect information from a group of people or from the environment. Surveys of a
group of people can be conducted by telephone, by mail, or in person. Some
surveys are done by interviewing a group of people [see prevalence survey].

Synergistic effect
A biologic response to multiple substances where one substance worsens the
effect of another substance. The combined effect of the substances acting
together is greater than the sum of the effects of the substances acting by
themselves [see additive effect and antagonistic effect].

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Teratogen
A substance that causes defects in development between conception and birth. A
teratogen is a substance that causes a structural or functional birth defect.

Toxic agent
Chemical or physical (for example, radiation, heat, cold, microwaves) agents
that, under certain circumstances of exposure, can cause harmful effects to
living organisms.

Toxicological profile
An ATSDR document that examines, summarizes, and interprets information about a
hazardous substance to determine harmful levels of exposure and associated
health effects. A toxicological profile also identifies significant gaps in
knowledge on the substance and describes areas where further research is needed.

Toxicology
The study of the harmful effects of substances on humans or animals.

Tumor
An abnormal mass of tissue that results from excessive cell division that is
uncontrolled and progressive. Tumors perform no useful body function. Tumors can
be either benign (not cancer) or malignant (cancer).

Uncertainty factor
Mathematical adjustments for reasons of safety when knowledge is incomplete. For
example, factors used in the calculation of doses that are not harmful (adverse)
to people. These factors are applied to the lowest-observed-adverse-effect-level
(LOAEL) or the no-observed-adverse-effect-level (NOAEL) to derive a minimal risk
level (MRL). Uncertainty factors are used to account for variations in people’s
sensitivity, for differences between animals and humans, and for differences
between a LOAEL and a NOAEL. Scientists use uncertainty factors when they have
some, but not all, the information from animal or human studies to decide
whether an exposure will cause harm to people [also sometimes called a safety
factor].

Urgent public health hazard
A category used in ATSDR’s public health assessments for sites where short-term
exposures (less than 1 year) to hazardous substances or conditions could result
in harmful health effects that require rapid intervention.

Volatile organic compounds (VOCs)
Organic compounds that evaporate readily into the air. VOCs include substances
such as benzene, toluene, methylene chloride, and methyl chloroform.

 

Other glossaries and dictionaries:

Environmental Protection AgencyExternal

National Library of Medicine (NIH)External


Page last reviewed: January 1, 2009
Content source: Agency for Toxic Substances and Disease Registry
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