ATSDR Glossary of Terms
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,
1-888-422-8737.
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General Terms
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 Service.
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.
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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.
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