This glossary defines words used by ATSDR in communications with the public. It is not a complete dictionary of environmental health 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 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.
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.
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].
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]
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].
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 Agency (http://www.epa.gov/OCEPAterms/)
National Library of Medicine (NIH) (http://www.nlm.nih.gov/medlineplus/mplusdictionary.html)