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Glossary of Terms
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Air Toxics:
Synonym for “hazardous air pollutants.” (See below).
Ambient Air:
Outdoor air, any unconfined portion of the atmosphere, open air
Asthma:
A chronic inflammatory disorder of the lungs. Symptoms include wheezing,
breathlessness, chest tightening, and cough.
Attention-Deficit/Hyperactivity Disorder (ADHD):
A disorder in which the prominent symptoms are hyperactivity, inattention,
and impulsivity. Also referred to as ADD (attention deficit disorder).
Benzene:
A colorless, volatile, flammable, toxic liquid aromatic hydrocarbon
(C6H6) used in organic synthesis, as a solvent, and as a component
of motor fuel. Benzene is a known human carcinogen and an important
hazardous air pollutant.
Cadmium:
A heavy metal used primarily for metal plating and coating operations,
in applications such as transportation equipment, machinery and
baking enamels, photography, and television phosphors. It also is
used in nickel-cadmium and solar batteries, and in pigments. It
also is found in cigarette smoke and is an important hazardous air
pollutant.
Carcinoma:
A form of cancer that begins in the tissues lining or covering
an organ.
Carbon Monoxide (CO):
A colorless, odorless, poisonous gas produced by incomplete combustion
of fossil fuels; one of the six “criteria” pollutants
for which EPA has set National Ambient Air Quality Standards under
the Clean Air Act.
Carbon Tetrachloride:
A manufactured compound, most often found as a colorless gas. Because
of its harmful effect on the ozone layer, the production and use
of carbon tetrachloride in industrialized nations was banned in
1996 under the Montreal Protocol on Substances that Deplete the
Ozone Layer. It is highly persistent and remains at levels of concern
in the environment in the United States; it is an important hazardous
air pollutant.
Cardiopulmonary Mortality:
Death due to malfunction of the heart and lungs; also refers to
the death rate from these causes.
Cardiovascular Effects:
Health effects related to the heart and circulatory system.
Chlorinated Dibenzofurans (CDFs):
A family of 135 individual compounds with varying harmful health
and environmental effects. CDFs typically are released to the environment
through the incineration of municipal and industrial waste, accidental
combustion of polychlorinated biphenyls (PCBs), and the manufacture
of certain metals and paper products.
Chromium:
A heavy metal that is an important hazardous air pollutant. (See
“heavy metals.”) It is used for making steel, dyes and
pigments, chrome plating, leather tanning, and wood preservation
Contaminant:
Any physical, chemical, biological, or radiological substance or
matter in air, water, or soil that can have adverse health effects.
Cotinine:
A major metabolite of nicotine found in blood and urine. Currently
regarded as the best biomarker for exposure of nonsmokers to environmental
tobacco smoke.
Criteria Pollutant:
One of the six pollutants for which EPA is required to set National
Ambient Air Quality Standards to protect human health and welfare.
Criteria pollutants include ozone (ground-level), carbon monoxide,
particulate matter, sulfur dioxide, lead, and nitrogen oxides. They
are called “criteria” pollutants because the Clean Air
Act required EPA to describe the criteria for setting or revising
standards.
Deciliter:
One-tenth of a liter (0.1 liter).
Diesel:
A petroleum-based fuel. Diesel exhaust is an important source of
particulates and other pollutants that adversely affect human health.
Dioxins:
A group of harmful chemical compounds that are released into the
air from combustion processes such as commercial or municipal waste
incineration and from burning fuels such as wood, coal, or oil.
Disinfection Byproducts:
Organic and inorganic compounds that often result from the reaction
between a disinfectant and naturally occurring materials in water;
chloroform is a commonly found example.
Down Syndrome:
A genetic condition usually caused by having an extra copy of the
21st chromosome. Also called trisomy 21.
Environmental Tobacco Smoke:
Mixture of smoke exhaled by a smoker and the smoke from the burning
end of the smoker’s cigarette, pipe, or cigar. Also known
as secondhand smoke. Environmental tobacco smoke is an important
indoor air pollutant.
Epidemiological Studies:
Studies that research the incidence, distribution, and control of
disease in a population.
Ewing’s Sarcoma:
A type of bone cancer that usually forms in the middle (shaft) of
large bones
Exacerbation of Asthma:
Increase in the frequency or severity of asthma attacks or symptoms
in individuals who have asthma.
Exposure:
Human contact with environmental contaminants in media including
air, water, soil, and food.
Formaldehyde:
A colorless, pungent-smelling gas; an important hazardous air pollutant.
High concentrations may trigger attacks in people with asthma. Sources
include environmental tobacco smoke and other combustion sources;
pressed wood products (such as particle board); and certain textiles,
foams, and glues.
Gastrointestinal:
Relating to, affecting, or including the stomach and/or intestine.
Germ Cell Tumor:
A type of tumor found in the ovaries or testicles.
Gonadal Tumor:
Tumor specific to the gonads.
Ground level ozone:
Ground-level ozone (smog) is formed by a chemical reaction between
volatile organic pollutants (VOCs) and oxides of nitrogen (NOx)
in the presence of sunlight. Ozone concentrations can reach unhealthy
levels when the weather is hot and sunny with little or no wind.
Ozone at the ground level causes adverse effects on lung function
and other adverse respiratory effects. It is one of the six “criteria”
pollutants for which EPA has adopted National Ambient Air Quality
Standards.
Hazardous Air Pollutants:
Air pollutants identified in the Clean Air Act Amendments of 1990
as reasonably expected to cause or contribute to irreversible illness
or death. Such pollutants include asbestos, beryllium, mercury,
benzene, coke oven emissions, radionuclides, and vinyl chloride.
A total of 188 hazardous air pollutants are listed in section 112(b)
of the Clean Air Act, as amended in 1990. There are no ambient air
quality standards for these pollutants.
Heavy Metals:
Metallic elements with high atomic weights, e.g., mercury, chromium,
cadmium, arsenic, and lead; can damage living things at low concentrations.
Hodgkin’s Lymphoma:
A cancer of the lymphatic system that is characterized by enlargement
of lymph nodes, the spleen, or other lymphatic tissue.
Hypospadias:
A birth defect found in boys in which the urinary tract opening
is not located properly at the tip of the penis.
Immunodeficiency:
A disorder in which the immune system is reduced or absent.
Ionizing Radiation:
Radiation that can strip electrons from atoms, i.e., alpha, beta,
and gamma radiation. High doses can causes massive tissue damage;
lower doses can lead to cancer and harmful genetic mutations.
Leukemia:
A cancer in which the body produces a large number of abnormal blood
cells.
Lymphocytic Leukemia:
The most common form of childhood leukemia, also known as lymphoblastic
leukemia. In this disease, the bone marrow produces large quantities
of immature lymphocytes (white blood cells).
Lymphoma:
Lymphomas are tumors in the lymph system, which is responsible for
fighting diseases in the body and is part of the immune system.
Maximum Contaminant Level (MCL):
The highest level of a contaminant that is allowed in drinking water
as delineated by the National Primary Drinking Water Regulations.
These levels are based on consideration of health risks, technical
feasibility of treatment, and cost-benefit analysis.
Media:
Specific environments such as air, water, food, and soil.
Mercury:
A heavy metal that is highly toxic if breathed or swallowed. The
organic form of mercury, methylmercury, bioaccumulates in ecosystems
and can cause adverse effects on children exposed before birth or
adults at higher concentrations. The largest human-generated source
of mercury emissions in the United States is the burning of coal.
Other sources include the combustion of waste and industrial processes
that use mercury.
Methemoglobinemia:
A condition that reduces the ability of the blood to transport oxygen
throughout the body for essential metabolism; it is due to the replacement
of hemoglobin with methemoglobin in the blood. A small amount of
methemoglobin is present in the blood normally, but injury or toxic
agents—such as nitrites—convert a larger proportion
of hemoglobin into methemoglobin.
Methylmercury:
An organic form of mercury, created from metallic or elemental mercury
by bacteria in sediments. Methylmercury is easily absorbed into
the living tissue of aquatic organisms and is not easily eliminated.
Therefore, it accumulates in organisms at the top of food chains
such as tuna or humans. It can cause adverse effects in children
exposed before or after birth.
Microgram (µg):
One-millionth of a gram.
µg/dL:
Microgram per deciliter.
Microorganisms:
Tiny living organisms that can be seen only with the aid of a microscope.
Some microorganisms can cause acute health problems when consumed
in drinking water. Also known as microbes.
Monitoring and Reporting Violation:
Violation of monitoring and reporting requirements that specify
how and when water must be tested for the presence of contaminants
as defined by the Safe Drinking Water Act.
Mortality:
The number of deaths in a population, or death rate.
Myeloid Leukemia:
One form of cancer of the blood-forming tissue, primarily the bone
marrow and lymph nodes.
National Ambient Air Quality Standards
(NAAQS):
Standards established by EPA for maximum allowable concentrations
of six “criteria” pollutants in outdoor
air. The six pollutants are carbon monoxide, lead, ground-level
ozone, nitrogen dioxide, particulate matter, and sulfur dioxide.
The standards are set at a level that protects public health with
an adequate margin of safety.
National Priorities List:
List of sites under EPA’s Superfund program, which investigates
and cleans up hazardous sites nationwide. Sites on the National
Priorities List have undergone preliminary assessment and site inspection
and have been determined to require remediation due to potential
threats to persons living or working near the site.
Neuroblastomas:
Cancer that arises in immature nerve cells and affects mostly infants
and children.
Nitrates and Nitrites:
Nitrogen-oxygen chemical units that combine with various organic
and inorganic compounds. Once taken into the body, nitrates are
converted into nitrites. The greatest use of nitrates is as a fertilizer.
Other sources include animal manure and human sewage.
Nitrogen Dioxide (NO2):
A chemical that results from nitric oxide combining with oxygen
in the atmosphere; a major component of photochemical smog. One
of the six “criteria” pollutants for which EPA has set
national ambient air quality standards.
Nitrogen Oxides:
A family of highly reactive gases (including nitrogen dioxide, above)
that form when fuel is burned at high temperatures. Emitted principally
from motor vehicle exhaust and stationary sources such as electric
power plants and industrial boilers.
Non-Hodgkin’s Lymphoma:
A group of cancers of the lymphoid system.
Oral Cleft Defects:
An abnormal opening in a structure around the mouth and face. Clefts
may occur in the lip, the roof of the mouth (hard palate), or the
tissue in the back of the mouth (soft palate).
Organophosphate Pesticides:
A group of approximately 40 closely related pesticides that affect
functioning of the nervous system. Examples include chlorpyrifos,
phosmet, and methyl parathion.
Ozone:
A gas that results from complex chemical reactions between nitrogen
dioxide and volatile organic compounds; the major component of smog.
Ozone at the ground level is one of the six “criteria”
pollutants for which EPA has established national ambient air quality
standards.
Particulate Matter:
Particles in the air, such as dust, dirt, soot, smoke, and droplets.
Small particles (PM-10 or PM-2.5) have significant effects on human
health. Particulate matter is one of the six “criteria”
pollutants for which EPA has established national ambient air quality
standards.
Plasticizers:
Small, often volatile molecules that are added to hard, stiff plastics
to make them softer and more flexible.
Polychlorinated Biphenyls (PCBs):
A group of toxic, persistent chemicals used in electrical transformers
and capacitors for insulating purposes, and in gas pipeline systems
as a lubricant. The sale and new use of PCBs were banned by law
in 1979 although large reservoirs of PCBs remain in the environment.
Poverty Level:
An income level below which an individual or family is considered
poor. The U.S. Census Bureau defines poverty level based on a set
of money income thresholds that vary by family size and composition.
If a family’s total income is less than that family’s
threshold, then that family, and every individual in it, is considered
poor. The Census Bureau updates its poverty thresholds annually.
In 2000, a family of two adults and two children with total income
below $17,463 was considered below the poverty level. Tables showing
the Census Bureau’s poverty thresholds are available at http://www.census.gov/hhes/poverty/threshld.html. 
Prenatal:
Occurring, existing, or performed before birth.
Radionuclides:
Radioactive isotopes or unstable forms of elements.
Retinoblastomas:
Tumors of the eye.
Respiratory Effects:
Effects on the process of breathing or on the lungs.
Respiratory Mortality:
Death or the death rate due to respiratory illness.
Reference Dose (RfD):
Oral reference dose. EPA defines a reference dose as an estimate,
with uncertainty spanning perhaps an order of magnitude, of a daily
oral exposure to the human population (including sensitive subgroups)
that is likely to be without an appreciable risk of deleterious
effects during a lifetime.
Solvents:
Substances used to dissolve another substance. Some commonly used
solvents, such as TCE, are important environmental contaminants.
Sudden Infant Death Syndrome (SIDS):
The sudden and unexpected death of an apparently healthy infant,
without an apparent cause.
Sulfur Dioxide (SO2):
A pungent, colorless, gaseous pollutant formed primarily by the
combustion of fossil fuels. One of the six “criteria”
pollutants for which EPA has set national ambient air quality standards.
Superfund:
An EPA program to remediate sites contaminated by release of hazardous
substances. Activities include establishing a National Priorities
List, investigating sites for inclusion on the list, determining
their priority, and conducting and/or supervising cleanup and other
remedial actions. Superfund is operated under the legislative authority
of the Comprehensive Environmental Response, Compensation and Liability
Act of 1980 (CERCLA). Some remedial actions are funded directly
by Superfund, through a tax on chemical feedstocks, but the majority
are paid for by parties that are liable for the release of the hazardous
substances.
Trichloroethylene (TCE):
A stable, low boiling-point colorless liquid, toxic if inhaled.
Used as a solvent or metal decreasing agent, and in other industrial
applications.
Volatile Organic Pollutants:
Carbon-containing compounds that easily go from a solid to a gaseous
form at normal temperatures. Sources include household products
such as paints, paint strippers, and other solvents; wood preservatives;
aerosol sprays; cleansers and disinfectants; moth repellents and
air fresheners; stored fuels and automotive products; hobby supplies;
dry-cleaned clothing.
Wilms’ Tumor:
A kidney cancer that occurs in children usually younger than 5 years.