Exposure to a chemical for a short duration of time. The U.S.
Environmental Protection Agency (EPA) defines this duration as less than or
equal to 24 hours; the Agency for Toxic Substances and Disease Registry (ATSDR)
defines the duration as 1-14 days.
Agency for Toxic Substances and Disease Registry (ATSDR):
A federal governmental
agency within the U.S. Department of Health and Human Services whose mission
is to take responsive public health actions and provide health information to
prevent harmful exposures and disease related to toxic substances.
Ambient:
Surrounding environment. "Ambient air" and "outside
air" are used interchangeably.
American Conference of Governmental Industrial Hygienists (ACGIH):
A voluntary
member-based organization of professional industrial hygiene personnel in governmental
or educational institutions whose purpose is to advance worker health and safety.
Arizona Ambient Air Quality Guidelines (AAAQG):
Draft residential screening
values for contaminants in ambient air developed by the Arizona Department of
Health Services (ADHS). Contaminant concentrations that exceed the Arizona Ambient
Air Quality Guidelines should be evaluated further to determine if they present
a true health risk.
Arizona Department of Health Services (ADHS):
The Arizona state agency whose
mission is to protect and ensure the health of the state's population.
Ceiling limit:
The maximum allowable exposure limit for an airborne chemical,
which is not to be exceeded even momentarily.
Chronic exposure:
Repeated exposure or contact with a toxic substance over a
long period. The U.S. Environmental Protection Agency defines this period as
a significant fraction of the animal's or human's lifetime. The Agency for Toxic
Substances and Disease Registry defines chronic exposure as greater than 364
days.
Comparison value (CV):
Media-specific screening chemical concentrations developed
by the Agency for Toxic Substances and Disease Registry that are used by health
assessors to select environmental contaminants for further evaluation.
Criteria air pollutants:
Six widespread and common air pollutants regulated
by the U.S. Environmental Protection Agency by standards to protect public health
or the environment. The six criteria pollutants are carbon monoxide, lead, nitrogen
dioxide, ozone, particulate matter, and sulfur dioxide.
Exposure:
Contact made between a chemical, physical, or biological agent and
the outer boundary of an organism. Exposure is quantified as the amount of an
agent available at the exchange boundaries of the organism (e.g., skin, lungs,
gut).
Hazardous air pollutants (HAPs):
One of the chemicals listed in section 112(b)
of the Clean Air Act Amendments of 1990. Hazardous air pollutants are pollutants
known or suspected to cause cancer or other serious health effects or adverse
environmental effects. Hazardous air pollutants are regulated by the U.S. Environmental
Protection Agency using technology-based standards.
Intermediate exposure:
The Agency for Toxic Substances and Disease Registry
defines intermediate exposure as spanning 15-364 days.
Lower explosive limit:
The lowest concentration of a substance in air that will
produce a fire or flash when an ignition source (flame, spark, etc.) is present.
It is expressed in percent of vapor or gas in the air by volume.
Lowest-observed-adverse-effect level (LOAEL):
From the U.S. Environmental Protection
Agency-the lowest dose of chemical that produces statistically or biologically
significant increases in frequency or severity of adverse effects between the
exposed population and its appropriate control group.
Milligrams per cubic meter (mg/m3):
A way of expressing the concentration of dusts, gases, aerosols, or mists
in the air. A milligram (mg) is a unit of weight in the metric system–1,000
milligrams equals 1 gram. A cubic meter (m3) is a volume measurement
in the metric system–1 m3 is about 35.3 cubic feet or 1.3
cubic yards.
Minimal risk level (MRL):
An estimate of the daily human exposure to a hazardous
substance that is likely to be without appreciable risk of adverse noncancer
health effects over a specified duration of exposure. Minimal risk levels are
developed by the Agency for Toxic Substances and Disease Registry.
National Institute for Occupational Safety and Health (NIOSH):
A federal governmental
agency which tests and certifies respiratory devices, recommends occupational
exposure limits, and assists the Occupational Safety and Health Administration
(OSHA) by conducting research and investigations. The National Institute for
Occupational Safety and Health is part of the Centers for Disease Control and
Prevention in the U.S. Department of Health and Human Services.
No-observed-adverse-effect level (NOAEL):
From the U.S. Environmental Protection
Agency- the dose of chemical at which there are no statistically or biologically
significant increases in frequency or severity of adverse effects between the
exposed population and its appropriate control group; some effects may be produced
at this dose, but they are not considered to be adverse, nor precursors to adverse
effects.
Occupational Safety and Health Administration (OSHA):
A federal government agency
within the U.S. Department of Labor that develops and enforces occupational
safety and health standards for most industry and businesses in the United States.
Odor threshold:
The lowest concentration of a substance's vapor, in air, that
a person can detect by smell. Odor thresholds are highly variable, depending
on the individual and the nature of the substance.
pH:
A measure of how acidic or basic (caustic) a substance is on a scale of
1 (very acidic) to 14 (very basic); pH 7 indicates that the substance is neutral.
Parts per million (ppm):
A measurement used to express very small concentrations
of a given substance present in a mixture; often used as a unit to measure the
parts (by volume) of a gas or vapor in a million parts of air.
Peak:
Maximum one-time exposure, usually 10 minutes. No other exposure is allowed.
(Occupational Safety and Health Administration standard)
Permissible exposure limit (PEL):
An exposure limit that is published and enforced
by the Occupational Safety and Health Administration as a legal standard. A
permissible exposure limit may be either a time-weighted-average (TWA) exposure
limit (8 hour), a 15-minute short-term exposure limit (STEL), or a ceiling limit
(CL).
Recommended exposure level (REL):
An 8- or 10-hour time-weighted-average or
ceiling limit exposure concentration recommended by the National Institute for
Occupational Safety and Health that is based on an evaluation on health effects
data.
Reference concentration (RfC):
An estimate (with uncertainty spanning perhaps an order of magnitude) of a
continuous inhalation exposure to the human population that is likely to be
without risk of deleterious effects during a lifetime. It can be derived from
a no-observed- adverse-effect-level (NOAEL), lowest-observed-adverse-effect-level
(LOAEL), or benchmark concentration, with uncertainty factors generally applied
to reflect limitations of the data used. Reference concentrations are generally
used in the U.S. Environmental Protection Agency's noncancer health assessments
and expressed in milligrams per cubic meter (mg/m3).
Short-term exposure limit (STEL):
The maximum concentration to which workers
can be exposed for up to 15 minutes continually. There may be no more than four
exposure periods per day, and there must be at least 1 hour between exposure
periods. The daily time-weighted-average may not be exceeded, however.
Threshold limit value (TLV):
Recommended guidelines for occupational exposure
to airborne contaminants published by the American Conference of Governmental
Industrial Hygienists. Threshold limit values represent the average concentrations
in milligrams per cubic meter for an 8-hour workday and a 40-hour workweek to
which nearly all workers may be repeatedly exposed, day after day, without adverse
effect.
Total reduced sulfur (TRS):
All reduced sulfur compounds including but not limited
to hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide.
Time-weighted average (TWA):
An allowable exposure concentration averaged over
a normal 8-hour workday or 40-hour workweek.
Uncertainty factor (UF):
One of several, generally 10-fold factors, used in
deriving the reference concentration from experimental data. Uncertainty factors
are intended to account for: 1) the variation in sensitivity among the members
of the human population; 2) the uncertainty in extrapolating animal data to
humans; 3) the uncertainty of extrapolating from data obtained in a study that
is less than lifetime exposure to lifetime exposure, i.e., extrapolating from
subchronic to chronic exposure; 4) the uncertainty in extrapolating from an
lowest-observed-adverse-effect-level (LOAEL) rather than from a no-observed-adverse-effect-level
(NOAEL); and 5) the uncertainty of extrapolating from animal data when the database
is incomplete.
U.S. Environmental Protection Agency (EPA):
The federal agency whose mission is to protect human health and safeguard
the natural environment–air, land, and water.
