Occurring over a short time (compare with chronic).
Agency for Toxic Substances and Disease Registry
(ATSDR):
The principal federal public health agency involved with hazardous waste
issues, responsible for preventing or reducing the harmful effects that
exposure to hazardous substances has on human health and quality of life.
ATSDR is part of the U.S. Department of Health and Human Services.
Aquifer:
An underground formation consisting of materials such as sand, soil, or
gravel that can store and/or supply groundwater to wells and springs.
Cancer Risk Evaluation Guide (CREG):
The concentration of a chemical in air, soil, or water that is expected
to cause no more than one excess cancer case in a million persons exposed
over a lifetime. The CREG is a comparison value used to select
contaminants of potential health concern and is based on the cancer
slope factor.
Cancer Slope Factor (CSF):
A number assigned to a cancer-causing chemical that estimates its potential
to cause cancer in humans.
Carcinogen:
Any substance that causes cancer.
Chronic:
Occurring over a long time (more than 1 year) (compare with acute).
Comparison value:
Calculated concentration of a substance in air, water, food, or soil
that is unlikely to cause harmful (adverse) health effects in exposed persons.
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.
Contaminant:
A substance that is present either in an environment where it does not
belong or at levels that might cause harmful (adverse) health effects.
Dose (for chemicals that are not radioactive):
The amount of a substance to which a person is exposed over a given time
period. Dose is a measurement of exposure. Dose is often expressed as milligrams
(amount) of a substance encountered or consumed per kilogram (a measure
of body weight) per day (a measure of time). 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.
Environmental Media Evaluation Guide (EMEG):
A concentration in air, soil, or water below which adverse non-cancer
health effects are not expected to occur. The EMEG is a comparison value
used to select contaminants of potential health concern and is based on
ATSDR's minimal risk level (MRL).
Environmental Protection Agency (EPA):
The federal agency that develops and enforces environmental laws to protect
the environment and the public's health.
Exposure:
Contact with a substance through swallowing, breathing, or touching (skin
or eyes). Exposure may be short-term (acute exposure),
of intermediate duration, or long-term (chronic exposure).
Groundwater:
Water beneath the earth's surface in the spaces between soil particles
and between rock surfaces (compare with surface water).
Ingestion:
The act of absorbing something by eating, drinking, or mouthing. A hazardous
substance can enter the body this way (see route of exposure).
Ingestion rate:
The amount of an environmental medium that could typically be ingested
on a daily basis. Units for IR are usually liters/day for water and milligrams/day
for soil.
Lowest Observed Adverse Effect Level (LOAEL):
The lowest tested dose of a substance that has been reported to cause
harmful (adverse) health effects in persons or animals.
Maximum Contaminant Level (MCL):
A drinking water regulation established by the federal Safe Drinking Water
Act. It is the maximum permissible concentration of a contaminant in water
that can be delivered to the free flowing outlet of the ultimate user of
a public water system. MCLs are enforceable standards.
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).
Monitoring wells:
Special wells drilled at locations on or off a hazardous waste site so
that water can be sampled at selected depths and studied to determine the
movement of groundwater and the amount, distribution, and type of contaminant.
No apparent public health hazard:
A category used in ATSDR's public health assessments for sites at which
human exposure to contaminated media might be occurring, might have occurred
in the past, or might occur in the future, but at which 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 persons or animals.
No public health hazard:
A category used in ATSDR's public health assessment documents for sites
at which persons have never and will never come into contact with harmful
amounts of site-related substances.
Oral Reference Dose (RfD):
An amount of chemical ingested into the body (i.e., dose) below which
health effects are not expected to occur. EPA publishes RfDs.
Parts per billion (ppb)/Parts per million (ppm):
Units commonly used to express low concentrations of contaminants. For
example, 1 ounce of trichloroethylene (TCE) in 1 million ounces of water
is 1 ppm. 1 ounce of TCE in 1 billion ounces of water is 1 ppb. If one drop
of TCE is mixed in a competition-size swimming pool, the water will contain
about 1 ppb of TCE.
Plume:
The volume of a substance that moves from its source to places 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.
Remedial investigation:
The CERCLA process for determining the type and extent of hazardous material
contamination at a site.
Route of exposure:
The way persons come into contact with hazardous substances. Three routes
of exposure are breathing [inhalation], eating or drinking [ingestion], and
contact with the skin [dermal contact].
