Occurring over a short period of time. An acute exposure is one which lasts
for less than 2 weeks.
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 of exposure
to hazardous substances on human health and quality of life. ATSDR is part
of the U.S. Department of Health and Human Services.
Aquifer:
An underground formation composed 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 in 1 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
(CSF).
Cancer Slope Factor :
A number assigned to a cancer-causing chemical that is used to estimate
its ability to cause cancer in humans.
Carcinogen:
Any substance that can cause or contribute to the production of cancer.
Chronic :
A long period of time. A chronic exposure is one which lasts for a year
or longer.
Comparison value :
A concentration of a chemical in soil, air, or water that, if exceeded,
requires further evaluation as a contaminant of potential health concern.
The terms comparison value and screening level are often used synonymously.
Contaminant :
Any chemical that exists in the environment or living organisms that is
not normally found there.
Dose :
A dose is the amount of a substance that gets into the body through ingestion,
skin absorption, or inhalation. It is calculated per kilogram of body weight
per day.
Environmental Media Evaluation Guide (EMEG) :
A concentration in air, soil, or water below which adverse noncancer 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).
Exposure :
Contact with a chemical by swallowing, by breathing, or by direct contact
(such as through the skin or eyes). Exposure might be short-term (acute) or
long-term (chronic).
Groundwater :
Water found underground that fills pores between materials such as sand,
soil, or gravel. In aquifers, groundwater often occurs in quantities where
it can be used for drinking water, irrigation, and other purposes.
Hazardous substance :
Any material that poses a threat to public health and/or the environment.
Typical hazardous substances are materials that are toxic, corrosive, ignitable,
explosive, or chemically reactive.
Indeterminate public health hazard :
Sites for which no conclusions about public health hazard can be made because
data are lacking.
Ingestion rate :
The amount of an environmental medium which could be ingested typically
on a daily basis. Units for IR are usually liter/day for water, and mg/day
for soil.
Lowest Observed Adverse Effect Level (LOAEL) :
LOAELs have been classified into "less serious" or "serious" effects. In
dose-response experiments, the lowest exposure level at which there are statistically
or biologically significant increases in the frequency or severity of adverse
effects between the exposed population and its appropriate control.
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 is delivered to the free-flowing outlet of the ultimate user of a public
water system. MCLs are enforceable standards.
Media:
Soil, water, air, plants, animals, or any other part of the environment
that can contain contaminants.
Minimal Risk Level (MRL) :
An amount of chemical that gets into the body (i.e., dose) below which health
effects are not expected. MRLs are derived by ATSDR for acute, intermediate,
and chronic duration exposures by the inhalation and oral routes.
Monitoring wells :
Resource protection wells installed at locations on or off a hazardous waste
site so groundwater 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 :
Sites where human exposure to contaminated media is occurring or has occurred
in the past, but the exposure is below a level of health hazard.
Oral Reference Dose (RfD) :
An amount of chemical ingested into the body (i.e., dose) below which health
effects are not expected. RfDs are published by the U.S. Environmental Protection
Agency (EPA).
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 :
An area of contaminants in a specific media such as groundwater.
U.S. Environmental Protection Agency (EPA) :
Established in 1970 to bring together parts of various government agencies
involved with the control of pollution.
Volatile organic compound (VOC) :
An organic (carbon-containing) compound that evaporates (volatilizes) easily
at room temperature. A significant number of the VOCs are commonly used as
solvents.
