Safe Drinking Water Act maximum contaminant level goal
MRL
ATSDR minimal risk level
µg
microgram
mg
milligram
MTCA
Department of Ecology Model Toxics Cleanup Act regulation
NOAEL
no observed adverse effect level
ppb
parts per billion
ppm
parts per million
PAHs
polycyclic aromatic hydrocarbons
PHA
public health assessment
RfD
oral reference dose
RMEG
ATSDR reference dose media evaluation guide
RI
remedial investigation
RCRA
Resource Conservation and Recovery Act
SVE
soil vapor extraction
USGS
United States Geological Survey
VOC
volatile organic compound
GLOSSARY
Acute:
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).
Epidemiology :
The study of the occurrence and causes of health effects in human populations. An epidemiological
study often compares two groups of people who are alike except for one factor, such as exposure to a
chemical or the presence of a health effect. The investigators try to determine if any factor (i.e., age,
sex, occupation, economic status) is associated with the health effect.
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.
Inorganic :
Compounds composed of mineral materials, including elemental salts and metals such as iron, aluminum, mercury, and zinc.
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.
Model Toxics Control Act (MTCA) :
The hazardous waste clean-up law for Washington State.
Monitoring wells :
Special wells drilled at locations on or off a hazardous waste site so 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 :
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.
No observed adverse effect level (NOAEL) :
The dose of a chemical at which there were no statistically or biologically significant increases in
frequency or severity of adverse effects seen between the exposed population and its appropriate
control. Effects might be observed at this dose but were judged not to be "adverse."
No public health hazard :
Sites for which data indicate no current or past exposure or no potential for exposure and therefore
no 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 EPA.
Organic :
Compounds composed of carbon, including materials such as solvents, oils, and pesticides, which
are not easily dissolved in water.
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.
Reference dose media evaluation guide (RMEG) :
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 EPA's oral reference dose (RfD).
Remedial investigation :
A study designed to collect the data necessary to determine the nature and extent of contamination at
a site.
Route of exposure :
The way in which a person might contact a chemical substance that includes ingestion, skin contact,
and breathing.
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.
