are listed prior to definitions.
As provided by the United States Environmental
Protection Agency and several other sources.
This database will continue to grow with your
MAC— Mobile Air Conditioner
MAPSIM— Mesoscale Air Pollution Simulation
MATC— Maximum Acceptable Toxic Concentration
MBAS— Methylene-Blue-Active Substances
MCL— Maximum Contaminant Level
MCLG— Maximum Contaminant Level Goal
MCS— Multiple Chemical Sensitivity
MDL— Method Detection Limit
MEC— Model Energy Code
MEI— Maximally (or most) Exposed Individual
MEP— Multiple Extraction Procedure
MHDDV— Medium Heavy-Duty Diesel Vehicle
MOBILE5A— Mobile Source Emission Factor
MOE— Margin Of Exposure
MOS— Margin of Safety
MP— Manufacturing-use Product; Melting
MPCA— Microbial Pest Control Agent
MPI— Maximum Permitted Intake
MPN— Maximum Possible Number
MPWC— Multiprocess Wet Cleaning
MRF— Materials Recovery Facility
MRID— Master Record Identification number
MRL— Maximum-Residue Limit (Pesticide
MSW— Municipal Solid Waste
MTD— Maximum Tolerated Dose
MUP— Manufacturing-Use Product
MWC— Machine Wet Cleaning
soil features such as root holes or desiccation
cracks that can create significant conduits
for movement of NAPL and dissolved contaminants,
or vapor-phase contaminants.
Magnetic Separation— Use
of magnets to separate ferrous materials from
mixed municipal waste stream.
Major Modification— This
term is used to define modifications of major
stationary sources of emissions with respect
to Prevention of Significant Deterioration
and New Source Review under the Clean Air
Major Stationary Sources—
Term used to determine the applicability of
Prevention of Significant Deterioration and
new source regulations. In a nonattainment
area, any stationary pollutant source with
potential to emit more than 100 tons per year
is considered a major stationary source. In
PSD areas the cutoff level may be either 100
or 250 tons, depending upon the source.
Majors— Larger publicly
owned treatment works (POTWs) with flows equal
to at least one million gallons per day (mgd)
or servicing a population equivalent to 10,000
persons; certain other POTWs having significant
water quality impacts.
Man-Made (Anthropogenic) Beta
Particle and Photon Emitters— All radionuclides
emitting beta particles and/or photons listed
in Maximum Permissible Body Burdens and Maximum
Permissible Concentrations of Radonuclides
in Air and Water for Occupational Exposure.
Management Plan— Under
the Asbestos Hazard Emergency Response Act
(AHERA), a document that each Local Education
Agency is required to prepare, describing
all activities planned and undertaken by a
school to comply with AHERA regulations, including
building inspections to identify asbestos-containing
materials, response actions, and operations
and maintenance programs to minimize the risk
Managerial Controls— Methods
of nonpoint source pollution control based
on decisions about managing agricultural wastes
or application times or rates for agrochemicals.
Mandatory Recycling— Programs
which by law require consumers to separate
trash so that some or all recyclable materials
are recovered for recycling rather than going
Manifest— A one-page form
used by haulers transporting waste that lists
EPA identification numbers, type and quantity
of waste, the generator it originated from,
the transporter that shipped it, and the storage
or disposal facility to which it is being
shipped. It includes copies for all participants
in the shipping process.
Manifest System— Tracking
of hazardous waste from “cradle-to-grave”
(generation through disposal) with accompanying
documents known as manifests.
Manual Separation— Hand
sorting of recyclable or compostable materials
A list of substances or component parts as
described by the maker of a coating, pesticide,
or other product containing chemicals or other
Manufacturing Use Product—
Any product intended (labeled) for formulation
or repackaging into other pesticide products.
Margin of Safety— Maximum
amount of exposure producing no measurable
effect in animals (or studied humans) divided
by the actual amount of human exposure in
Margin of Exposure (MOE)—
The ratio of the no-observed adverse-effect-level
to the estimated exposure dose.
Marine Sanitation Device—
Any equipment or process installed on board
a vessel to receive, retain, treat, or discharge
Marsh— A type of wetland
that does not accumulate appreciable peat
deposits and is dominated by herbaceous vegetation.
Marshes may be either fresh or saltwater,
tidal or non-tidal.
Material Category— In
the asbestos program, broad classification
of materials into thermal surfacing insulation,
surfacing material, and miscellaneous material.
Material Safety Data Sheet
(MSDS)— A compilation of information
required under the OSHA Communication Standard
on the identity of hazardous chemicals, health,
and physical hazards, exposure limits, and
precautions. Section 311 of SARA requires
facilities to submit MSDSs under certain circumstances.
Material Type— Classification
of suspect material by its specific use or
application; e.g., pipe insulation, fireproofing,
and floor tile.
Materials Recovery Facility
(MRF)— A facility that processes residentially
collected mixed recyclables into new products
available for market.
Maximally (or Most) Exposed
Individual— The person with the highest
exposure in a given population.
Maximum Acceptable Toxic Concentration—
For a given ecological effects test, the range
(or geometric mean) between the No Observable
Adverse Effect Level and the Lowest Observable
Adverse Effects Level.
Maximum Available Control Technology
(MACT)— The emission standard for sources
of air pollution requiring the maximum reduction
of hazardous emissions, taking cost and feasibility
into account. Under the Clean Air Act Amendments
of 1990, the MACT must not be less than the
average emission level achieved by controls
on the best performing 12 percent of existing
sources, by category of industrial and utility
Maximum Contaminant Level—
The maximum permissible level of a contaminant
in water delivered to any user of a public
system. MCLs are enforceable standards.
Maximum Contaminant Level Goal
(MCLG)— Under the Safe Drinking Water
Act, a non-enforceable concentration of a
drinking water contaminant, set at the level
at which no known or anticipated adverse effects
on human health occur and which allows an
adequate safety margin. The MCLG is usually
the starting point for determining the regulated
Maximum Contaminant Level.
Maximum Exposure Range—
Estimate of exposure or dose level received
by an individual in a defined population that
is greater than the 98th percentile dose for
all individuals in that population, but less
than the exposure level received by the person
receiving the highest exposure level.
Maximum Residue Level—
Comparable to a U.S. tolerance level, the
Maximum Residue Level the enforceable limit
on food pesticide levels in some countries.
Levels are set by the Codex Alimentarius Commission,
a United Nations agency managed and funded
jointly by the World Health Organization and
the Food and Agriculture Organization.
Maximum Tolerated Dose—
The maximum dose that an animal species can
tolerate for a major portion of its lifetime
without significant impairment or toxic effect
other than carcinogenicity.
Measure of Effect/ Measurement
Endpoint— A measurable characteristic
of ecological entity that can be related to
an assessment endpoint; e.g. a laboratory
test for eight species meeting certain requirements
may serve as a measure of effect for an assessment
endpoint, such as survival of fish, aquatic,
invertebrate or algal species under acute
Measure of Exposure— A
measurable characteristic of a stressor (such
as the specific amount of mercury in a body
of water) used to help quantify the exposure
of an ecological entity or individual organism.
Mechanical Aeration— Use
of mechanical energy to inject air into water
to cause a waste stream to absorb oxygen.
Using mechanical means to separate waste into
Random irregularities of fluid motion in air
caused by buildings or other nonthermal, processes.
Media— Specific environments—air,
water, soil—which are the subject of
regulatory concern and activities.
A periodic comprehensive review of a worker’s
health status; acceptable elements of such
surveillance program are listed in the Occupational
Safety and Health Administration standards
Medical Waste— Any solid
waste generated in the diagnosis, treatment,
or immunization of human beings or animals,
in research pertaining thereto, or in the
production or testing of biologicals, excluding
hazardous waste identified or listed under
40 CFR Part 261 or any household waste as
defined in 40 CFR Sub-section 261.4 (b)(1).
Medium-size Water System—
A water system that serves 3,300 to 50,000
Meniscus— The curved top
of a column of liquid in a small tube.
Mercury (Hg)— Heavy metal
that can accumulate in the environment and
is highly toxic if breathed or swallowed.
and lakes which contain moderate quantities
of nutrients and are moderately productive
in terms of aquatic animal and plant life.
Metabolites— Any substances
produced by biological processes, such as
those from pesticides.
Metalimnion— The middle
layer of a thermally stratified lake or reservoir.
In this layer there is a rapid decrease in
temperature with depth. Also called thermocline.
Methane— A colorless,
nonpoisonous, flammable gas created by anaerobic
decomposition of organic compounds. A major
component of natural gas used in the home.
Methanol— An alcohol that
can be used as an alternative fuel or as a
gasoline additive. It is less volatile than
gasoline; when blended with gasoline it lowers
the carbon monoxide emissions but increases
hydrocarbon emissions. Used as pure fuel,
its emissions are less ozone-forming than
those from gasoline. Poisonous to humans and
animals if ingested.
Method 18— An EPA test
method which uses gas chromatographic techniques
to measure the concentration of volatile organic
compounds in a gas stream.
Method 24— An EPA reference
method to determine density, water content
and total volatile content (water and VOC)
Method 25— An EPA reference
method to determine the VOC concentration
in a gas stream.
that causes adverse health effects in domestic
water supplies and is toxic to freshwater
and marine aquatic life.
Methyl Orange Alkalinity—
A measure of the total alkalinity in a water
sample in which the color of methyl orange
reflects the change in level.
Microbial Growth— The
amplification or multiplication of microorganisms
such as bacteria, algae, diatoms, plankton,
A microorganism that is used to kill a pest,
but is of minimum toxicity to humans.
Microclimate— 1. Localized
climate conditions within an urban area or
neighborhood. 2. The climate around a tree
or shrub or a stand of trees.
A method for sequentially assessing exposure
for a series of microenvironments that can
be approximated by constant concentrations
of a stressor.
surroundings such as the home, office, or
kitchen that can be treated as uniform in
terms of stressor concentration.
Million-Gallons Per Day (MGD)—
A measure of water flow.
Minimization— A comprehensive
program to minimize or eliminate wastes, usually
applied to wastes at their point of origin.
Mining of an Aquifer—
Withdrawal over a period of time of ground
water that exceeds the rate of recharge of
Mining Waste— Residues
resulting from the extraction of raw materials
from the earth.
Minor Source— New emissions
sources or modifications to existing emissions
sources that do not exceed NAAQS emission
Minors— Publicly owned
treatment works with flows less than 1 million
gallons per day.
Miscellaneous ACM— Interior
asbestos-containing building material or structural
components, members or fixtures, such as floor
and ceiling tiles; does not include surfacing
materials or thermal system insulation.
Interior building materials on structural
components, such as floor or ceiling tiles.
Miscible Liquids— Two
or more liquids that can be mixed and will
remain mixed under normal conditions.
Missed Detection— The
situation that occurs when a test indicates
that a tank is “tight” when in
fact it is leaking.
Mist— Liquid particles
measuring 40 to 500 micrometers (pm), are
formed by condensation of vapor. By comparison,
fog particles are smaller than 40 micrometers
taken to reduce adverse impacts on the environment.
Mixed Funding— Settlements
in which potentially responsible parties and
EPA share the cost of a response action.
Mixed Glass— Recovered
container glass not sorted into categories
(e.g. color, grade).
Mixed Liquor— A mixture
of activated sludge and water containing organic
matter undergoing activated sludge treatment
in an aeration tank.
Mixed Metals— Recovered
metals not sorted into categories such as
aluminum, tin, or steel cans or ferrous or
Mixed Municipal Waste—
Solid waste that has not been sorted into
specific categories (such as plastic, glass,
yard trimmings, etc.)
Mixed Paper— Recovered
paper not sorted into categories such as old
magazines, old newspapers, old corrugated
Mixed Plastic— Recovered
plastic unsorted by category.
Mobile Incinerator Systems—
Hazardous waste incinerators that can be transported
from one site to another.
Mobile Source— Any non-stationary
source of air pollution such as cars, trucks,
motorcycles, buses, airplanes, and locomotives.
Model Plant— A hypothetical
plant design used for developing economic,
environmental, and energy impact analyses
as support for regulations or regulatory guidelines;
first step in exploring the economic impact
of a potential NSPS.
Modified Bin Method—
Way of calculating the required heating or
cooling for a building based on determining
how much energy the system would use if outdoor
temperatures were within a certain temperature
interval and then multiplying the energy use
by the time the temperature interval typically
Modified Source— The
enlargement of a major stationary pollutant
sources is often referred to as modification,
implying that more emissions will occur.
Moisture Content— 1.The
amount of water lost from soil upon drying
to a constant weight, expressed as the weight
per unit of dry soil or as the volume of water
per unit bulk volume of the soil. For a fully
saturated medium, moisture content indicates
the porosity. 2. Water equivalent of snow
on the ground; an indicator of snowmelt flood
Molecule— The smallest
division of a compound that still retains
or exhibits all the properties of the substance.
Molten Salt Reactor—
A thermal treatment unit that rapidly heats
waste in a heat-conducting fluid bath of carbonate
or continuous surveillance or testing to determine
the level of compliance with statutory requirements
and/or pollutant levels in various media or
in humans, plants, and animals.
Monitoring Well— 1. A
well used to obtain water quality samples
or measure groundwater levels. 2. A well drilled
at a hazardous waste management facility or
Superfund site to collect ground-water samples
for the purpose of physical, chemical, or
biological analysis to determine the amounts,
types, and distribution of contaminants in
the groundwater beneath the site.
Monoclonal Antibodies (Also
called MABs and MCAs)— 1. Man-made (anthropogenic)
clones of a molecule, produced in quantity
for medical or research purposes. 2. Molecules
of living organisms that selectively find
and attach to other molecules to which their
structure conforms exactly. This could also
apply to equivalent activity by chemical molecules.
Monomictic— Lakes and
reservoirs which are relatively deep, do not
freeze over during winter, and undergo a single
stratification and mixing cycle during the
year (usually in the fall).
Montreal Protocol— Treaty,
signed in 1987, governs stratospheric ozone
protection and research, and the production
and use of ozone-depleting substances. It
provides for the end of production of ozone-depleting
substances such as CFCS. Under the Protocol,
various research groups continue to assess
the ozone layer. The Multilateral Fund provides
resources to developing nations to promote
the transition to ozone-safe technologies.
Moratorium— During the
negotiation process, a period of 60 to 90
days during which EPA and potentially responsible
parties may reach settlement but no site response
activities can be conducted.
Morbidity— Rate of disease
Mortality— Death rate.
Most Probable Number—
An estimate of microbial density per unit
volume of water sample, based on probability
Muck Soils— Earth made
from decaying plant materials.
Mudballs— Round material
that forms in filters and gradually increases
in size when not removed by backwashing.
Mulch— A layer of material
(wood chips, straw, leaves, etc.) placed around
plants to hold moisture, prevent weed growth,
and enrich or sterilize the soil.
Joint approach to several environmental media,
such as air, water, and land.
Multiple Chemical Sensitivity—
A diagnostic label for people who suffer multi-system
illnesses as a result of contact with, or
proximity to, a variety of airborne agents
and other substances.
Multiple Use— Use of
land for more than one purpose; e.g., grazing
of livestock, watershed and wildlife protection,
recreation, and timber production. Also applies
to use of bodies of water for recreational
purposes, fishing, and water supply.
Multistage Remote Sensing—
A strategy for landscape characterization
that involves gathering and analyzing information
at several geographic scales, ranging from
generalized levels of detail at the national
level through high levels of detail at the
Discharge of effluent from waste water treatment
plants which receive waste water from households,
commercial establishments, and industries
in the coastal drainage basin. Combined sewer/separate
storm overflows are included in this category.
Municipal Sewage— Wastes
(mostly liquid) orginating from a community;
may be composed of domestic wastewaters and/or
Municipal Sludge— Semi-liquid
residue remaining from the treatment of municipal
water and wastewater.
Municipal Solid Waste—
Common garbage or trash generated by industries,
businesses, institutions, and homes.
An agent that causes a permanent genetic change
in a cell other than that which occurs during
normal growth. Mutagenicity is the capacity
of a chemical or physical agent to cause such