Environmental Health Center:
Glossary
I
impermeable: Not easily penetrated, The property of a material or soil that does not allow, or allows only with great difficulty, the movement or passage of water.
in situ: In place, the original location, in the natural environment.
in vitro: In glass; a laboratory experiment performed in a test tube or other vessel.
in vivo: With in a living organism; a laboratory experiment performed in which the substance under study is inserted into a living organism.
incineration: The destruction of solid, liquid, or gaseous wastes by controlled burning at high temperatures. Hazardous organic compounds are converted to ash, carbon dioxide, and water. Burning destroys organics, reduces the volume of waste, and vaporizes water and other liquids the wastes may contain. The residue ash produced may contain some hazardous material, such as non-combustible heavy metals, concentrated from the original waste.
incompatible waste: A waste unsuitable for mixing with another waste or material because it may react to form a hazard.
indigenous: Living or occurring naturally in a specific area or environment; native.
indirect discharge: Introduction of pollutants from a non-domestic source into a publicly owned waste-treatment system. Indirect dischargers can be commercial or industrial facilities whose wastes enter local sewers.
indoor air: Breathing air inside a habitable structure, often highly polluted because of lack of exchange with fresh oxygen from outdoors. Solvents, smoke, paints, furniture glues, carpet padding, and other synthetic chemicals trapped inside contribute to an often unhealthy environment.
indoor air pollution: Chemical, physical, or biological contaminants in indoor air.
industrial source reduction: Practices that reduce the amount of any hazardous substance, pollutant, or contaminant entering any waste stream or otherwise released into the environment; Also reduces the threat to public health and the environment associated with such releases. Term includes equipment or technology modifications, substitution of raw materials, and improvements in housekeeping, maintenance, training or inventory control.
industrial waste: Unwanted materials produced in or eliminated from an industrial operation and categorized under a variety of headings, such as liquid wastes, sludge, solid wastes, and hazardous wastes.
inert ingredient: Substances that are not active, such as water, petroleum distillates, talc, corn meal, or soaps. When discussing pesticides, inert ingredients do not attack a particular pest, but some are chemically or biologically active, causing health and environmental problems.
infectious agent: Any organism, such as a virus or bacterium, that is pathogenic and capable of being communicated by invasion and multiplication in body tissues.
infectious waste: Hazardous waste with infectious characteristics, including: contaminated animal waste; human blood and blood products; isolation waste, pathological waste; and discarded sharps (needles, scalpels or broken medical instruments.)
infiltration gallery: A subsurface groundwater collection system, typically shallow in depth, constructed with open jointed or perforated pipes that discharge collected water into a water-tight chamber. From this chamber the water is pumped to treatment facilities and into the distribution system. Infiltration galleries are usually located close to streams or ponds and may be under the direct influence of surface water.
inflow: Entry of extraneous rain water into a sewer system from sources other than infiltration, such as basement drains, manholes, storm drains, and street washing.
influent: Water or other liquid-raw or partially flowing INTO a reservoir, basin, treatment process or treatment plant.
ingestion: Type of exposure through the mouth.
inhalation: Type of exposure through the lungs.
inorganic: Material such as sand, salt, iron, calcium salts and other mineral materials. Inorganic substances are of mineral origin, whereas organic substances are usually of animal or plant origin.
insecticide: A pesticide compound specifically used to kill or prevent the growth of insects.
integrated exposure assessment: A summation over time, in all media, of the magnitude of exposure to a toxic chemical.
integrated pest management (IPM): A combination of biological, cultural, and genetic pest control methods with use of pesticides as the last resort. IPM considers a targeted species' life cycle and intervenes in reproduction, growth, or development to reduce the population. Land use practices are examined for possible change; other animals, birds, or reptiles in the ecosystem are used as natural predators.
interceptor sewers: Large sewer lines that, in a combined system, control the flow of sewage to the treatment plant. In a storm, they allow some of the sewage to flow directly into a receiving stream, thus keeping it from overflowing onto the streets. Also used in separate systems to collect the flows from main and trunk sewers and carry them to treatment points.
interstate carrier water supply: A source of water for drinking and sanitary use on planes, buses, trains, and ships operating in more than one state. These sources are federally regulated.
inversion: An atmospheric condition caused by increasing temperature with elevation, resulting in a layer of warm air preventing the rise of cooler air trapped beneath. This condition prevents the rise of pollutants that might otherwise be dispersed. Trapping pollutants near the ground increases ozone to harmful levels.
ion exchange treatment: A common water-softening method often found on a large scale at water purification plants that remove some organics and radium by adding calcium oxide or calcium hydroxide to increase the ph to a level where the metals will precipitate out.
irradiated food: Food that has been briefly exposed to radioactivity (usually gamma rays) to kill insects, bacteria, and mold. Irradiated food can be stored without refrigeration or chemical preservatives and has a long “shelf life.”
irreversible effect: Effect characterized by the inability of the body to partially or fully repair injury caused by a toxic agent.
irrigation: Applying water or wastewater to land areas to supply the water and nutrient needs of plants.
irritant: A substance that can cause irritation of the skin, eyes, or respiratory system. An irritant can cause an acute effect from a single high-level exposure, or chronic effects from repeated, low-level exposures. Some examples of irritants are chlorine, nitric acid, and various pesticides. isotope: A variation of an element that has the same atomic number of protons but a different weight because of the number of neutrons. Various isotopes of the same element may have different radioactive behaviors, some are highly unstable.
J/K
kinetic energy: Energy possessed by a moving body of matter, such as water, as a result of its motion.
[ back to top ] L
lagoon: A shallow, artificial treatment pond where sunlight, bacterial action, and oxygen work to purify wastewater; a stabilization pond. An aerated lagoon is a treatment pond that uses oxygen to speed up the natural process of biological decomposition of organic wastes. A lagoon is regulated as a point source under the Clean Water Act if there is a direct surface water discharge. Some lagoons that discharge into ground water also are regulated if they have a direct hydrogeologic connection to surface water. In other areas, lagoons were historically used to dump various liquid, solid, and hazardous wastes from manufacturing or industrial processes. These wastes typically flooded and polluted surrounding environs or seeped underground. Such lagoons are now regulated under RCRA but some must be cleaned up under Superfund.
landfill: A method for final disposal of solid waste on land. The refuse is spread and compacted and a cover of soil applied so that effects on the environment (including public health and safety) are minimized. Under current regulations, landfills are required to have liners and leachate treatment systems to prevent contamination of ground water and surface waters. An industrial landfill disposes of non-hazardous industrial wastes. A municipal landfill disposes of domestic waste including garbage, paper, etc. This waste may include toxins that are used in the home, such as insect sprays and powders, engine oil, paints, solvents, and weed killers.
large quantity generator: Person or facility which generates more than 2,200 pounds of hazardous waste per month. In 1989, only 1% of more than 20,000 generators fell into this category. Those generators produced nearly 97% of the nation's hazardous waste. These generators are subject to all requirements of RCRA.
latency: Time from the first exposure to a chemical until the appearance of a toxic effect.
laundering weir: Sedimentation basin overflow weir. A plate with V-notches along the top to assure a uniform flow rate and avoid short-circuiting.
leachate: A liquid that results from water collecting contaminants as it trickles through wastes, agricultural pesticides or fertilizers. Leaching may occur in farming areas, feedlots, and landfills, and may result in hazardous substances entering surface water, ground water, or soil.
leaching: The process by which soluble constituents are dissolved and filtered through the soil by a percolating fluid.
lead (Pb): A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.
legionella: A genus of bacteria, some species of which have caused a type of pneumonia called Legionnaires Disease.
lesion: A pathological or traumatic discontinuity of tissue or loss of function of a part.
level of concern (LOC): The concentration in air of an extremely hazardous substance above which there may be serious immediate health effects to anyone exposed to it for short periods
lifetime exposure: Total amount of exposure to a substance that a human would receive in a lifetime (usually assumed to be 70 years).
limestone scrubbing: Use of a limestone and water solution to remove gaseous stack-pipe sulfur before it reaches the atmosphere.
limnology: The study of the physical, chemical, hydrological, and biological aspects of fresh water bodies.
lindane: A pesticide that causes adverse health effects in domestic water supplies and is toxic to freshwater fish and aquatic life.
lipid solubility: The maximum concentration of a chemical that will dissolve in fatty substances. Lipid soluble substances are insoluble in water. They will very selectively disperse through the environment via uptake in living tissue.
liquefaction: Changing a solid into a liquid.
littoral zone: 1. That portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants. 2. The strip of land along the shoreline between the high and low water levels.
local emergency planning committee (LEPC): A committee appointed by the State Emergency Response Commission (SERC), as required by EPCRA, which develops comprehensive emergency plans for Local Emergency Planning Districts, collects MSDS forms and chemical release reports, and provides this information to the public. Each county and some large city governments participate in an LEPC.
low-level radioactive waste (LLRW): Wastes less hazardous than most of those associated with nuclear reactor; generated by hospitals, research laboratories, and certain industries. The Department of Energy, Nuclear Regulatory Commission, and EPA share responsibilities for managing them.
lower explosive limit (LEL): The concentration of a gas below which the concentration of vapors is insufficient to support an explosion. LELs for most organics are generally 1 to 5 percent by volume. magnehelic gauge: a sensitive differential pressure or vacuum gauge manufactured by Dwyer Instrument Co. that uses a precision diaphragm to measure pressure differences. This gauge is manufactured in specific pressure or vacuum ranges such as 0 to 2 inches of water column. Magnehelic gauges are typically used to measure SVE system vacuums.
[ back to top ]
M
macroscopic organisms: Organisms big enough to be seen by the eye without the aid of a microscope.
malignant: Very dangerous or virulent, causing or likely to cause death.
manifest system: Tracking of hazardous waste from "cradle to grave" (generation through disposal) with accompanying documents known as manifests.
manufacturers formulation: A list of substances or component parts as described by the maker of a coating, pesticide, or other product containing chemicals or other substances.
margin of safety (MOS): Maximum amount of exposure producing no measurable effect in animals (or studied humans) divided by the actual amount of human exposure in a population.
marine sanitation device: Any equipment or process installed on board a vessel to receive, retain, treat, or discharge sewage.
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 safety data sheet (MSDS): Printed material concerning a hazardous chemical, or Extremely Hazardous Substance, including its physical properties, hazards to personnel, fire and explosion potential, safe handling recommendations, health effects, fire fighting techniques, reactivity, and proper disposal. Originally established for employee safety by OSHA.
maximum contaminant level (MCL): The maximum permissible level of a contaminant in water which is delivered to the free flowing outlet of the ultimate user of a public water system, except in the case of turbidity where the maximum permissible level is measured at the point of entry to the distribution system. Contaminants added to the water under circumstances controlled by the user are excluded from this definition, except those contaminants resulting from the corrosion of piping and plumbing caused by water quality.
media: Specific environments -- air, water, soil -- which are the subject of regulatory concern and activities.
mercury: A heavy metal that can accumulate in the environment and is highly toxic if breathed or swallowed.
mesotrophic: Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.
metabolism: The sum of the chemical reactions occurring within a cell or a whole organism; includes the energy-releasing breakdown of molecules (catabolism) and the synthesis of new molecules (anabolism).
metabolites: Any substances produced by biological processes, such as those from pesticides.
metastatic: Pertaining to the transfer of disease from one organ or part to another not directly connected with it.
methane: A colorless, nonpoisonous, flammable gas created by anaerobic decomposition of organic compounds.
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 that those from gasoline.
methoxychlor: Pesticide that causes adverse health effects in domestic water supplies and is toxic to freshwater and marine aquatic life.
microbial growth: The activity and growth of microorganisms such as bacteria, algae, diatoms, plankton and fungi.
microcosm: A diminutive, representative system analogous to a larger system in composition, development, or configuration. As used in biodegradation treatability studies, microcosms are typically constructed in glass bottles or jars.
micrograms per liter (mg/L): One microgram of a substance dissolved in each liter of water: This unit is equal to parts per billion (ppb) since one liter of water is equal in weight to one billion micrograms.
micron: A unit of length. One millionth of a meter or one thousandth of a millimeter. One micron equals 0.00004 of an inch.
microorganisms: Bacteria, yeasts, simple fungi, algae, protozoans, and a number of other organisms that are microscopic in size. Most are beneficial but some produce disease. Others are involved in composting and sewage treatment. Milligrams/liter (mg/l): A measure of concentration used in the measurement of fluids. Mg/l is the most common way to present a concentration in water and is roughly equivalent to parts per million.
mineralization: The release of inorganic chemicals from organic matter in the process of aerobic or anaerobic decay.
minimization: Measures or techniques that reduce the amount of wastes generated during industrial production processes; this term also is applied to recycling and other efforts to reduce the volume of waste going to landfills. This term is interchangeable with waste reduction and waste minimization.
miscible liquids: Two or more liquids that can be mixed and will remain mixed under normal conditions.
mist: Liquid particles measuring 40 to 500 microns, are formed by condensation of vapor. By comparison, fog particles are smaller than 40 microns.
mitigation: Measures taken to reduce adverse effects on the environment.
mobile source: Any non-stationary source of air pollution such as cars, trucks, motorcycles, buses, airplanes, locomotives.
modeling: Use of mathematical equations to simulate and predict real events and processes.
molecular weight: The molecular weight of a compound in grams is the sum of the atomic weights of the elements in the compound. The molecular weight of sulfuric acid (H2SO4) in grams is 98.
molecule: The smallest division of a compound that still retains or exhibits all the properties of the substance.
monitoring wells: Wells used to collect ground-water samples for analysis to determine the amount, type, and spread of contaminants In ground water.
monomictic: Lakes and reservoirs which are relatively deep, do not freeze over during the winter months, and undergo a single stratification and mixing cycle during the year (usually in the fall).
morbidity: Rate of disease incidence.
motile: Capable of self-propelled movement. A term that is sometimes used to distinguish between certain types of organisms found in water.
mulch: Any substance spread or allowed to remain on the soil surface to conserve soil moisture and shield soil particles from the erosive forces of raindrops and runoff.
multiple use: Use of land for more than one purpose; i.e., 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.
municipal discharge: 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) originating from a community; may be composed of domestic waste waters and/or industrial waste waters.
mutagen: An agent that causes a permanent genetic change in a cell other than that which occurs during normal genetic recombination.
mutagenicity: The capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cells.
[ back to top ]
N
national ambient air quality standards (NAAQS): Standards established by EPA that apply for outside air throughout the country.
national emissions standards for hazardous air pollutants (NESHAP): Emission standards set by EPA for an air pollutant not covered by NAAQS that may cause an increase in deaths or serious, irreversible, or incapacitating illness. Primary standards are designed to protect human health, secondary standards to protect public welfare.
national pollutant discharge elimination system (NPDES): A provision of the Clean Water Act which prohibits discharge of pollutants into waters of the United States unless a special permit is issued by EPA, a state, or, where delegated, a tribal government on an Indian reservation.
national priorities list (NPL): EPA's list of the most serious uncontrolled or abandoned hazardous waste sites identified for possible long-term remedial action under Superfund. The list is based primarily on the score a site receives from the Hazard Ranking System. EPA is required to update the NPL at least once a year. A site must be on the NPL to receive money from the Trust Fund for remedial action.
national response yeam (NRT): Representatives of 13 federal agencies that, as a team, coordinate federal responses to nationally significant incidents of pollution-an oil spill, a major chemical release, or a Superfund response action-and provide advice and technical assistance to the responding agency(ies) before and during a response action.
national strike force (NSF): Operated by the U.S. Coast Guard, the NSF is composed of three strategically located teams (Atlantic, Pacific, and Gulf coasts) who back up the federal On-Scene Coordinator. These teams are extensively trained and equipped to respond to major oil spills and chemical releases. These capabilities are especially suited to incidents in a marine environment but also include site assessment, safety, action plan development, and documentation for both inland and coastal zone incidents. The NSF Coordination Center is at Elizabeth City, NC.
navigable waters: Traditionally, waters sufficiently deep and wide for navigation by all, or specified vessels; such waters in the United States come under federal jurisdiction and are protected by certain provisions of the Clean Water Act.
necrosis: Death of plant or animal cells or tissues. In plants, necrosis can discolor stems or leaves or kill a plant entirely.
nematodes: Roundworms, any of which are pathogenic for plants and sometimes animals.
neoplasm: An abnormal growth or tissue, as a tumor.
netting: A concept in which all emissions sources in the same area that are owned or controlled by single company are treated as one large source, thereby allowing flexibility in controlling individual sources in order to meet a single emissions standard.
neurotoxicity: Exerting a destructive or poisonous effect on nerve tissue.
neutralization: Decreasing the acidity or alkalinity of a substance by adding alkaline or acidic materials, respectively.
nitrate: Plant nutrient and inorganic fertilizer that enters water supply sources from septic systems, animal feed lots, agricultural fertilizers, manure, industrial waste waters, sanitary landfills and garbage dumps.
nitric oxide: A gas formed by combustion under high temperature and high pressure in an internal combustion engine; changes into nitrogen dioxide in the ambient air and contributes to photochemical smog.
nitrification: The process whereby ammonia in wastewater is oxidized to nitrite and then to nitrate by bacterial or chemical reactions.
nitrogen dioxide: The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog.
nitrogen fixation: The biological or chemical process by which elemental nitrogen, from the air, is converted to organic or available nitrogen.
nitrogen oxide: Product of combustion from transportation and stationary sources and a major contributor to the formation of ozone in the troposphere and to acid deposition.
nitrogenous: A term used to describe chemical compounds (usually organic) containing nitrogen in combined forms. Proteins and nitrates are nitrogenous compounds.
no till: Planting crops without prior seedbed preparation, into an existing cover crop, sod, or crop residues, and eliminating subsequent tillage operations.
noble metal: Chemically inactive metal (such as gold). A metal that does not corrode easily and is much scarcer (and more valuable) than the so-called useful or base metals. Also see base metal.
non-attainment area: Area that does not meet one or more of the National Ambient Air Quality Standards for the criteria pollutants designated in the Clean Air Act.
non-binding allocations of responsibility (NBAR): Process for EPA to propose a way for potentially responsible parties to allocate costs among themselves.
non-conventional pollutant: Any pollutant which is not a statutorily listed or which is poorly understood by the scientific community.
non-point source: Diffuse pollution sources (i.e., without a single point of origin or not introduced into a receiving stream from a specific outlet). The pollutants are generally carried off the land by storm water. Common nonpoint sources are agriculture, forestry, urban, mining, construction, dams, channels, land disposal, saltwater intrusion, and city streets.
non-potable: Water that is unsafe or unpalatable to drink because in contains objectionable pollution, contamination, minerals, or infective agents.
nutrient pollution: Contamination of water resources by excessive inputs of nutrients. In surface waters, excess algal production is a major concern.
nutrient: Any substance assimilated by living things that promotes growth. The term is generally applied to nitrogen and phosphorus in wastewater, but is also applied to other essential and trace elements.
[ back to top ]
O
obligate aerobes: Organisms that require the presence of molecular oxygen ([O(2)] for their metabolism.
obligate anaerobes: Organisms for which the presence of molecular oxygen is toxic. These organisms derive the oxygen needed for cell synthesis from chemical compounds.
off-site facility: A hazardous waste treatment, storage or disposal area that is located away from the generating site.
oil fingerprinting: A method that identifies sources of oil and allows spills to be traced to their source.
oil spill: An accidental or intentional discharge of oil which reaches bodies of water. Can be controlled by chemical dispersion, combustion, mechanical containment, and/or adsorption. Spills from tanks and pipelines can also occur away from water bodies, contaminating the soil, getting into sewer systems and threatening underground water sources.
olfactory fatigue: A condition in which a person's nose, after exposure to certain odors, is no longer able to detect the odor.
oligotrophic: Reservoirs and lakes which are nutrient poor and contain little aquatic plant or animal life.
on-site facility: A hazardous waste treatment, storage or disposal area that is located on the generating site.
oncology: Study of cancer.
opacity: The amount of light obscured by particulate pollution in the air; clear window glass has zero opacity, a brick wall is 100 percent opaque. Opacity is an indicator of changes in performance of particulate control systems.
organic chemicals/compounds: Animal or plant-produced substances containing mainly carbon, hydrogen, nitrogen, and oxygen.
organic matter: Carbonaceous waste contained in plant or animal matter and originating from domestic or industrial sources.
organically grown: Food, feed crops, and livestock grown within an intentionally-diversified, self-sustaining agro-ecosystem. In practice, farmers build up nutrients in the soil using compost, agricultural wastes, and cover crops instead of synthetically derived fertilizers to increase productivity, rotate crops, weed mechanically, and reduce dramatically their dependence on the entire family of pesticides. Farmers must be certified to characterize crops as organically grown and can only use approved natural and synthetic biochemicals, agents, and materials for three consecutive years prior to harvest. Live stock must be fed a diet that includes grains and forages that have been organically grown and cannot receive hormones, sub-therapeutic antibiotics, or other growth promoters.
organism: Any living being, whether plant, mammal, bird, insect, reptile, fish, crustacean, aquatic or estuarine animal, or bacterium.
organophosphates: Pesticides that contain phosphorus; short-lived, but some can be toxic when first applied.
osmosis: The passage of a liquid from a weak solution to a more concentrate solution across a semipermeable membrane that allows passage of the solvent (water) but not the dissolved solids. This process tends to equalize the conditions on either side of the membrane.
overdraft: The pumping of water from a groundwater basin or aquifer in excess of the supply flowing into the basin: This pumping results in a depletion or "mining" of the groundwater in the basin.
overfire air: Air forced into the top of an incinerator or boiler to fan the flames.
overturn: The almost spontaneous mixing of all layers of water in a reservoir or lake when the water temperature becomes similar from top to bottom. This may occur in the fall/winter when the surface waters cool to the same temperature as the bottom waters and also in the spring when the surface waters warms after the ice melts.
oxidant: A substance containing oxygen that reacts chemically in air to produce a new substance; the primary ingredient of photochemical smog.
oxidation: Oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. In the environment, organic matter is oxidized to more stable substances. The opposite of reduction
oxygenated fuels: Gasoline which has been blended with alcohols or ethers that contain oxygen in order to reduce carbon monoxide and other emissions.
ozonation: The application of ozone to water for disinfection or for taste and odor control.
ozone: Found in two layers of the atmosphere, the stratosphere and the troposphere. In the stratosphere (the atmospheric layer 7 to 10 miles or more above the earth's surface) ozone is a natural form of oxygen that provides a protective layer shielding the earth from ultraviolet radiation.In the troposphere (the layer extending up 7 to 10 miles from the earth's surface), ozone is a chemical oxidant and major component of photochemical smog. It can seriously impair the respiratory system and is one of the most widespread of all the criteria pollutants for which the Clean Air Act required EPA to set standards. Ozone in the troposphere is produced through complex chemical reactions of nitrogen oxides, which are among the primary pollutants emitted by combustion sources; hydrocarbons, released into the atmosphere through the combustion, handling and processing of petroleum products; and sunlight.
ozone depletion: Destruction of the stratospheric ozone layer which shields the earth from ultraviolet radiation harmful to life. This destruction of ozone is caused by the breakdown of certain chlorine and/or-bromine containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules.
ozone hole: Thinning break in the stratospheric ozone layer. Designation of amount of such depletion as a "ozone hole" is made when detected amount of depletion exceeds fifty percent. seasonal ozone holes have been observed over both the Antarctic region and the Arctic region and part of canada and the extreme northeastern United States.
ozone layer: The protective layer in the atmosphere, about 15 miles above the ground, that absorbs some of the sun's ultraviolet rays, thereby reducing the amount of potentially harmful radiation reaching the earth's surface.
[ back to top ]
P
packed bed scrubber: An air pollution control device in which emissions pass through alkaline water to neutralize hydrogen chloride gas.
packed tower aeration: A method of treating water to remove volatile organic chemical (VOCs) contaminants. As water is mixed with air, VOCs move from water to air which then passes through carbon filters to trap the contaminants.
particulate: 1. Fine liquid or solid particles such as dust, smoke, mist, fumes, or smog found in air or emissions. 2, Very small solid suspended in water. They vary in size, shape, density, and electrical charge, can be gathered together by coagulation and flocculation.
pathogen: Microorganisms that can cause disease in other organisms or in humans, animals and plants (e.g., bacteria, viruses, or parasites) found in sewage, in runoff from farms or rural areas populated with domestic and wild animals, and in water used for swimming. Fish and shellfish contaminated by pathogens, or the contaminated water itself, can cause serious illness.
pathology: The study of disease.
perched water: Zone of unpressurized water held above the water table by impermeable rock or sediment.
percolation: 1. The movement of water downward and radially through subsurface soil layers, continuing downward to groundwater. Can also involve upward movement of the water. 2. Slow seepage of water through a filter.
periphyton: Microscopic plants and animals that are firmly attached to solid surfaces under water such as rocks, logs, pilings and other structures.
permeability: A qualitative description of the relative ease with which rock, soil, or sediment will transmit a fluid (liquid or gas). Often used as a synonym for hydraulic conductivity or coefficient of permeability.
permissible dose: The dose of a chemical that may be received by an individual without the expectation of a significantly harmful result.
persistent pesticides: Pesticides that do not break down chemically or break down very slowly and remain in the environment after a growing season.
pest: An insect, rodent, nematode, fungus, weed or other form of terrestrial or aquatic plant or animal life that is injurious to health or the environment.
pesticide: Substances intended to repel, kill, or control any species designated a "pest" including weeds, insects, rodents, fungi, bacteria, or other organisms. The family of pesticides includes herbicides, insecticides, rodenticides, fungicides, and bactericides.
petroleum derivatives: Chemicals formed when gasoline breaks down in contact with ground water.
pH: A measure of the acidity of a solution. pH is equal to the negative logarithm of the concentration of hydrogen ions in a solution. A pH of 7 is neutral. Values less than 7 are acidic, and values greater than 7 are basic.
pharmacokinetics: The dynamic behavior of chemicals inside biological systems; it includes the processes of uptake, distribution, metabolism, and excretion.
phenols: Organic compounds that are byproducts of petroleum refining, tanning, and textile, dye, and resin manufacturing. Low concentrations cause taste and odor problems in water; higher concentrations can kill aquatic life and humans.
phosphates: Certain chemical compounds containing phosphorus.
phosphorus: An essential chemical food element that can contribute to the eutrophication of lakes and other water bodies. Increased phosphorus levels result from discharge of phosphorus-containing materials into surface waters.
photochemical oxidants: Air pollutants formed by the action of sunlight on oxides of nitrogen and hydrocarbons.
photosynthesis: A process in which organisms, with the aid of chlorophyll (green plant enzyme), convert carbon dioxide and inorganic substances into oxygen and additional plant material, using sunlight for energy. All green plants grow by this process.
phototrophs: Organisms that use light to generate energy (by photosynthesis) for cellular activity, growth, and reproduction.
phytoplankton: Small, usually microscopic plants (such as algae), found in lakes, reservoirs, and other bodies of water.
pico: A prefix used in the metric system and other scientific systems of measurement which means 10-12 or 0.000000000001
picocurie (pCi): A measure of radioactivity. One picocurie of radioactivity is equivalent to 0.037 nuclear disintegrations per second.
plankton: 1) Small, usually microscopic, plants (phytoplankton) and animals (zooplankton) in aquatic systems. 2) All of the smaller floating, suspended or self-propelled organisms in a body of water.
plastics: Non-metallic chemoreactive compounds molded into rigid or pliable construction materials, fabrics, etc.
plume: 1. A visible or measurable discharge of a contaminant from a given point of origin. Can be visible or thermal in water as it extends downstream from the pollution source, or visible in air as, for example, a plume of smoke. 2. The area of radiation leaking from a damaged reactor. 3. Area downwind within which a release could be dangerous for those exposed to leaking fumes.
plutonium: A radioactive metallic element chemically similar to uranium.
point source: A stationary location or fixed facility such as an industry or municipality that discharges pollutants into air or surface water through pipes, ditches, lagoons, wells, or stacks; a single identifiable source such as a ship or a mine.
pollutant: Generally, any substance introduced into the environment that adversely affects the usefulness of a resource.
pollution: Any substances in water, soil, or air that degrade the natural quality of the environment, offend the senses of sight, taste, or smell, or cause a health hazard. The usefulness of the natural resource is usually impaired by the presence of pollutants and contaminants.
polychlorinated biphenyls (PCBs): A group of toxic, persistent chemicals used in electrical transformers and capacitors for insulating purposes, and in gas pipeline systems as a lubricant. The sale and new use of PCBs were banned by law in 1979.
polymer: A chemical formed by the union of many monomers (a molecule of low molecular weight). Polymers are used with other chemical coagulants to aid in binding small suspended particles to larger chemical flocs for their removal from water. All polyelectrolytes are polymers, but not all polymers are polyelectrolytes.
polyvinyl chloride: A tough, environmentally indestructible plastic that releases hydrochloric acid when burned.
porosity: Degree to which soil, gravel, sediment or rock is permeated with pores or cavities through which water or air can move.
potable water: Raw or treated water that is considered safe to drink.
potentially responsible party (PRP): Any individual or company-including owners, operators, transporters or generators-potentially responsible for, or contributing to a spill or other contamination at a Superfund site. Whenever possible, through administrative and legal actions, GPA requires PRPs to clean up hazardous sites they have contaminated.
precipitation: 1) The process by which atmospheric moisture falls onto a land or water surface as rain, snow, hail, or other forms of moisture. 2) The chemical transformation of a substance in solution into an insoluble form (precipitate).
predation: The act or practice of capturing another creature (prey) as a means for securing food.
prescriptive: Water rights which are acquired by diverting water and putting it to use in accordance with specified procedures. These procedures include filing a request to use unused water in a strewn, river or lake with a state agency.
pretreatment: Methods used by industry and other non-household sources of wastewater to remove, reduce, or alter the pollutants in wastewater before discharge to a POTW.
prevalence study: An epidemiological study which examines the relationships between diseases and exposures as they exist in a defined population at a particular point in time.
prevention of significant deterioration (PSD): EPA program in which state and/or federal permits are required in order to restrict emissions from new or modified sources in places where air quality already meets or exceeds primary and secondary ambient air quality standards.
primary waste treatment: First steps in wastewater treatment; screens and sedimentation tanks are used to remove most materials that float or will settle. Primary treatment removes about 30 percent of carbonaceous biochemical oxygen demand from domestic sewage.
procaryotes: A cellular organism in which the nucleus has no limiting membrane.
propellant: Liquid in a self-pressurized pesticide product that expels the active ingredient from its container.
proteins: Complex nitrogenous organic compounds of high molecular weight made of amino acids; essential for growth and repair of animal tissue. Many, but not all, proteins are enzymes.
protoplast: A membrane-bound cell from which the outer wall has been partially or completely removed. The term often is applied to plant cells.
protozoa: Single-celled, eucaryotic microorganisms without cell walls. Most protozoa are free-living although many are parasitic. The majority of protozoa are aerobic or facultatively anaerobic heterotrophs.
public water system: A system for the provision to the public of piped water for human consumption, If such system has at least fifteen service connections or regularly least 60 days out of the year. Such term includes: 1) any collection, treatment, storage, and distribution facilities under control of the operator of such system and used primarily in connection with such system, and 2) any collection or pretreatment storage facilities not under such control which are used primarily in connection with such system. A public water system is either a "community water system" or a "non-community water system.'
putrefaction: Biological decomposition of organic matter, with the production of ill smelling and tasting products, associated with anaerobic (no oxygen present) conditions.
[ back to top ] |