EXTOXNET FAQs - Glossary

Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

Select the first letter of the word from the list above to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the '#' link.

- A -

the entry or uptake of a substance into the body, either across a tissue or cells.
Acceptable Daily Intake (ADI)
The maximum amount of a substance that can be taken into the body daily over the course of a lifetime without posing a health risk.
The buildup of a substance in the body due to either long term (chronic) exposure or repeat exposure.
A compound is considered acidic when its pH is below 7. An example would be lemon juice or vinegar.
Action Level
The concentration of lead or copper in water which determines the treatment requirements that a water system is required to complete.
Acute Exposure
Either a single or short term exposure to a compound.
The condensation of gases, liquids, or dissolved substances on the surfaces of solids.
Adverse Health Effect
An effect that causes functional impairment, or a pathological lesion which may affect how the organism performs, or reduce its ability to respond to new changes in the environment.
A compound that counteracts or neutralizes the effect of a toxicant.
A process that requires oxygen to continue or persist. An example would be aerobic bacteria which require oxygen to live.

A compound is considered alkaline or basic when its pH is above 7. An example would be bleach or baking soda.

Anaerobic degradation
The metabolism of substances by bacteria that do not require oxygen to live.

A rheumatism of the joints, which could be any of a variety of disorders marked by inflammation, degeneration, or metabolic derangement of the connective tissue structures of the body.

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- B -

Background level
The normal concentration of a chemical in the environment.

A microscopic organism that consists of a single cell

Alkaline; a compound with a pH above 7.
The accumulation within living organisms of toxic substances occuring in the environment.
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- C -

A disease that tends to have rapid, uncontrolled growth of cells into tumors.

A cancer causing substance.

The development of cancer

Tending to induce the formation of cataracts

Central Nervous System (CNS)
The part of the nervous system that contains the brain and the spinal cord.

A process of adding chlorine to water to disinfect it, to aid in coagulation, or to remove odors and smells. See also disinfection.


A long term exposure to a chemical, either continuously or periodically through that period of time.

The clumping together of fine particles into larger particles, caused by the use of chemicals. the larger particles are then easier to separate from the water.

The amount of the compound present in a specified quantity of dilutant (i.e. water). Can be expressed as ml/L, oz/gallon, etc.

Any impurity or substance that pollutes another; an agent of contamination accidently or inadvertantly introduced into food, water, soil, or air, that may or may not be harmful or potentially poisonous.

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- D -

Pertaining to the skin. Some chemicals can be absorbed through or by the skin.
The movement of a chemical from a high concentration area to a low concentration area. Eventually, an equilibrium is reached where chemical is in equal concentrations throughout the system.
The process in which most microorganisms are killed, especially pathogenic microbes. See chlorination.
The total amount of the compound given to or taken by an organism.
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- E -

Efflux pump
Located in the cell membrane are pumps made of proteins, which transport molecules in and out of the cell. An efflux pump would be one that transports molecules out of the cell.
Enteric Virus
A virus of intestinal origin.
Environmental Fate
The fate of the chemical after it has been released into the environment. The fate depends upon the specific characteristics of the chemical and the physical and biological forces which may act upon that chemical, such as heat, water or soil microorganisms among others.
Coming into contact with a compound which may or may not result in a toxic effect. The main routes of exposure are by mouth, skin and by breathing.
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- F -

A process of removing particles from water by passing it through a porous media such as a filter.
A process of gathering fine particles in the water into larger particles by the addition of a chemical agent. See also coagulation.
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- G -

Toxic action occurring among the heritable chromosomes. Heritable chromosomes can be transmitted from parent to offspring.

Water which is located in zones below the soil surface. Wells and springs can be fed by groundwater.
Groundwater residue guidance level.
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- H -

The potential that the use of a compound could result in a toxic effect.
Health Advisory (HA)
A non-enforceable guideline set by the EPA used to evaluate the health significance of a contaminant in drinking water when no MCL has been set for that contaminant by the EPA.
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- I -

Substances or compounds that do not contain carbon and are generally not derived from plants and animals, such as minerals, salts, and metals.
The amount of a compound that is inhaled, ingested, or absorbed over a certain period of time.
An electrically charged atom, formed by the loss or gain of one or more electron.

in vitro
A biological process made to occur in a laboratory vessel or other controlled experimental environment rather than within a living organism or natural setting.

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- L -

Having an affinity for fat.
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- M -

Maximum Contaminant Level (MCL)
A drinking water standard which is set by the EPA. The MCL is the maximum amount of a compound that can be present in drinking water at any given time.
Maximum Tolerated Dose (MTD)
The highest dose of a chemical that does not shorten the organism's lifespan or cause severe damage to the organism.

Microgram (mcg)
One millionth of a gram i.e. 10-6 g. Also is one thousandth of a milligram i.e. 10-3 g. Is often designated by the symbol g.

Minimata Disaster
In 1953, an epidemic hit fishermen and their families in villages on Japan's Minamata Bay. A number of people who were highly dependent on seafood showed signs of brain damage. Some of these cases were fatal. An investigation revealed that a local chemical plant was discharging organic mercury into the bay, and the fish in the area had absorbed the mercury and eventually passed it on to the villagers.
Muscular dystrophy
A group of genetic degenerative myopathies characterized by weakness and atrophy of muscle without involvement of the nervous system.
A substance that causes permanent damage to genes, that would not normally occur.
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- N -

No Observable Effect Level (NOEL)
The highest dose given which does not show an observable adverse effect to the organism.
A substance that will not become a gas or vaporize into the air.
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- O -

Any gene that is a causative factor in the initiation of cancerous growth. When activated these genes can transform the cell from normal to one which does not have regulated cell growth.
Capable of inducing tumor formation
Egg like forms of a parasite such as cryptosporidium which are infectious.
Carbon containing compounds including those existing in or derived from plants and animals, also including man-made carbon based compounds.
A treatment process in which ozone is applied to the water for disinfection, or for taste and odor control.
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- P -

A substance or mixture of substances used to prevent, destroy, or repel a pest.
Parts per billion; This is a measure of the concentration of a compound. 1 ppb is equal to one microgram per kilogram. An example of this would be one ppb is equal to one second in thirty-two years.
Parts per million; This is a measure of concentration of a compound. 1 ppm is equal to one mg per kg. An example of this would be one ppm is equal to one minute in two years.
Priority Pollutants
A group of toxic chemicals or classes of chemicals listed under section 307(a)(1) of the Clean Water Act of 1977 (U.S.C. 466). This list was established for the purpose of providing guidelines for regulating industrial effluent discharge with the primary goal of protecting public health.
A unicellular microorganism that has the means to move around either by cilia or a flagella.

A tranquilizer, sedative, antidepressant or mood altering drug.

Pulmonary dysfunction
Dysfunction of the lungs.

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- Q -

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- R -

Reference Dose (RfD)
A level of exposure that is considered acceptable or safe. Also known as the "acceptable daily intake".
The possibility that an adverse effect will occur.
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- S -

A water treatment in which solid particles are settled out of the water in a sedimentation basin or clarifier.
The concentration of a compound that dissolves in a solvent (i.e. water).
Surface Water
Water at the soil surface. Examples include oceans, lakes, streams, rivers, etc.
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- T -

Harmful, poisonous.
Any chemical which can produce toxic effects; includes toxins which are toxicants produced by living organisms. Example: DDT and PCBs are toxicants, strychnine and pyrethrins are toxins produced by plants.
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- U -

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- V -

The smallest microorganism that is capable of causing a disease.

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- Y -

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Revised: May 04, 1998.