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E  X  T  O  X  N  E  T
Extension Toxicology Network

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

Extoxnet Glossary

Publication Date: 9/93

The uptake of water or dissolved chemicals by a cell or an organism. The movement of a chemical into or across a tissue.

The class of pesticides used to kill mites and ticks; also known as "miticide."

Acceptable Daily Intake (ADI)
The maximum dose of a substance that is anticipated to be without health risk to humans when taken daily over the course of a lifetime. ADIs are set by the EPA.

The automatic adjustment of the eye lens to allow for seeing at different distances.

The buildup of a chemical in the body due to long-term or repeated exposure.

An enzyme present in nerve tissue, muscles and red blood cells that catalyzes the hydrolysis of acetylcholine to choline and acetic acid, allowing neural transmission across synapses to occur; true cholinesterase.

Acetylcholinesterase inhibitor
A compound or group of compounds (e.g., organophosphorus compounds) which block the action of the enzyme acetylcholinesterase, interfering with the transmission of impulses between nerve cells.

American Conference of Governmental Industrial Hygienists; establishes exposure limits for workers.

Sour; having a pH of less than 7.

In mutagenicity testing, the exposure of the tested chemical to a source of enzymes, e.g., liver microsomes, which metabolize the chemical. The metabolic products may exhibit mutagenic activity where the original chemical did not.

Active transport
An energy-expending mechanism by which a cell moves a chemical across a cell membrane from a point of lower concentration to a point of higher concentration, against the diffusion gradient.

Active ingredient (a.i.)
An ingredient in a formulated pesticide product which will prevent, destroy, repel or mitigate any pest.

Single or short-term exposure; used to describe brief exposures and effects which appear promptly after exposure.

Additive effect
Combined effect of two or more chemicals equal to the sum of their individual effects.

A benign tumor of glandular origin.

Substance added to a formulated pesticide product to act as a wetting or spreading agent, sticker, penetrant, or emulsifier in order to enhance the physical characteristics of the product.

The process by which chemicals are held on a solid surface, especially soil particles.

Adsorption coefficient (Koc)
A measure of a material's tendency to adsorb to soil particles. High Koc values indicate a tendency for the material to be adsorbed by soil particles rather than remain dissolved in the soil solution. Strongly adsorbed molecules will not leach or move unless the soil particle to which they are adsorbed moves (as in erosion). Koc values of less than 500 indicate little or no adsorption and a potential for leaching.
              conc. adsorbed/conc. dissolved
       Koc = _________________________________
               % organic carbon in the soil

A process requiring oxygen or free air; conditions in which oxygen is present.

Basic; having a pH of greater than 7.

Environmental or surrounding conditions.

A process which does not require oxygen or free air; conditions in which oxygen is absent.

The combined action of two or more substances to produce an effect less than the sum of their individual effects; the opposite of synergism.

Aquatic invertebrates
Organisms that do not have a spinal column and live in water. Includes insects, crayfish, mites, etc.

Watery; pertaining to water.

Organisms such as insects, arachnides (spiders and mites) and crustaceans which lack backbones (invertebrates).

Analysis to determine the presence, absence or quantity of a particular chemical or effect.

The wasting away or reduction in the size of a cell, tissue, or organ(s).

The examination of a dead body. Most autopsies involve an examination of the internal organs and some microscopic examination of tissues.

The class of pesticides used to kill birds.

Background level
Normal environmental concentration of a chemical.

Alkaline; having a pH of greater than 7.

Benign tumor
A non-cancerous tumor.

An inadequacy in experimental design that leads to results or conclusions not representative of the population under study.

The absorption, via breathing, eating, drinking or active uptake, and concentration of a substance in plants or animals.

Test which determines the effect of a chemical on a population of living organisms.

A material that has the capacity to kill all forms of life.

The accumulation of a chemical in tissues of an organism (such as fish) to levels that are greater than the level in the medium (such as water) in which the organism resides; Movement of a substance such as a pesticide from the surrounding environment (abiotic) into living organisms, especially via passive absorption.

Bioconcentration factor
A measure of the tendency for a chemical to accumulate. The ratio of the concentration of a substance in a living organism (mg/kg) to the concentration of that substance in the surounding environment (mg/l for aquatic systems).
               conc. in organism         =     mg/kg
        BCF = _______________________         _______
               conc. in environment             mg/l

Decomposition of a substance into more elementary compounds by the action of microorganisms such as bacteria.

Process by which substances such as pesticides or heavy metals move up the food chain, becoming more concentrated with each succeeding step up the chain.

Bone marrow
The soft tissue contained inside the bone.

Broad spectrum pesticide
A pesticide which kills a wide range of pest species, as opposed to a pesticide which kills a single or limited number of species.

A disease characterized by the rapid and uncontrolled growth of aberrant cells into malignant tumors.

Any substance capable of producing cancer or a chemical which causes or induces cancer.

The ability of a substance to produce cancer.

A malignant tumor of epithelial origin

Cardiovascular system
The heart and blood vessels.

Material added to an active ingredient to facilitate its preparation, storage, shipment, or use.

Chemical Abstracts Service Registry Number. The CAS No. is assigned to a specific compound and is used for cross referencing chemical names which refer to the same compound.

A clouding of the eye that interferes with light entering the eye.

see "Signal Word."

Central nervous system (CNS)
Portion of the nervous system which consists of the brain and spinal cord.

Certified applicator
A person who has been trained and certified as a pesticide applicator by a state agency which has been authorized to do so by EPA.

resembling acetylcholine, especially in physiological action. Cholinergic symptoms include nausea, vomiting, headache and sweating.

An enzyme of the body necessary for proper nerve function; also called serum cholinesterase.

Chromosomal aberration
An irregularity in the number or constitution of chromosomes which may cause abnormalities in a developing embryo.

Rod-like structure in the nucleus of a cell that forms during mitosis; composed of DNA and protein; chromosomes contain the genes responsible for heredity.

Occurring over a long period of time, either continuously or intermittently, used to describe ongoing exposures and effects that develop only after a long exposure.

Of or related to cilia; related to the suspension of the lens of the eye.

A soil component consisting of very fine particles (<0.002 mm diameter). Clay particles provide ample surface area for adsorption of molecules. Clay soils provide the most resistance to leaching. Soil texture and many other soil characteristics are determined by the relative amounts of sand, silt, clay and loam in a soil.

Cleft palate
A defect existing before, or at birth which results in a groove or crack in the roof of the mouth.

Clinical studies
Studies of humans under controlled conditions.

Common names
Common names for pesticides are established or accepted by the following organizations: A common name generally is not accepted for use on EPA registered labels or in CFR regulations until it has been accepted by ANSI.

The amount of active ingredient or pesticide equivalent in a quantity of diluent, expressed as lb/gal, ml/liter, etc.

Concentration factors
Concentration factors indicate whether or not a compound is accumulated in the tissue of an organism. It is calculated by dividing the concentration of the compound in the tissue by the concentration ingested in the diet or taken up from the surrounding medium.

Confounding factors
Variables other than those being tested which can affect the incidence or degree of a parameter being measured.

Existing at birth but acquired in the uterus rather than inherited.

A compound resulting from the bonding of two other compounds. Examples include glucoside conjugates formed from pesticides in plants and glucuronide conjugates formed from pesticides in animals.

Inflammation of the conjunctiva, the membrane that lines the inner surface of the eyelids.

Contact dermatitis
Skin swelling due to either initial acute irritation from short-term contact with a substance, or from chronic sensitization that develops from long-term skin contact with an irritating substance.

Contact poison
A poison which affects the target organisms through physical contact rather than through ingestion or inhalation (animals) or translocation (plants). Compare with "Stomach Poison."

Control group
A group of experimental subjects which are not exposed to a chemical or treatment being investigated so that they can be compared to experimental groups which are exposed to the chemical or treatment.

The transparent front portion of the eyeball.

Cost/benefit analysis
A quantitative evaluation of the costs which would be incurred versus the overall benefits to society of a proposed action such as the establishment of an acceptable dose of a toxic chemical.

Cumulative exposure
The summation of exposures of an organism to a chemical over a period of time.

Cytological aberration
A deviation from normal cell structure or function.

The capacity of a material to interfere with cell metabolism.

see "Signal Word."

Data gap
Missing information; used in this context to refer to that data which is required by the U. S. Environmental Protection Agency for registration of pesticides, herbicides, etc.

A chemical alteration to a pesticide. Chemical or biological breakdown of a complex compound into simpler compounds.

The study of the characteristics of human populations such as size, growth, density, distribution, and vital statistics.

The destruction or removal of the myelin sheath which is composed of a lipoid substance and envelops certain nerve fibers.

Of the skin: through or by the skin.

The movement of suspended or dissolved particles from a more concentrated region to a less concentrated region as a result of the random movement of individual particles. Diffusion tends to distribute particles uniformly throughout the available volume.

An order of insects that includes flies and mosquitoes.

The movement of a chemical from the blood to other tissues.

Dominant lethal assay
A mutagenic bioassay used in assessing the ability of a chemical to penetrate gonadal tissue and produce genetic damage. Male animals are treated with a test substance acutely (single dose) or over the entire period of sperm production. These males are then mated with females, which after about the 14th day of pregnancy are sacrificed and examined for the number of total implantations and viable fetuses.

A measure of exposure. Dose is often expressed in milligrams per kilogram (mg/kg) or parts per million (ppm).

Dose response
A quantitative relationship between the dose of a chemical and the degree/severity of an effect caused by the chemical.

A pesticide formulation which consists of an active ingredient impregnated on a finely ground carrier such as clay, talc, or calcium carbonate.

The study of the interrelationships between living organisms and their environment, both physical and biological.

The interacting system of a biological community and its non-living environment.

Effective dose
The ED50 is the effective dose for 50 percent of tested subjects.

The removal of a chemical from the body, primarily in the urine, feces or exhaled air.

The developing animal during pregnancy, especially during the early stages.

Pertaining to embryos, young organisms in the early stages of development.

Emulsifiable Concentrate (EC)
A pesticide formulation consisting of an active ingredient and an emulsifying agent in an organic solvent. The solvent is usually not soluble in water. When an EC product is mixed with water prior to application, the resulting mix is a dispersion of fine, oily particles in water.

A compound-induced toxic effect on the embryo during the initial phase of pregnancy.

Endangerment assessment
A site-specific risk assessment of the actual or potential danger to human health or welfare and the environment from the release of hazardous substances or waste.

A biological effect used as an index of the effect of a chemical on an organism.

Environmental fate
The destiny of a chemical after release to the environment; involves considerations such as transport through air, soil and water, bioconcentration, degradation, etc.

A protein, synthesized by a cell, that acts as a catalyst in a specific chemical reaction.

United States Environmental Protection Agency.

The study of the incidence and distribution of disease and/or toxic effects in a population.

The removal of a chemical from the body in urine, feces or expired air.

Contact with a chemical. Some common routes of exposure are dermal (skin), oral (by mouth) and inhalation (breathing).

Estimation of unknown values by extending or projecting from known values.

Food and Agriculture Organization of the United Nations.

FDA monitoring
The collection and analysis for pesticide residues carried out by the Food and Drug Administration. The primary components of the monitoring are the Total Diet Studies, which entail examining ready-to-eat foods, and the Compliance Programs, special assignments, and surveys on both domestic and imported foods, which include both surveillance and compliance examinations of fresh fruits and vegetables, grains, milk and dairy products, fish, and a variety of processed products and by-products.

Fetal resorption
Following the in utero death of a fetus, for whatever reason, the fetal tissues will undergo either partial or complete dissolution and the resulting products will be absorbed by the maternal tissue.

A compound-induced toxic effect on the fetus during the latter phase of pregnancy.

Unborn or unhatched vertebrate, especially one that has attained the basic structure of its kind; a developing human, usually from three months after conception until birth.

Flash point
The lowest temperature at which a liquid gives off ignitable vapors.

Food chain
A sequence of species in which each species serves as a food source for the next species. Food chains usually begin with species which consume detritus or plant material (herbivores) and proceed to larger and larger carnivores. Example: grasshopper eaten by snake eaten by owl.

Formulated pesticide product
A mixture of one or more pesticidal active ingredients with inert ingredients such as carriers, diluents, etc.; a packaged, ready-for-sale pesticide product. Types of formulations include liquids, dusts, emulsifiable concentrates, ultra-low volume and granular products.

A class of pesticides used to kill fungi, primarily those which cause diseases of plants.

Gastrointestinal tract (GI tract)
The entire digestive canal from mouth to anus.

Forced feeding by stomach tube.

General Use Pesticide (GUP)
A pesticide which may be purchased and used by individuals without any special certification or licensing. Pesticides classified by the EPA as GUP have not been shown to pose undue hazards to applicators, the general public or to the environment. Compare with "Restricted Use Pesticide."

Any toxic modification or alteration of the structure or function of genetic material.

The duration of pregnancy. In the human, gestation is normally nine months.

Enlargement of the thyroid gland.

A material capable of causing goiter.

Granular formulation
a dry, ready-to-use pesticide product which consists of an active ingredient mixed with or impregnated into a carrier such as coarse particles of clay.

Water located in saturated zones below the soil surface. Many wells and springs are fed by groundwater.

Groundwater residue guidance level.

see "General Use Pesticide."

see "Health Advisory."

The time required for half of the residue to lose its analytical identity whether through dissipation, decomposition, metabolic alteration or other factors. The half-life concept may be applied to residues in crops, soil, water, animals or specific tissues.

The potential that the use of a product would result in an adverse effect on man or the environment in a given situation.

Health Advisory (HA or LHA)
A non-enforceable guideline set by EPA and used to evaluate the health significance of a contaminant in drinking water when no Maximum Contaminant Level has been set by EPA for that contaminant. HAs are set at a concentration of contamination that can be consumed daily in drinking water over the course of a lifetime with no adverse health effects. HAs may or may not include consideration of cancer risks posed by the contaminant. Also known as "Lifetime Health Advisory."

The production of blood and blood cells; hemopoiesis.

A measure of area in the metric system approximately equal to 2.47 acres.

A toxic effect on blood components or properties such as changes in hemoglobin, pH, electrolytes, or protein of the plasma.

Henry's Law Constant
A parameter used in evaluating air exposure pathways. Values for Henry's Law Constant (H) were calculated using the following equation and the values previously recorded for solubility, vapor pressure, and molecular weight:
                         Vapor Pressure (atm) x Mole Wt (g/mole)
   H(atm-meter3/mole) =______________________________________
                          Water Solubility (g/cubic meter).

A malignant tumor occurring in the liver.

A pesticide used for killing or inhibiting plant growth. A weed or grass killer.

The study of the structure of cells and tissues; usually involves microscopic examination of tissue slices.

Maintenance of a constant internal environment in an organism.

A chemical substance secreted in one part of an organism and transported to another part of that organism where it has a specific effect.

Host-mediated assay
This assay evaluates the genotoxicity of a substance to microbial cells introduced (e.g., by intravenous injection) into a host animal. The host animal receives the test compound orally, and therefore acts as a source of chemical metabolism, distribution and excretion of the test compound.

Human equivalent dose
A dose which, when administered to humans, produces an effect equal to that produced by a dose in animals.

The study of the properties, distribution, behavior and effects of water on the earth's surface, in the soil and underlying rocks and in the atmosphere.

The chemical process of decomposition involving the splitting of a molecule and the addition of a water molecule.

To subject to hydrolysis; to undergo hydrolysis.

A decreased sense of touch.

A deficiency of oxygen.

Inert ingredient
An ingredient in a formulated pesticide product which will not prevent, destroy, repel or mitigate any pest and which is intentionally included in the product. Includes carriers and materials which dilute the active ingredient.

Drawing of air into the lungs.

A class of pesticides used to kill insects.

Amount of material inhaled, ingested, or absorbed dermally during a specified period of time.

Intraperitoneal (I.P.)
The introduction (e.g., by injection) of a substance into the peritoneal cavity which is comprised of the abdominal and pelvic spaces and contains the large internal organs.

The insertion of a tube; for example, the passing of a tube from the mouth through the esophagus and into the stomach as a means of facilitating the accurate, oral dosing of a test animal with a substance.

In vitro studies
Studies of chemical effects conducted in tissues, cells or subcellular extracts from an organism (i.e., not in the living organism).

In vivo studies
Studies of chemical effects conducted in intact living organisms.

Organisms which lack a spinal column.

Permanent, incurable.

The colored circular portion of the eyeball.

Two or more chemical compounds having the same structure but different properties.

Soil-water adsorption coefficient, calculated by using measurements of pesticide distribution between soil and water.

see "Adsorption coefficient."

see "Octanol-water partition coefficient."

Laboratory Information Bulletin (LIB)
An internal publication of FDA, for the dissemination of information concerning analytical methodology among FDA laboratories.

The immature form and stage of development of some insect species that go through extreme changes in the developmental process of becoming an adult.

A class of pesticides used to kill insect larvae. Usually refers to chemicals used for controlling mosquito larvae, but also to chemicals for controlling caterpillars on crops.

Time from the first exposure to a chemical until the appearance of a toxic effect.

Lethal Concentration.

The concentration of toxicant necessary to kill 50 percent of the organisms being tested. It is usually expressed in parts per million (ppm).

LC50/96 hr
Lethal concentration in a 96-hour test.

Lethal concentration, low. The lowest concentration to cause death in test animals.

Lethal dose.

The amount of a chemical that is lethal to one-half (50%) of the experimental animals exposed to it. LD50s are usually expressed as the weight of the chemical per unit of body weight (mg/kg). It may be fed (oral LD50), applied to the skin (dermal LD50), or administered in the form of vapors (inhalation LD50).

Lethal dose, low. The lowest dose which causes death in test animals.

The movement of a pesticide chemical or another substance downward through soil as a result of water movement, potentially causing contamination of groundwater resources.

Lowest Effect Level. In a series of dose levels tested, it is the lowest level at which an effect is observed in the species tested.


see "Health Advisory."

Lifetime Health Advisory
see "Health Advisory."

Lowest-Observed-Adverse-Effect-Level; the lowest dose in an experiment which produced an observable adverse effect.

A soil of intermediate texture containing moderate amounts of sand, silt and clay. Soil texture and many other soil characteristics are determined by the relative amounts of sand, silt, clay and loam in a soil.

Lowest-Observed-Effect-Level; the lowest dose in an experiment which produced an observable effect.

Malignant tumor
A cancerous tumor.

The class of organisms that have backbones (vertebrates); includes all animals that have hair and suckle their young.

Maximum Acceptable Tolerance Concentration.

Maximum Contaminant Level. The highest amount of a contaminant allowed by EPA in water supplied by a municipal water system; also referred to as "drinking water standard."

Metabolic enzymes
Protein-based substances that promote change in bodily cells.

The process of chemical change by which energy is provided in living cells.

Any product of metabolism, especially a transformed chemical.

Milligrams per kilogram.

Milligrams per kilogram per day.

Milligrams per liter.

Usual unit of measurement for contaminants of water; ug/l; equivalent to parts per billion (ppb).

Milligrams of material per cubic meter (of air or water).

Microgram per cubic meter (ug/m3) (of air or water).

Decreased pupil (eye) size.

Minimum Lethal Dose; the smallest of several doses which kills one of a group of test animals.

mm Hg
Millimeters of mercury.

Use of mathematical equations to simulate and predict real events and processes.

A class of pesticides used to kill mollusks, primarily snails and slugs.

Measuring concentrations of substances in environmental media or in human or other biological tissues.

Margin of Safety. Refer to "Uncertainty Factor."

Maximum Permissible Intake. A limit established by EPA, usually expressed as mg/day for a 60 kg person, which is used to determine the level of pesticide residues permitted on crops for human consumption.

Maximum Tolerated Dose; the highest dose of a chemical that does not alter the life span or severely affect the health of an animal.

Mucous membranes
Any tissue lining body cavities and canals which come in contact with the air, and kept moist by secretions of various types of glands (e.g., inside the mouth).

Musculoskeletal system
Composed of, or pertaining to the muscles and the skeleton.

An agent that causes a permanent genetic change in a cell other than that which occurs during normal genetic recombination.

The ability of a substance to produce a detectable and heritable change in genetic material which may be transmitted to the progeny of affected individuals through germ cells (germinal mutation) or from one cell generation to another within the individual (somatic mutation).

An alteration in genetic structure which is passed from one generation to the next.

An excessive dilation of the pupil of the eye.

The examination of a dead body, autopsy. The term necropsy is often used with respect to examination of animals other than humans.

Death of cells or tissue.

The No-Effect-Level of a pollutant is the concentration at or below which there will be no defined effect, either deleterious or beneficial, on a member of a population exposed to the pollutant in question.

Nervous system
Includes the brain and all the nerves.

Neural tube
A hollow tube in vertebrate embryos which changes and eventually forms the brain and spinal cord.

The ability of a substance to destroy nerve tissues or affect behavior.

Any substance that is capable of destroying or adversely affecting nerve tissue.

National Institute of Occupational Safety and Health; a branch of the U.S. Department of Health and Human Services and the U.S. Department of Labor. Responsible for setting limits to exposure which workers should be allowed to receive in their work.

No-Observed-Adverse-Effect Level; the highest dose in an experiment which did not produce an observable adverse effect.

The dosage or exposure level at which no toxicologically significant adverse effect(s) can be detected. The NOEL has been used interchangeably with the NEL (no effect level). However, there is a distinction which is based on the interpretation of the occurrence of an effect. An NEL denotes that at a particular dose, there was absolutely no effect. In reality, an effect may have occurred but went undetected for a variety of reasons. Thus, the more accepted terminology is the NOEL, which indicates that while an effect was not observed under a particular set of test conditions, it does not preclude the possibility that some effect may have occurred.

Will not vaporize or become a gas.

Not capable of affecting the entire system; limited to particular areas of a plant or animal.

Nontarget vegetation
Vegetation which is not expected or not planned to be affected by an herbicide application.

Nontarget species
Any plant, animal, or pest which is not intended to be treated with a pesticide application.

Octanol-water partition coefficient (Kow)
A measurement of how a chemical is distributed at equilibrium between octanol and water. It is an important parameter and is used often in the assessment of environmental fate and transport for organic chemicals. Additionally, Kow is a key variable used in the estimation of other properties.

Of or relating to the eye muscles.

Any substance capable of inducing tumors; a carcinogen.

The ability of a substance to produce either benign or malignant tumors.

Organophosphate Pesticide.

Of the mouth; through or by the mouth.

Organic carbon partition coefficient (Koc)
A measure of the tendency for organics to be adsorbed by soil and sediment and is expressed as:
              mg chemical adsorbed/kg organic carbon
     Koc =  __________________________________________
              mg chemical dissolved/liter of solution

The Koc is chemical specific and is largely independent of soil properties.

Organic Matter (OM)
Soil particles created by the decomposition of plant tissues. Soil OM has a high adsorptive capacity (higher than clay) and offers resistance to leaching of soil water and dissolved molecules.

The time period during embryonic development in which all major organs and organ systems are formed. During this period, the embryo is most susceptible to factors interfering with development.

Occupational Safety and Health Administration, a branch of the U.S. Department of Labor.

Provisional Acceptable Daily Intake (PADI)
The maximum dose of a substance that is anticipated to be without health risk to humans when taken daily over the course of a lifetime. PADIs are set by the EPA.

Any disease-causing agent, usually applied to living agents.

Causing or capable of disease.

Permissible Exposure Level; OSHA air standard.

EPA defines a pesticide as, "... any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest, and any substance or mixture of substances intended for use as a plant regulator, defoliant or dessicant." The following are a list of pesticides as classified by their target species:
Acaricide mites, ticks
algaecide algae
attractant insects, birds, other vertebrates
avicide birds
bactericide bacteria
defoliant unwanted plant leaves
desiccant unwanted plant tops
fungicide fungi
growth regulator insect and plant growth
herbicide weeds
insecticide insects
miticide mites
molluscicide snails, slugs
nematicide nematodes
piscicide fish
predacide vertebrates
repellents insects, birds, other vertebrates
rodenticide rodents
silvicide trees and woody vegetation
slimicide slime molds
sterilants insects, vertebrates

Hydrogen ion concentration; used to express the degree of acidity or alkalinity of a material.

The dynamic behavior of chemicals inside biological systems; includes the processes of uptake, distribution, metabolism and excretion.

Toxicity resulting from sequential exposure to a photosensitizing agent and sunlight.

Having to do with the mechanics of body function.

The resulting form of many small molecules joined together; a mixture of compounds formed by a specific molecular process called polymerization.

A measure of the relative strength of a chemical.

The ability of a substance to increase the toxic effect(s) of another compound.

Parts per billion; a measure of concentration. May represent the concentration of a residue in soil, water or whole animals. For example, one ppb is equivalent to one second in 32 years.

Parts per million; a measure of concentration. May represent the concentration of a residue in soil, water or whole animals. For example, one ppm is equivalent to one minute in 2 years.

The opening in the colored portion (iris) of the eye, through which light passes.

Descriptive of size, magnitude or degree.

The amount of active ingredient or acid equivalent applied per unit area or other treatment unit.

(1) In biochemistry: a specialized molecule in a cell that binds a specific chemical with high specificity and high affinity; (2) In exposure assessment: an organism that receives, may receive, or has received environmental exposure to a chemical.

Reentry interval
The period of time designated by Federal law between the application of certain hazardous pesticides to crops, and the entrance of workers into the fields of crops without protective clothing.

Registration standard
A document produced by the EPA, which details the various conditions which chemical registrants must meet in order to reregister pesticide products containing active ingredients. Through its Registration Standards program, EPA is reexamining, by current scientific standards, the health and environmental safety of approximately 600 active ingredients contained in some 45,000 currently registered products.

Pertaining to the kidney.

Reproductive effects
Changes which may occur during the reproductive process including mutagenesis, teratogenesis, diminished fertility, death, growth retardation, functional disorders, and prematurity or death of the offspring.

A tissue in an organism or a place in the environment where a chemical accumulates, from which it may be released at a later time.

That quantity of pesticide, its degradation products, and/or its metabolites remaining on or in the soil, plant parts, animal tissues, whole organisms, and surfaces.

Resorption of fetuses
The disappearance of part, or all, of a fetus caused by biochemical reactions that may involve dissolution, absorption and/or other actions.

Respiratory system/tract
All the passages through which air is taken in and out of the body with breathing, including the nose, trachea, larynx, and lungs, where an exchange of oxygen and carbon dioxide takes place.

Restricted Use Pesticide (RUP)
A designation given to a pesticide by the EPA which restricts purchase and use of that pesticide to certified applicators. The designation is given to pesticides which pose a potential hazard to applicators, the general public or to the environment or may be highly toxic.

Reference dose.

Risk assessment
A qualitative or quantitative evaluation of the environmental and/or health risk resulting from exposure to a chemical or physical agent (pollutant); combines exposure assessment results with toxicity assessment results to estimate risk.

The potential for realization of unwanted negative consequences or events.

A class of pesticides which kills rodents, especially rats and mice.

Risk reference dose.

see "Restricted Use Pesticide."

A soil component consisting of coarse particles (0.05 to 2.0 mm diameter). Sand particles provide relatively little surface area for adsorption of molecules. Soil water and dissolved materials move/leach easily through sandy soils. Soil texture and many other soil characteristics are determined by the relative amounts of sand, silt, clay and loam in a soil.

Refers to the external pouch that contains the testes in most mammals.

Selective herbicide
One that kills specific undesirable plants, sparing other desirable plants; this is done through different types of toxic action or by the manner in which the material is used (its formulation, dosage, timing, placement, etc.).

The development of a hypersensitive or allergic reaction upon reexposure to a substance. The reaction may be immediate or delayed and may be of short-term or chronic duration.

Signal word
One of three words which must appear in large, bold letters on a pesticide label. Signal words usually indicate the level of acute toxicity posed by the pesticide product.
Signal WordToxicity
DANGER highly toxic
WARNING moderately toxic
CAUTION slightly toxic or relatively non-toxic

A soil component consisting of moderately sized particles (0.002 to 0.05 mm diameter). Silt particles provide a moderate amount of surface area for adsorption of molecules, providing some resistance to leaching of charged molecules. Soil texture and many other soil characteristics are determined by the relative amounts of sand, silt, clay and loam in a soil.

A place in the environment where a compound or material collects.

Suggested No Adverse Response Level.

Soil mobility
Movement of a compound through soil from the treated area by leaching, volatilization, adsorption and desorption, or dispersal by water. Leaching is of particular concern because of the potential for contamination of groundwater.

The concentration of a substance that dissolves in a given solvent. HIGH SOLUBILITY: readily dissolves. LOW SOLUBILITY: does not dissolve very well.

Soil organic matter
see "Organic Matter."

Solvent solubility
Concentration of a material that dissolves in a given solvent.

A surface phenomenon which may be either absorption or adsorption, or a combination of the two; often used when the specific mechanism is not known.

Special review
An intensive analysis of all the data on a chemical, including its risks and benefits. The initiation of a special review process is an announcement of EPA's concern about the safety of a pesticide's use. Existing pesticides suspected of posing unreasonable risks to human health, nontarget organisms or the environment are referred to EPA for special review. This process may or may not lead to the cancellation of a material.

An organ near the stomach or intestines of most vertebrates; the site of final destruction of blood cells, blood storage, and production of lymphocytes.

Statistically significant
Probably caused by something other than mere chance.

Short-Term Exposure Limit. The maximum allowable concentration, or ceiling, not to be exceeded at any time during a 15-minute exposure period up to four times per day. The level to which persons may be exposed continuously for 15 minutes without adverse effects.

Total inability to reproduce.

Stomach poison
A pesticide which must be eaten in order to kill or poison an organism. Compare with "Contact poison."

Intermediate between acute and chronic toxicities; subchronic toxicity studies involve repeated daily exposures of animals to a chemical for part (not exceeding 10%) of a lifespan. In rodents, this period extends up to 90 days of exposure.

Under the skin.

Surface water
Water at the soil surface in open bodies such as streams, rivers, ponds, lakes and oceans.

Capacity to be adversely affected by pesticide treatment.

An interaction of two or more chemicals that results in an effect that is greater than the sum of their effects taken independently.

Affecting the body generally; distributed throughout the body.

Systemic insecticide
Capable of being absorbed by plants into the plant sap, or by animals into the blood stream, without undue harm to the plant or animal; capable of poisoning insects feeding on the plant juice or animal blood. For example, a systemic insecticide can be applied to the soil, enter the roots of the plant, travel to the leaves, and kill insects feeding on the leaves.

Systemic toxicity
Poisoning of the whole system or organism, rather than poisoning which affects, for example, a single organ.

T 1/2
see "Half-life."

The target species is the organism which the pesticide is intended to control. Conversely, the non-target species are those which because they are either beneficial or harmless, are not to be killed by the pesticide.

Toxic dose; the dose of a chemical that produces signs of toxicity.

The lowest dose which produces signs of toxicity.

Any substance capable of producing structural abnormalities of prenatal origin, present at birth or manifested shortly thereafter.

The ability to produce birth defects. A teratogenic agent has the ability to induce or increase the incidence of congenital malformations, i.e., permanent structural or functional deviations arising during embryogenesis.

The ability of a substance to produce irreversible birth defects or anatomical or functional disorders as a result of an effect on the developing embryo or fetus.

Testicular atrophy
The acquired local reduction in the size of testicles caused by disease or physiological imbalance.

Referring to the testes, a pair of male reproductive glands.

Theoretical Maximum Residue Contribution (TMRC)
The amount of a substance that would be present in a 1.5 kg "average" daily diet if all commodities with established tolerances bore residues at the tolerance level. The percentages of various commodities in the "average" diet are those used by EPA and are based on the "1965-66 Household Food Consumption Survey" conducted by USDA.

The lowest dose of a chemical at which a specified measurable effect is observed and below which it is not observed.

An immune system gland located at the base of the neck in young vertebrates; it tends to disappear or become nonfunctional in adults.

Thyroid carcinoma
Malignant tumor of the thyroid gland, an endocrine gland which lies in front of the trachea.

Thyroid gland
An endocrine gland which lies in front of the trachea, or wind pipe.

A group of similar cells.

TLm TL50
Median tolerance limit; for example, the concentration of chemical in water necessary to kill 50 percent of the test aquatic organisms during a specific exposure period. The TLm is usually expressed as parts per million parts of water for 24, 48, 72, or 96 hours of exposure.

Threshold Limit Value. The highest allowable air concentration of a chemical in which workers may work for many years (8 hours a day, 40 hours per week) without negative health effects. Expressed as milligrams (mg) per cubic meter of air (mg/m3). The level to which persons may be exposed for an 8-hour workday without adverse effects.

Threshold Limit Value-Time Weighted Average. The time-weighted average concentration for a normal 8-hour workday and a 40-hour work week, to which nearly all workers may be repeatedly exposed without adverse effect.

(1) A legal limit, established by EPA, for the maximum amount of a pesticide residue which may be present in or on a food. Pesticide tolerances on raw agricultural commodities are listed in Part 180, CFR 40; tolerances on processed foods are listed in Part 193, CFR 21; and tolerances on processed animal feeds are listed in Part 561, CFR 21. Temporary tolerances, which cover residues resulting from an experimental use, generally expire after one year. (2) Capacity to withstand pesticide treatment without adverse effect on normal growth and function.

Harmful; poisonous.

(l) The capacity or property of a substance to cause adverse effects. (2) The specific quantity of a substance which may be expected, under specific conditions, to do damage to a specific living organism.

Acquisition by a cell of the property of uncontrolled growth.

Transport of a substance through a plant from the site of absorption to other parts of the plant.

Small tubes which serve to transport bodily substances.

An abnormal mass of cells produced by unregulated overgrowth of cells, and which has no physiologic function. Tumors may be benign or malignant.

The Time-Weighted Average concentration is the average exposure concentration based on the duration of exposure to airborne concentration as it varies during an 8-hour workday.

see "micrograms per liter."

Ultra-Low Volume (ULV)
A liquid pesticide product which is applied undiluted at a rate of one-half gallon per acre or less.

Uncertainty factor
A number (equal to or greater than one) used to divide NOAEL or LOAEL values derived from measurements in animals or small groups of humans, in order to estimate a NOAEL value for the whole human population; also called margin-of-safety.

Vapor pressure
A relative measure of the volatility of a chemical in its pure state. The pressure exerted by a gas that is in equilibrium with its solid or liquid form.

Capable of vaporizing or evaporating readily.

Virtually Safe Dose.

see "Signal Word."

Water solubility
The maximum concentration of a chemical that dissolves in pure water at a specific temperature and pH.

World Health Organization.