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IUPAC Glossary of Terms Used in Toxicology - Terms Starting with C

Imagined perception of vile odors, including coprosmia (smelling feces) and necrosmia (the smell of death).

Form of mineralization in which organic tissue becomes hardened by deposition of calcium salts within its substance.


calibration material
See reference material

Disease resulting from the development of a malignant tumor.

Compound which is formed between carbon monoxide and hemoglobin in the blood of animals and humans and which is incapable of transporting oxygen.

See carbonylhemoglobin

carcinogen n., -ic adj.
Agent (chemical, physical or biological) which is capable of increasing the incidence of malignant neoplasms, thus causing cancer.
Note: Annex 3 describes the classification systems for carcinogens.

carcinogen/esis n., -etic adj.
Induction, by chemical, physical, or biological agents, of malignant neoplasms and thus cancer.

Process of induction of malignant neoplasms, and thus cancer, by chemical, physical or biological agents.

carcinogenicity test

Malignant tumor of an epithelial cell.

Chemically harmful to the cells of the heart.


  1. Substance in appreciable amount which, when associated with a trace of a specified substance, will carry the trace with it through a chemical or physical process.
  2. Person who is heterozygous, that is carries only one allele, for a recessive genetic character leading to disease, and hence does not, under most circumstances, display the disease phenotype but can pass it on to the next generation.
  3. Gas, liquid, or solid substance (often in particulate form) used to absorb, adsorb, dilute or suspend a substance to facilitate its transfer from one medium to another.

carrier-linked prodrug
carrier prodrug
Compound that contains a temporary linkage between a given active substance and a transient carrier group, the latter producing improved physicochemical or pharmacokinetic properties and easily removable in vivo.

carrier protein

  1. Protein to which a specific ligand or hapten is conjugated
  3. Protein added to prevent nonspecific interaction of reagents with surfaces, sample components, and each other.
  4. Protein found in cell membranes which facilitates transport of a ligand across the membrane.

carrier substance
Substance which binds to another substance and transfers it from one site to another.


  1. Transfer in farming and agricultural processing of a component from one system such as soil or feed to another system such as a plant, animal or human being: carry-over is expressed as the concentration of the component in the second system divided by its concentration in the first.
  2. Process in analytical studies by which materials are carried into a reaction mixture in which they do not belong.
  3. Persistence of a substance in soil, e.g., a pesticide, such that injury may occur subsequently to a new crop.
  4. Persistence of a test substance in participants undergoing a cross-over clinical trial study, in which each participant randomly receives the placebo and test substance with an intervening washout period.

case cohort study
Variant of the case control study in which the controls are drawn from the same cohort as the cases but are identified before the cases develop; some of the controls may later become cases.

case control study
case comparison study
case compeer study
case history study
case referent study
retrospective study
Study which starts with the identification of persons with the disease (or other outcome variable) of interest, and a suitable control (comparison, reference) group of persons without the disease. The relationship of an attribute to the disease is examined by comparing the diseased and non-diseased with regard to how frequently the attribute is present or, if quantitative, the levels of the attribute, in the two groups.

antonym anabolism

  1. Reactions involving the oxidation of organic substrates to provide chemically available energy (for example ATP) and to generate metabolic intermediates.
  2. Generally, process of breakdown of complex molecules into simpler ones, often providing biologically available energy.

Schizophrenia marked by excessive, and sometimes violent, motor activity and excitement, or by generalized inhibition.

See laxative

ceiling value (CV)
Airborne concentration of a potentially toxic substance which should never be exceeded in a worker's breathing zone.

cell cycle
Regulated biochemical steps that cells go through involving DNA replication and cell division, usually depicted as a sequential cyclical series of events.

cell line
Defined unique population of cells obtained by culture from a primary source through numerous generations.
See also transformed cell line

cell-mediated hypersensitivity
State in which an individual reacts with allergic effects caused by the reaction of antigen-specific T-lymphocytes following exposure to a certain substance (allergen) after having been exposed previously to the same substance or chemical group.

cell-mediated immunity
Immune response mediated by antigen-specific T-lymphocytes.

cell proliferation
Rapid increase in cell number.

cell strain
Cells having specific properties or markers derived from a primary culture or cell line.

censored data
Sample observations for which the complete distribution is not known: for example, a cohort study in which some persons cannot be followed to the predetermined end of the study (“right-censored data”) or environmental assay data in which some results are less than the sample detection limit (“left-censored data”).

certified reference material (CRM)
Reference material, accompanied by documentation issued by an authoritative body and referring to valid procedures used to obtain a specified property value with uncertainty and traceability.
Example: human serum with assigned quantity value for the concentration of cholesterol and associated measurement uncertainty stated in an accompanying certificate, used as calibrator or measurement trueness control material.

chain of custody
Sequence of responsibility for a substance from the manufacturer to the distributor, to the user, or to the person(s) ultimately responsible for waste disposal. This term is also used in controlled transmission of samples from collection to analysis, especially of samples of materials used for medico-legal or forensic purposes.

chelation therapy
Treatment with a chelating agent to enhance the elimination or reduce the toxicity of a metal ion.

Sensations that arise when chemical compounds activate receptor mechanisms for other effectors, such as light, pain, pressure, and heat, in the eye, skin, nose, mouth and throat; e.g., the burning feeling from chili pepper, the cooling from the menthol in mouthwash, and the stinging feeling of carbonation.

chemical etiologic agent
See toxic substance

chemical conversion
Change from one chemical species to another.

chemical etiologic agent
See toxic substance

chemical oxygen demand (COD)
Measure of the amount of oxygen, divided by the volume of the system, required to oxidize the organic (and inorganic) matter in wastewater using a chemically oxidizing agent. In practice, it is usually expressed in milligrams O2 per litre.

chemical safety
Practical certainty that there will be no exposure of organisms to toxic amounts of any substance or group of substances: this implies attaining an acceptably low risk of exposure to potentially toxic substances.

chemical species (of an element)

chemical warfare
Military operations using the toxic properties of chemical agents to kill, injure or incapacitate human beings, animals, or plants.

Irrational fear of chemicals.

Chemically induced swelling around the eye caused by edema of the conjunctiva.

Substance used to sterilize mites, insects, rodents or other animals.

Acne-like eruption caused by exposure to certain chlorinated organic substances such as polychlorinated biphenyls or 2,3,7,8-tetrachlorodibenzo-p-dioxin [2,3,7,8-tetrachlorooxanthrene] and other polychlorinated dibenzo dioxins and furans.

See parasympathomimetic

cholinesterase inhibitor
Substance which inhibits the action of acetylcholinesterase (EC and related enzymes which catalyse the hydrolysis of choline esters: such a substance causes hyperactivity in parasympathetic nerves.
Note: Examples include organophosphate and carbamate pesticides.

Either of two filaments joined at the centromere into which a chromosome divides as it duplicates itself during cell division.

Stainable complex of DNA and proteins present in the nucleus of a eukaryotic cell.

chromosomal aberration
Abnormality of chromosome number or structure.

Self-replicating structure consisting of DNA complexed with various proteins and involved in the storage and transmission of genetic information; the physical structure that contains the genes.

antonym acute
Long-term, (in relation to exposure or effect).

  1. In experimental toxicology, chronic refers to mammalian studies lasting considerably more than 90 days or to studies occupying a large part of the lifetime of an organism.
  2. In clinical medicine, long established or long lasting.

chronic effect
long-term effect
antonym acute effect
Consequence which develops slowly and (or) has a long-lasting course: may be applied to an effect which develops rapidly and is long lasting.

chronic exposure
long-term exposure
antonym acute exposure
Continued exposure or exposures occurring over an extended period of time, or a significant fraction of the test species' or of the group of individuals', or of the population's life-time.

chronic toxicity
long-term toxicity
antonym acute toxicity

  1. Adverse effects following chronic exposure.
  2. Effects which persist over a long period of time whether or not they occur immediately upon exposure or are delayed.

chronic toxicity test
long-term toxicity test
antonym acute toxicity test

Study of the influence of biological rhythms on the toxicity of substances or of the influence of a toxicant on biological rhythms.

ciguateratoxin poisoning
Serious illness caused by eating carnivorous fish such as snappers and barracuda that have become contaminated by toxins produced by the micro-alga, Gambierdiscus toxicus; gastrointestinal symptoms may accompany a wide variety of neurological symptoms including ataxia, vertigo, flaccid paralysis, respiratory arrest, and reversed perception of hot and cold; the neurological symptoms may persist for many years.

Relating to or exhibiting an approximately 24-hour periodicity.

circulation of substances in the environment
Movement of xenobiotic substances in the environment with air flow, river current, soil, water, etc.


  1. Liver disease defined by histological examination and characterized by increased fibrous tissue, abnormal morphological and physiological changes such as loss of functional liver cells, and increased resistance to blood flow through the liver (portal hypertension).
  2. Chronic interstitial inflammation and fibrosis of an organ.

Describing an organ showing cirrhosis.

Agent causing chromosome breakage and (or) consequent gain, loss or rearrangement of pieces of chromosomes.

Formation (or generation) of chromosomal breaks and (or) consequent gain, loss or rearrangement of pieces of chromosomes.

clearance (general) (co/ci)(ΔV t)
Product of the concentration co of a component in an output system and the volume flow rate of the output system divided by the concentration ci of this component in the input system.
Note: The term ‘mean volume rate’ is recommended for this quantity.

clearance (in physiology and toxicology)

    Note : Total clearance is the sum of the clearances of each eliminating organ or tissue for that component
  2. (in pulmonary toxicology) Volume or mass of lung cleared divided by time of elimination; used qualitatively to describe removal of any inhaled substance which deposits on the lining surface of the lung.
  3. (in renal toxicology) Quantification of the removal of a substance by the kidneys by the processes of filtration and secretion; clearance is calculated by relating the rate of renal excretion to the plasma concentration.

cleavage (of a molecule)
Splitting of a molecule into smaller molecular entities.

clinical toxicology
Scientific study involving research, education, prevention and treatment of diseases caused by substances such as drugs and toxins.
Note: Often refers specifically to the application of toxicological principles to the treatment of human poisoning.

clon/e n., -al adj.

  1. Population of genetically identical cells or organisms having a common ancestor.
  2. To produce such a population.,
  3. Recombinant DNA molecules all carrying the same inserted sequence.

Pertaining to alternate muscular contraction and relaxation in rapid succession.

cloning vector
Small circle of DNA (e.g., a plasmid) or modified bacteriophage (bacterial virus) that can carry a segment of foreign DNA into an appropriate host organism (e.g. a bacterial, yeast or mammalian cell).
After [9]

cluster sampling

  1. A method of sampling in which the population is divided into aggregates (or clusters) of items bound together in a certain manner. A sample of these clusters is taken at random and all the items which constitute them are included in the sample.
  2. A sampling method in which each unit selected is a group of persons (all persons in a city block, a family, etc.) rather than an individual.

See agonist

Chemical, physical or biological factor which intensifies the effect of a carcinogen.

Codex Alimentarius
Collection of internationally adopted food standards drawn up by the Codex Alimentarius Commission, the principal body implementing the joint FAO/WHO Food Standards Programme.


cohort analysis

cohort study
concurrent study
follow-up study
incidence study
longitudinal study
prospective study
Analytic study of epidemiological study in which subsets of a defined population can be identified who are, have been, or in the future may be exposed or not exposed, or exposed in different degrees, to a factor or factors hypothesized to influence the probability of occurrence of a given disease or other outcome. The main feature of the method is observation of a large population for a prolonged period (years), with comparison of incidence rates of the given disease in groups that differ in exposure levels.

combined effect of poisons
Simultaneous or successive effect of two or more poisons on the organism by the same route of exposure.

Process by which a normally non-biodegradable substance is biodegraded only in the presence of an additional carbon source.
See also metabolism

comet assay
Means of measuring DNA damage, particularly DNA strand breaks. A cell is embedded in agar and exposed to a DNA-damaging agent. The cell is then permeabilized with a detergent and an electric field is applied. If the cell's genomic DNA has been broken into small fragments, these fragments move out of the cell by electrophoresis and form a streak or “tail” leading away from the cell which looks like a comet.

comparison group
See control group

comparative genomics
Study of the relationship of genome structure and function across different biological species.
After [9]

comparative risk
See relative excess risk


compartmental analysis
Mathematical process leading to a model of transport of a substance in terms of compartments and rate constants, usually taking the form C = Aet + Be - βt… where each exponential term represents one compartment. C is the substance concentration; A, B, … are proportionality constants; α, β, … are rate constants; and t is time.

Separate into compartments.

Adaptation of an organism to changing conditions of the environment (especially chemical) is accompanied by the emergence of stresses in biochemical systems which exceed the limits of normal (homeostatic) mechanisms. Compensation is a temporary concealed pathology which later on can be manifested in the form of explicit pathological changes (decompensation).

competent authority
In the context of European Community Council Directive 79/831/EEC, the Sixth Amendment to the European Community Council Directive 67/548/EEC relating to the Classification, Packaging and Labeling of Dangerous Substances, official government organization or group receiving and evaluating notifications of new substances.

competent bacteria
Culture of bacteria (or yeast) treated in such a way that their ability to take up DNA molecules without transduction or conjugation has been enhanced.

complementary DNA (cDNA)
DNA generated from an expressed messenger RNA through a process known as reverse transcription.

complete mineralization
Complete breakdown of a complex organic compound to carbon dioxide, water, oxides and oxidative inorganic products such as nitrate or sulfate.

comprehensive effect of poisons
Simultaneous or successive effect made on an organism by poisons entering from different media, from air, from water, from food or through the skin.

computational toxicology


  1. Any one of a group of three quantities characterizing the composition of a mixture and defined as one of mass, amount of substance (chemical amount) or number divided by volume, giving, respectively, mass, amount (of substance) or number concentration.
  2. Short form for amount (of substance) concentration (substance concentration in clinical chemistry).

concentration-effect curve
exposure-effect curve
Graph of the relation between exposure concentration and the magnitude of the resultant biological change.

concentration-effect relationship
exposure-effect relationship

Association between exposure concentration and the resultant magnitude of the continuously graded change produced, either in an individual or in a population.

concentration-response curve
exposure-response curve
Graph of the relation between exposure concentration and the proportion of individuals in a population responding with a defined effect.

concentration-response relationship
exposure-response relationship
Association between exposure concentration and the incidence of a defined effect in an exposed population.

concord/ance n., -ant adj.
Pairs or groups of individuals of identical phenotype.
Note: In twin studies, this is a condition in which both twins exhibit or fail to exhibit a trait under investigation.

concurrent study
See cohort study

concurrent validity
Measurement and its criterion refer to the same point in time: an example would be a visual inspection of a wound for evidence of infection validated against bacteriological examination of a specimen taken at the same time.

confounding (in data analysis)

  1. Situation in which the effects of two processes are not distinguishable from one another: the distortion of the apparent effect of an exposure on risk brought about by the association of other factors which can influence the outcome.

confounding variable
Changing factor that can cause or prevent the outcome of interest, is not an intermediate variable, and is associated with the factor under investigation.

One of two or more substances related to each other by origin, structure, or function.

Trait, condition or disorder that exists in an organism from birth.
After [9]

conjugate (in biochemistry)

  1. Chemical species produced in living organisms by covalently linking two chemical moieties from different sources.
    Example; A conjugate of a xenobiotic with some group such as glutathione, sulfate or glucuronic acid, to make it soluble in water or compartmentalized within the cell.
    See also phase II reaction
  2. Material produced by attaching two or more substances together, e.g. a conjugate of an antibody with a fluorochrome, or an enzyme.

Mucous membrane which covers the eyeball and lines the under-surface of the eyelid.

Inflammation of the conjunctiva.

conservative assessment of risk
Assessment of risk which assumes the worst possible case scenario and therefore gives the highest possible value for risk: risk management decisions based on this value will maximize safety.

construct validity

contact dermatitis
Inflammatory condition of the skin resulting from dermal exposure to an allergen (sensitizer) or an irritating (corrosive, defatting) substance.

contact poison

  1. Chemical which injures the target organism through physical contact and skin absorption rather than through ingestion or inhalation.
  2. Pesticide (herbicide) that causes injury to only the plant tissue to which it is applied or which is not appreciably translocated within plants.

Process by which possible release, discharge or spill of a toxic substance during normal use or after an accident is prevented by appropriate action.


  1. Minor impurity present in a substance.
  2. Extraneous material inadvertently added to a sample prior to or during chemical or biological analysis
  3. In some contexts, as in relation to gas cleaning equipment, used as a synonym for “pollutant”, especially on a small scale.
  4. Unintended component in food that may pose a hazard to the consumer.

content validity

antonym indication
Any condition which renders some particular line of treatment improper or undesirable.

control group
comparison group
Selected subjects of study, identified as a rule before a study is done, which comprises humans, animals, or other species who do not have the disease, intervention, procedure or whatever is being studied, but in all other respects are as nearly identical to the test group as possible.

control, matched

convection (as applied to air and water motion)
Predominantly vertical motion of air or of water, induced by the expansion of the air or of water heated by the earth’s surface, or by human activity, and its resulting buoyancy.

See chemical conversion, biotransformation

core grade
Quality rating, based on standard evaluation criteria established by the US Office of Pesticide Programs regulatory agencies, given to toxicological studies after submission by registrants.


count mean diameter
Mean of the diameters of all particles in a population.
See also mass mean diameter

count median diameter
Calculated diameter in a population of particles in a gas or liquid phase above which there are as many particles with larger diameters as there are particles below it with smaller diameters.
See also mass mean diameter

See crepitations

Abnormal respiratory sounds heard on auscultation of the chest, produced by passage of air through passages which contain secretion or exudate or which are constricted by spasm or a thickening of their walls; also referred to as rhonchi.
Note: Auscultation is the process of listening for sounds within the body by ear unassisted or using a stethoscope.

criteri/on (pl. -a)
Validated set of data used as a basis for judgment.

criterion validity

critical concentration (for a cell or an organ)

critical dose

critical effect

critical end-point
Toxic effect used by the USEPA as the basis for a reference dose.

critical group
Part of a target population most in need of protection because it is most susceptible to a given toxicant.

critical organ (in toxicology)
Organ which first attains the critical concentration of a substance and exhibits the critical effect under specified circumstances of exposure and for a given population.
After [2]

critical organ concentration (of a substance)
Mean concentration of a substance in the critical organ at the time the substance reaches its critical concentration in the most sensitive type of cell in the organ.

critical period (of development)
Stage of development of an organism, e.g., organogenesis in the fetus, that is of particular importance in the life cycle if the normal full development of some anatomical, physiological, metabolic, or psychological structure or function is to be attained.

critical study
pivotal study
Investigation yielding the no-observed-adverse-effect-level that is used by the USEPA as the basis of the reference dose.

cross-product ratio
See odds ratio

cross-sectional study (of disease prevalence and associations)
disease frequency survey
prevalence study
Note: Disease prevalence rather than incidence is normally recorded in a cross-sectional study and the temporal sequence of cause and effect cannot necessarily be determined.

cumulative death rate
Proportion of a defined group that die within the specified time period (e.g., month, year).
Note: It may refer to all deaths or to deaths from a specific cause or specific causes.

cumulative effect
Overall change which occurs after repeated doses of a substance or radiation.

cumulative incidence
incidence proportion
Number or proportion of individuals in a group who experience the onset of a health-related event during a specified time interval.
Note: This interval is generally the same for all members of the group, but, as in lifetime incidence, it may vary from person to person without reference to age.

cumulative incidence rate
Proportion of the cumulative incidence to the total population.

cumulative incidence ratio
Value obtained by dividing the cumulative incidence rate in the exposed population by the cumulative incidence rate in the unexposed population.

cumulative median lethal dose
Estimate of the total administered amount of a substance which is associated with the death of half a population of animals when the substance is administered repeatedly in doses which are generally fractions of the median lethal dose.

cumulative risk

  2. Total probability of a harmful effect over time.

Pertaining to the skin.

Compounds able to produce cyanide.
Examples: Cyanogenic glycosides such as amygdalin in peach and apricot stones.

Bluish coloration, especially of the skin and mucous membranes and fingernail beds, caused by abnormally large amounts of reduced hemoglobin in the blood vessels as a result of deficient oxygenation.

Toxin produced by Cyanobacteria, sometimes called bluegreen algae.
Note: Examples are microcystin and cylindrospermin.

cyclo-oxygenase specific inhibitors
Substances, such as aspirin and ibuprofen, which block the activity of cyclo-oxygenase (COX), an enzyme that is responsible for the formation of prostanoids (including prostaglandins, prostacyclin and thromboxane); inhibition of COX can provide relief from inflammation and pain.

Conjugated proteins containing heme as the prosthetic group and associated with electron transport and with redox processes.

cytochrome P-420
Inactive derivative of cytochrome P-450 found in microsomal (see microsome) preparations.

cytochrome P-448
Obsolete term for cytochrome P-450 I, A1, and A2, one of the major families of the cytochromes P-450 hemoproteins.
Note: During the mono-oxygenation of certain substances, often a detoxification process, these iso-enzymes may produce intermediates which can initiate mutations, cancer, immunotoxic reactions and adverse effects.

cytochrome P-450 (CYP)
Member of a superfamily of heme-containing mono-oxygenases involved in xenobiotic metabolism, cholesterol biosynthesis, and steroidogenesis, in eukaryotic organisms found mainly in the endoplasmic reticulum and inner mitochondrial membrane of cells. ‘P-450’ refers to the observation that a solution of this enzyme exposed to carbon monoxide strongly absorbs light at a wavelength of 450nm compared with the unexposed solution, (a difference spectrum caused by a thiolate in the axial position of the heme opposite to the carbon monoxide ligand).
After [2]

Branch of genetics which correlates the structure and number of chromosomes as seen in isolated cells with variation in genotype and phenotype.

Any of a group of soluble proteins that are released by a cell causing a change in function or development of the same cell (autocrine), an adjacent cell (paracrine), or a distant cell (endocrine); cytokines are involved in reproduction, growth and development, normal homeostatic regulation, response to injury and repair, blood clotting, and host resistance (immunity and tolerance).

Fundamental substance or matrix of the cell (within the plasma membrane) which surrounds the nucleus, endoplasmic reticulum, mitochondria and other organelles.

Causing damage to cell structure or function.