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

Prefix meaning rapid as in tachycardia and tachypnoea.

antonym bradycardia
Abnormally fast heartbeat.

antonym bradypnoea
Abnormally fast breathing.

Substance intended to kill tapeworms.

target (in biology)
Any organism, organ, tissue, cell or cell constituent that is subject to the action of an agent.

target population (in epidemiology)

  1. Collection of individuals, items, measurements, etc. about which inferences are required: the term is sometimes used to indicate the population from which a sample is drawn and sometimes to denote any reference population about which inferences are needed.
  2. Group of persons for whom an intervention is planned.

T cell
See T lymphocyte

technical directive
See standard

Structure which terminates the arm of a chromosome.
Note: A similar term ‘telomer’, with a different meaning is found in the IUPAC Gold Book

temporary acceptable daily intake
Value for the acceptable daily intake proposed for guidance when data are sufficient to conclude that use of the substance is safe over the relatively short period of time required to generate and evaluate further safety data, but are insufficient to conclude that use of the substance is safe over a lifetime.
Note: A higher-than-normal safety factor is used when establishing a temporary ADI and an expiration date is established by which time appropriate data to resolve the safety issue should be available.

temporary maximum residue limit
Regulatory value established for a specified, limited time when only a temporary acceptable daily intake has been established for the pesticide concerned or, with the existence of an agreed acceptable daily intake, the available residue data are inadequate for firm maximum residue recommendations.

Agent that, when administered prenatally (to the mother), induces permanent structural malformations or defects in the offspring.


  1. Potential to cause the production of nonheritable structural malformations or defects in offspring.
  2. Production of nonheritable structural malformations or defects in offspring.

Study of malformations, monstrosities or serious deviations from normal development in organisms.

testing of chemicals

  1. In toxicology, evaluation of the therapeutic and potentially toxic effects of substances by their application through relevant routes of exposure with appropriate organisms or biological systems so as to relate effects to dose following application.
  2. In chemistry, qualitative or quantitative analysis by the application of one or more fixed methods and comparison of the results with established standards.

Pertaining to tetanus, characterized by tonic muscle spasm.

theoretical maximum daily intake (TMDI)
Predicted maximum daily intake of a residue, assuming that it is present at the maximum residue level and that average daily consumption of foods per person is represented by assessed regional diets: it is expressed in milligrams of residue per person per day.
After [14]

therapeutic cloning
Generation and manipulation of stem cells with the objective of deriving cells of a particular organ or tissue to treat a disease.

therapeutic index
Ratio between toxic and therapeutic doses (the higher the ratio, the greater the safety of the therapeutic dose).

three-dimensional quantitative structure-activity relationship (3D-QSAR)
Quantitative association between the three-dimensional structural properties of a substance and its biological properties.
See quantitative structure-activity relationship

Dose or exposure concentration below which a defined effect will not occur.
See also critical effect

threshold concentration
See threshold

threshold dose
See threshold

threshold limit value-ceiling (TLV-C)
As defined by ACGIH, concentration of a potentially toxic substance that should not be exceeded during any part of the working exposure.

threshold limit value-short term exposure limit (TLV-STEL)
As defined by ACGIH, concentration to which it is believed that workers can be exposed continuously for a short period of time without suffering from 1) irritation, 2) chronic or irreversible tissue damage, or 3) narcosis of sufficient degree to increase the likelihood of accidental injury, impair self rescue or materially reduce work efficiency, and provided that the daily TLV-TWA is not exceeded.
Note: It is not a separate independent exposure guideline; rather, it supplements the TLV-TWA limit where there are recognized acute effects from a substance whose toxic effects are primarily of a chronic nature. TLV-STELs are recommended only where toxic effects have been reported from high short-term exposures in either humans or animals.

threshold limit value-time-weighted average (TLV-TWA)
As defined by ACGIH, time-weighted average concentration for a conventional 8-hour workday and a 40-hour workweek, to which it is believed nearly all workers may be repeatedly exposed, day after day, without adverse effect.

threshold of toxicological concern (TTC)
Human exposure threshold value for a group of chemicals below which there should be no appreciable risk to human health.

Decrease in the number of blood platelets (thrombocytes).

Condition resulting from excessive concentrations of thyroid hormones, as in hyperthyroidism, characterized by bulging eyes and rapid heart rate.

tidal volume
Quantity of air or test gas that is inhaled and exhaled during one respiratory cycle.

time-weighted-average-exposure (TWAE), or concentration (TWAC)
Concentration in the exposure medium at each measured time interval multiplied by that time interval and divided by the total time of observation.
Note: For occupational exposure a working shift of eight hours is commonly used as the averaging time.

Continual noise in the ears, such as ringing, buzzing, roaring, or clicking.

tissue dose
Amount of a substance or physical agent (radiation) absorbed by a tissue.

tissue/plasma partition coefficient
See partition ratio

T lymphocyte
Animal cell which possesses specific cell surface receptors through which it binds to foreign substances or organisms, or those which it identifies as foreign, and which initiates immune responses.

tolerable daily intake (TDI)
Estimate of the amount of a potentially harmful substance (e.g. contaminant) in food or drinking water that can be ingested daily over a lifetime without appreciable health risk.
Note 1: For regulation of substances that cannot be easily avoided, a provisionally tolerable weekly intake (PTWI) may be applied as a temporary limit.
Note 2: Acceptable Daily Intake is normally used for substances not known to be harmful, such as food additives.

tolerable risk
Probability of suffering disease or injury that can, for the time being, be tolerated, taking into account the associated benefits, and assuming that the risk is minimized by appropriate control procedures.

tolerable weekly intake (TWI)
Estimate of the amount of a potentially harmful substance (e.g. a contaminant) in food or drinking water that can be ingested weekly over a lifetime without appreciable health risk.

  1. Adaptive state characterized by diminished effects of a particular dose of a substance: the process leading to tolerance is called “adaptation”.
  2. In food toxicology, dose that an individual can tolerate without showing an effect.
  3. Ability to experience exposure to potentially harmful amounts of a substance without showing an adverse effect.
  4. Ability of an organism to survive in the presence of a toxic substance: increased tolerance may be acquired by adaptation to constant exposure.
  5. In immunology, state of specific immunological unresponsiveness.
  1. Characterized by tension, especially muscular tension.
  2. Medical preparation that increases or restores normal muscular tension.

topical (in medicine)
Applied directly to the surface of the body.

topical effect
Consequence of application of a substance to the surface of the body which occurs at the point of application.

torsade (de pointes)
potentially lethal form of ventricular tachycardia following chronic abuse of alcohol and mainly due to hypomagnesemia.

total diet study
  1. Study designed to establish the pattern of pesticide residue intake by a person consuming a defined diet.
  2. Study undertaken to show the range and amount of various foodstuffs in the typical diet or to estimate the total amount of a specific substance in a typical diet.

total terminal residue (of a pesticide)
Summation of levels of all the residues of a defined pesticide in a food.
See also residue
After [6]

toxemia (blood poisoning)
  1. Condition in which the blood contains toxins produced by body cells at a local source of infection or derived from the growth of microorganisms.
  2. Pregnancy-related condition characterized by high blood pressure, swelling and fluid retention, and proteins in the urine.

Able to cause injury to living organisms as a result of physicochemical interaction.

See toxic substance

toxic chemical
See toxic substance

toxic dose
super-threshold dose
Amount of a substance which produces intoxication without lethal outcome.

  1. Capacity to cause injury to a living organism defined with reference to the quantity of substance administered or absorbed, the way in which the substance is administered and distributed in time (single or repeated doses), the type and severity of injury, the time needed to produce the injury, the nature of the organism(s) affected and other relevant conditions.
  2. Adverse effects of a substance on a living organism defined as in 1.
  3. Measure of incompatibility of a substance with life: this quantity may be expressed as the reciprocal of the absolute value of median lethal dose (1/LD50) or concentration (1/LC50).

toxicity equivalency factor (TEF, f)
Ratio of the toxicity of a chemical to that of another structurally related chemical (or index compound) chosen as a reference.

toxicity equivalency factor (in risk assessment) (TEF), f
Ratio of the toxicity of a chemical to that of another structurally related chemical (or index compound) chosen as a reference. Factor used to estimate the toxicity of a complex mixture, commonly a mixture of chlorinated dibenzo-p-dioxins [oxanthrenes], furans, and biphenyls: in this case, TEF is based on relative toxicity to 2,3,7,8-tetrachlorodibenzo-p-dioxin [2,3,7,8-tetrachlorooxanthrene] for which the f = 1.

toxicity equivalent (TEQ), Txe
Contribution of a specified component (or components) to the toxicity of a mixture of related substances.
Note 1: The amount-of-substance (or substance) concentration of total toxicity equivalent is the sum of that for the components B, C … N.
Note 2: Toxicity equivalent is most commonly used in relation to the reference toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin [2,3,7,8-tetrachlorooxanthrene] by means of the toxicity equivalency factor (TEF, f) which is 1 for the reference substance. Hence, where c is the amount-of-substance concentration:

toxicity equivalent TEQ equation

See half-life, half-time

toxicity exposure ratio (TER)
Ratio of the measure of the effects (e.g., LD50, LC50, NOEC) to the estimated exposure.
Note: It is the reciprocal of a risk quotient or hazard quotient.

toxicity test
Experimental study of the adverse effects of exposure of a living organism to a substance for a defined duration under defined conditions.

toxic material
See toxic substance

toxic substance
chemical etiologic agent
toxic chemical
toxic material
Material causing injury to living organisms as a result of physicochemical interactions.

Process of interaction of potentially toxic substances with target sites, and the biochemical and physiological consequences leading to adverse effects.

Scientific sub-discipline that combines toxicology with genomics to determine how an organism’s genetic make-up influences its response to a toxic substance.

Study of the influence of hereditary factors on the effects of potentially toxic substances on individual organisms.

  1. Generally, the overall process of the absorption (uptake) of potentially toxic substances by the body, the distribution of the substances and their metabolites in tissues and organs, their metabolism (biotransformation), and the elimination of the substances and their metabolites from the body.
  2. In validating a toxicological study, the collection of toxicokinetic data, either as an integral component in the conduct of non-clinical toxicity studies or in specially designed supportive studies, in order to assess systemic exposure.

toxicological data sheet
Document that gives in a uniform manner data relating to the toxicology of a substance, its production and application, properties and methods of identification.
Note: The data sheet may also include recommendations on protective measures.

toxicologically based pharmacokinetic modeling (TBPK)
See physiologically based pharmacokinetic modeling

Scientific discipline involving the study of the actual or potential danger presented by the harmful effects of substances on living organisms and ecosystems, of the relationship of such harmful effects to exposure, and of the mechanisms of action, diagnosis, prevention and treatment of intoxications.

Term sometimes used to indicate a combination of investigative methods and techniques for making a quantitative assessment of toxicity and the hazards of potentially toxic substances.

Morbid dread of poisons.

toxicophoric group
toxogenic group
toxophoric group
Structural moiety that upon metabolic activation exerts toxic effects: the presence of a toxicophoric group indicates only potential and not necessarily actual toxicity of a drug or other substances.

Active process of identification, investigation, and evaluation of various toxic effects in the community with a view to taking measures to reduce or control exposure(s) involving the substance(s) which produces these effects.

Metabolic conversion of a potentially toxic substance to a product that is more toxic.

Poisonous substance produced by a biological organism such as a microbe, animal, plant or fungus.
Note: Examples are botulinum toxin, tetrodotoxin, pyrrolizidine alkaloids and amanitin.

Scientific discipline involving the study of the chemistry, biochemistry, pharmacology and toxicology of toxins.

toxogenic group
See toxicophoric group

toxophoric group
See toxicophoric group

traceability (in metrology)
Property of a measurement result whereby the result can be related to a stated reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.


  1. Means by which something may be followed; for example a radioactive isotope may replace a stable chemical element in a toxic compound enabling the toxicokinetics to be followed.
  2. Labeled member of a population used to measure certain properties of that population.

tracer substance
Substance which can be tracked through one or more reactions or systems, often by detecting an incorporated isotope.

Process by which the genetic information encoded in a linear sequence of nucleotides in one strand of DNA is copied into an exactly complementary sequence of RNA.

Total messenger RNA expressed in a cell or tissue at a given point in time.

Global analysis of gene expression to identify and evaluate changes in synthesis of mRNA after chemical exposure.

  1. Alteration of a cell by incorporation of foreign genetic material and its subsequent expression in a new phenotype.
  2. Conversion of cells growing normally to a state of rapid division in culture resembling that of a tumor.
  3. Chemical modification of substances in the environment.

transformed cell
Cell which has become genetically altered spontaneously or by incorporation of foreign DNA to produce a cell with an extended lifetime in culture.

transformed cell line
See cell line, transformed cell

Gene from one source that has been incorporated into the genome of another organism.

Adjective used to describe animals carrying a gene introduced by micro-injecting DNA into the nucleus of the fertilized egg.

Process through which a polypeptide chain of amino acid molecules is generated as directed by the sequence of a particular messenger RNA sequence.

Mobile nucleic acid element.

In relation to waste water, the amenability of substances to removal without adversely affecting the normal operation of biological treatment processes (such as a sewage treatment plant).

  1. Process for sorting people into groups based on their need for or likely benefit from immediate medical treatment.
    Note: Triage is used in hospital emergency rooms, on battlefields, and at disaster sites when limited medical resources must be allocated.
  2. System used to allocate a scarce commodity, such as food, to those most likely to benefit from it.
  3. Process in which things are ranked in terms of importance or priority.

trophic level
Amount of energy in terms of food that an organism needs.
Note: Organisms not needing organic food, such as plants, are said to be on a low trophic level, whereas predator species needing food of high energy content are said to be on a high trophic level. The trophic level indicates the level of the organism in the food chain.

Closeness of agreement between the average of an theoretically infinite number of replicate measured quantity values and a reference quantity value.

tubular reabsorption
Transfer of solutes from the renal tubule lumen to the tubular epithelial cell and normally from there to the peritubular fluid.

Able to cause tumors.

  1. Any abnormal swelling or growth of tissue, whether benign or malignant.
  2. An abnormal growth, in rate and structure, that arises from normal tissue, but serves no physiological function.

tumor necrosis factor (TNF)
Protein produced by several of the body's cell types, such as white blood cells, red blood cells, and other cells that line the blood vessels; it promotes the destruction of some types of cancer cells and is a cytokine involved in systemic inflammation.

tumor progression
Sequence of changes by which a benign tumor develops from the initial lesion to a malignant stage.

tumor suppressor gene
Gene which serves to protect cells from entering a cancerous state.
Note: According to Knudson’s “two-hit” hypothesis, both alleles of a particular tumor suppressor gene must acquire a mutation before the cell will enter a transformed state.

turnover time
See mean life

two-compartment model
Product of compartmental analysis requiring two compartments.
See compartmental modeling, multicompartment analysis