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Toxicology Glossary - T

tachy-: Prefix meaning rapid as in tachycardia and tachypnoea

tachycardia: Abnormally fast heartbeat
AN bradycardia

tachypnoea: Abnormally fast breathing
AN bradypnoea

taeniacide: Substance intended to kill tapeworms

target (biological): Any organism, organ, tissue, cell or cell constituent that is subject to the action of a pollutant or other chemical, physical, or biological agent
WHO, 1979
RT receptor

target (of environmental pollution): Human being or any organism, organ tissue, cell, resource, or any constituent of the environment, living or not, that is subject to the activity of a pollutant or other chemical or physical activity or other agent
WHO, 1979
RT receptor

target organ(s): Organ(s) in which the toxic injury manifests itself in terms of dysfunction or overt disease
WHO, 1979
RT receptor

target population (epidemiology):

1. Collection of individuals, items, measurements, etc. about which we want to make inferences: 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 required
2. Group of persons for whom an intervention is planned

Last, 1988

T cell: See T lymphocyte.

technical directive: See RT standard

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. 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
RT acceptable daily intake
After de Koning, 1987

temporary maximum residue limit: Temporary maximum residue limit is established for a specified, limited period when:

1. Only a temporary acceptable daily intake has been established for the pesticide concerned
2. Although an acceptable daily intake has been established, the residue data are inadequate for firm maximum residue recommendations
   WHO, 1976

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

teratogenicity: Potential to cause or the production of structural malformations or defects in offspring
After WHO, 1987
RT developmental toxicity, embryotoxicity

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

tetanic: Pertaining to tetanus, characterized by tonic muscle spasm

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

threshold: Dose or exposure concentration below which an effect is not expected

threshold limit value (TLV): Concentration in air of a substance to which it is believed that most workers can be exposed daily without adverse effect (the threshold between safe and dangerous concentrations). These values are established (and revised annually) by the American Conference of Governmental Industrial Hygienists) and are time-weighted concentrations for a 7 or 8 hour workday and a 40 hour workweek. For most substances the value may be exceeded, to a certain extent, provided there are compensatory periods of exposure below the value during the workday (or in some cases the week). For a few substances (mainly those that produce a rapid response) the limit is given as a ceiling concentration (maximum permissible concentration - designated by "C") that should never be exceeded

thrombocytopenia: Decrease in the number of blood platelets (thrombocytes)

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: for occupational exposure a working shift of eight hours is commonly used as the averaging time
WHO, 1979

tinnitus: 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

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
RT B lymphocyte, immune response, lymphocyte

tolerable daily intake (TDI): Regulatory value equivalent to the acceptable daily intake established by the European Commission Scientific Committee on Food. Unlike the ADI, the TDI is expressed in mg/person, assuming a body weight of 60 kg. TDI is normally used for food contaminants
RT acceptable daily intake

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
PS acceptable risk

tolerance:

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

tonic:

1. Characterised by tension, especially muscular tension.
2. Medical preparation that increases or restores normal muscular tension

topical: Pertaining to a particular area, as in a topical effect that involves only the area to which the causative substance has been applied

total diet study:

1. Study designed to establish the pattern of pesticide residue intake by a person consuming a defined diet.
   WHO, 1976.
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
   After WHO, 1989a

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

toxicant: See SN toxic substance

toxic chemical: See SN toxic substance

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

toxicity:

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 (inhalation, ingestion, topical application, injection) 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 with reference to the quantity of substance administered or absorbed, the way in which the substance is administered (inhalation, ingestion, topical application, injection) 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.
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)
   RT acute toxicity, chronic toxicity, subacute toxicity, subchronic toxicity

toxicity equivalency factor (TEF): Factor used in risk assessment to estimate the toxicity of a complex mixture, most commonly a mixture of chlorinated dibenzo-p-dioxins, furans and biphenyls: in this case, TEF is based on relative toxicity to 2,3,7,8 -tetrachlorodibenzo-p-dioxin (TEF = 1)

toxicity equivalent (TEQ): Contribution of a specified component (or components) to the toxicity of a mixture of related substances. The amount-of-substance (or substance concentration) of total toxicity equivalent is the sum of that for the components B, C.....N:


Toxicity equivalent is most commonly used in relation to the reference toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-TCDD by means of the toxicity equivalency factor (TEF, f) which is 1 for the reference substance, hence:


toxicity test: Experimental study of the adverse effects of exposure of a living organism to a substance for a defined duration under defined conditions
RT acute toxicity test, carcinogenicity test, chronic toxicity test, subchronic toxicity test

toxic material: See SN toxic substance

toxicodynamics: Process of interaction of potentially toxic substances with target sites, and the biochemical and physiological consequences leading to adverse effects
RT adverse effect, pharmacodynamics, target

toxicogenetics: Study of the influence of hereditary factors on the effects of potentially toxic substances on individual organisms
RT ecogenetics, pharmacogenetics, polymorphism

toxicokinetics: Process of the uptake of potentially toxic substances by the body, the biotransformation they undergo, the distribution of the substances and their metabolites in the tissues, and the elimination of the substances and their metabolites from the body. Both the amounts and the concentrations of the substances and their metabolites are studied. The term has essentially the same meaning as pharmacokinetics, but the latter term should be restricted to the study of pharmaceutical substances
BT chemobiokinetics
RT biotransformation, pharmacokinetics
WHO, 1979

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; the data sheet may also include recommendations on protective measures
PS toxicological profile, toxicological dossier
IRPTC, 1982

toxicology: Scientific discipline involving the study of the actual or potential danger presented by the harmful effects of substances (poisons) 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
NT chemical toxicology

toxicometry: 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

toxicophobia: Morbid dread of poisons
RT chemophobia

toxicophoric (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
SN toxogenic group

toxicovigilance: 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

toxic substance: Material causing injury to living organisms as a result of physicochemical interactions
SN chemical etiologic agent, poison, toxicant, toxic chemical, toxic material

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

toxin: Poisonous substance produced by a biological organism such as a microbe, animal or plant
PS venom

toxinology: Scientific discipline involving the study of the chemistry, biochemistry, pharmacology and toxicology of toxins
RT toxicology, toxin.

toxogenic group: See SN toxicophoric group.

tracer:

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. Labelled member of a population used to measure certain properties of that population
   Gold, Loening, McNaught and Sehmi, 1987

transcription: 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
RT reverse transcription

transformation:

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

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

treatability: 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)

triage: Assessment of sick, wounded and injured persons following a disaster to determine priority needs for efficient use of available medical facilities

trophic level: Amount of energy in terms of food that an organism needs: 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
WHO, 1979

tumorigenic: Able to cause tumours

tumour:

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
   SN neoplasm

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

turnover time: See SN mean life