IUPAC Glossary of Terms Used in Toxicology, 2nd Edition
IUPAC Recommendations, 2007

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

Any adverse condition resulting from medical treatment.

Excess of bile pigment in the blood and consequent deposition and retention of bile pigment in the skin and the sclera.

idiopathic environmental intolerance
See multiple chemical sensitivity

Genetically based unusually high sensitivity of an organism to the effect of certain substances.

immediately-dangerous-to-life-or-health-concentration (IDLHC)
According to the US NIOSH, the maximum exposure concentration from which one could escape within thirty minutes without any escape-impairing symptoms or any irreversible health effects.

Environmental concentration of a pollutant resulting from a combination of emissions and dispersals (often synonymous with exposure).

Ligand-binding assay that uses a specific antigen or antibody, capable of binding to the analyte, to identify and quantify substances. The antibody can be linked to a radioisotope (radioimmunoassay, RIA) or to an enzyme which catalyses an easily monitored reaction (enzyme-linked immunosorbent assay, ELISA), or to a highly fluorescent compound by which the location of an antigen can be visualized (immunofluorescence).

immune complex
Product of an antigen-antibody reaction that may also contain components of the complement system.

immune response
Selective reaction of the body to substances that are foreign to it, or that the immune system identifies as foreign, shown by the production of antibodies and antibody-bearing cells or by a cell-mediated hypersensitivity reaction.

immune system
Integrated network of organs, glands, and tissues that has evolved to protect the body from foreign substances, including bacteria, viruses, and other infection-causing parasites and pathogens.
Note: The immune system may produce hypersensitivity reactions reactions which, in the extreme, can be fatal. If the immune system misidentifies normal body components as foreign, this leads to autoimmune disorders, such as lupus, in which the body destroys its own constituents.

Study of biochemical and molecular aspects of immunology, especially the nature of antibodies, antigens and their interactions.

See antigen

Family of closely related glycoproteins capable of acting as antibodies and present in plasma and tissue fluids; immunoglobulin E (IgE) is the source of antibody in Type I hypersensitivity (allergic) reactions.

immunoglobulin E-mediated hypersensitivity
State in which an individual reacts with allergic effects caused fundamentally by the reaction of antigen-specific immunoglobulin E following exposure to a certain substance (allergen) after having been exposed previously to the same substance.

Modification of the functioning of the immune system by the action of a substance that increases or reduces the ability to produce antibodies.

Enhancement of the capacity of the immune system to produce an effective response.

Reduction in the functional capacity of the immune response; may be due to:

  1. Inhibition of the normal response of the immune system to an antigen.
  2. Prevention, by chemical or biological means, of the production of an antibody to an antigen by inhibition of the processes of transcription, translation or formation of tertiary structure.
Mechanisms by which the immune system is able to recognize and destroy malignant cells before the formation of an overt tumor.

Harmful to the immune system.

Of a membrane, not allowing a given substance to pass through. When applied to nonbiological membranes with no qualification, the term normally refers to water.

Attachment of the fertilized ovum (blastocyst) to the endometrium and its subsequent embedding in the compact layer, occurring 6 or 7 days after fertilization of the ovum.

Phrase applied to data generated and analysed using computer modeling and information technology.

antonym in vivo
In glass, referring to a study in the laboratory usually involving isolated organ, tissue, cell, or biochemical systems.

antonym in vitro
In the living body, referring to a study performed on a living organism.

Number of occurrences of illness commencing, or of persons falling ill, during a given period in a specific population: usually expressed as a rate.
Note: When expressed as a rate, it is the number of ill persons divided by the average number of persons in the specified population during a defined period, or alternatively divided by the estimated number of persons at the mid-point of that period.

incidence rate (epidemiology)
Measure of the frequency at which new events occur in a population.
Note: This is the value obtained by dividing the number of new events that occur in a defined period by the population at risk of experiencing the event during this period, sometimes expressed as person-time.

incremental unit risk estimate
For an air pollutant, this is the additional lifetime cancer risk occurring in a hypothetical population in which all individuals are exposed continuously from birth throughout their lifetimes to a concentration of 1 microgram per cubic meter (μg m-3) of the pollutant in the air they breathe.

Quantity value provided by a measuring instrument or a measuring system.

indirect exposure

  1. Exposure to a substance in a medium or vehicle other than the one originally receiving the substance.
  2. Exposure of people to a substance by contact with a person directly exposed.

individual monitor
See personal sampler

individual protective device (IPD)
personal protective device (PPD)
See personal protective equipment

individual risk
Probability that an individual person will experience an adverse effect.

Substance that causes induction.

Increase in the rate of synthesis of an enzyme in response to the action of an inducer or environmental conditions.
Note: Often the inducer is the substrate of the induced enzyme or a structurally similar substance (gratuitous inducer) that is not metabolized.

induction period
latent period
Time from the onset of exposure to the appearance of signs of disease.

industrial hygiene
See occupational hygiene

inert chemical
Substance that is not generally reactive.

inert ingredient
Any intentionally added ingredient of a mixture which does not contribute to the desired biological effect: this definition does not include impurities and does not imply that the inert ingredient has no biological effects.
Related term: active ingredient

infertility (in human medicine)
Inability to become pregnant within 1 year of unprotected intercourse.

Reaction of the body to injury or to infectious, allergic, or chemical irritation; characterized by redness, swelling, heat, and pain resulting from dilation of the blood vessels accompanied by loss of plasma and leucocytes (white blood cells) into the tissues.

infusion (in physiology)
Therapeutic introduction of a fluid other than blood, as a (usually saline) solution, into a vein.


  1. Process of taking food and drink into the body by mouth.
  2. Process of taking in particles by a phagocytic cell.

Act of drawing in of air, vapor or gas and any suspended particulates into the lung.

inherently biodegradable
Class of compounds for which there is unequivocal evidence of biodegradation (primary or ultimate) in any test of biodegradability.

inhibitory concentration (IC)
Concentration of a substance that causes a defined inhibition of a given system.
Note: IC50 is the median concentration that causes 50% inhibition.

inhibitory dose (ID)
Dose of a substance that causes a defined inhibition of a given system.
Note: ID50 is the median dose that causes 50% inhibition.


  1. Agent that induces a change in a chromosome or gene that leads to the induction of tumors after a second agent, called a promoter, is administered to the tissue.
  2. Substance that starts a chain reaction
    Note: An initiator is consumed in a chain reaction, in contrast to a catalyst.

Substance intended to kill insects.

Amount of a substance that is taken into the body, regardless of whether or not it is absorbed: the total daily intake is the sum of the daily intake by an individual from food, drinking-water, and inhaled air.

integral indicator of toxic effect
Parameter (such as body weight or temperature) characterizing the overall changes in the general state of the organism exposed to a toxic substance.

Large scale protein–protein interaction map.

interfacial layer
Inhomogeneous space region intermediate between two bulk phases in contact, and where properties are significantly different from, but related to, the properties of the bulk phases.

intermittent effect
discontinuous effect
Biological change that comes and goes at intervals.

internal dose
See absorbed dose

internal validity
Selection and comparison of index and comparison groups in such a manner that, apart from sampling error, the observed differences between these groups with respect to dependent variables under study may be attributed only to the hypothesized effect under investigation.

Estimation of a value between two known data points.

interpretation (of data or findings)
Evaluation of the observations from an investigation or study in order to determine their significance for human health, for the environment or for both.

interspecies dose conversion
Process of extrapolating from the doses of one animal species to another, for example from rodent dose to human equivalent.

interstitial fluid
Aqueous solution filling the narrow spaces between cells.

interstitial pneumonia
Chronic form of pneumonia involving increase of the interstitial tissue and decrease of the functional lung tissue.

intervention study
Epidemiological investigation designed to test a hypothesized cause-effect relationship by intentional change of a supposed causal factor in a population.

intestinal reabsorption
Absorption further down the intestinal tract of a substance or substances that have been absorbed before and subsequently excreted into the intestinal tract, usually through the bile.


  1. Poisoning: pathological process with clinical signs and symptoms caused by a substance of exogenous or endogenous origin.
  2. Drunkenness following consumption of beverages containing ethanol or other compounds affecting the central nervous system.

intrinsic activity
Maximal stimulatory effect induced by a compound in relation to that of a given reference compound.

intrinsic clearance
Volume of plasma or blood from which a substance is completely removed in a period of time under unstressed conditions.

intrinsic factor (in biochemistry)
Specific protein required for the absorption of vitamin B12 and secreted by cells in the gastric glands of the stomach.

Non-coding sequence within genes which separates the exons (coding regions).
Note: Introns are spliced out of the messenger RNA molecule created from a gene after transcription and prior to translation.
After [9]

in vitro
antonym in vivo
In glass, referring to a study in the laboratory usually involving isolated organ, tissue, cell, or biochemical systems.

in vivo
antonym in vitro
In the living body, referring to a study performed on a living organism.

ionizing radiation
Any radiation consisting of directly or indirectly ionizing particles or a mixture of both or photons with energy higher than the energy of photons of ultraviolet light or a mixture of both such particles and photons.

irreversible alteration
Change from normal structure or function that persists or progresses after cessation of exposure of the organism.


  1. n., Substance that causes inflammation following immediate, prolonged or repeated contact with skin, mucous membrane, or other biological material.
    Note: A substance capable of causing inflammation on first contact is called a primary irritant.
  2. adj., Causing inflammation following immediate, prolonged or repeated contact with skin, mucous membrane or other tissues.

Local deficiency of blood supply and hence oxygen to an organ or tissue owing to constriction of the blood vessels or to obstruction.

Denoting a liquid exerting the same osmotic pressure or chemical potential of water (water potential) as another liquid with which it is being compared.

itai-itai disease
Illness (renal osteomalacia) observed in the Toyama prefecture of Japan, resulting from the ingestion of cadmium-contaminated rice.
Note: Damage occurred to the renal and skeleto-articular systems, the latter being very painful (“itai” means “ouch” in Japanese and refers to the intense pain caused by the condition).