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

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

See lacrimation

Secretion and discharge of tears.

See lacrimator

Substance that irritates the eyes and causes the production of tears or increases the flow of tears.

Substance intended to kill larvae.

Reflex spasmodic closure of the sphincter of the larynx, particularly the glottic sphincter.

Main organ of voice production, the part of the respiratory tract between the pharynx and the trachea.

Weakness; exhaustion.

See latent period

latent effect
See delayed effect

latent period

  1. Delay between exposure to a harmful substance and the manifestations of a disease or other adverse effects.
  2. Period from disease initiation to disease detection.

Irrigation or washing out of a hollow organ or cavity such as the stomach, intestine or the lungs.

Substance that causes evacuation of the intestinal contents.

lead colic (painters’ colic)
Chronic intestinal pains and constipation caused by lead poisoning.


  1. Area of pathologically altered tissue.
  2. Injury or wound.
  3. Infected patch of skin.

Deadly; fatal; causing death.

lethal concentration (LC)
Concentration of a substance in an environmental medium that causes death following a certain period of exposure.

lethal dose (LD)
Amount of a substance or physical agent (e.g. radiation) that causes death when taken into the body.

lethal synthesis
Metabolic formation of a highly toxic compound often leading to death of affected cells.

Progressive, malignant disease of the blood-forming organs, characterized by distorted proliferation and development of leucocytes and their precursors in the bone marrow and blood.

Reduced concentration of leukocytes in the blood.
See lgPow



Logarithm to the base 10 of the partition coefficient of a substance between octan-1-ol and water.
Note: This is used as an empirical measure for lipophilicity in calculating bioaccumulation, fish toxicity, membrane adsorption and penetration etc.

library (in DNA bio-informatics)
Collection of DNA sequences in a searchable electronic form.

library (in molecular biology)
Collection of genomic or complementary DNA sequences that have been cloned in a vector and grown in an appropriate host organism (e.g. bacteria, yeast).
After [9]

life-long exposure
Subjection to a potentially toxic substance during the whole lifetime.

Ion, molecule, or molecular group that binds to another chemical entity to form a larger complex.

Substance intended to kill mollusks including the gastropod mollusk, Limax.

limit recommended
See recommended exposure limit

limit test
Acute toxicity test in which, if no ill-effects occur at a pre-selected maximum dose, no further testing at greater exposure levels is required.

limit value (LV)
Limit concentration at or below which Member States of the European Community must set their environmental quality standard and emission standard for a particular substance according to Community Directives.

limited evidence
According to the US EPA's guidelines for Carcinogen Risk Assessment, “limited evidence” is a collection of facts and accepted scientific inferences that suggests that an agent may be causing an effect, but this suggestion is not strong enough to be considered established fact.

linearized multistage model
Sequence of steps in which (a) a multistage model is fitted to tumor incidence data; (b) the maximum linear term consistent with the data is calculated; (c) the low-dose slope of the dose-response function is equated to the coefficient of the maximum linear term; and (d) the resulting slope is then equated to the upper bound of potency.

lipophilic/ adj., -ity n.
hydrophobic/ adj., -ty n.
antonyms hydrophilic/ -ity, lipophobic/ -ity
Having an affinity for fat and high lipid solubility.
Note: This is a physicochemical property which describes a partitioning equilibrium of solute molecules between water and an immiscible organic solvent, favoring the latter, and which correlates with bioaccumulation.

lipophobic/ adj., -ity n.
hydrophilic/ adj., -ity n.
antonyms hydrophobic/ adj. ity n., lipophilic/ adj. ity n.
Having a low affinity for fat and a high affinity for water.


  1. Artificially formed lipid droplet, small enough to form a relatively stable suspension in aqueous media, useful in membrane transport studies and in drug delivery.
  2. Lipid droplet in the endoplasmic reticulum of a fatty liver.
    After [1]

local effect
Change occurring at the site of contact between an organism and a toxicant.

In competitive binding assays, the logit-log dose relationship, in which the response is defined by:
R = logit (y) = lg [y/(1 – y)]
where y = b/b0 with b = fraction of tracer bound and b0 = value of b with no unlabelled ligand in the system.
Note: Logit-transformed assay data frequently yield straight-line dose-response data, amenable to statistical analysis. More generally in toxicology, the transformation is applied to dose-response data where b0 denotes the maximum response in the absence of a toxic substance.

log-normal distribution
Distribution function F(y), in which the logarithm of a quantity is normally distributed, i.e.
F(y) = ƒgauss(ln y)
where ƒgauss(χ) is a Gaussian (or normal) distribution.

log-normal transformation
Transformation of data with a logarithmic function that results in a normal distribution.

long-term effect
See chronic effect

long-term exposure
See chronic exposure

long-term toxicity
See chronic toxicity

lowest effective dose (LED)
Lowest dose of a chemical inducing a specified effect in a specified fraction of exposed individuals.

lowest lethal concentration found
See minimum lethal concentration

lowest-observed-adverse-effect level (LOAEL)
Lowest concentration or amount of a substance (dose), found by experiment or observation, which causes an adverse effect on morphology, functional capacity, growth, development, or life span of a target organism distinguishable from normal (control) organisms of the same species and strain under defined conditions of exposure.

lowest-observed-effect level (LOEL)
Lowest concentration or amount of a substance (dose), found by experiment or observation, that causes any alteration in morphology, functional capacity, growth, development, or life span of target organisms distinguishable from normal (control) organisms of the same species and strain under the same defined conditions of exposure.

Animal cell that interacts with a foreign substance or organism, or one which it identifies as foreign, and initiates an immune response against the substance or organism.
Note: There are two main groups of lymphocytes, B lymphocytes and T lymphocytes.

General term comprising tumors and conditions allied to tumors arising from some or all of the cells of lymphoid tissue.

Laboratory column of selected representative soil or a protected monolith of undisturbed field soil with which it is possible to sample and monitor the movement of water and substances.

Membrane-bound cytoplasmic organelle containing hydrolytic enzymes.
Note: Release of these enzymes from lysosomes damaged by xenobiotics can cause autolysis of the cell.