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

Process which reverses the effect of a mutation which had inactivated a gene; thus it restores the wild phenotype.

bacterial artificial chromosome (BAC)
DNA vector into which large DNA fragments can be inserted and cloned in a bacterial host.

Substance intended to kill bacteria.

Lung disease caused by the inhalation of dust from sugar-cane residues.

basal lamina, pl -ae
Triple-layered structure on which epithelium sits: it consists of an electron dense layer (lamina densa) between two electron transparent layers (lamina lucida). The lamina densa is composed of type IV collagen and the lamina lucida contains the glycoprotein laminin.

base pairing
Linking of the complementary pair of polynucleotide chains of nucleic acids by means of hydrogen bonds between complementary purine and pyrimidine bases, adenine with thymine or uracil, cytosine with guanine.

basement membrane
Specialized layers of extra-cellular matrix (basal laminae) that separate epithelial tissue from underlying connective tissue: cancer cells must break through the basement membrane in order to migrate to other parts of the body and form metastases.

Bateman function
Equation expressing the build up and decay in concentration of a substance (usually in plasma) based on first order uptake and elimination in a one compartment model, having the form
C = [ƒDκa/Va - κe)][exp(-κet) - exp(-κat)]
where C is the concentration and D the dose of the substance, ƒ the fraction absorbed, and V the volume of distribution. κa and κe) are the first order rate constants of uptake and elimination, respectively, and t is time.

See B lymphocyte

benchmark concentration (BMC)
Statistically calculated lower 95% confidence limit on the concentration that produces a defined response (called the benchmark response or BMR, usually 5 % or 10 %) for an adverse effect compared to background, often defined as 0 % or 5%.

benchmark dose (BMD)
Statistically calculated lower 95 % confidence limit on the dose that produces a defined response (called the benchmark response or BMR, usually 5 % or 10 %) of an adverse effect compared to background, often defined as 0 % or 5 %.

benchmark guidance value
Biological monitoring guidance value set at the 90th percentile of available biological monitoring results collected from a representative sample of workplaces with good occupational hygiene practices.

benchmark response
Response, expressed as an excess of background, at which a benchmark dose or benchmark concentration is set.

Advantage to or improvement in condition of an individual or a population.

antonym malignant

  1. Of a disease, producing no persisting harmful effects.
  2. Tumor which does not invade other tissues (see metastasis), having lost growth control but not positional control.
    Note: Such a tumor is not carcinogenic but may cause mechanical damage to adjacent tissues.

See beryllium disease

beryllium disease
Serious and usually permanent lung damage resulting from chronic inhalation of beryllium.


  1. Deviation of results or inferences from the truth, or processes leading to such deviation.
  2. Any trend in the collection, analysis, interpretation, publication, or review of data which can lead to conclusions which are systematically different from the truth.

biased sample
antonym random sample
Any sample which is not a random sample.

Orange-yellow pigment, a breakdown product of heme-containing proteins (hemoglobin, myoglobin, cytochromes), which circulates in the blood plasma bound to albumin or as water soluble glucuronide conjugates, and is excreted in the bile by the liver.

Potential for a substance to come in contact with a living organism and then interact with it. This may lead to absorption.
Note: A substance trapped inside an insoluble particle is not bio-accessible although substances on the surface of the same particle are accessible and may also be bio-available. Bio-accessibility, like bio-availability, is a function of both chemical speciation and biological properties. Even surface-bound substances may not be accessible to organisms which require the substances to be in solution.

Able to come in contact with a living organism and interact with it.
See bio-accessibility

Progressive increase in the amount of a substance in an organism or part of an organism which occurs because the rate of intake exceeds the organism's ability to remove the substance from the body.
Note: Bio-accumulation often correlates with lipophilicity.
See also bioconcentration, biomagnification

bio-accumulation potential
Ability of living organisms to concentrate a substance obtained either directly from the environment or indirectly through its food.

Metabolic conversion of a xenobiotic to a more toxic derivative or one which has more of an effect on living organisms.

Procedure for estimating the concentration or biological activity of a substance by measuring its effect on a living system compared to a standard system.

bio-availability (general)
biological availability
physiological availability
Extent of absorption of a substance by a living organism compared to a standard system.

bio-availability (in toxico- or pharmacokinetics)
Ratio of the systemic exposure from extravascular (ev) exposure to that following intravenous (iv) exposure as described by the equation:

F = AevDiv / Biv Dev

where F (fraction of dose absorbed) is a measure of the bioavailability, A and B are the areas under the (plasma) concentration time curve following extravascular and intravenous administration respectively, and Dev and Div are the administered extravascular and intravenous doses.

Able to be absorbed by living organisms.
See bio-availability

biochemical mechanism
Reaction or series of reactions, usually enzyme-catalysed, associated with a specific physiological event in a living organism.

biochemical (biological) oxygen demand (BOD)
Amount concentration of oxygen taken up through the respiratory activity of micro-organisms growing on organic compounds present when incubated at a specified temperature (usually 20° C) for a fixed period (usually 5 days). It is regarded as a measure of that organic pollution of water which can be degraded biologically but includes the oxidation of inorganic material such as sulfide and iron(II). The empirical test used in the laboratory to determine BOD also measures the oxygen used to oxidize reduced forms of nitrogen unless their oxidation is prevented by an inhibitor such as allyl thiourea.

biocid/e n., -al adj.
Substance intended to kill living organisms.

Process leading to a higher concentration of a substance in an organism than in environmental media to which it is exposed.
See bioaccumulation

bioconcentration factor (BCF)
Measure of the tendency for a substance in water to accumulate in organisms, especially fish.
Note 1. The equilibrium concentration of a substance in fish can be estimated by multiplying its concentration in the surrounding water by its bioconcentration factor in fish.
Note 2. This parameter is an important determinant for human intake of aquatic food by the ingestion route.

See conjugate

See biotransformation

Breakdown of a substance catalysed by enzymes in vitro or in vivo. This may be characterized for purposes of hazard assessment as:

  1. Primary. Alteration of the chemical structure of a substance resulting in loss of a specific property of that substance.
  2. Environmentally acceptable. Biodegradation to such an extent as to remove undesirable properties of the compound. This often corresponds to primary biodegradation but it depends on the circumstances under which the products are discharged into the environment.
  3. Ultimate. Complete breakdown of a compound to either fully oxidized or reduced simple molecules (such as carbon dioxide/methane, nitrate/ammonium, and water. It should be noted that the products of biodegradation can be more harmful than the substance degraded.

Removal, usually from the aqueous phase, of a test substance in the presence of living organisms by biological processes supplemented by physico-chemical reactions.

bio-equivalen/ce n., -t adj.
Relationship between two preparations of the same drug in the same dosage form that have a similar bioavailability.

Metabolic conversion of a xenobiotic to a less toxic derivative.

Discipline encompassing the development and utilization of computational facilities to store, analyse and interpret biological data.

biokinetics (in toxicology)
Science of the movements involved in the distribution of substances.

biological absorption
See absorption, biological

biological accessibility
See bio-accessibility

biological acclimatization
See acclimatization, biological

biological assessment of exposure
See biological monitoring

biological availability
See bioavailability

biological cycle
Complete circulatory process through which a substance passes in the biosphere. It may involve transport through the various media (air, water, soil), followed by environmental transformation, and carriage through various ecosystems.

biological effect monitoring (BEM)
Continuous or repeated measurement of early biological effects of exposure to a substance to evaluate ambient exposure and health risk by comparison with appropriate reference values based on knowledge of the probable relationship between ambient exposure and biological effects.

biological exposure indices (BEI)
Guidance values recommended by ACGIH for assessing biological monitoring results.

biological half life
For a substance the time required for the amount of that substance in a biological system to be reduced to one half of its value by biological processes, when the rate of removal is approximately exponential.

biological half time, t1/2
See biological half life

biological indicator
Species or group of species which is representative and typical for a specific status of an ecosystem, which appears frequently enough to serve for monitoring and whose population shows a sensitive response to changes, e.g., the appearance of a toxicant in an ecosystem.

biological marker
See biomarker

biological monitoring
biological assessment of exposure
Continuous or repeated measurement of any naturally occurring or synthetic chemical, including potentially toxic substances or their metabolites or biochemical effects in tissues, secreta, excreta, expired air or any combination of these in order to evaluate occupational or environmental exposure and health risk by comparison with appropriate reference values based on knowledge of the probable relationship between ambient exposure and resultant adverse health effects.

biological oxygen demand
See biochemical oxygen demand

biological preparation
Compound derived from living organisms and their products for use in medicine or as a pesticide etc.

biological specimen

  1. Organ, tissue (including blood), secretion or excretion product taken from an organism as a sample reflecting the state of the whole organism.
  2. Organism taken as a sample reflecting the state of a population or their environment.

biological warfare
Military operations using any organism (bacteria, virus or other disease-causing organism) or toxin found in nature, to kill, injure or incapacitate human beings, animals, or plants.

ecological magnification
Sequence of processes in an ecosystem by which higher concentrations are attained in organisms at higher trophic levels (at higher levels in the food web); at its simplest, a process leading to a higher concentration of a substance in an organism than in its food.

Indicator signaling an event or condition in a biological system or sample and giving a measure of exposure, effect, or susceptibility.
Note: Such an indicator may be a measurable chemical, biochemical, physiological, behavioral or other alteration within an organism.

biomarker of effect
effect biomarker
Biomarker that, depending upon the magnitude, can be recognized as associated with an established or possible health impairment or disease.

biomarker of exposure
exposure biomarker
Biomarker that relates exposure to a xenobiotic to the levels of the substance or its metabolite, or of the product of an interaction between the substance and some target molecule or cell that can be measured in a compartment within an organism.

biomarker of susceptibility
susceptibility biomarker
Biomarker of an inherent or acquired ability of an organism to respond to exposure to a specific substance.


  1. Total amount of biotic material, usually expressed per unit surface area or volume, in a medium such as water.
  2. Material produced by the growth of micro-organisms, plants or animals.

Complete conversion of organic substances to inorganic derivatives by living organisms, especially micro-organisms.

Substance that is synthesized by and occurs naturally in living organisms.

See biological monitoring

Biological agent with pesticidal activity, e.g., the bacterium Bacillus thuringiensis when used to kill insects.
After [6]

Excision of a small piece of living tissue for microscopic or biochemical examination; usually performed to establish a diagnosis.

Portion of the planet earth which supports and includes life.

Adjective applied to a substance which arrests the growth or multiplication of living organisms.

All living organisms as a totality.

Chemical conversion of a substance that is mediated by living organisms or enzyme preparations derived there from.

British anti-Lewisite
Metal chelator which has been used in the treatment of arsenic, antimony, gold, mercury and lead poisoning.

Mammalian embryo at the stage at which it is implanted into the wall of the uterus.

blood-brain barrier
Physiological interface between brain tissues and circulating blood created by a mechanism that alters the permeability of brain capillaries, so that some substances are prevented from entering brain tissue, while other substances are allowed to enter freely.
After [2]

blood-placenta barrier
Physiological interface between maternal and fetal blood circulations that filters out some substances which could harm the fetus while favoring the passage of others such as nutrients: many fat soluble substances such as alcohol are not filtered out and several types of virus can also cross this barrier.
Note: The effectiveness of the interface as a barrier varies with species and different forms of placentation.

blood plasma
See plasma (in biology)

blood substitution
See exchange transfusion

blood-testis barrier
Physiological interface between the blood supply and the spermatozoa of the seminiferous tubules.
Note: This interface consists of specific junctional complexes between Sertoli cells.
After [2]

B lymphocyte
B cell
Type of lymphocyte which synthesizes and secretes antibodies in response to the presence of a foreign substance or one identified by it as foreign. The protective effect can be mediated to a certain extent by the antibody alone (contrast T lymphocyte).

body burden
Total amount of a substance present in an organism at a given time.


  1. Single dose of a substance, originally a large pill.
  2. Dose of a substance administered by a single rapid intravenous injection.
  3. Concentrated mass of food ready to be swallowed.

botanical pesticide
Substance with activity against pests, that is produced naturally within a plant and may act as a defense against predators.

Acute food poisoning caused by botulinum toxin produced in food by the bacterium Clostridium botulinum and characterized by muscle weakness and paralysis, disturbances of vision, swallowing, and speech, and a high mortality rate.

antonym tachy-
Prefix meaning slow as in bradycardia or bradypnoea.

antonym tachycardia
Abnormal slowness of the heartbeat.

antonym tachypnoea
Abnormally slow breathing.

breathing zone
Space within a radius of 0.5 m from a person’s face.

British anti-Lewisite (BAL)
See 2,3-bis(sulfanyl)propan-1-ol

antonym bronchodilation
Narrowing of the air passages through the bronchi of the lungs.

antonym bronchoconstriction
Expansion of the air passages through the bronchi of the lungs.

Intermittent violent contraction of the air passages of the lungs.

builder (in chemistry)
Material which enhances or maintains the cleaning efficiency of a surfactant, in a detergent, principally by inactivating water hardness; complex phosphates (especially sodium tripolyphosphate, i.e. pentasodium triphosphate), sodium carbonate, and sodium silicate are the builders most commonly used.

Pneumoconiosis caused by inhalation of dust and associated microbial contaminants and observed in cotton, flax, and hemp workers.

bystander exposure
Liability of members of the general public to come in contact with substances arising from operations or processes carried out by other individuals in their vicinity.