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


  1. Unduly rapid or throbbing heartbeat that is noted by a patient; it may be regular or irregular.
  2. Undue awareness by a patient of a heartbeat that is otherwise normal.

Loss or impairment of motor function.

paralytic shellfish poisoning (PSP)
Serious illness which is a consequence of consumption of toxic bivalve shellfish (mollusks) such as mussels, oysters and clams that have ingested, by filter feeding, large quantities of micro-algae containing saxitoxin or its derivatives.
Note: Initially there is tingling, numbness and burning of the tongue and lips, which spreads to the face, neck, arms, fingertips, legs and toes and this is followed by weakness of the upper and lower limbs, loss of motor coordination and, in severe cases, paralysis.

para-occupational exposure
  1. Exposure of a worker’s family to substances carried from the workplace to the home.
  2. Exposure of visitors to substances in the workplace.

Of, relating to, or affecting the parasympathetic nervous system which stimulates digestive secretions, slows the heart, constricts the pupils of the eyes, and dilates blood vessels

Producing effects resembling those caused by interruption of the parasympathetic nerve; also called anticholinergic.

Producing effects resembling those caused by stimulation of the parasympathetic nervous system.

parenteral dosage
Method of introducing substances into an organism avoiding the gastrointestinal tract (subcutaneously, intravenously, intramuscularly etc.).

Slight or incomplete paralysis.

Abnormal or unexplained tingling, pricking, or burning sensation on the skin.

particulate matter (in atmospheric chemistry)
  1. General term used to describe airborne solid or liquid particles of all sizes.
    Note: The term aerosol is recommended to describe airborne particulate matter.
  2. Particlesin air, usually of a defined size and specified as PMn where n is the maximum aerodynamic diameter (usually expressed in μm) of at least 50% of the particles.

partition coefficient
Concentration of a substance in one phase divided by the concentration of the substance in the other phase when the heterogeneous system of two phases is in equilibrium.
Note 1: The ratio of concentrations (or, strictly speaking, activities) of the same molecular species in the two phases is constant at constant temperature.
Note 2: The octanol/water partition coefficient is often used as a measure of the bioconcentration factor for modeling purposes.
Note 3: This term is in common usage in toxicology but is not recommended by IUPAC for use in chemistry and should not be used as a synonym for partition constant, partition ratio or distribution ratio.

partition ratio,KD
Ratio of the concentration of a substance in a single definite form, A, in the extract to its concentration in the same form in the other phase at equilibrium, e.g. for an aqueous/organic system:
KD(A) = [A]orgc/[A]caq

passive sampler
Device for taking samples of environmental media following diffusional contact with a suitable collecting material.
See personal sampler

passive smoking
Inhalation of sidestream smoke by people who do not smoke themselves.
See also sidestream smoke

patch test
Test for allergic sensitivity in which a suspected allergen is applied to the skin on a small surgical pad.
Note: Patch tests may be used to detect exposure to pesticides.

peak daily average concentration of an air pollutant
See maximum average daily concentration of an atmospheric pollutant

penetration (in cell biology)
  1. Action of entering or passing through a cell membrane.
  2. Ability or power to enter or pass through a cell membrane.

perceived environment
perceived risk
See subjective environment

Through the skin following application on the skin.

perfusion (in physiology)
  1. Act of pouring over or through, especially the passage of a fluid through the vessels of a specific organ.
  2. Liquid poured over or through an organ or tissue.

Relating to the period shortly before and after birth, usually from the twentieth to the twenty-ninth week of gestation to one to four weeks after birth.

peritoneal dialysis
Method of artificial detoxication in which a toxic substance from the body is transferred into liquid that is instilled into the peritoneum.
Note: Effectively this represents the employment of the peritoneum surrounding the abdominal cavity as a dialysing membrane for the purpose of removing waste products or toxins accumulated as a result of renal failure.

Ability or power to enter or pass through a cell membrane.

permeability coefficient,P
Quantity defining the permeability of molecules across a cell membrane and expressed as:

permeability coefficient equation

where K is the partition coefficient, D is the diffusion coefficient, and Δx is the thickness of the cell membrane.
Note: SI units m s-1; frequently-used units cm s-1, with units cm2 s-1 for D, cm for Δx.

Of a membrane, allowing a given substance to pass through.
Note: When applied to nonbiological membranes with no qualification, the term normally refers to water.

Action of entering or passing through a cell membrane.

permissible-exposure-limit (PEL)
Recommendation by US OSHA for a TWA concentration that must not be exceeded during any 8-hour work shift of a 40h working week.

Organelle, similar to a lysosome, characterized by its content of catalase (EC, peroxidase (EC and other oxidative enzymes.

Attribute of a substance that describes the length of time that the substance remains in a particular environment before it is physically removed or chemically or biologically transformed.

persistent inorganic pollutant (PIP)
Inorganic substance that is stable in the environment, is liable to long-range transport, may bio-accumulate in human and animal tissue, and may have significant impacts on human health and the environment.
Note 1: Examples are arsenides, fluorides, cadmium salts and lead salts.
Note 2: Some inorganic chemicals, like crocidolite asbestos, are persistent in almost all circumstances, but others, like metal sulfides, are persistent only in unreactive environments; sulfides can generate hydrogen sulfide in a reducing environment or sulfates and sulfuric acid in oxidizing environments. As with organic substances, persistence is often a function of environmental properties.

persistent organic pollutant (POP)
Organic chemical that is stable in the environment, is liable to long-range transport, may bio-accumulate in human and animal tissue, and may have significant impacts on human health and the environment.
Examples: dioxin, PCBs, DDT, tributyltin oxide (TBTO).
Note: The Stockholm Convention on Persistent Organic Pollutants was adopted at a Conference of Plenipotentiaries held from 22 to 23 May 2001 in Stockholm, Sweden; by signing this convention, governments have agreed to take measures to eliminate or reduce the release of POPs into the environment.

personal monitoring
Type of environmental monitoring in which an individual's exposure to a substance is measured and evaluated.
Note: This is normally carried out using a personal sampler.

personal protective device (PPD)
See personal protective equipment

personal protective equipment (PPE)
individual protective device (IPD)
personal protective device (PPD)
Equipment (clothing, gloves, hard hat, respirator and so on) worn by an individual to prevent exposure to a potentially toxic substance

personal sampler
individual sampler
Compact, portable instrument for individual air sampling, measuring, or both, the content of a harmful substance in the respiration zone of a working person.
See also passive sampler

Organism that may harm public health, that attacks food and other materials essential to mankind, or otherwise affects human beings adversely.

A substance intended to kill pests.
Note: In common usage, any substance used for controlling, preventing, or destroying animal, microbiological or plant pests.

pesticide residue
Any substance or mixture of substances found in man or animals or in food and water following use of a pesticide: the term includes any specified derivatives, such as degradation and conversion products, metabolites, reaction products and impurities considered to be of toxicological significance.

Process by which particulate material is endocytosed by a cell.
See also endocytosis, pinocytosis

Medicinal drug.

Process of interaction of pharmacologically active substances with target sites in living systems, and the biochemical and physiological consequences leading to therapeutic or adverse effects.

Study of the influence of genetic factors on the effects of drugs on individual organisms.

Methods and science permitting identification of the genes which influence individual variation in the efficacy or toxicity of therapeutic agents, and the application of this information in clinical practice.


  1. Process of the uptake of drugs by the body, the biotransformation they undergo, the distribution of the drugs and their metabolites in the tissues, and the elimination of the drugs and their metabolites from the body.
  2. Study of such processes.
Science of the use and effects of drugs: may be subdivided into pharmacokinetics and pharmacodynamics defined above.

Throat, the part of the digestive tract between the esophagus below and the mouth and nasal cavities above and in front.

phase I reaction of biotransformation
Enzymic modification of a substance by oxidation, reduction, hydrolysis, hydration, dehydrochlorination or other reactions catalysed by enzymes of the cytosol, of the endoplasmic reticulum (microsomal enzymes) or of other cell organelles.
See also cytochrome P450

phase II reaction of biotransformation
Binding of a substance, or its metabolites from a phase I reaction, with endogenous molecules (conjugation), making more water-soluble derivatives that may be excreted in the urine or bile.
Note: Phase II reactions include glucuronidation, sulfation, acetylation, amino acid (e.g., glycine) and glutathione conjugation.

phase III reaction of biotransformation
Further metabolism of conjugated metabolites produced by phase II reactions.

Complete phenotypic description of an organism (by analogy with genome).

Observable structural and functional characteristics of an organism determined by its genotype and modulated by its environment.

See feromone

Inflammation of the skin caused by exposure to light, especially that due to metabolites formed in the skin by photolysis.

Cleavage of one or more covalent bonds in a molecular entity resulting from absorption of light, or a photochemical process in which such cleavage is an essential part.
Note: Term often used incorrectly to describe irradiation of a sample, although in the combination flash photolysis this usage is accepted.

Oxidation reactions induced by light. Common processes are:
(1) Loss of one or more electrons from a chemical species as a result of photoexcitation of that species;
(2) Reaction of a substance with oxygen under the influence of ultraviolet, visible, or infrared light. When oxygen remains in the product this latter process is also called photooxygenation. Reactions in which neither the substrate nor the oxygen are electronically excited (i.e., photosensitized oxidations) are sometimes called photoinitiated oxidations.

Abnormal visual intolerance of light.

photosensitization of skin
Allergic reaction (see allergy) due to a metabolite formed by the influence of light.

Adverse effects produced by exposure to light energy, especially those produced in the skin.

physical map (in genetics)
Map showing how much DNA, measured in base pairs, separates two genes.
Note: Not to be confused with a genetic map which shows the position of genes in relation to each other, based on the frequency of crossing overs.

physiological availability
See bioavailability

physiological pharmacokinetic model
See physiologically-based pharmacokinetic modeling

physiologically based pharmacokinetic modeling (PBPK)
toxicologically based pharmacokinetic modeling (TBPK)
Mathematical modeling of kinetic behavior of a substance, based on measured physiological parameters.

Type of endocytosis in which soluble materials are taken up by the cell and incorporated into vesicles for digestion.

Substance intended to kill fish.

pivotal study
See critical study

  1. Formation of a placenta in the uterus.
  2. Type or structure of a placenta.
  3. In botany, arrangement of placentas within the plant ovary.
plasma (in biology)
  1. Fluid component of blood in which the blood cells and platelets are suspended.
  2. Fluid component of semen produced by the accessory glands, the seminal vesicles, the prostate, and the bulbo-urethral glands.
  3. Cell substance outside the nucleus, i.e. the cytoplasm.

plasma half-life
See elimination half-life

Removal of blood from the body and centrifuging it to obtain plasma and packed red blood cells: the blood cells are resuspended in a physiologically compatible solution (usually type-specific fresh frozen plasma or albumin) and returned to the donor or injected into a patient who requires blood cells rather than whole blood.

Autonomous self-replicating extra-chromosomal circular DNA molecule present in bacteria and yeast.
Note 1: Plasmids replicate autonomously each time a bacterium divides and are transmitted to the daughter cells.
Note 2: DNA segments are commonly cloned using plasmid vectors.
After [9]

Lining of the lung.

Term indicating the number of sets of chromosomes present in an organism.

Chronic poisoning caused by absorption of lead or lead salts.

Usually fibrosis of the lungs that develops owing to (prolonged) inhalation of inorganic or organic dusts.
Note: Cause-specific types of pneumoconiosis are:

  1. anthracosis: from coal dust.
  2. asbestosis: from asbestos dust.
  3. byssinosis: from cotton dust.
  4. siderosis: from iron dust.
  5. silicosis: from silica dust.
  6. stannosis: from tin dust.

Inflammation of the lung.

point mutation
Reaction that changes a single base pair in DNA.

point source
Single emission source in a defined location.

poison (in toxicology)
Substance that, taken into or formed within the organism, impairs the health of the organism and may kill it.

Containing a poison.

Morbid condition produced by a poison.

Any undesirable solid, liquid or gaseous matter in a solid, liquid or gaseous environmental medium.
Note 1: ‘Undesirability’ is often concentration-dependent, low concentrations of most substances being tolerable or even essential in many cases.
Note 2: A primary pollutant is one emitted into the atmosphere, water, sediments or soil from an identifiable source.
Note 3: A secondary pollutant is a pollutant formed by chemical reaction in the atmosphere, water, sediments, or soil.

Introduction of pollutants into a solid, liquid, or gaseous environmental medium, the presence of pollutants in a solid, liquid, or gaseous environmental medium, or any undesirable modification of the composition of a solid, liquid or gaseous environmental medium.

polyclonal antibody
Antibody produced by a number of different cell types.

Chronic excessive thirst.

polymerase chain reaction(PCR)
Technique by which specific DNA segments are amplified selectively using cycles of annealing, chain extension, and thermal dissociation.
After [9]

polymorphism (polymorphia) in metabolism
Interindividual variations in metabolism of endogenous and exogenous compounds due to genetic influences, leading to enhanced side effects or toxicity of drugs (for example, poor versus fast metabolizers) or to different clinical effects (metabolism of steroid hormones).

Excessive production and discharge of urine.

population (in statistics)
Totality of related items under consideration.
Note 1: A clearly defined part of a population is called a subpopulation. The term ‘population segment’ is sometimes used as a synonym for subpopulation.
Note 2: In the case of a random variable, the probability distribution is considered as defining the population of that variable.

population (in epidemiology)
Assemblage of individuals with defined characteristics.

Persons who can and may develop an adverse health effect and who are potentially exposed to a substance under study. People already having chronic disease are excluded from the population at risk in studies of the incidence of the adverse effect.

population critical concentration (PCC)
Concentration of a substance in the critical organ at which a specified percentage of the exposed population has reached the individual critical organ concentration.
Note: The percentage is indicated by PCC-10 for 10%, PCC-50 for 50% etc. (similar to the use of the term LD50).

population effect
Absolute number or incidence rate of cases occurring in a group of people.

population risk
See societal risk

Disturbance of porphyrin metabolism characterized by increased formation, accumulation, and excretion of porphyrins and their precursors.

Natural pigment containing a fundamental skeleton of four pyrrole nuclei united through the α-positions by four methine groups to form a macrocyclic structure (porphyrin is designated porphine in Chemical Abstracts indexes).

Pharmacological study of the choice of appropriate dose of a drug in relation to the physiological factors, such as age, that may influence its effect.

post-translational modification
Processes by which proteins are biochemically modified within a cell following their synthesis in the ribosomes.

potency (in toxicology)
Expression of relative toxicity of an agent as compared to a given or implied standard or reference.

Dependent action in which a substance or physical agent at a concentration or dose that does not itself have an adverse effect enhances the harm done by another substance or physical agent.
See also synergism

practical certainty (of safety)
Numerically specified low risk of exposure to a potentially toxic substance (for example, 1 in 1000) or socially acceptable low risk of adverse effects from such an exposure applied to decision making in regard to chemical safety.

precautionary principle
Approach to risk management that can be applied in circumstances of scientific uncertainty, reflecting a perceived need to take action in the face of a potentially serious risk without waiting for definitive results of scientific research.
Note: The 1992 Rio Declaration on Environment and Development says: “In order to protect the environment, the precautionary approach shall be widely applied by states according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.”

precision (in metrology)
Closeness of agreement between indications obtained by replicate measurements on the same or similar objects under specified conditions.
Note: Measurement precision is usually expressed numerically by measures of imprecision, such as standard deviation, variance, or coefficient of variation under the specified conditions of measurement.

Pertaining to the region over the heart and lower thorax.

Substance from which another, usually more biologically active, substance is formed.

predicted environmental concentration (PEC)
predicted exposure concentration
See estimated environmental concentration

predicted no effect concentration (PNEC)
Concentration that is expected to cause no adverse effect to any naturally occurring population in an environment at risk from exposure to a given substance.

predictive validity
Reliability of a measurement expressed in terms of its ability to predict the criterion: an example would be an academic aptitude test that was validated against subsequent academic performance.

predictive value
Percentage of positive results that are true positives or of negative results that are true negatives.

premature ovarian failure
Follicular depletion by the age of 35 years.

Before the formation of a tumor.

Number of instances of existing cases of a given disease or other condition in a given population at a designated time; sometimes used to mean prevalence rate.
Note: When used without qualification, refers usually to the situation at a specified time (point prevalence).

prevalence rate (ratio)
Total number of individuals who have an attribute or disease at a particular time (or during a particular period) divided by the population at risk of having the attribute or disease at this point in time or midway through the period.

primary pollutant
See pollutant

prior informed consent (PIC)
Concept in law and medicine which states that before one is subjected to a risk, especially a risk of bodily harm, one is entitled to be fully informed well in advance of the nature of that risk in order to make an informed decision about whether to accept it or not.

primary protection standard
Accepted maximum level of a pollutant (or its indicator) in the target organism, or some part thereof, or an accepted maximum intake of a pollutant or nuisance into the target under specified circumstances.

Probability unit obtained by adding 5 to the normal deviates of a standardized normal distribution of results from a dose response study.
Note 1: Addition of 5 removes the complication of handling negative values.
Note 2: A plot of probit against the logarithm of dose or concentration gives a linear plot if the response follows a logarithmic normal distribution. Estimates of the LD50 and ED50 (or LC50 and EC50) can be obtained from this plot.

Substance that has to be metabolized before it becomes a carcinogen.

Precursor converted to an active form of a drug within the body.

progression (in oncology)
Increase in the size of a tumor or spread of cancer in the body.

Unicellular organism, characterized by the absence of a membrane-enclosed nucleus.
Note: Prokaryotes include bacteria, blue-green algae and mycoplasmas.

promoter (in molecular genetics)
Sequence of nucleotides in a DNA molecule to which RNA polymerase binds so as to start transcription.

promoter (in oncology)
Agent that induces cancer when administered to an animal or human being who has been exposed to a cancer initiator.

Erroneous spelling of promoter (in molecular genetics), found in some literature.

Substance applied in a form that is not active as a pesticide and which becomes active once it enters an organism and undergoes chemical modification.

Latent state of a phage genome in a lysogenic bacterium.

proportional mortality rate (ratio)
Proportion of observed deaths from a specified condition in a defined population divided by the proportion of deaths expected from this condition in a standard population, expressed either

prosthetic group
Nonprotein entity essential for an enzyme’s activity and tightly bound to the enzyme molecule in its active form.

Excretion of excessive amounts of protein (derived from blood plasma or kidney tubules) in the urine.

Description of the complete set of proteins encoded by the genome.

Global analysis of gene expression using a variety of techniques to identify and characterize proteins.
Note: It can be used to study changes caused by exposure to chemicals and to determine if changes in mRNA expression correlate with changes in protein expression: the analysis may also show changes in post-translational modification, which cannot be distinguished by mRNA analysis alone.

provisional tolerable weekly intake (PTWI)
See tolerable weekly intake

pseudo-acceptable daily intake (PADI)
Intake for a substance derived by applying a thousandfold uncertainty factor to the lowest low-effect level for noncarcinogenic endpoints.

Apparent adaptation of an organism to changing conditions of the environment (especially chemical) associated with stresses in biochemical systems that exceed the limits of normal (homeostatic) mechanisms.
Note: Essentially there is a temporary concealed pathology that later on can be manifested in the form of explicit pathological changes sometimes referred to as ‘decompensation’.

Any major mental disorder characterized by derangement of the personality and loss of contact with reality.

Exerting an effect upon the mind and capable of modifying mental activity.

public health impact assessment
Applying risk assessment to a specific target population of known size, giving as the end product a quantitative statement about the number of people likely to be affected in a particular population.

Pertaining to the lung(s).

See laxative

Condition in which the temperature of a human being or mammal is above normal.

Any substance that produces fever.