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

Microscopic particle whose size is measured in nanometers, often restricted to so-called nanosized particles (NSPs; < 100 nm in aerodynamic diameter), also called ultrafine particles (see separate entry).

Scientific discipline involving the study of the actual or potential danger presented by the harmful effects of nanoparticles 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.

  1. Nonspecific usage - an agent that produces insensibility or stupor.
  2. Specific usage - an opioid, any natural or synthetic drug that has morphine-like actions.

Substance increasing the rate of excretion of sodium ion in the urine.

natural occurrence
Presence of a substance in nature, as distinct from presence resulting from inputs from human activities.
Note: The contamination of the natural environment by some man-made compounds may be so widespread that it is practically impossible to get access to biota with a truly natural level; only ‘normal’ levels can be measured, those which are usually prevalent in places where there is no obvious local contamination.

See autopsy

necro/sis n., /tic adj.
Sum of morphological changes resulting from cell death by lysis and (or) enzymatic degradation, usually accompanied by inflammation and affecting groups of cells in a tissue.
Note: Not to be confused with apoptosis

negligible risk
  1. Probability of adverse effects occurring that can reasonably be described as trivial.
  2. Probability of adverse effects occurring that is so low that it cannot be reduced appreciably by increased regulation or investment of resources.

Substance used for the control of nematodes.

neonat/e n., /al adj.
Infant during the first 4 weeks of postnatal life
Note: For statistical purposes some scientists have defined the period as the first seven days of postnatal life. The precise definition varies from species to species.

neoplas/ia, -m
New and abnormal formation of tissue as a tumor or growth by cell proliferation that is faster than normal and continues after the initial stimulus (i) that initiated the proliferation has ceased.

Inflammation of the kidney, leading to kidney failure, usually accompanied by proteinuria, hematuria, edema, and hypertension.

Any disease or abnormality of the kidney.

Disease of the kidneys marked by degeneration of renal tubular epithelium.

Chemically harmful to the cells of the kidney.

Pertaining to a nerve or to the nerves.

neurologic shellfish poisoning (NSP)
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 brevetoxin; symptoms include gastroenteritis; rectal burning; paresthesias of the face, trunk, and limbs; myalgias; ataxia; vertigo; and reversal of hot/cold sensation.
See also amnesic shellfish poisoning, diarrheal shellfish poisoning

Nerve cell, the morphological and functional unit of the central and peripheral nervous systems.

Any disease of the central or peripheral nervous system.

neurotoxic/ adj., /ity n.
Able to produce chemically an adverse effect on the nervous system: such effects may be subdivided into two types.
  1. Central nervous system effects (including transient effects on mood or performance and pre-senile dementia such as Alzheimer's disease).
  2. Peripheral nervous system effects (such as the inhibitory effects of organophosphorus compounds on synaptic transmission).

Sequential oxidation of ammonium salts to nitrite and nitrate by micro-organisms.

nitrosative stress
Adverse effects occurring when the generation of reactive nitrogen species in a system exceeds the system’s ability to neutralize and eliminate them; nitrosative stress may lead to nitrosylation reactions that can alter protein structure thus inhibiting normal function.

This expression is applicable to a substance for which the available information is not sufficient to establish its safety, or when the specifications for identity and purity are not adequate, or when the available data show that the substance is hazardous and should not be used.
Note: The basis for the use of the expression should be determined before action is taken; in the first two cases above, not being able to allocate an ADI does not mean that the substance is unsafe.

n-octanol-water partition coefficient
Obsolete for octan-1-ol-water partition coefficient
See octan-1-ol-water partition coefficient

Small node or boss that is solid and can be detected by touch.

no-effect level (NEL)
Maximum dose (of a substance) that produces no detectable changes under defined conditions of exposure.
Note: This term tends to be substituted by no-observed-adverse-effect level (NOAEL) or no-observed-effect level (NOEL).

non-bioenvironmental transformation
Change in the chemical or physical nature of a substance occurring as a result of physicochemical conditions and independent of any biological system.

no-effect dose (NED)
subthreshold dose
Amount of a substance that has no effect on the organism.
Note: It is lower than the threshold of harmful effect and is estimated while establishing the threshold of harmful effect.

non-ionizing radiation
Electromagnetic radiation of low energy that is not capable of causing ionization.

non-occupational exposure
Environmental exposure outside the workplace to substances that are otherwise associated with particular work environments and (or) activities and processes that occur there.

See deterministic.

non-target organism
Organism affected by a pesticide although not the intended object of its use.

no-observed-adverse-effect level (NOAEL)
Greatest concentration or amount of a substance, found by experiment or observation, which causes no detectable adverse alteration of morphology, functional capacity, growth, development, or life span of the target organism under defined conditions of exposure.

no-observed-effect level (NOEL)
Greatest concentration or amount of a substance, found by experiment or observation, that causes no alterations of morphology, functional capacity, growth, development, or life span of target organisms distinguishable from those observed in normal (control) organisms of the same species and strain under the same defined conditions of exposure.

no-response level (NRL)
Maximum dose of a substance at which no specified response is observed in a defined population and under defined conditions of exposure.

Associated with a hospital or infirmary, especially used of diseases that may result from treatment in such an institution.

noxious substance
See harmful substance

nucle/us (in cell biology) sing., /ei pl.
Compartment in the interphase eukaryotic cell bounded by a double membrane and containing the genomic DNA, with the associated functions of transcription and processing.

nuisance threshold
Lowest concentration of an air pollutant that can be considered objectionable.

nutritional table method
Procedure for evaluating the dietary intake of a large number of people.
Note 1: The accuracy of the method depends on the accuracy with which records of the food consumption can be established and the accuracy of the nutritional tables specifying the concentration of various nutrients, vitamins, essential, and non-essential substances including pesticide residues.
Note 2: For each record of quantity of food consumed during a certain time period, the daily intake of the substance in question is calculated by multiplying the substance concentration in the food item (as obtained from the nutritional table) by the quantity of food consumed and dividing by the time of observation.

Relating to or exhibiting a nychthemeron or 24-hour period.

Involuntary, rapid, rhythmic movement (horizontal, vertical, rotary, mixed) of the eyeball, usually caused by a disorder of the labyrinth of the inner ear or a malfunction of the central nervous system.