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

S9 fraction
Supernatant fraction obtained from an organ (usually liver) homogenate by centrifuging at 9000 g for 20 minutes in a suitable medium; this fraction contains cytosol and microsomes.

Reciprocal of risk: practical certainty that injury will not result from a hazard under defined conditions.
Note 1. Safety of a drug or other substance in the context of human health: the extent to which a substance may be used in the amount necessary for the intended therapeutic purpose with a minimum risk of adverse health effects.
Note 2. Safety (toxicological): The high probability that injury will not result from exposure to a substance under defined conditions of quantity and manner of use, ideally controlled to minimize exposure.

safety data sheet
Single page giving toxicological and other safety advice, usually associated with a particular preparation, substance or process.

safety factor (SF)
See uncertainty factor

safety pharmacology
Science directed to the discovery, development and safe therapeutic use of biologically active substances as a result of the identification, monitoring and characterization of potentially undesirable pharmacodynamic activities of these substances in nonclinical studies.

See natriuretic

sample (in statistics)
  1. Group of individuals often taken at random from a population for research purposes.
  2. One or more items taken from a population or a process and intended to provide information on the population or process.
  3. Portion of material selected from a larger quantity so as to be representative of the whole.

sampling error
That part of the total error (the estimate from a sample minus the population value) associated with using only a fraction of the population and extrapolating to the whole, as distinct from analytical or test error.
Note: Sampling error arises from a lack of homogeneity in the parent population.

Malignant tumor arising in a connective tissue and composed primarily of anaplastic cells resembling supportive tissue (see anaplasia).

saturable elimination
Elimination that becomes concentration-independent at a concentration at which the elimination process is functioning maximally.

Pain in a joint resulting from lead poisoning.

Intoxication caused by lead.

Scatchard plot
Method for analysing data for freely reversible ligand/receptor binding interactions.
Note: The graphical plot is [bound ligand]/[free ligand] against [bound ligand], with slope the negative reciprocal of the binding affinity and intercept on the x-axis the number of receptors.

Area of diminished or lost vision within the visual field, surrounded by an area of less affected or normal vision.

Hardening of an organ or tissue, especially that due to excessive growth of fibrous tissue.

  1. Carrying out of a test or tests, examination(s) or procedure(s) in order to expose undetected abnormalities, unrecognized (incipient) diseases, or defects: examples are mass X-rays and cervical smears.
  2. Pharmacological or toxicological screening consists of a specified set of procedures to which a series of compounds is subjected to characterize pharmacological and toxicological properties and to establish dose-effect and dose-response relationships.

screening level
Decision limit or cut-off point at which a screening test is regarded as positive.

secondary metabolite
Product of biochemical processes other than the normal metabolic pathways, mostly produced in micro-organisms or plants after the phase of active growth and under conditions of nutrient deficiency.

secondhand smoke
See sidestreamsmoke

second messenger
Intracellular effector substance increasing or decreasing as a result of the stimulation of a receptor by an agonist, considered as the ‘first messenger’.


  1. Process by which a substance such as a hormone or enzyme produced in a cell is passed through a plasma membrane No Entry to the outside, for example the intestinal lumen or the blood (internal secretion).
  2. Solid, liquid or gaseous material passed from the inside of a cell through a plasma membrane to the outside as a result of cell activity.

Substance that exerts a soothing or tranquillizing effect.

self-cleaning of water (in a reservoir)
Water purification by natural biological and physico-chemical processes.

self-purification of the atmosphere
Purification of the atmosphere from contaminants by natural biological and physico-chemical processes.

See subchronic

Substance produced by plants or animals, or a synthetic analogue thereof, that evokes a behavioral response in individuals of the producing species or other species (e.g. allomones, kairomones, pheromones, and synomones).

semipermeable (selectively or differentially permeable) membrane
Membrane that will preferentially allow certain molecules or ions to pass through it while preventing the passage of others.

See sensitization

sensitivity (in metrology and analytical chemistry), A
  1. Quotient of the change in the indication and the corresponding change in the value of the quantity being measured.
  2. Slope of the calibration curve. If the curve is in fact a ‘curve’, rather than a straight line, then of course sensitivity will be a function of analyte concentration or amount. If sensitivity is to be a unique performance characteristic, it must depend only on the chemical measurement process, not upon scale factors.

sensitivity (of a screening test)
Extent (usually expressed as a percentage) to which a method gives results that are free from false negatives.
Note 1: The fewer the false negatives, the greater the sensitivity.
Note 2: Quantitatively, sensitivity is the proportion of truly diseased persons in the screened population who are identified as diseased by the screening test.

Immune response whereby individuals become hypersensitive to substances, pollen, dandruff, or other agents that make them develop a potentially harmful allergy when they are subsequently exposed to the sensitizing material (allergen).

Substance causing sensitization.

sensory effect level
  1. Intensity, where the detection threshold level is defined as the lower limit of the perceived intensity range (by convention the lowest concentration that can be detected in 50% of the cases in which it is present).
  2. Quality, where the recognition threshold level is defined as the lowest concentration at which the sensory effect can be recognized correctly in 50% of the cases.
  3. Acceptability and annoyance, where the nuisance threshold level is defined as the concentration at which not more than a small proportion of the population, less than 5%, experiences annoyance for a small part of the time, less than 2%.
    Note: Since annoyance will be influenced by a number of factors, a nuisance threshold level cannot be set on the basis of concentration alone.

Clear watery fluid especially that moistening the surface of serous membranes or that exuded through inflammation of any of these membranes.

blood serum
Watery proteinaceous portion of the blood that remains after clotting.

shellfish poisoning
Serious illness which is a consequence of consumption of bivalve shellfish (mollusks) such as mussels, oysters and clams that have ingested, by filter feeding, large quantities of micro-algae.
See amnesic shellfish poisoning, diarrheal shellfish poisoning, neurologic shellfish poisoning, paralytic shellfish poisoning

short-term effect
See acute effect

short-term exposure limit (STEL)
Fifteen minute time weighted average (TWA) exposure recommended by ACGIH which should not be exceeded at any time during a workday, even if the 8-hour TWA is within the threshold limit value-time-weighted average, TLV-TWA.
Note: Workers can be exposed to a maximum of four STEL periods per 8 hour shift, with at least 60 minutes between exposure periods.

short-term toxicity
See acute toxicity.

Action of a drug other than that desired for beneficial pharmacological effect.

  1. Pneumoconiosis resulting from the inhalation of iron dust.
  2. Excess of iron in the urine, blood or tissues, characterized by hemosiderin granules in urine and iron deposits in tissues.

sidestream smoke
environmental tobacco smoke (ETS)
secondhand smoke
Cloud of small particles and gases that is given off from the end of a burning tobacco product (cigarette, pipe, cigar) between puffs and is not directly inhaled by the smoker.
Note: This is the smoke that gives rise to passive inhalation on the part of bystanders.

Objective evidence of a disease, deformity or an effect induced by an agent, perceptible to an examining physician.

signal transduction
Molecular pathways through which a cell senses changes in its external or internal environment and changes its pattern of gene expression or enzyme activity in response.
After [9]

Pneumoconiosis resulting from inhalation of silica dust.

simulation test
Procedure designed to predict the rate of biodegradation of a compound under relevant environmental conditions.

single nucleotide polymorphism (SNP)
Single base variation at a chromosomal locus which exists stably within populations (typically defined as each variant form being present in at least 1-2% of individuals).
After [8]

In environmental chemistry, an area or part of the environment in which, or a process by which, one or more pollutants is removed from the medium in which it is dispersed.
Note: For example - moist ground acts as a sink for sulfur dioxide in the air.

sister chromatid exchange (SCE)
Reciprocal exchange of chromatin between two replicated chromosomes that remain attached to each other until anaphase of mitosis; used as a measure of mutagenicity of substances that produce this effect.

skeletal fluorosis
Osteosclerosis due to fluoride.

Substance intended to kill slime-producing organisms.
Note: Used on paper stock, water cooling systems, paving stones etc.

slope factor
Value, in inverse concentration or dose units, derived from the slope of a dose-response curve; in practice, limited to carcinogenic effects with the curve assumed to be linear at low concentrations or doses.
Note: The product of the slope factor and the exposure is taken to reflect the probability of producing the related effect.

societal risk
Total probability of harm to a human population including the probability of adverse effects to health of descendants and the probability of disruption resulting from loss of services such as industrial plant or loss of material goods and electricity.

soil partition coefficient (soil Kd)
Experimental ratio of a substance's concentration in the soil to that in the aqueous (dissolved) soil phase at equilibrium: it is valid only for the specific concentration and solid/solution ratio of the test.
See also organic carbon partition coefficient

solvent abuse
solvent sniffing
Deliberate inhalation (or drinking) of volatile solvents, in order to become intoxicated.

‘solvent sniffing’
See solvent abuse

  1. Pertaining to the body as opposed to the mind.
  2. Pertaining to nonreproductive cells or tissues.
  3. Pertaining to the framework of the body as opposed to the viscera.

Substance producing sleep.

Noncommittal term used instead of adsorption or absorption when it is difficult to discriminate experimentally between these two processes.

speciation (in chemistry)
Distribution of an element amongst defined chemical species in a system.

speciation analysis (in chemistry)
Analytical activities of identifying and (or) measuring the quantities of one or more individual chemical species in a sample.

  1. In biological systematics, group of organisms of common ancestry that are able to reproduce only among themselves and that are usually geographically distinct.
  2. See chemical species

species differences in sensitivity
Quantitative or qualitative differences of response to the action(s) of a potentially toxic substance on various species of living organisms.

species-specific sensitivity
Quantitative and qualitative features of response to the action(s) of a potentially toxic substance that are characteristic for a particular species of living organism.

specific death rate
Death rate computed for a subpopulation of individual organisms or people having a specified characteristic or attribute, and named accordingly.
Example: age-specific death rate, the number of deaths of persons of a specified age during a given period of time, divided by the total number of persons of that age in the population during that time.

specificity (of a screening test)
Proportion of truly non-diseased persons who are identified by the screening test.

specific pathogen free (SPF)
Describing an animal removed from its mother under sterile conditions just prior to term and subsequently reared and kept under sterile conditions.

Specifically selected portion of any substance, material, organism (specifically tissue, blood, urine or faeces) or environmental medium assumed to be representative of the parent substance etc. at the time it is taken for the purpose of diagnosis, identification, study or demonstration.

spectral radiant power
The radiant power at wavelength lambda (λ) per unit wavelength interval.

Processes through which introns are removed from a messenger RNA prior to translation and the exons joined.

Agent used in some pesticide formulations to extend the even disposition of the active ingredient.

stability half-life (half-time)
Time required for the amount of a substance in a formulation to decrease, for any reason, by one-half (50%).
See also half life, half time

That which is established as a measure or model to which others of a similar nature should conform.

standard (in law or regulation)
technical directive
Technical specification, usually in the form of a document available to the public, drawn up with the consensus or general approval of all interests affected by it, based on the consolidated results of science, technology and experience, aimed at the promotion of optimum community benefits and approved by a body recognized on the national, regional or international level.

standard (in analytical chemistry)
See reference material, standard material

  1. Making any substance, drug or other preparation conform to type or precisely defined characteristics.
  2. Establishment of precisely defined characteristics, or precisely defined methods, for future reference.
  3. Definition of precise procedures for administering, scoring and evaluating the results of a new method that is under development.

standard material (in analytical chemistry)
See reference material

standard(ized) mortality (morbidity) ratio SMR
Ratio of the number of deaths observed in the study group or population to the number of deaths that would be expected if the study population had the same specific rates as the standard population, multiplied by 100.
Note: This ratio is usually expressed as a percentage.

Pneumoconiosis resulting from inhalation of tin dust.

steady state (in chemistry and toxicology)
State of a system in which the conditions do not change in time.
Note: For further information, see [3].

stem cell
Multipotent cell with mitotic potential that may serve as a precursor for many kinds of differentiated cells.

stereoselective synthesis
Chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecule and which produces the stereoisomeric (enantiomeric or diastereoisomeric) products in unequal amounts.
Note: Traditionally called asymmetric synthesis.

Specificity of chemical reactivity of stereoisomers based on their three-dimensional molecular structure.

Pertaining to or arising from chance and hence obeying the laws of probability.

stochastic effect
stochastic process
Phenomenon pertaining to or arising from chance, and hence obeying the laws of probability.

stochastic process
See stochastic effect

stratification (in epidemiology)
Process of or result of separating a sample into several subsamples according to specified criteria such as age groups, socio-economic status, etc.

stratified sample
Subset of a population selected according to some important characteristic.

stress proteins
See heat shock proteins

structural alert
Chemical grouping which is known to be associated with a particular type of toxic effect, e.g. mutagenicity.

structure activity relationship (SAR)
Association between specific aspects of molecular structure and defined biological action.
See also quantitative structure-activity relationship

structure-metabolism relationship (SMR)
Association between the physicochemical and (or) the structural properties of a substance and its metabolic behavior.

See subchronic

Repeated over a short period, usually about 10 % of the life span; an imprecise term used to describe exposures of intermediate duration.

subchronic effect
Biological change resulting from an environmental alteration lasting about 10 % of the lifetime of the test organism.
Note: In practice with experimental animals, such an effect is usually identified as resulting from multiple or continuous exposures occurring over 3 months (90 days). Sometimes a subchronic effect is distinguished from a subacute effect on the basis of its lasting for a much longer time.

subchronic toxicity test
Animal experiment serving to study the effects produced by the test substance when administered in repeated doses (or continually in food, drinking-water, air) over a period of up to about 90 days.

subclinical effect
Biological change with detectable symptoms following exposure to an agent known to cause disease either before symptoms of the disease occur or when they are absent.

Fertility below the normal range for a given species.

subjective environment
perceived environment
Surrounding conditions as perceived by persons living in these conditions.

substrate (in biology)
  1. Substance material on which an enzyme acts.
  2. Surface on which an organism grows or to which is attached.

subthreshold dose
See non-effective dose

See diaphoretic

sufficient evidence
According to the USEPA's Guidelines for Carcinogen Risk Assessment, sufficient evidence is a collection of facts and scientific references that is definite enough to establish that an adverse effect is caused by the agent in question.

suggested no adverse response level (SNARL)
Maximum dose or concentration that on current understanding is likely to be tolerated by an exposed organism without producing any harm.

suicide reaction
Formation of irreversible cleavage complexes (also referred to as ‘suicide complexes’) leading to cell death.

summary sheet
Two-to-four page summary of a risk assessment.

summation (in neurophysiology)
Process of addition of separate postsynaptic responses caused by stimuli that are adjacent in time and space.
Note: Excitation of a synapse evokes a graded potential change in the postsynaptic membrane that may be below the threshold required to trigger an impulse. If two or more such potentials are caused either nearly simultaneously, at different synapses on the same neuron (spatial summation), or in rapid succession at the same synapse (temporal summation), the summed response may be sufficient to trigger a postsynaptic impulse. Summation may occur between excitatory potentials, inhibitory potentials, or between an excitatory and an inhibitory potential.

Federal authority, established by the US Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) in 1980, to respond directly to releases or threatened releases (such as from landfills or waste disposal areas) of hazardous substances that may endanger health or welfare.

superoxide dismutase
Enzymatic antioxidant that removes the potentially toxic superoxide ion (O2- ) by disproportionating it to O2 and hydrogen peroxide (H2O2).

super-threshold dose
See toxic dose

surface layer
Region of space comprising and adjoining the phase boundary between a solid and liquid phase, between a solid and gas phase, or between a liquid and gas phase within which properties of matter are significantly different from the values in the adjoining bulk phases.

Relatively well studied toxicant whose properties are assumed to apply to an entire chemically and toxicologically related class; for example, benzo(a)pyrene data may be used as toxicologically equivalent to that for all carcinogenic polynuclear aromatic hydrocarbons.

Systematic ongoing collection, collation, and analysis of data and the timely dissemination of information to those who need to know in order that action can be taken to initiate investigative or control measures.

Describing a group of organisms more vulnerable to a given exposure than the majority of the population to which they belong.
Note: Susceptibility may reflect gender, age, physiological status, or genetic constitution of the organisms at risk.

susceptibility biomarker
See biomarker of susceptibility

Condition of lacking the power to resist a particular disease or infection; thus in susceptible people ‘normal expected’ results occur but with a lower exposure (or dose) than in the rest of the population.


  1. adj., Blocking transmission of impulses from the adrenergic (sympathetic) postganglionic fibers to effector organs or tissues.
  2. n., Agent that blocks transmission of impulses from the adrenergic (sympathetic) postganglionic fibers to effector organs or tissues.


  1. adj., Producing effects resembling those of impulses transmitted by the postganglionic fibers of the sympathetic nervous system.
  2. n., Agent that produces effects resembling those of impulses transmitted by the postganglionic fibers of the sympathetic nervous system.

Any subjective evidence of a disease or an effect induced by a substance as perceived by the affected subject.

General description of all of the signs and symptoms of exposure to a toxicant
Note: Signs are the overt (observable) responses associated with exposure (such as convulsions, death, etc.) whereas symptoms are covert (subjective) responses (such as nausea, headache, etc.).

Functional junction between two neurons, where a nerve impulse is transmitted from one neuron to another.

synaptic transmission
See synapse

Set of signs and symptoms occurring together and often characterizing a particular disease-like state.

synergism (in toxicology)
synergistic effect
synergy (in toxicology
Pharmacological or toxicological interaction in which the combined biological effect of exposure to two or more substances is greater than expected on the basis of the simple summation of the effects of each of the individual substances.

synergist (in toxicology)
Substance which contributes more than additively to a mutual effect with another substance.

synergistic effect
See synergism

See synergism

Semiochemical that is produced by one organism inducing a response in an organism of another species that is favorable to both the emitter and the responding organism.
See allomone, kairomone

Property of genes which reside on the same chromosome.

systematic sample
Subset selected according to some simple rule such as specified date or alphabetic classification.


  1. Relating to the body as a whole.
  2. Occurring at a site in the body remote from the point of contact with a substance.
    After [1]

systemic effect
Consequence that is either of a generalized nature or that occurs at a site distant from the point of entry of a substance.
Note: A systemic effect requires absorption and distribution of the substance in the body.

systems biology
Study of the mechanisms underlying complex biological processes as integrated systems of many, diverse, interacting components.
Note: It involves (1) collection of large sets of experimental data (by high-throughput technologies and/or by mining the literature of reductionist molecular biology and biochemistry), (2) proposal of mathematical models that might account for at least some significant aspects of this data set, (3) accurate computer solution of the mathematical equations to obtain numerical predictions, and (4) assessment of the quality of the model by comparing numerical simulations with the experimental data.