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

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

objective environment
Actual physical, chemical, and social environment as described by objective measurements, such as noise levels in decibels and concentrations of air pollutants.

occupational environment
Surrounding conditions at a workplace.

occupational exposure
Experience of substances, intensities of radiation etc. or other conditions while at work.

occupational exposure limit (OEL)
Regulatory level of exposure to substances, intensities of radiation etc. or other conditions, specified appropriately in relevant government legislation or related codes of practice.

occupational exposure standard (OES)
  1. Level of exposure to substances, intensities of radiation etc. or other conditions considered to represent specified good practice and a realistic criterion for the control of exposure by appropriate plant design, engineering controls, and, if necessary, the addition and use of personal protective clothing.
  2. In GBR, health-based exposure limit defined under COSHH Regulations as the concentration of any airborne substance, averaged over a reference period, at which, according to current knowledge, there is no evidence that it is likely to be injurious to employees, if they are exposed by inhalation, day after day, to that concentration, and set on the advice of the HSE Advisory Committee on Toxic Substances.

occupational hygiene
Identification, assessment and control of physicochemical and biological factors in the workplace that may affect the health or well-being of those at work and in the surrounding community.

occupational medicine
Specialty devoted to the prevention and management of occupational injury, illness and disability, and the promotion of the health of workers, their families, and their communities.

occupational safety and health
See occupational hygiene

octanol-water partition coefficient Pow, Kow

Ratio of the solubility of a chemical in octanol divided by its solubility in water.
Note: Measure of lipophilicity, used in the assessment of both the uptake and physiological distribution of organic chemicals and prediction of their environmental fate.

Pertaining to the eye.

Ratio of the probability of occurrence of an event to that of non-occurrence, or the ratio of the probability that something is so, to the probability that it is not so.

odds ratio (OR), Θ
cross-product ratio
relative odds
Quotient obtained by dividing one set of odds by another. The term “odds” or “odds ratio” is defined differently according to the situation under discussion. Consider the following notation for the distribution of a binary exposure and a disease in a population or a sample.






No disease



The odds ratio (cross-product ad/bc.
Note 1: The exposure-odds ratio for a set of case control data is the ratio of the odds in favor of exposure among the cases (a/b) to the odds in favor of exposure among non-cases (c/d), which is equal to ad/(bc). With incident cases, unbiased subject selection, and a “rare” disease (say, under 2% cumulative incidence rate over the study period), ad/bc is an approximate estimate of the risk ratio. With incident cases, unbiased subject selection, and density sampling of controls, ad/bc is an estimate of the ratio of the person-time incidence rates (force of morbidity) in the exposed and unexposed. No rarity assumption is required for this.
Note 2: The disease-odds (rate-odds) ratio for a cohort or cross section is the ratio of the odds in favor of disease among the exposed population (a/c) to the odds in favor of disease among the unexposed (b/d), which is equal to ad/bc and hence is equal to the exposure-odds ratio for the cohort or cross section.
Note 3: The prevalence-odds ratio refers to an odds ratio derived cross sectionally, as, for example, an odds ratio derived from studies of prevalent (rather than incident) cases.
Note 4: The risk-odds ratio is the ratio of the odds in favor of getting disease, if exposed, to the odds in favor of getting disease if not exposed. The odds ratio derived from a cohort study is an estimate of this.

odor threshold
odour threshold
odor detection threshold
In principle, the lowest concentration of an odorant in the air that can be detected by a human being.
Note: In practice, a panel of “sniffers” is often used, and the threshold taken as the concentration at which 50% of the panel can detect the odorant (although some workers have also used 100% thresholds). The odor concentration at the detection threshold may be defined as one odor unit.

See edema

unit used to measure scent emission of people and objects; one olf is defined as the scent emission of an “average person”, a sitting adult that takes an average of 0.7 baths per day and whose skin has a total area of 1.8 m2; the scent emission of an object or person is measured by specially trained personnel comparing it to normed scents.
Note: The olf should not be confused with the of unit of scent immission (as opposed to emission), the decipol which also takes into account the ventilation system’s air volume flow.

Apparatus for testing the power of the sense of smell.

Sperm concentration less than a reference value.

Excretion of a diminished amount of urine in relation to fluid intake.

-omics, -omes
Neologism referring to the fields of study in biology ending in the suffix -omics, such as genomics or proteomics: the related neologism -omes are the objects of study of the field such as the genome or proteome, respectively.

Gene that can cause neoplastic (see neoplasia) transformation of a cell; oncogenes are slightly changed equivalents of normal genes known as proto-oncogenes.

Production or causation of tumors.

Capable of producing tumors in animals, either benign (non-cancerous) or malignant (cancerous).

one-compartment model
Kinetic model, where the whole body is thought of as a single compartment in which the substance distributes rapidly, achieving an equilibrium between blood and tissue immediately.

one-hit model
Dose-response model of the form
P =1 - e-bd
where P is the probability of cancer death from a continuous dose rate, d, and b is a constant.

Loosening or detachment of the nail from the nail bed following some destructive process.

Process of formation of the ovum (plural ova), the female gamete.

Complete unit of gene expression and regulation, including structural genes, regulator gene(s) and control elements in DNA recognized by regulator gene product(s).

Pertaining to the eye.

organ dose
Amount of a substance or physical agent (radiation) absorbed by an organ.

Microstructure or separated compartment within a cell that has a specialized function, for example ribosome, peroxisome, lysosome, Golgi apparatus, mitochondrion, nucleolus, nucleus.

organic carbon partition coefficient, Koc

Measure of the tendency for organic substances to be adsorbed by soil or sediment, expressed as:

Koc = (mass adsorbed substance) / (mass organic carbon)____

(mass concentration of absorbed substance)

The Koc is substance-specific and is largely independent of soil properties.

Involving an organ, especially a sense organ as of taste, smell or sight.

Prefix meaning pertaining to bone.

Abnormal development of bone.

Formation or development of bone.

Condition marked by softening of the bones (due to impaired mineralization, with excess accumulation of osteoid), with pain, tenderness, muscular weakness, anorexia and loss of weight, resulting from deficiency of vitamin D and calcium.

Significant decrease in bone mass with increased porosity and increased tendency to fracture.

Substance intended to kill eggs.

oxidative stress
Adverse effects occurring when the generation of reactive oxygen species (ROS) in a system exceeds the system’s ability to neutralize and eliminate them; excess ROS can damage a cell’s lipids, protein or DNA.