Toxicology Glossary - O
objective environment: Actual physical, chemical, and social environment as described by objective measurements, such as noise levels in decibels and concentrations of air pollutantsWHO, 1979
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):
- 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.
- 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 Substancs.
octanol-water partition coefficient (POW, KOW): Measure of lipophilicity by determination of the equilibrium distribution between octan-1-ol and water, as used in pharmacological studies and in the assessment of environmental fate and transport of organic chemicals.
RT lipophilicity, lgKOW, lgPOW
ocular: Pertaining to the eye
odds: 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
Last, 1988
odds ratio: 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
| Exposed | Nonexposed | |
| Disease |
a
|
b
|
| No disease |
c
|
d
|
The odds ratio (cross-product ratio) is ad/(bc).
Notes:
- The exposure-odds ratio for a set of case control data is the ratio of the odds in favour of exposure among the cases (a/b) to the odds in favour of exposure among non-cases (c/d). This reduces 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 (forces of morbidity) in the exposed and unexposed. No rarity assumption is required
- The disease-odds (rate-odds) ratio for a cohort or cross section is the ratio of the odds in favour of disease among the exposed population (a/c) to the odds in favour of disease among the unexposed (b/d). This reduces to ad/(bc) and hence is equal to the exposure-odds ratio for the cohort or cross section
- The prevalence-odds refers to an odds ratio derived cross sectionally, as, for example, an odds ratio derived from studies of prevalent (rather than incident) cases
- The risk-odds ratio is the ratio of the odds in favour getting disease, if exposed, to the odds in favour of getting disease if not exposed. The odds ratio derived from a cohort study is an estimate
SN cross-product ratio, relative odds
Last, 1988
oedema: Presence of abnormally large amounts of fluid in intercellular spaces of body tissues
olfactometer: Apparatus for testing the power of the sense of smell
oliguria: Excretion of a diminished amount of urine in relation to fluid intake
oncogene: Gene that can cause neoplastic transformation of a cell; oncogenes are slightly changed equivalents of normal genes known as proto-oncogenes
RT transformation
oncogenesis: Production or causation of tumours
one-hit model: Dose-response model of the form
P(d) = 1 - exp(-bd)where P(d) is the probability of cancer death from a continuous dose rate (d) and b is a constant. The one-hit model is based on the concept that a tumour can be induced after a single susceptible target or receptor has been exposed to a single effective dose unit of an agent.
IRIS, 1986
onycholysis: Loosening or detachment of the nail from the nailbed following some destructive process
oogenesis: Process of formation of the ovum (plural ova), the female gamete
operon: Complete unit of gene expression and regulation, including structural genes, regulator gene(s) and control elements in DNA recognized by regulator gene product(s)
ophthalmic: Pertaining to the eye
organ dose: Amount of a substance or physical agent (radiation) absorbed by an organ
organelle: Microstructure or separated compartment within a cell that has a specialized function, for example ribosome, peroxisome, lysosome, Golgi apparatus, mitochondrion, nucleolus, nucleus
After Nagel et al. (eds), 1991
organic carbon partition coefficient (KOC): Measure of the tendency for organic substances to be adsorbed by soil and sediment, expressed as:
(mg substance adsorbed)/(kg organic carbon) KOC = --------------------------------------------USEPA, 1986
(mg substance dissolved)/(litre of solution) The KOC is substance-specific and is largely independent of soil properties
organoleptic: Involving an organ, especially a sense organ as of taste, smell or sight
osteo-: Prefix meaning pertaining to bone
osteodystrophy: Abnormal development of bone.
osteogenesis: Formation or development of bone
osteoporosis: Significant decrease in bone mass with increased porosity and increased tendency to fracture
ovicide: Substance intended to kill eggs