Risk Analysis Glossary: A - C

Abatement

1. The reduction in degree or intensity of pollution.

Absorbed dose

1. The energy imparted to a unit mass of matter by ionizing radiation. The unit of absorbed dose is the rad. One rad equals 100 ergs per gram.
2. The amount of a substance absorbed into the body, usually per unit of time. The most common unit of dose is mg per kg body weight per day (mg/kg-day). [S. L. Brown]

Absorption

1. The penetration of one substance into or through another.
2. Specifically, the penetration of a substance into the body from the skin, lungs, or digestive tract. [S. L. Brown]

Accident

1. That occurrence in a sequence of events which usually produces unintended injury, death or property damage.

Accident type

1. Describes the occurrence leading to injury or property damage.

Accuracy

1. The degree of agreement between a measured value and the true value; usually expressed as +/- percent of full scale.

Acidity

1. The quantitative capacity of aqueous solutions to react with hydroxyl ions. It is measured by titration with a standard solution of a base to a specified end point. Usually expressed as milligrams per liter of calcium carbonate.

Act of God

1. An act occasioned by an unanticipated grave natural disaster.

Acute

1. Acute-diseases or responses with short and generally severe course (often due to high pollutant concentrations).

Acute respiratory disease

1. Respiratory infection, characterized by rapid onset and short duration.

Acute toxicity

1. Any poisonous effect produced within a short period of time following exposure, usually up to 24-96 hours, resulting in biological harm and often death.

Adsorption

1. The attachment of the molecules of a liquid or gaseous substance to the surface of a solid.

Advanced air emission control devices

1. Air pollution control equipment, such as electrostatic precipitators and high energy scrubbers, that are used to treat an air discharge which has been treated initially by equipment including knockout chambers and low energy scrubbers.

Advection

1. Process of transport of an atmospheric property, or substance within the atmosphere, solely by the mass motion of the atmosphere.

Aerodynamic diameter

1. Expression of aerodynamic behavior of an irregularly shaped particle in terms of the diameter of an idealized particle; that is, aerodynamic diameter is the diameter of a sphere of unit density that has aerodynamic behavior identical to that of the particle in question. Thus, particles having the same aerodynamic diameter may have different dimensions and shapes.

Aerodynamic particle size

1. Sphere of unit density that has aerodynamic behavior identical to that of the particle in question.

Aerosol

1. System in which the dispersion medium is a gas and the dispersed phase (composed of solid particles or liquid droplet) does not settle out under the influence of gravity.

Aerosol particles

1. Solid particles <10-6 m in diameter, dispersed in gas.

Air emissions

1. The release or discharge of a pollutant (from a stationary source) into the ambient air. For anthropogenic sources this may involve release (1) by means of a stack or (2) as a fugitive dust, mist or vapor as a result inherent to the manufacturing or formulating process. Pollutants may also be discharged from mobile sources, from area sources such as roads and fields, and from non-manufacturing, stationary sources.

Air monitoring

1. The continuous sampling for, and measuring of, pollutants present in the atmosphere.

Air pollutant

1. Dust, fumes, mist, smoke and other particulate matter, vapor, gas, odorous substances, or any combination thereof; any air pollution agent or combination of such agents, including any physical, chemical, biological, radioactive (including source material, special nuclear material, and by-product material) substance or matter which is emitted into or otherwise enters the ambient air.

Air pollution

1. The presence in the outdoor atmosphere of any dust, fumes, mist, smoke, other particulate matter, vapor, gas, odorous substances, or a combination thereof, in sufficient quantities and of such characteristics and duration as to be, or likely to be, injurious to health or welfare, animal or plant life, or property, or as to interfere with the enjoyment of life or property.

Air quality criteria

1. The levels of pollution and lengths of exposure above which adverse effects may occur on health and welfare.

Air quality standards

1. The level of pollutants prescribed by law or regulation that cannot be exceeded during a specified time in a defined area.

Air sampling

1. The collection and analysis of air samples for detection or measurement of radioactive substances, particulate matter, or chemical pollutants.

Aliphatic

1. One of the major groups of organic compounds characterized by straight-chain arrangement of the constituent carbon atoms.

Alkalinity

1. The measurable ability of solutions or aqueous suspensions to neutralize an acid.

Alpha radiation

1. An emission of alpha particles (helium nuclei) from a material undergoing nuclear transformation.

Ambient level

1. The level (of pollutant) in the general environment as characterized by an average over a suitably long time and large volume.

Anthropogenic

1. Of human origin.

Anticarcinogen

1. A substance or agent that opposes the action of carcinogens.

Aquifer

1. An underground bed or layer of earth, gravel, or porous stone that contains water.

Aromatic (arene)

1. A major group of unsaturated cyclic hydrocarbons containing one or more rings (e.g., benzene) (These highly reactive and chemically versatile compounds have a strong, but not unpleasant, odor; thus the name aromatic.)

Attributable risk

1. The rate of a disease in exposed individuals that can be attributed to the exposure. This measure is derived by subtracting the rate (usually incidence or mortality) of the disease among nonexposed persons from the corresponding rate among exposed individuals.

 

Background level

1. In air pollution, the level of pollutants present in ambient air from natural sources.
2. More generally, the level of pollution present in any environmental medium attributable to natural or ubiquitous sources. [S. L. Brown]

Background radiation

1. Radiation in the natural human environment originating from cosmic rays and from the naturally radioactive elements of the earth, including those within the human body.
2. The level of radioactivity in an area which is produced by sources other than the one of specific interest.

BaP

1. Benzo(a)pyrene.

Benefit

1. The degree to which effects are judged desirable.

Benzo(a)pyrene (BaP)

1. A carcinogenic polycyclic aromatic hydrocarbon.

Best available control technology

1. An emission limitation (including a visible emission standard) based on the maximum degree of reduction for each pollutant subject to regulation under the [Clean Air] act which would be emitted from any proposed major stationary source or major modification which the Administrator, on a case-by-case basis, taking into account energy, environmental, and economic impacts and other costs, determines is achievable for such source or modification through application of production processes or available methods, systems, and techniques, including fuel cleaning or treatment or innovative fuel combustion techniques for control of such pollutant.

Beta particle

1. An elementary particle emitted from nucleus during radioactive decay. It has a single negative electric charge and a mass equal to 1/1837 that of a proton. A beta particle is identical to an electron.

Bias

1. Any difference between the true value and that actually obtained due to all causes other than sampling variability.

Bioaccumulation

1. The process whereby certain toxic substances collect in living tissues, thus posing a substantial hazard to human health or the environment.

Bioassay

1. Using living organisms to measure the effect of a substance, factor, or condition.

Biochemical oxygen demand (BOD)

1. The dissolved oxygen required to decompose organic matter in water. It is a measure of pollution because heavy waste loads have a high demand for oxygen.

Biological half-life

1. The time required for a biological system (such as a human or animal) to eliminate, by natural processes, half the amount of a substance (such as a radioactive material) that has been absorbed into that system.

Biological magnification

1. The concentration of certain substances up a food chain. A very important mechanism in concentrating pesticides and heavy metals in organisms such as fish.

Biota

1. The sum total of the living organisms of any designated area.

BOD

1. Biochemical oxygen demand.

Body burden

1. The total amount of a specific substance (for example, lead) in an organism, including the amount stored, the amount that is mobile, and the amount absorbed.

Cancer

1. An abnormal, potentially unlimited, disorderly new tissue growth.

Carbon monoxide (CO)

1. A colorless, odorless, very toxic gas produced by any process that involves the incomplete combustion of carbon-containing substances. One of the major air pollutants, it is primarily emitted through the exhaust of gasoline-powered vehicles.

Carcinogen

1. A substance or agent that produces or incites cancerous growth.

Carcinogenesis

1. Development of carcinoma; or, in more recent usage, producing any kind of malignancy.

Carcinogenic

1. Cancer causing.

Carcinogenic potency

1. The gradient of the dose-response curve for a carcinogen.

Carcinoma

1. Malignant new growth made up of epithelial cells tending to infiltrate the surrounding tissues and give rise to metastases.

Case-control study

1. An inquiry in which groups of individuals are selected in terms of whether they do (the cases) or do not (the controls) have the disease of which the etiology is to be studied, and the groups are then compared with respect to existing or past characteristics judged to be of possible relevance to the etiology of the disease.

Case-fatality rate

1. A ratio of the number of deaths due to a disease to the number of cases of that disease in a specified period of time. It expresses the frequency with which affected individuals die of the disease.

Chemical oxygen demand (COD)

1. Laboratory measurement of the amount of oxygen consumed under specific conditions in the oxidation of organic material by a strong chemical oxidant that decomposes both biodegradable (measured by biochemical oxygen demand) and nonbiodegradable organic matter.

Chlorosis

1. Discoloration of normally green plant parts that can be caused by disease, lack of nutrients, or various air pollutants.

Chromatid

1. One of the pair of stands, formed by longitudinal splitting of a chromosome that are joined by a single centromere in somatic cells during mitosis; one of tetrad of strands formed by lengthwise splitting of paired chromosomes during the diplotene stage of meiosis.

Chromosomes

1. Threadlike structures in animal or plant nuclei, seen during karyolinesis (nuclear division characteristic of mitosis) that carry the linearly arranged genetic material.

Chronic

1. Having a persistent, recurring or long-term nature. As distinguished from acute.

Chronic respiratory disease

1. A persistent or long-lasting intermittent disease of the respiratory tract.

CO

1. Carbon monoxide.

COD

1. Chemical oxygen demand.

Coefficient of haze (COH)

1. A measurement of visibility interference in the atmosphere.

Cohort study

1. See prospective study.

Combustion nucleus

1. Condensation nucleus formed as a result of industrial or natural combustion processes.

Comparative risk

1. An expression of the risks associated with two (or more) actions leading to the same goal; may be expressed quantitatively (a ratio of 1.5) or qualitatively (one risk greater than another risk).
2. Any comparison among the risks of two or more hazards with respect to a common scale. [S. L. Brown]

Common mode failures

1. Several errors in a technological system occurring simultaneously.

Concentration ratio

1. The ratio of the concentration of a compound or radionuclide in an organism or its tissues to the concentration in the surrounding under equilibrium, or steady-state conditions.

Confidence interval

1. A range of values (a₁ < a < a₂) determined from a sample of definite rules so chosen that, in repeated random samples from the hypothesized population, an arbitrarily fixed proportion of that range will include the true value, x, of an estimated parameter. The limits, a₁ and a₂, are called confidence limits; the relative frequency with which these limits include a is called the confidence coefficient; and the complementary probability is called the confidence level. As with significance levels, confidence levels are commonly chosen as 0.05 or 0.01, the corresponding confidence coefficients being 0.95 or 0.99. Confidence intervals should not be interpreted as implying that the parameter itself has a range of values; it has only one value, a. On the other hand, the confidence limits (a₁, a₂) being derived from a sample, are random variables, the values of which on a particular sample either do or do not include the true value a of the parameter. However, in repeated samples, a certain proportion of these intervals will include a provided that the actual population satisfied the initial hypothesis.

Confounding factors

1. Variables that may introduce differences between cases and controls which do not reflect differences in the variables of primary interest.

Contamination

1. Contact with an admixture of an unnatural agent, with the implication that the amount is measurable.

Convection

1. Atmospheric motions that are predominantly vertical, resulting in vertical transport and mixing of atmospheric properties.

Cost-benefit analysis

1. A formal quantitative procedure comparing costs and benefits of a proposed project or act under a set of preestablished rules. To determine a rank ordering of projects to maximize rate of return when available funds are unlimited, the quotient of benefits divided by costs is the appropriate form; to maximize absolute return given limited resources, benefits-costs is the appropriate form.

Criteria

1. As used in the Clean Air Act, information on adverse effects of air pollutants on human health or the environment at various concentrations. The information is collected pursuant to section 108 of the Clean Air Act and used to set national ambient air quality standards.

Critical toxic effect

1. The most sensitive and specific biological change which is outside of acceptable physiological variation.

Cross-sectional study

1. An epidemiological study design in which measurements of cause and effect are made at the same point in time.

Curie (Ci)

1. A measure of radioactivity equal to 3.7 x 10¹⁰ disintegrations per second.