Risk Analysis Glossary: G - I

Gamma Multihit Model

1. A generalization of the one-hit dose-response model which provides a better description of dose-response data.

Gamma rays

1. High-energy, short-wavelength electromagnetic radiation emitted by a nucleus. Gamma radiation usually accompanies alpha and beta emissions and always accompanies fission.

Gaussian distribution model

1. A commonly used assumption about the distribution of values for a parameter, also called the normal distribution. For example, a Gaussian air dispersion model is one in which the pollutant is assumed to spread in air according to such a distribution and described by two parameters, the mean and standard deviation of the normal distribution. [Modified by S. L. Brown]

Genetic effects

1. Effects that are inheritable and appear in the descendants of those exposed.

Groundwater

1. The supply of fresh water under the Earth's surface that forms a natural reservoir.

Half-life

1. The time in which half the atoms of a given quantity of a particular radioactive substance disintegrate to another nuclear form. Measured half-lives vary from millionths of a second to billions of years.
2. Similarly, the time in which half the molecules of a chemical substance disappear as a result of chemical or biochemical transformation. [S. L. Brown]

Half-life, biological

1. The time required for a living organism to eliminate, by natural processes, half the amount of a substance that has entered it.

Half-life, effective

1. The time required for a radionuclide contained in a biological system to reduce its activity by half due to the combined result of radioactive decay and biological elimination.

Hazard

1. A condition or physical situation with a potential for an undesirable consequence, such as harm to life or limb.

Hazard assessment

1. An analysis and evaluation of the physical, chemical and biological properties of the hazard.

Hazard identification

1. The process of determining whether exposure to an agent can cause an increase in the incidence of a health condition.

Hazardous waste

1. Any waste or combination of wastes which pose a substantial present or potential hazard to human health or living organisms because such wastes are nondegradable or persistent in nature or because they can be biologically magnified, or because they can be lethal, or because they may otherwise cause or tend to cause detrimental cumulative effects; also, a waste or combination of wastes of a solid, liquid, contained gaseous, or semisolid form which may cause, or contribute to, an increase in mortality or an increase in serious irreversible, or incapacitating reversible illness, taking into account the toxicity of such waste, its persistence and degradability in nature, its potential for accumulation or concentration in tissue, and other factors that may otherwise cause or contribute to adverse acute or chronic effects on the health of persons or other organisms.

Health and safety study

1. Any study of any effect of a chemical substance or mixture on health or the environment or on both, including underlying data and epidemiological studies, studies of occupational exposure to a chemical substance or mixture, toxicological, clinical, and ecological studies of a chemical substance or mixture, and any test performed pursuant to this [TSCA] Act.

Health effect

1. A deviation in the normal function of the human body.

Health effect assessment

1. The component of risk assessment which determines the probability of a health effect given a particular level or range of exposure to a hazard.

Health risk

1. Risk in which an adverse event affects human health.

Healthy worker effect

1. The difference in mortality risk due to selection forces between a population of active workers healthy enough to have been (and remain) employed and the general population which includes sick and disabled persons. If working in a safe environment, such a population of active workers has been variously estimated to have a mortality risk 60-90% that of the general population.

Heavy metals

1. Metallic elements like mercury, chromium, cadmium, arsenic, and lead, with high molecular weights. They can damage living things at low concentrations and tend to accumulate in the food chain.

Heterocyclic

1. A cyclic or ring structure in which one or more of the atoms in the ring is an element other than carbon. (Common heterocyclics are pyridine, pyrrole, furan, thiophene, and purine.)

Hockey stick regression function

1. A dose-response curve that shows zero response up to a presumed physiological threshold value and then a linear increase thereafter. [Modified by S. L. Brown]

Homeostasis

1. A tendency to stability in the normal body states of the organism.

Hydrocarbons

1. Compounds that contain carbon and hydrogen.

Hydrology

1. The science dealing with the properties, distribution, and circulation of water.

ICRP

1. International Commission on Radiological Protection.

Impact

: The force of impression of one thing on another.

Incidence

1. The number of new cases of a disease in a population over a period of time.

Indicator organisms

1. A species, whose presence or absence may be characteristic of environmental conditions in a particular area of habitat; however, species composition and relative abundance of individual components of the population or community are usually considered to be a more reliable index of water quality.

Individual risk

1. The risk to an individual rather than to a population.

Individual susceptibility

1. The marked variability in the manner in which individuals will respond to a given exposure to a toxic agent.

Inversion

1. An atmospheric condition caused by a layer of warm air preventing the rise of relatively cool air trapped beneath it. This holds down pollutants that might otherwise be dispersed, and can cause an air pollution episode.

In vitro

1. Outside the living organism.
2. Literally, in glass. [S. L. Brown]

In vivo

1. Within the living organism.

Isopleth

1. Lines on a graph connecting points of constant value; e.g., isopleths of visibility are lines of equal visibility.

Isotope

1. One of two or more forms of an element that differ in atomic weight. Nuclides with the same atomic number, (i.e., the same chemical element, characterized by the number of protons contained in the atomic nucleus) but with different atomic masses (i.e., different numbers of neutrons contained in the nucleus). Although chemical properties are the same, radioactive and nuclear (radioactive decay) properties may be quite different for each isotope of an element.