Risk Analysis Glossary: M - O

Mass-median diameter

1. The diameter that divides the mass distribution of an aerosol in half.

Melanoma

1. A pigmented, highly malignant form of cancer of the skin.

Meteorology

1. A study of the weather and processes of the atmosphere.

Mobile source

1. A moving producer of air pollution, mainly forms of transportation - cars, motorcycles, planes.

Mobility

1. The ability of a chemical element or a pollutant to move into and through the environment (e.g., the mobilization of an element from a water column to sediment)

Monitoring

1. Periodic or continuous sampling to determine the level of pollution or radioactivity.

Morbidity

1. A departure from a state of physical or mental well-being, resulting from disease or injury. Frequently used only if the affected individual is aware of the condition. Awareness itself connotes a degree of measurable impact. Frequently, but not always, there is a further restriction that some action has been taken such as restriction of activity, loss of work, seeking of medical advice, etc.

Mortality

1. Death; the death rate; ratio of number of deaths to a given population.

Mortality rate

1. The number of deaths that occur in a given population during a given time interval; usually deaths per l0³ or l0⁵ people per year. Can be age, sex, race, and cause specific.

Multistage model

1. A carcinogenesis dose-response model where it is assumed that cancer originates as a "malignant" cell, which is initiated by a series of somatic-like mutations occurring in finite steps. It is also assumed that each mutational stage can be depicted as a Poisson process in which the transition rate is approximately linear in dose rate.

Mutagen

1. A substance that can induce alterations in the DNA of either somatic or germinal cells.

Neoplasm

1. An aberrant new growth of abnormal cells or tissue in which the growth is uncontrollable and progressive.

Nitrogen dioxide (NO₂)

1. The result of nitric oxide combining with oxygen in the atmosphere; a major component of photochemical smog.

NO₂

1. Nitrogen dioxide.

Nonfatal injury accident

1. An accident in which at least one person is injured, and no injury terminates fatally.

Nonpoint source

1. A contributing factor to water pollution that cannot be traced to a specific spot; like agricultural fertilizer runoff, sediment from construction.

Off-gas

1. The gas given off in any stage of an industrial process.

Oncogenic

1. A substance that causes tumors, whether benign or malignant.

One-hit model

1. The basic dose-response model based on the concept that a tumor can be induced by a single receptor that has been exposed to a single quantum or effective dose unit of a chemical.

Ozone (O₃)

1. A pungent, colorless, toxic gas that contributes to photochemical smog.