Risk Analysis Glossary: P - R

PAH

1. Polycyclic aromatic hydrocarbons.

PAN

1. Peroxyacetyl nitrate.

Particle

1. A tiny mass of material. Airborne particles, material that exist in the atmosphere as a solid or liquid, can be natural, caused by stirring of soil dusts, or anthropogenic. They vary in size from coarse (diameter > 3 µm) to fine (< 3µm) . Sometimes inhalable or respirable is used to describe those particles (< 2 µm) which can be inhaled through the nose and enter the lungs.

Particulates

1. Fine liquid or solid particles such as dust, smoke, mist, fumes, or smog, found in the air or emissions.

Percolation

1. Downward flow or filtering of water through pores or spaces in rock or soil.

Permanent disability

1. Includes any degree of permanent impairment of the body such as amputation, permanent impairment of vision and other permanently crippling nonfatal injury ranging from the permanent stiffening of a joint or a finger amputation, to permanent, complete crippling.

Permeability, soil

1. The quality of the solid that enables it to transmit water or air. Terms usually used to describe permeability in inches per hour are:

   very slow	less than 0.06 inches
   slow	0.06 to 0.2 inches
   moderately slow	0.2 to 0.6 inches
   moderate	0.6 to 2.0 inches
   moderately rapid	2.0 to 6.0 inches
   rapid	6.0 to 20.0 inches
   very rapid	more than 20.0 inches

Peroxyacetyl nitrate (PAN)

1. A pollutant created by the action of sunlight on hydrocarbons and nitrogen oxides in the air. An ingredient of smog.

Person-rem

1. Used as a unit of population dose; the average dose per individual expressed in rems times the population affected.

Person-year

1. The sum of the number of years each person in the study population is at risk; a metric used to aggregate the total population at risk assuming that 10 people at risk for one year is equivalent to 1 person at risk for 10 years.

pH

1. A measure of the acidity or alkalinity of a material, liquid or solid (pH is represented on a scale of 0 to 14 with 7 representing a neutral state, 0 representing the most acid, and 14 the most alkaline).

Photochemical oxidants

1. Air pollutants formed by the action of sunlight on oxides of nitrogen and hydrocarbons.

Plume

1. The cloud of steam or smoke that comes from a chimney stack and blows downwind.
2. The contaminated portion of groundwater that moves past a source of pollution. [S. L. Brown]

PM₁₀

1. Particulate matter in air less than 10 µm in diameter. Currently used as the measure of exposure for potential effects on human health of particulate matter. [S. L. Brown}

PMR

1. Proportionate mortality ratio.

Point source

1. A single isolated stationary source of pollution.

Pollutant

1. Any material entering the environment that has undesired effects.

Pollution

1. The presence of matter or energy whose nature, location or quantity produces undesired environmental effects.

Polycyclic aromatic hydrocarbons (PAH)

1. A highly reactive group of multi-ring organic compounds, at least some of which are carcinogens.

Polycyclic organic matter (POM)

1. A class of chemical compounds; organic, multiring compounds which include polycyclic aromatic hydrocarbons and heterocyclic compounds containing nitrogen, oxygen, and sulfur.

Population at risk

1. A limited population that may be unique for a specific dose-effect relationship; the uniqueness may be with respect to susceptibility to the effect or with respect to the dose or exposure itself.

Population dose (population exposure)

1. The summation of individual radiation doses received by all those exposed to the source or event being considered.

ppm

1. Parts per million. A measurement of concentration such as 1 µg per gram.

Precipitation scavenging

1. The process by which rain or snow removes particulates or reactive vapors from the atmosphere and deposits them on the ground surface.

Precision

1. A measure of how consistently the result is determined by repeated determinations without reference to any "true" value.

Premature death

1. A death that occurs before statistical expectation, usually attributable to a specific cause, and usually referring to deaths statistically estimated in a population rather than to individuals.

Prevalence

1. The number of existing cases in a population who have the disease at a given point (or during a given period) of time.

Probability

1. A probability assignment is a numerical encoding of the relative state of knowledge.

Probable error

1. The magnitude of error which is estimated to have been made in determination of results.

Probit analysis

1. A statistical transformation which will make the cumulative normal distribution linear. In analysis of dose-response, when the data on response rate as a function of dose are given as probits, the linear regression line of these data yields the best estimate of the dose-response curve. The probit unit is y = 5 + Z(p) , where p = the prevalence of response at each dose level and Z(p) = the corresponding value of the standard cumulative normal distribution.

Process wastes

1. Any designated toxic pollutant or combination of pollutants, whether in wastewater or otherwise present, which is inherent to or unavoidable resulting from any manufacturing process, including that which comes into direct contact with or results from the production or use of any raw material, intermediate product, finished product, byproduct or waste product and is discharged into the navigable waters.

Proportionate mortality ratio (PMR)

1. The fraction of all deaths from a given cause in the study population divided by the same fraction from a standard population. A tool for investigating cause-specific risks when only data on deaths are available. If data on the population at risk are also available, SMRs are preferred.

Prospective study

1. An inquiry in which groups of individuals are selected in terms of whether they are or are not exposed to certain factors, and then followed over time to determine differences in the rate at which disease develops in relation to exposure to the factor. Also called cohort study.

Public accident

1. Any accident other than motor vehicle that occurs in the public use of any premises. Includes deaths in recreation (swimming, hunting, etc.), transportation except motor vehicle, public buildings, etc., and deaths from widespread natural disasters even though some may have happened on home premises. Excludes accidents to persons in the course of gainful employment.

Pulmonary function

1. The performance of the respiratory system in supplying oxygen to, and removing carbon dioxide from, the body (via the circulating blood). This requires that air move into and out of the alveoli at an adequate rate (ventilation), that blood circulate through pulmonary capillaries adjacent to alveoli at an adequate rate (perfusion), and that oxygen pass freely from alveoli to blood as carbon dioxide passes in the opposite direction (diffusion). Pulmonary function tests are used to try to identify and locate abnormalities in performance capability.

Rad

1. A unit of measurement of any kind of radiation absorbed by humans. One rad is equal to the absorption of 100 ergs of radiation energy per gram of material.

Radiation

1. The emission of particles or rays by the nucleus of an atom.

Radioactive (decay)

1. Property of undergoing spontaneous nuclear transformation in which nuclear particles or electromagnetic energy are emitted.

Radioactivity

1. The spontaneous decay or disintegration of unstable atomic nuclei, accompanied by the emission of radiation.

Radioisotope

1. A radioactive isotope. An unstable isotope of an element that decays or disintegrates spontaneously, emitting radiation. More that 1300 natural and artificial radioisotopes have been identified.

Radionuclides

1. Radioactive elements. These may be subdivided into natural radionuclides such as radium or uranium which are normally present in the earth, or artificial radionuclides which are not normally present (or normally present in very small amounts) and are produced by nuclear fission.

Rainout

1. The removal of a pollutant within clouds.

Random error

1. Indefiniteness of result due to finite precision of experiment. Measure of fluctuation in result upon repeated experimentation.

Rate

1. In epidemiologic usage, the frequency of a disease or characteristic expressed per unit of size of the population or group in which it is observed. The time at or during which the cases are observed is a further specification.

RAUs

1. Risk analysis units.

Relative potency

1. A comparison of the potency of two or more reference chemicals. Potency of a test chemical is reviewed at all levels of biological organization (subcellular, cellular, animal, human).

Relative risk

1. The ratio of the rate of the disease (usually incidence or mortality) among those exposed to the rate among those not exposed.

Release rate

1. The quantity of a pollutant released from a source over a specified period of time.

Reliability

1. The probability a system performs a specified function or mission under given conditions for a prescribed time.

rem

1. A dose unit which takes into account the relative biological effectiveness (RBE). The rem is defined as the dose of a particular type of radiation required to produce the same biological effect as one roentgen of (0.25 MeV) gamma radiation.

Reproducibility

1. The degree of variation obtained when the same measurement is made with similar instruments and many operators.

Residence time

1. The period of time during which a substance resides in a designated area.

Respirable particle

1. Particle of the size (<5.0 µm) most likely to be deposited in the pulmonary portion of the respiratory tract.

Response

1. The proportion or absolute size of a population that demonstrates a specific effect. May also refer to the nature of the effect.

Retrospective study

1. See case-control study.

Risk

1. The potential for realization of unwanted, adverse consequences to human life, health, property, or the environment; estimation of risk is usually based on the expected value of the conditional probability of the event occurring times the consequence of the event given that it has occurred.
2. Thomas Cool provides an alternative definition of risk in the context of uncertainty.

Risk analysis

1. A detailed examination including risk assessment, risk evaluation, and risk management alternatives, performed to understand the nature of unwanted, negative consequences to human life, health, property, or the environment; an analytical process to provide information regarding undesirable events; the process of quantification of the probabilities and expected consequences for identified risks.

Risk assessment

1. The process of establishing information regarding acceptable levels of a risk and/or levels of risk for an individual, group, society, or the environment.

Risk estimation

1. The scientific determination of the characteristics of risks, usually in as quantitative a way as possible. These include the magnitude, spatial scale, duration and intensity of adverse consequences and their associated probabilities as well as a description of the cause and effect links.

Risk evaluation

1. A component of risk assessment in which judgments are made about the significance and acceptability of risk.

Risk identification

1. Recognizing that a hazard exists and trying to define its characteristics. Often risks exist and are even measured for some time before their adverse consequences are recognized. In other cases, risk identification is a deliberate procedure to review, and it is hoped, anticipate possible hazards.

Roentgen (R)

1. A measure of the ability of x-rays or radioactive decay products to produce ionization in air. One roentgen corresponds to the absorption of about 86 ergs (100 ergs = 6.24 x 10 million electron volts, MeV) of energy from x- or gamma radiation, per gram of air. The corresponding absorption of energy in tissue may be from one-half to two times as great, depending on the energy and type of the radiation and the chemical composition of the tissue.

Runoff

1. Water from rain, snow melt, or irrigation that flows over the ground surface and returns to streams. It can collect pollutants from air or land and carry them to the receiving waters.