ATSDR Draft Toxicological Profile for Radon_September 2008.pdf

RADON 22610. GLOSSARYRadioactivity, Induced—Radioactivity produced in a substance after bombardment withneutrons or other particles. The resulting activity is "natural radioactivity" if formed by nuclearreactions occurring in nature and "artificial radioactivity" if the reactions are caused by man.Radioactivity, Natural—The property of radioactivity exhibited by more than 50 naturallyoccurring radionuclides.Radioisotope—An unstable or radioactive isotope of an element that decays or disintegratesspontaneously, emitting radiation.Radionuclide—Any radioactive isotope of any element. Approximately 5,000 natural and artificialradioisotopes have been identified.Radiosensitivity—Relative susceptibility of cells, tissues, organs, organisms, or any living substance tothe injurious action of radiation. Radiosensitivity and its antonym, radioresistance, are usedcomparatively, rather than absolutely.Recommended Exposure Limit (REL)—A National Institute for Occupational Safety and Health(NIOSH) time-weighted average (TWA) concentration for up to a 10-hour workday during a 40-hourworkweek.Reference Concentration (RfC)—An estimate (with uncertainty spanning perhaps an order ofmagnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups)that is likely to be without an appreciable risk of deleterious noncancer health effects during a lifetime.The inhalation reference concentration is for continuous inhalation exposures and is appropriatelyexpressed in units of mg/m 3 or ppm.Reference Dose (RfD)—An estimate of the daily exposure of the human population to a potential hazardthat is likely to be without risk of deleterious effects during a lifetime. The RfD is operationally derivedfrom the NOAEL (from animal and human studies) by a consistent application of uncertainty factors thatreflect various types of data used to estimate RfDs and an additional modifying factor, which is based ona professional judgment of the entire database on the chemical. The RfDs are not applicable to nonthresholdeffects such as cancer.Relative Biological Effectiveness (RBE)—The RBE is a factor used to compare the biologicaleffectiveness of absorbed radiation doses (i.e., rad) due to different types of ionizing radiation. Morespecifically, it is the experimentally determined ratio of an absorbed dose of a radiation in question to theabsorbed dose of a reference radiation (typically 60 Co gamma rays or 200 kVp x rays) required to producean identical biological effect in a particular experimental organism or tissue (see Quality Factor).Rem—The traditional unit of dose equivalent that is used in the regulatory, administrative, andengineering design aspects of radiation safety practice. The dose equivalent in rem is numerically equalto the absorbed dose in rad multiplied by the quality factor (1 rem is equal to 0.01 sievert).Reportable Quantity (RQ)—The quantity of a hazardous substance that is considered reportable underCERCLA. Reportable quantities are (1) 1 pound or greater or (2) for selected substances, an amountestablished by regulation either under CERCLA or under Sect. 311 of the Clean Water Act. Quantitiesare measured over a 24-hour period.***DRAFT FOR PUBLIC COMMENT***