An expression of risk based on the assumption that the excess risk from exposure to ionizing radiation is added to the underlying (baseline) risk by an increment that is dependent on dose but independent of the underlying baseline risk.
Absorbed dose (D).
The mean energy absorbed in material from any type of ionizing radiation divided by the mass of the material. Absorbed dose, D, has the dimensions of energy divided by mass and is expressed in gray (Gy) or rad.
The tendency of measurements (estimates) of a quantity to yield, on average, the true value of the quantity. Accuracy is the complement of bias.
Active subslab depressurization.
Mechanically assisted method, e.g., fan or suction device, to remove soil gas from beneath the foundation of a building.
Bulk flow of gas due to temperature or pressure differences.
The descriptive size of any type of aerosol based on the diameter of a sphere of water that has the same settling velocity as the aerosol of interest.
Alpha particle (α).
A particle emitted during the decay of certain radioactive elements. It is identical to the nucleus of helium containing two protons and two neutrons.
Alternative maximum contaminant level (AMCL).
For the case of radon in water, the AMCL is the concentration in water that will contribute an incremental increase in indoor air concentration equal to the national average ambient-air concentration.
The process of developing new blood vessels, especially for growing tissues or tumors.
A process of degradation by proteases (caspases) and nucleases which results in a noninflammatory mechanism of cell destruction and resorption.
A site in DNA that remains after a damaged base has been removed by an enzyme that cleaves the deoxyribose-base bond.
Attributable risk (AR).
The proportion of excess cancer deaths in a defined population that could, in theory, be prevented if all exposures to radon were reduced to background concentrations.
The process used to clean a filter bed after the flow of water being treated is reduced due to clogging.
A statistical methodology that allows for the incorporation of prior information and the use of subjective probability.
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--> Glossary A Absolute risk. An expression of risk based on the assumption that the excess risk from exposure to ionizing radiation is added to the underlying (baseline) risk by an increment that is dependent on dose but independent of the underlying baseline risk. Absorbed dose (D). The mean energy absorbed in material from any type of ionizing radiation divided by the mass of the material. Absorbed dose, D, has the dimensions of energy divided by mass and is expressed in gray (Gy) or rad. Accuracy. The tendency of measurements (estimates) of a quantity to yield, on average, the true value of the quantity. Accuracy is the complement of bias. Active subslab depressurization. Mechanically assisted method, e.g., fan or suction device, to remove soil gas from beneath the foundation of a building. Advection. Bulk flow of gas due to temperature or pressure differences. Aerodynamic diameter. The descriptive size of any type of aerosol based on the diameter of a sphere of water that has the same settling velocity as the aerosol of interest. Alpha particle (α). A particle emitted during the decay of certain radioactive elements. It is identical to the nucleus of helium containing two protons and two neutrons. Alternative maximum contaminant level (AMCL). For the case of radon in water, the AMCL is the concentration in water that will contribute an incremental increase in indoor air concentration equal to the national average ambient-air concentration. Angiogenesis. The process of developing new blood vessels, especially for growing tissues or tumors. Apoptosis. A process of degradation by proteases (caspases) and nucleases which results in a noninflammatory mechanism of cell destruction and resorption. Apurinic site. A site in DNA that remains after a damaged base has been removed by an enzyme that cleaves the deoxyribose-base bond. Attributable risk (AR). The proportion of excess cancer deaths in a defined population that could, in theory, be prevented if all exposures to radon were reduced to background concentrations. B Backwashing. The process used to clean a filter bed after the flow of water being treated is reduced due to clogging. Bayesian. A statistical methodology that allows for the incorporation of prior information and the use of subjective probability.
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--> Becquerel (Bq). A quantity of radioactivity equivalent to 1 decay per second. The Becquerel is a SI unit named on behalf of the French scientist Henri Becquerel. BEIR IV. The fourth in a series of National Research Council reports called the Biological Effects of ionizing Radiation. The 1988 report is titled: Health Risks of Radon and Other Internally Deposited Alpha-Emitters. BEIR VI. The sixth in a series of National Research Council reports called the Biological Effects of Ionizing Radiation. The 1999 report is titled: Health Risks of Exposure to Radon. Best available technology (BAT). The most efficient treatment method for removal of a given contaminant. Beta particle (β). A particle emitted during the decay of certain radioactive elements. It is identical to an electron. Bias. The difference between the average value obtained from a measurement (estimate) of a specific quantity and the true value of that quantity. Bias is the complement of accuracy. C Cancer. A malignant tumor of potentially unlimited growth, capable of invading surrounding tissue or spreading to other parts of the body by metastasis. Carcinogen. An agent that can cause cancer. Caspase. A family of proteolytic enzymes that are normally found complexed with peptide inhibitors which are released by caspase activity itself. This results in an autocatalytic increase in pretense activity (cascade) that degrades specific protein substrates especially those involved in structural components of the cell. Chromatin. The combination of DNA and proteins which together make up the main structural units of the nucleus and the chromosomes. The first order of structure consists of DNA wrapped around specific histone proteins packed together to form nucleosomes. Countercurrent flow. The hydraulic regime in a treatment unit where the flow of the fluid being cleaned is in the opposite direction to that of the fluid to which the contaminant is transferred. Crypts. Pits formed by depressions in the surface of the stomach or intestinal lining cells within the crypts divide and secrete digestive enzymes. Curie (Ci). A quantity of radioactivity equivalent to 3.7 × 10l0 (37 billion) decays per second. The curie is a traditional unit named on behalf of the French scientist Marie Curie. Cytogenetics. The branch of genetics devoted to the study of chromosomes. Cytokines. Extracellular molecules that transmit signals to control gene expression in target cells, often through interaction with specific receptors on the cell surface. D Diploid. The normal state of the genome of cells in most body tissues172.16.50.51 in which each cell has two copies of each chromosome, one copy originating from each parent. Disinfection by-products (DBPs). Compounds formed when organic matter in raw water is oxidized by disinfectants. For example, chloroform is formed when natural organic matter is oxidized by chlorine. DNA homologs. Two DNA sequences or chromosomal regions which have sufficiently similar nucleotide sequence to represent the same genes or intervening sequences. E Effective dose (HE). The product of the equivalent dose, HT, in a tissue, T, multiplied by the tissue weighting factor wT. The purpose of this is to take into consideration the difference in sensitivity of various tissues or organs to radiation induced cancer. Electron volt (eV). A unit of energy equal to the kinetic energy gained by a particle having one electronic charge when it passes in a vacuum through a potential difference of 1 volt. 1 eV = 1.602 × 1019 joules, 1 MeV = 1,000,000 eV. 1 kev = 1,000 eV. Empty bed contact time (EBCT). The average interval of time that a fluid containing a contaminant remains in contact with a bed of granular activated carbon. EBCT is the volume of the reactor (not containing GAC) divided by the flow rate of water being treated. Endogenous. A term describing sources of reactive molecules that originate from within the cell. Episome. A small circular DNA molecule that can be maintained for varying periods of time within the nucleus but is not a functional part of the DNA for the host cell.
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--> Epithelial tissue. The cell types on the outer surface of mammalian tissues. Endothelia cell layers are on the inner surfaces of tissues. Cells in-between are mesothelial. Equilibrium ratio (F). The ratio of the potential alpha energy concentration of radon decay products to the concentration of radon. Under ideal conditions, when all of the radon decay products remain suspended in air, they reach equilibrium with radon and F approaches 1.0. In family dwellings, F is typically near 0.4. Equilibrium-equivalent radon concentration (EEC). The concentration of radon in equilibrium with the short-lived decay products that has the same potential alpha concentration as a given mixture of decay products. Equivalent dose (H). The product of absorbed dose, D, and a radiation weighting factor, wR, that depends on the type of radiation responsible for the dose. H = wR.D. The purpose is to account for the differences in biological response for different types of radiation. If dose is measured in Gy, H has units of Sievert (Sv). If D is measured in rad, H has units of rem. Excess relative risk (ERR). A model, which assumes that health effects from ionizing radiation are based on a relative risk factor, RR, that multiplies the baseline risk. Excess relative risk, ERR, is then defined formally as: RR-1. Exogenous. A source of exposure that is outside the body. F Fluvial. Pertaining to, produced by, or formed in a stream or river. Fos/jun. Two oncogenes that interact as a dimer which binds to specific DNA control sequences regulating the transcription of genes. Fos/jun is particularly responsive to DNA damage and induces transcription of damage-responsive genes. Fusion gene. A gene produced by breakage and rejoining of DNA within gene sequences to produce a new gene with altered function. Bc12 is involved in a well-known fusion gene produced during some classes of hematopoetic cancer. G G1 and G2. The periods in the cell cycle that are respectively before and after, the period of semiconservative DNA synthesis called the S phase. In the process of cell division, mitosis, follows the completion of G2. Most cells in somatic tissues are either in the G1 phase of the mitotic cycle, or are not in a mitotic cycle at all and are then classified as being in G0. Gamma ray (γ). A particle emitted during the decay of certain radioactive elements. It is a form of electromagnetic radiation also referred to as a photon. Gamma rays have energies usually between 10 kev and 10 MeV. Genomic stability. The concept where the genome of a normal diploid cell maintains a complement of maternal and paternal genes by specific mechanisms. These become deranged in malignant cells and can cause changes in gene copy number, chromosome numbers, heterozygosity, total DNA content, etc. Geometric mean (GM). The nth root of the product of n observations. Geometric Standard Deviation (GSD). The exponential of the standard deviation of the natural logarithms of a set of observations. Granular activated carbon (GAC). Organic matter such as wood, bone or coconut shells, that is exposed to high heat and pressure. This increases the surface area and improves the capability to adsorb contaminants. Gray (gy). A quantity of absorbed dose equal to 1 Joule kg-1. One Gy = 100 rad. The gray is a SI unit named on behalf of the British scientist L.H. Gray. Groundwater disinfection rule (GWDR). Pending rule proposed by USEPA that will require public drinking water supplies that use groundwater to disinfectant the drinking water prior to distribution. H Half-life (t1/2). The amount of time required for a given quantity of radioactivity to be reduced by one half. This only includes the radioactive decay process and does not include removal radioactivity by other methods such as biological elimination or migration. Hematopoeitic. The lineage of cells in the bone marrow, spleen and thymus that produces the erythrocytes, lymphocytes, platelets and other cells of the peripheral blood.
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--> Heterotrophic plate counts (HPC). A plating method for enumerating the number of viable organic carbon-using (heterotrophic) bacteria m a water sample. Heterozygosity. The genetic state in which the two genes specifying a particular enzyme or protein, from both parents contain DNA sequence inferences. Homeostasis. The stable expression of total cellular metabolism. Homologous recombination. A mechanism of DNA repair and genetic exchange between two DNA homologs. Hormesis. The concept that very low doses of ionizing radiation may be beneficial to the irradiated cells or organisms. I ICRP. International Commission on Radiological Protection and Measurements, founded in 1928 and since 1950 has been providing general guidance on radiation protection. Immunoglobulin. The protein consisting of pairs of heavy and light chains that make the circulating antibodies which exhibit great diversity in recognition and binding target molecules known as antigens. Interphase. The period of the cell cycle during which chromosomes are not visible as discrete structures. At this time the nucleus of the cell is somewhat like a spherical zone surrounded by a nuclear membrane that contains the encapsulated DNA and also regulates the traffic of molecules between the inner volume of the nucleus and the outer volume of the cytoplasm. Interphase can be subdivided into Gl, S, and G2 phases according to the state of duplication of the DNA. Ion exchange treatment. A method used to remove anionic or cationic contamination from water. The contaminants adhere to locations containing anions or cations normally associated with the resin. When the resin becomes saturated with the contaminant, it is regenerated with a brine containing a high concentration of the originally-sorbed anion or cation. Ionization. A process by which a neutral atom or molecule loses or gains electrons, thereby acquiring a net electric charge. Ionization can be produced by the interaction of ionizing radiation with matter. K Karstic. A type of topography characterized by sink-holes, caves, and underground drainage, usually formed in limestone or salt deposits. Karyotype. The full set of chromosomes in the nucleus of a cell that is characteristic of a particular individual or species. L Lacustrine. Pertaining to, produced by, or formed in a lake. Linear no-threshold (LNT) model. A risk-projection model that expresses the effect (e.g., mutation or cancer) as a proportional (linear) function of the dose and assumes that no minimum ( threshold) dose exists below which radiation injury does not occur. Loss of heterozygosity (LOH). A process occurring during tumor progression by which one chromosome of a pair is lost and the partner is duplicated. Lumen. The interior open space of an organ such as a blood vessel or intestine. M Maximum contaminant level (MCL). The highest concentration of a contaminant permitted by regulations in public drinking water supplies. Meiotic. The process by which a germ cell in the testis or ovary divides into two cells with a reduction in chromosome number such that each cell has one copy of each chromosome, and ultimately develops into either sperm or egg cells. Meta-analysis. An analysis of epidemiological data based on grouping or pooling information obtained from several studies. Microsatellite repeats. Regions of DNA in which the same short sequence is repeated numerous times to create characteristic sequence motifs useful for individual identification and which slow expansion and reduction in size in some tumors. Mitochondria. Organelles in the cytoplasm of cells that contain a small circular DNA molecule which encodes many of the genes required for oxidative phosphorylation and provides most of the energy for the cell through ATP production.
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--> Mitotic. The process by which a cell divides into two identical daughter cells with no change in chromosome number; also used to refer to the whole cell cycle during which this cell division occurs. Mitotic cell death. The result of cells attempting to go through mitotic cell division with broken or fused chromosomes such that the daughter cells do not receive the full complement of DNA necessary for survival. Monte Carlo (analysis, methods, simulation). A numerical technique that samples values at random from specified probability distributions. MutT. An enzyme which hydrolyzes 8-ozyguanine triphosphates to monophosphates and eliminates them as precursors for DNA and RNA synthesis. N Necrosis. An ill-defined form of cell death that may be different from apoptosis, and is often characterized by sudden collapse of nuclear and cytoplasmic structures and loss of membrane integrity. Neoplastic. An alternative term for malignant or cancer cells that result in new and abnormal growth. Nonhomologous recombination. A mechanism of DNA repair in which two dissimilar broken ends of DNA are ligated using the set of end-binding proteins, polymerase and ligase. This is also called illegitimate recombination. O Oncogene. Those genes that exert a dominant effect in expressing one or more characteristics of malignancy. They are often a result of specific mutations. 8-oxyguanine. The product of an oxygenation reaction from endogenous metabolism or exposure to ionizing radiation that adds an oxygen atom to the 8-position of the guanine base in DNA. This is one of the more common products of oxygenation reactions in DNA and in nucleotide pools. P p53. A protein having a molecular weight of 53 kilodalton. It has a large variety of functions including transcriptional activation, binding to DNA repair proteins and to single stranded DNA, Holliday junctions, and other damaged DNA structures. The gene coding for the p53 protein is conventionally represented in italics as p53; a convention which is generally employed in distinguishing proteins from their genes. Packed tower aeration (PTA). A method for removing volatile contaminants from water by passing a flow of air over a thin film of the water. PBPK models. Physiologically-based pharmaco-kinetic models: mathematical models that incorporate physiological principles, e.g., blood-flow to tissues, to simulate the movement (kinetic behavior) of contaminants (e.g., radon) in the body. Phenotype. The visible expression of genetic information contained in the DNA of an organism (i.e., its genotype). picocurie (pCi). A quantity of radioactivity equivalent to 3.7 × 10-2 decays per second or 2.22 decays per minute. One pCi = 0.037 Bq. Plug flow reactor (PFR). A treatment unit where the fluid enters the influent end and travels as a discrete packet (plug) to the effluent end of the unit without mixing with packets of fluid ahead or behind it. Point-of-entry treatment (POE). A process where a contaminant is removed from water just before it is used in an individual household or business, as, opposed to treatment at a central location before the water is distributed to many users. Potential alpha energy. The total kinetic energy of all the alpha particles emitted by a mixture of radon decay products when all of the atoms in the mixture have completely decayed into 210 Pb. Potential alpha energy is measured in Joules (J) or MeV. Potential alpha energy concentration (PAEC). The concentration of potential alpha energy for radon decay products suspended in a volume air. PAEC is measured in quantities of J m-3 or Working Level (1 WL = 2.08 × 10-5 J m-3). Precision. The uncertainty in a single result from a measurement or procedure that is caused by inherent variability in the processes that are combined to form the result. Precision is a complement to variability.
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--> Preneoplastic. Cells with altered genetic stares that are not yet completely malignant. Probability. A number expressing the chance that a specified event will occur. It can range from 0 (indicating that the event is certain not to occur) to 1 (indicating that the event is certain to occur). Proliferative cells. Those cells in a tissue that divide by mitosis to become the expanding population that serves as the source for the fully differentiated cells which ultimately carry out the functions of the tissue. R rad. A quantity of absorbed dose equal to 100 erg g-1. This is the traditional unit of dose and 1 rad = 0.01 gray (Gy). Radiation. Any combination of elementary particles that have sufficient kinetic energy to interact with and transfer energy to material that intercepts their path. If the energy transferred is sufficient to produce ionization in the material, it is classified as ionizing radiation. Radiation exposure. The total electrical charge of one sign produced in air by photons interacting in volume of air divided by the mass of air in that volume. It has the dimensions of charge divided by mass, Coulomb kg-1. The special unit of exposure is the Roentgen (R). Radiation weighting factor (wR). A modifying factor used to obtain equivalent dose from absorbed dose. It depends on the biological effectiveness of the specified radiation but does not depend on the tissue or organ under consideration. Radioactivity. A quantity of radioactive material based on the rate that the atoms or nuclei spontaneously transform and emit radiation. Radioactivity is described in terms of a becquerel (Bq), or curie (Ci). Radon. The element with atomic number 88. It is an inert gas within the same family of elements as helium, neon, argon, and xenon. Although there are several isotopes of radon, the most common is 222Rn which is part of the decay series that begins with 238U. Radon decay products. The four short-lived radioactive isotopes in the 238U series immediately following the decay of 222Rn. They are the metals, 218Po, 214pb, 214Bi, 214Po, and are also called radon daughters or radon progeny. RCRA. Resource, Conservation and Recovery Act regulates the generation, storage, transportation, treatment and disposal of hazardous substances. rem. A measure of equivalent dose H, that is obtained when the dose (rad) is multiplied by the radiation weighting factor (wR). For example, if wR = 1, then one rem is numerically the same as one rad. Risk. Conceptually, risk is a measure of the chance that a specified health outcome will occur. Various quantities are used to describe different aspects of risk. For example, the probability of disease is the chance that an individual will develop a specified disease during a selected interval of age (often the entire lifetime). Risks expressed as incidence rates, or mortality rates, are the number of persons who are expected to develop or die from the disease within a selected time interval and population group. This could be expressed as the number of cases or deaths per 100,000 persons per year. Roentgen. A quantity of radiation exposure equivalent to 2.58 × 10 -4 Coulomb kg-1. The roentgen is a traditional unit named on behalf of the German scientist W. K. Roentgen. S Safe Drinking Water Act (SDWA). Legislation that originally became law in 1974 and was amended as recently as 1996. This act and its amendments are designed to provide safe drinking water for consumption by the public. Senescence. The stage in the life cycle of a cell when division stops and degenerative changes begin to occur. In human cells this happens after approximately 50 cell divisions. SI units. The International System of Quantities and Units derived by the General Conference of Weights and Measures. Base units are the meter, kilogram, second and coulomb. It is often referred to as the metric system. Sievert (Sv). A measure of equivalent dose, H, that is obtained when the Dose (Gy) is multiplied by the radiation weighting factor wR. For example, when wR = 1, then one Sv is numerically the
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--> same as one Gy. The Sievert is an SI unit named on behalf of the Swedish scientist Rolf Sievert. Signal transduction. The chain of events that starts from initial damage, or from an intercellular signal peptide, and propagates through intervening molecules to eventually cause such events as apoptosis, changes in gene expression or cell cycle delays. Somatic. The cells of the adult body tissues, in contrast to germ cells which are involved in sperm and egg cell production. Splanchnic. Pertaining to or affecting the organs in the viscera, especially the intestines, and their associated blood vessels. Stern cells. The cells in a tissue that have indefinite potential for cell division, and divide relatively slowly. They serve as a source for most of the cells in a tissue and act as a reserve for repopulation following tissue damage. Stochastic radiation injury. Health effects from ionizing radiation that occur randomly where the probability of occurrence is proportional to absorbed dose with no apparent threshold. T Teratogenic. An agent that tends to produce anomalies in developing embryos. Teratologic. That division of embryology and pathology which deals with abnormal development and congenital anomalies. Telomere. The specific DNA sequences that form the ends of chromosomes and are replicated by specific enzyme systems, telomerase, which contain a polyribonucleotide sequence that acts as a template for telomere replication. Threshold. A value of absorbed dose below which the probability of a specific radiation induced health effect is zero. Time-since-exposure (TSE) model. A risk projection model in which the risk varies with the time after exposure. Tissue weighting factor (wT). The ratio of the risk for developing radiation induced cancer in a tissue, T, to the combined risk of developing cancer in any organ following a uniform irradiation of the whole body to the same equivalent dose. TOC. Total organic carbon: sum of the particulate and dissolved organic matter in a sample such as water. Transcription. The process by which a gene sequence in DNA is used to synthesize a matching sequence of ribonucleic acid (RNA). Transfer factor (T). The average increment of the radon concentration in indoor air (a) divided by the average radon concentration in the water (w). Translation. The process where a specific RNA sequence is used for the synthesis of a protein in which a code based on 3 bases read together (triplet code) specifies an amino acid position in the protein. Trihalomethanes (THMs). A class of potentially toxic chemical byproducts such as chloroform, dibromochloromethane, dichlorobromomethane, and bromo-form, that can be formed when water that contains natural organic matter is disinfected by the addition of chlorine. Triplet repeats. Regions of DNA in which a sequence of three nucleotides is repeated many times. U UCL. Upper confidence limit; the upper bound of a confidence interval. Uncertainty. A lack of knowledge concerning the truth. This can be quantitative or qualitative. V Variability. The variation of a property or a quantity among members of a population. Such variation is inherent in nature and thus unavoidable. It is often assumed to be random, and can be represented by a frequency distribution. Volatile organic contaminants (VOCs). Those organic compounds that are considered contaminants in air or water. The compounds usually transfer spontaneously from water to air. W Working level (WLM). A quantity of potential alpha energy concentration equivalent to 2.08 × l0-5 J m-3. Working level month (WLM). An exposure to radon decay products suspended in air that is determined by PAEC multiplied by the residency time at that location. One WLM is equivalent to 1 WL for 170 hours which equals 12.7 J m-3 s.
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--> X X-ray. A type of electromagnetic radiation, also called a photon, that originates from an energy transition of the atom. These are generally less energetic than gamma rays that are emitted from nuclear transitions. Conversions between SI units and Traditional Units Concept Traditional SI Radioactivity 1 Ci 3.7 × 1010 Bq Radioactivity 1 pCi 0.037 Bq Concentration 1 pCi L-1 0.037 Bq L-1 Concentration 1 pCi L-1 37 Bq m-3 Absorbed Dose 1 rad 0.01 Gy Equivalent Dose 1 rem 0.01 Sv PAEC 1 WL 2.08 × 10-5 J m-3 PAEC Exposure 1 WLM 12.5 J m-3 s