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.


An enzyme which hydrolyzes 8-ozyguanine triphosphates to monophosphates and eliminates them as precursors for DNA and RNA synthesis.



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.


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.



Those genes that exert a dominant effect in expressing one or more characteristics of malignancy. They are often a result of specific mutations.


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.



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.


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).


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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