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| Partition Coefficient |
| | see Octanol/water partition coefficient. |
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| Passive Transfer |
| | The movement across a membrane by simple diffusion. |
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Pathology |
| | The branch of medicine that involves the functional and structural changes in tissues and organs which are caused by disease. |
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| PEL |
| | Permissible Exposure Level. The standard stipulated by OSHA for the highest safe level of exposure to a chemical in the workplace. |
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| Percutaneous |
| | Movement through the skin. |
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| Pharmacokinetics |
| | Quantitation of the time course of chemical absorption, distribution, metabolism, and elimination. |
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| Pharmacology |
| | The science that deals with the origin, nature, chemistry, effects and uses of drugs. |
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| Phototoxic |
| | The enhanced toxicity of a substance in or on the skin due to exposure to light (usually ultraviolet light). |
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| Physiologically-Based Pharmacokinetic Model (PB-PK) |
| | A risk assessment model that quantitates risk using biological data on the absorption of a foreign substance, its distribution, metabolism, storage is tissues, and elimination. |
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| Picogram (pg) |
| | A unit of weight consisting of one quadrillionth of a gram (1 x 10-12 g). |
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| Poison |
| | A substance capable of causing toxicity when absorbed into the body in a relatively small quantity. |
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| Polyploidy |
| | An increase in the normal number of chromosomes. |
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| Power of the Study |
| | The statistical ability of a study to detect an effect. |
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| PPB |
| | Parts per billion. The number of units of a substance in a billion units. PPB is a common concentration unit for dilute samples of dissolved substances or airborne substances. |
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| PPM |
| | Parts per million - the number of units of a substance in a million units. PPM is a common concentration unit for dilute samples of dissolved substances or airborne substances. |
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| Primary Dermal Irritation Test |
| | A test with laboratory animals (usually rabbits) that determines dermal toxicity of a substance when applied to the skin. It is manifest mainly by erythema, edema, and eschars. |
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| Probit Model |
| | A risk assessment model that assumes log normal distribution for tolerances of an exposed population. It is generally considered inappropriate for the assessment of cancer risk. |
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| Prospective Cohort Study |
| | An
epidemiology study in which cohorts are identified according to current exposures. The cohort is followed over time for the development of specific effects, such as cancer. |
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