Glossary-Chemical - Research Paper | CHE 480, Papers of Chemistry

Download Glossary-Chemical - Research Paper | CHE 480 and more Papers Chemistry in PDF only on Docsity! 1 Glossary - Chemical Glossary - Chemical abiotic: Nonliving, especially the nonliving elements in ecological systems. ablation: The functional destruction of an organ through surgery or exposure to large doses of radiation. absorbed dose: The amount of a substance (e.g., a chemical) that enters the body of an exposed organism. OR The energy imparted by ionizing radiation per unit of irradiated material. The units of absorbed dose are the rad and the gray (Gy). absorber: Any material that absorbs or lessons the intensity of ionizing radiation. Neutron absorbers (like boron, hafnium, and cadmium) are used in control roads for reactors. Concrete and steel absorb gamma rays and neutrons in reactor shields. A thin sheet of paper or metal will absorb or weaken alpha particles and all except the most energetic beta particles absorption: The movement of a substance (e.g., a chemical) through a membrane into the body after exposure has occurred. OR The process by which the number of partiles or photons entering a body of matter is reduced or attenuated by interation with the matter. absorption factor: The fraction of a substance (e.g., a chemical) making contact with an organism that is absorbed by the organism. acaricide: A pesticide that kills mites, See also miticide. acceptable daily intake (ADI): Estimate of the largest amount of a substance (e.g., chemical) to which a person can be exposed on a daily basis that is not anticipated to result in adverse effects. Usually expressed in milligrams per kilograms per day (mg/kg/day). Same as reference dose. acceptable intake for chronic exposure (AIC): An estimate similar in concept to the RFD, but derived using a less strictly defined methodology. Chronic RFDs have replaced AICs as the agency’s preferred values for use in evaluating potential noncarcinogenic health effects resulting from chronic exposure to a chemical. acceptable intake for subchronic exposure (AIS): An estimate similar in concept to the subchronic RFD, but derived using a less strictly defined methodology. Subchronic RFDs have replaced AISs as the agency’s preferred values for use in evaluating potential noncarcinogenic health effects resulting from chronic exposure to a chemical. Access Hatch (air lock): An airtight door system that preserves the pressure integrity of a reactor containment building while allowing access to personnel and equipment. 2 Glossary - Chemical accuracy: The quality of being from error, or the degree of conformity of a measure to a standard or a true value. activation: The process of making a material readioactive by bombardment with neutrons, protons, or other nuclear radiation. active transport: An energy-expending mechanism by which a cell moves a chemical across the cell membrane from a point lower concentration to a point of higher concentration, against the diffusion gradient. activity: The rate of disintegration (transformation) or decay of radioactive material. The units of activity are the curie (Ci) and the becquerel (Bq). activity median aerodynamic diameter (AMAD): The diameter of a unit density sphere with the same terminal settling velocity in air as that of the arerosol particle whose activity is the median for the entire aerosol. acute: Occurring over a short period of time; used to describe brief exposures and effects which appear promptly after exposure. acute effects: Effects that show up soon after exposure. acute exposure: Exposure over a short amount of time. OR The absorption of a relatively large amound of radiation (or intake of radioactive material) over a short period of time. additive effect: Refers to situations where the combined effect of two or more substances (e.g., two or more chemicals) is equal to the sum of their individual effects. adenoma: Glandlike benign growth (tumor). An adenoma in a rat that has received a test chemical is considered evidence that the chemical might cause cancer in a human. administered dose: The mass of a substance given to an organism and in contact with an exchange boundary (e.g., gastrointestinal tract) per unit body weight per unit time (e.g., mg/kg*day). adsorb: To take up by attraction and holding surface. Chemicals are often adsorbed by soil particles, dust, activated charcoal, or other substrates. adsorption: The process by which chemicals are held on the surface of a mineral or soil particle. Compare with absorption. aerosol: A liquid dispersed in air as a very fine mist. 5 Glossary - Chemical bioconcentration: The accumulation of a substance (e.g., a chemical) in tissues of an organism (such as fish) to levels that are greater than the level in the medium (such as water) in which the organism resides. See bioaccumulation. biodegradation: Decomposition of a substance into more elementary compounds by biological action. biomagnification: The serial accumulation of a substance (e.g., a chemical) by organisms in the food chain, with higher concentrations of the substance in each succeeding level. biotransformation: The enzymatic transformation of a foreign compound into a different one. The new compound may be more or less toxic than the old one. brominated: Pertaining to the presence of one or more atoms of the element bromine in a compound. cancer: The uncontrolled, invasive growth of cells. Cancerous cell can metastasize; they can break away from the original tumor, relocate, and grow elsewhere in the body. capillaries: Finest subdivisions of the blood vessels; they bring the blood into intimate contact with the tissue. carcinogen: A substance that causes or induces cancer. cardioactive: Affecting the heart. cardiovascular: Pertaining to the heart and blood vessels. CAS registration number: A number assigned by the Chemical Abstracts Service to identify a chemical. central nervous system (CNS): Portion of the nervous system that consists of the brain and spinal cord; protected from the rest of the body (and toxicants) by the blood brain barrier. chemicals of potential concern: Chemicals that are potentially site-related and whose data are of sufficient quality for use in the quantitative risk assessment. Chernobyl: The site in the Soviet Union of a major nuclear power plant accident. chloracne: A skin decease resembling the acne of adolescence and caused by exposure to chlorinated aromatic organic compounds. 6 Glossary - Chemical chromosome: Rodlike structure in the nucleus of a cell composed of DNA and protein. Chromosomes contain the genes responsible for heredity. chronic: Of long duration. Chronic exposure usually refers to long-term, low-level exposure. Chronic toxicity refers to the effects produced by such exposure. Chronic exposure may cause latent damage that does not appear until later. chronic daily intake (CDI): Exposure expressed as mass of a substance contacted per unit body weight per unit time, averaged over a long period of time (as a Superfund program guideline, seven years to a lifetime). chronic exposure: Long-term, low level exposure to a toxic chemical. chronic reference dose (RFD): An estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a daily exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable risk of deleterious effects during a lifetime. Chronic RFDs are specifically developed to be protective for long-term exposure to a compound (as a Superfund program guideline, seven years to lifetime). cilia: Small “hairs” on some cells. Cilia in the lungs push along a mucus stream that traps and removes many foreign particles. clinical studies: Studies of humans suffering from symptoms induced by chemical exposure. cocarcinogen: A substance that enhances the tumor production of a carcinogen. cohort: A group of individuals having a statistical factor (such as age or class membership) in common in a demographic or epidemiological study. combustible: See flammable. committed dose equivalent (HT,50): The total dose equivalent (average over tissue T) deposited over the 50 year period following the intake of a radionuclide. committed effective dose equivalent (HE,50): The weighted sum of committed dose equivalents to specified organs and tissues, in analogy to the effective dose equivalent. common laboratory contaminants: Certain organic chemicals (considered by EPA to be acetone, 2-butanone, methylene chloride, toluene, and the phthalate esters) that are commonly used in the laboratory and thus may be introduced into a sample from laboratory cross-contamination, not from the site. compound: A substance formed by the union of two or more elements. 7 Glossary - Chemical concentration: The quantity of a substance per unit volume or weight. Examples: amount of a chemical in drinking water or air; amount of poison relative or an organism (for example, amount per unit of blood volume). confidence interval: Specifies a range and probability that an uncertain quantity falls within this range. Expressed as “the X percent confidence interval.” confidence limits: The upper and lower boundary values of a range of statistical probability numbers. confounding factors: Variables other than chemical exposure level which can affect the incidence or degree of a parameter being measured. congenital: Pertaining to a condition existing before or at birth. contact rate: Amount of medium (e.g., groundwater, soil) contacted per unit time or event (e.g., liters of water ingested per day). contract laboratory program (CLP): Analytical program developed for Superfund waste site samples to fill the need for legally defensible analytical results supported by a high level of quality assurance and documentation. contract required quantitation limit (CRQL): Chemical-specific levels that a CLP laboratory must be able to routinely and reliably detect and quantitative specified samples matrices. May or may not be equal to the reported quantitation limit of a given chemical in a given sample. control: To verify the effect of a variable by holding several other variables constant. corrosive: A substance that erodes other material by oxidation or other chemical reactions. cost/benefit analysis: A quantitative evaluation of the costs which would be incurred versus the overall benefits to society of a proposed action such as the establishment of an acceptable dose of a toxic chemical. critical period: The time during development of an embryo or fetus when it is most sensitive to the effects of a chemical or virus. The critical period for many chemicals in humans is during the first three months of gestation. cumulative exposure: The summation of exposures of an organism to a substance (e.g., chemical) over a period of time. 10 Glossary - Chemical ecotoxicological studies: Measurement of effects of environmental toxicants on indigenous populations of organisms. ED50: The dose at which a particular effect is observed in 50 percent of the animals or humans tested. edema: Swelling, caused by excessive fluid buildup in tissues. effective dose equivalent (HF): The sum over specified tissues of the products of the dose equivalent in a tissue or organ (T) and the weighting factor for that tissue. effluent: Treated or untreated waste material discharged into the environment. Generally refers to water pollution. emetic: An agent that causes vomiting. empirical: Originating in or based on observation or experience. endangerment assessment: A site-specific risk assessment of the actual or potential danger to human health or welfare and the environment from the release of hazardous substances or waste. The endangerment assessment document is prepared in support of enforcement actions under CERCLA or RCRA. endemic: Pertaining to prevalence in a particular region. An endemic disease is one that is constantly present at a low incidence in a particular region. endogenous: Originating with the organism. endpoint: A biological effect used as an index of the effect of a substance on an organism. environmental fate: The destiny of a substance (e.g., a chemical) after release to the environment. Involves considerations such as transport through air, soil, and water, bioconcentration; and degradation. enzyme: A large protein that speeds up the rate of a biochemical reaction. epidemiological studies: Investigation of elements contributing to disease or toxic effects in human populations. epidemiology: The study of patterns of disease in groups of people. epigenetic: Pertaining to a nongenetic mechanism. 11 Glossary - Chemical excretion: Any physiological process through which waste or toxic materials are removed from the body; routes of exit may include urine, feces, sweat, milk, and expired air. exocrine: Type of gland that secretes through a duct to the outside of the body or to the gastrointestinal tract. expected value: Valuation of an uncertain numerical variable by weighting all possible outcome values by their probability of occurrence and then averaging. expert judgment: Opinions of persons well informed in an area that are incorporated into probability estimates. exposure: Contact between a substance (e.g., a chemical) and a potentially affected biological system that permits interaction. exposure assessment: The determination of estimation (qualitative or quantitative) of the magnitude, frequency, duration, route, and extent (number of people) of exposure to a substance. exposure coefficient: Term which combines information on the frequency, mode, and magnitude of contact with contaminated medium contacted per day. exposure event: An incident of contact with a chemical or physical agent. An exposure event can be defined by time (e.g., day, hour) or by the incident (e.g., eating a single meal of contaminated fish). exposure level, chemical: The amount (concentration) of a chemical at the absorptive surfaces of an organism. exposure pathway: The course a chemical or physical agent takes from a source to an exposed organism. An exposure pathway describes a unique mechanism by which an individual or population is exposed to chemicals or physical agents at or originating from a site. Each exposure pathway includes a source or release from a source, an exposure point, and an exposure route. If the exposure point differs from the source, a transport/exposure medium (e.g., air) or media (in cases of intermedia transfer) also in included. exposure point: A location of contact between an organism and a chemical or physical agent. exposure route: The way a chemical or physical agent comes in contact with an organism (e.g., by ingestion, inhalation, dermal contact). 12 Glossary - Chemical exposure scenario: A set of conditions or assumptions about sources, exposure pathways, concentrations of toxic chemicals, and populations (numbers, characteristic, and habits) that aid the investigator in evaluating and quantifying exposure in a given situation. external radiation: Radiations incident upon the body from an external source. extrapolation: Estimation of unknown values by extending or projecting from known values. fat-soluble: Dissolves in fat. fetus: The later stages of a developing organism. In the human, it is the unborn child during the period of uterine life from the end of the second month until birth. field sampling plan (FSP): Provides guidance for all field work by defining in detail the sampling and data gathering methods to be used on a project. first-order kinetics: See pharmacokinetics. flammable: Has a flash point below 100 degrees F. The flash point is the lowest temperature at which vapors over a material will ignite given an external sources of ignition. fog: Suspension in air of fine droplets of a liquid. fume: Suspension in air of usually irritating, offensive, or acrid particles, droplets, or gas molecules. gametogenesis: The production of germ cells (sperm and eggs). gas: A substance that is in a gaseous state (above its boiling point) under normal temperature and pressure. gastrointestinal (GI) tract: Includes the mouth, esophagus, stomach, duodenum, small intestines, appendix, or cecum, large intestines, and rectum. Gaussian statistical distribution: A commonly occurring statistical distribution characterized by a bell shape and having a mathematical representation expressed in terms of a mean and a variance. Also called the normal probability distribution. gavage: Force-feeding (or dosing) by stomach tube. gene: The unit of inheritance; part of a DNA molecule. 15 Glossary - Chemical incidence (of disease): The number of new cases of a disease, usually expressed as an incidence rate-the number of new cases occurring in a population during a specified time period divided by the number of persons exposed to the disease during that period. incidence of tumors: Percentage of population with tumors. independence (or probabilistic independence): The relationship between two or more events when knowledge of the probability of occurrence of one does not alter the probability of another. individual lifetime risk: The estimated incremental lifetime risk of an adverse effect incurred by an individual owing to exposure to a specified concentration of a risk agent for a given time period. initiator: An external stimulus or agent that produces a cell that is “latently premalignant.” An initiation event may be a mutational change in the cell’s genetic material. intake: Amount of material inhaled, absorbed through the skin, or ingested during a specified period of time. integrated exposure assessment: A summation over time, in all media, of the magnitude of exposure to a toxic substance or other risk agent. integrated risk information system (IRIS): An EPA data base containing verified RFDs and slope factors and up-to-date health risk and EPA regulatory information for numerous chemicals. IRIS is EPA’s preferred source for toxicity information for Superfund. internal radiation: Radiation emitted from radionuclides distributed within the body. internal extrapolation: The act of applying a set of data or an individual test result on one species, under certain conditions and subject to particular dose levels of a toxic substance and application methods, to another population of the same or different species tested under perhaps different conditions, dose levels, and application methods. interspecies extrapolation model: Model used to extrapolate from results observed in laboratory animals to humans. intestine: See gut. in vitro: Phrase-literally, in glass-used to refer to experiments that take place outside the living animal. 16 Glossary - Chemical in vivo: Phrase-literally, in the living being-used to refer to experiments that take place in living animals. ionization: Dissociation into ions. Ions are atoms or molecules that are electrically charged as a result of having gained or lost electrons. ionizing radiation: High-energy particles or waves that cause molecules to ionize. Includes alpha, beta, and neutron particles and gamma and X-rays. Nonionizing radiation includes microwaves, ultraviolet light, and lasers. irreversible effect: Effect characterized by the inability of the body to partially or fully repair injury caused by a toxic agent. irritation: Transient, reversible effects, including redness, pain, and itching. isomer: A molecule that has the same number and kind of atoms as another molecule but has a different arrangement of these atoms. jaundice: Yellowing of skin, eyes, or tissue owing to bile pigments. Kaposi’s sarcoma: Previously rare cancer that occurs often in AIDS patients. Kilogram (kg): A kilogram is about 2.2 pounds. linear energy transfer (LET): A measure of the rate of energy absorption, defined as the average energy imparted to the absorbing medium by a charged particle per unit distance (KeV per um). Liter (l): A liter is a little larger than a liquid quart. latency: Time from the first exposure to a substance (e.g., chemical) until the appearance of a toxic effect. For cancer, this period may be 10 to 20 years in humans. LC50 (mean lethal concentration): The concentration of a chemical that is expected to cause death in 50 percent of test animals. LD50 (mean lethal dose): The dose of a chemical that is expected to cause death in 50 percent of test animals. leukemia: A form of cancer characterized by the rapid multiplication of abnormal white bloods cells (leukocytes) in the blood and blood-forming tissue. lifetime average daily intake: Exposure expressed as the mass of a substance in contact with the exchange boundary per unit body weight per unit time (e.g., mg chemical/kg 17 Glossary - Chemical body weight*day). Also termed the normalized exposure rate, equivalent to administered dose. lifetime exposure: Total amount of exposure to a substance that a human would receive in the lifetime (usually assumed to be 70 years). likelihood: Statistical probability that an event such as harm or injury may occur as a result of exposure to a risk agent. linear relationship: Straight-line. When the statistical relationship between two variable increases on a direct unit-for-unit basis, this relationship, when plotted on a chart, will form a straight line. linearized multistage model: A type of dose-response model; a derivation of the multistage model, wherein the data are assumed to be linear at low doses. lipid: Fat and fat-like material; any substance that originates from living organisms and that dissolves in organic solvents, such as ethyl alcohol, ether, benzene, etc. Alone with proteins and carbohydrates, lipids are the principal structural element of living cells, especially cell membranes. logistic curve: In risk assessment , an S-shaped curve that, if plotting dose-response relationships, is linear at low doses, of higher degree at higher doses, and finally saturates at very high doses where the effect in question always occurs. lowest observed effect level (LOEL): The lowest exposure level at which effects are observed. These effects may or may not be serious. On the other hand, a LOAEL (the A stands for adverse) makes a judgment on the significance of the effect. lymphatic system: The system of vessels and nodes that returns the lymph (clear fluid that is collected from body tissues) to the blood. lymphoma: Any of several types of cancerous conditions of the lymphatic tissue, including lymphosacrcoma and Hodgkin’s disease. macromolecule: An extremely large molecule. malignant: A tumor that has invaded neighboring tissue and has undergone metastasis to distant body sites, at which point the tumor is called a cancer. margin of safety (MOS): The maximum amount of exposure producing no measurable effect in animals (or studied humans) divided by the actual amount of human exposure in a population. 20 Glossary - Chemical naturally occurring background levels: Ambient concentrations of chemicals that are present in the environment and have not been influenced by humans (e.g., aluminum, manganese). necrosis: Death of cells or tissue from irreversible damage. neoplasm: See tumor. neurotoxicity: Exerting a destructive or poisonous effect on nerve tissue. no observed adverse effect level (NOAEL): The highest dose in an experiment that does not produce an observable adverse effect. no observed effect level (NOEL): Dose level at which no effects are noted. non-detects (NDs): Chemicals that are not detected in a particular sample above a certain limit, usually the quantitation limit for the chemical in that sample. Non-detects may be indicated by a “U” data qualifier. nonionizing radiation: See ionizing radiation. normal probability distribution: See Gaussian statistical distribution. nuclear transformation: The spontaneous transformation of one radionuclide into a different nuclide or into a different energy state of the same nuclide. objective probability: Assignment of a number between zero and one to an event based on historical trials or occurrence estimation of similar events; probability that can be inferred from objective facts. ocular: Pertaining to the eye. odor threshold: The concentration of a substance in air at which it can just be smelled by the average person. oncogene: A gene that induces a cancer process. oncology: Study of cancer. one-hit model: A mathematical dose-response model based on the biological theory that a single “hit” of some minimum critical amount of a carcinogen at a cellular target can initiate an irreversible series of events, eventually leading to a tumor. oral: Of the mouth; through or by the mouth. 21 Glossary - Chemical ozone: A gas compound of molecules of triatomic oxygen (O3), the most reactive form of oxygen. pandemic: Epidemic disease spread over many regions. parasympathetic: Pertaining to part of the nervous system, below the level of consciousness, that participates in the regulation of the involuntary functions of the body (for example, heart beat, breathing rate). pathogenic: Causing or capable of causing disease. pathogenic agent: A substance, living or inanimate, or a force, the excessive presence or relative lack of which is the cause of a particular disease. pathologic: Pertaining to a disease state. peritoneal cavity: The abdominal cavity, which contains such organs as the stomach, intestines, and liver. permissible dose: The dose of a chemical that may be received by an individual without the expectation of significantly harmful result. permissible exposure level (PEL): The legal limit for occupational exposure to airborne concentrations of several hundred chemicals. Established by OSHA (Occupational Safety and Health Administration). persistence: Resistance to degradation. A persistent substance is expected to remain in the environment for a long time. pesticide: Any substance used for controlling, preventing, destroying, repelling, or mitigating any pest. Pests include insects, mites, birds, algae, bacteria, fungi, weeds, nematodes, fish, coyotes, and slimes. petrochemical: A chemical derived from petroleum. pH: A term used to express the degree of acidity or alkalinity of a solution. A pH of 7 is neutral. Acid solutions have pHs below 7, and alkaline solutions have pHs greater than 7. pharmaceutical: A therapeutic drug. pharmacokinetics: The study of changes in a toxicant in parts of the body over time. Involves absorption, distribution through the body, biotransformation, and excretion of the toxicant. 22 Glossary - Chemical pharmacology: The study of drugs. photolysis: Chemical decomposition induced by light. phylogenetic: Pertaining to organisms related in evolutionary development. placenta: The organ that forms the bridge between the fetal and maternal blood streams. plasma: The clear, yellowish fluid portion of blood, lymph, or intramuscular fluid in which cells are suspended. point source: A stationary location where pollutants are discharged, usually by an industry. poison: A substance that may be dangerous to life or health. Often considered to be a substance with relatively high acute toxicity; legally defined as having an acute oral toxicity of less than 50 milligrams per kilogram of body weight. Poisson distribution: A discrete frequency distribution of the number of times a rare event occurs within a defined time period or spatial area. polycyclic: In chemistry, pertaining to organic compounds whose molecules contain more than one circular structure (ring). polymer: A large molecule (macromolecule) formed from the chemical combination of many smaller molecules, usually of only a few kinds. Proteins, starch, and cellulose are examples of natural polymers. population at risk: A population subgroup that is more likely to be exposed to a substance (e.g., chemical), or is more sensitive to a substance (e.g., a chemical), than is the general population. positive data: Analytical results for which measurable concentrations (i.e., above a quantitation limit) are reported. May have data qualifiers attached (except a U which indicates a non-detect). potency: Amount of a substance or material necessary to produce a given level of deleterious effect. potentiation: The effect of one chemical to increase the effect of another chemical. precision: The exactness with which a quantity is stated. 25 Glossary - Chemical risk: In risk assessment, the probability that something will cause injury, combined with the potential severity of that injury. risk agent: Chemical substance, biological organism, radioactive material, or other potentially hazardous substance or activity. risk assessment: A qualitative or quantitative evaluation of the environmental and/or health risk resulting from exposure to a chemical or physical agent (pollutant); combines exposure assessment results with toxicity assessment results to estimate risk. risk characterization: The final phase of the risk-assessment process that involves integration of the data and analysis involved in hazard identification, source/release assessment, exposure assessment, and dose-response assessment to estimate the nature and likelihood of adverse effects. risk estimate: A description of the probability that organisms exposed to a specified dose of a substance (e.g., a chemical) will develop an adverse response (for example, cancer). risk factor: Characteristic (such as race, sex, age, or obesity) or variable (such as smoking or occupational exposure level) associated with increased probability of a toxic effect. risk-specific dose: The dose associated with a specified risk level. roentgen: A unit of X- or gamma radiation that describes the degree of ionization that results under certain specified conditions; named for the discoverer of X-rays, Wilhelm Roentgen (1845-1923). route of exposure (or entry): The avenue by which a substance (e.g., a chemical) comes into contact with an organism; such avenues include inhalation, ingestion, and dermal contact. routine analytical services (RAS): The set of CLP analytical protocols that are used to analyze most Superfund site samples. These protocols are provided in the EPA statements of work for the CLP (SOW for Inorganics, SOW for Organics) and must be followed by every CLP laboratory. safety: Practical certainty that a substance will not cause injury under carefully defined circumstances of use. sampling and analysis plan (SAP): Consists of a Quality Assurance Project Plan (QAPP) and a Field Sampling Plan (FSP). 26 Glossary - Chemical sample management office (SMO): EPA contractor providing management, operational, and administrative support to the CLP to facilitate optimal use of the program. sarcoma: A usually malignant tumor that occurs in connective tissue or other mesodermal cells (mesodermal cells are one of the basic tissue types). sensitivity analysis: A method used to examine the behavior of a model by measuring the variation in its outputs resulting from changes to its inputs. sensitization: The process (chemical exposure and immune response) through which a person acquires an antibody-mediated sensitivity to a chemical or other allergen. sievert (Sv): The special name for the SI unit of dose equivalent. 1 sv = 100 rem. sink: A place in the environment where a compound or material collects. See reservoir. skin cancer: Common cancers (over 500,000 cases per year in the United States) associated with excessive exposure to the sun and some occupational exposures. Most serious form is malignant melanoma. slope factor: A plausible upper-bound estimate of the probability of a response per unit intake of a chemical over a lifetime. The slope factor is used to estimate an upper-bound probability of an individual developing cancer as a result of a lifetime of exposure to a particular level of a potential carcinogen. solvent: A liquid capable of dissolving another substance. Many solvents are organic, or carbon-based; many of these are volatile, flammable, and toxic. Examples: acetone, trichloroethylene (TCE), perchloroethylene, benzene. Water is a nonorganic solvent. somatic: Pertaining to body cells, as opposed to reproductive cells. sorption: A surface phenomenon that may be either absorption or adsorption, or a combination of the two; often used when the specific mechanism is not known. source/release assessment: A step in risk assessment that estimates the amounts, frequencies, and locations of the introduction, release, or escape of risk agents into occupational, residential, or outdoor environments. special analytical services (SAS): Non-standardized analyses conducted under the CLP to meet user requirements that cannot be met using RAS, such as shorter analytical turnaround time, lower detection limits, and analysis of non-standard matrices or non- TCL compounds. 27 Glossary - Chemical standard deviation: The square root of the variance. See variance and probability density function. statement of work (SOW) for the CLP: A document that specifics the instrumentation, sample handling procedures, analytical parameters and procedures, required quantitation limits, quality control requirements, and report format to be used by CLP laboratories. The SOW also contains the TAL and TCL. statistically significant: Experimental results that are “not likely” to have occurred by chance. “Significant with .05 probability” means there is only a 5 percent probability that the results were attributable to chance and a 95 percent probability that the results were attributable to the experiment. stochastic: In risk assessment, a statistical concept based on the assumption that the actions of a substance result from probabilistic events. stratification: (1) The division of a population into subpopulations for sampling purposes. (2) The separation of environmental media into layers, as in lakes. subchronic: Of intermediate duration, usually used to describe studies or levels of exposure between 5 and 90 days. subchronic daily intake (SDI): Exposure expressed as mass of substance contacted per unit body weight per unit time averaged over a portion of a lifetime (as a Superfund program guide, two weeks to seven years). subchronic reference dose (RFDs): An estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a daily exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable risk of deleterious effects during a portion of a lifetime (as a Superfund program guideline, two weeks to seven years). sublethal: Pertaining to a dose level that is less than an amount necessary to cause death. substance: Refers to chemicals and other external, nonliving sources of potential hazard, such as ionizing radiation and microwaves. substrate: A chemical that serves as the substance acted upon by an enzyme. More generally, an underlying support or foundation. synergism: Effects from a combination of two or more events, efforts, or substances that are greater than would be expected from adding the individual effects. synthetic: Made by man.