benefit-cost analysis Estimates and comparison of short-term and long-term benefits (gains) and costs (losses) from an economic decision.

bioaccumulation An increase in the concentration of a chemical in specific organs or tissues at a level higher than would normally be expected. Compare biomagnification. 

Biological amplification See biomagnification. 

biomagnification Increase in concentration of DDT, PCBs, and other slowly degradable, fatsoluble chemicals in organisms at successively higher trophic levels of a food chain or web. Compare bioaccumulation. 

cancer Group of more than 120 different diseases, one for each type of cell in the human body. Each type of cancer produces a tumor in which cells multiply uncontrollably and invade surrounding tissue. See carcinogen, metastasis. 

carcinogen Chemicals, ionizing radiation, and viruses that cause or promote the development of cancer. See cancer. Compare mutagen, teratogen. 

cost-benefit analysis See benefit-cost analysis. 

DDT Dichlorodiphenyltrichloroethane, a chlorinated hydrocarbon that has been widely used as a pesticide but is now banned in some countries. 

dose Amount of a potentially harmful substance an individual ingests, inhales, or absorbs through the skin. See dose-response curve, median lethal dose. Compare response.

dose-response curve Plot of data showing effects of various doses of a toxic agent on a group of test organisms. See dose, median lethal dose, response. 

epidemiology Study of the patterns of disease or other harmful effects from exposure to toxic chemicals or disease organisms within defined groups of people to find out why some people get sick and some do not. 

gene mutation See mutation. 

Hazardous chemical Chemical that can cause harm because it (1) is flammable or explosive, (2) can irritate or damage the skin or lungs (such as strong acidic or alkaline substances), or (3) can cause allergic reactions of the immune system (allergens). See also toxic chemical. 

homeostasis Maintenance of favorable internal conditions in a system despite fluctuations in external conditions. See constancy, inertia, resilience. 

LD50 See median lethal dose. 

median lethal dose (LD50) Amount of a toxic material per unit of body weight of test animals that kills half the test population in a certain time.

meltdown Melting of the core of a nuclear reactor. 

metastasis Spread of malignant (cancerous) cells from a tumor to other parts of the body. See cancer. 

mutagen Chemical or form of radiation that causes inheritable changes (mutations) in the DNA molecules in the genes found in chromosomes. See carcinogen, mutation, teratogen.

mutation Random change in DNA molecules making up genes that can yield changes in anatomy, physiology, or behavior in offspring. See mutagen.

Nontransmissible disease Disease that is not caused by living organisms and does not spread from one person to another. Examples are most cancers, diabetes, cardiovascular disease, and malnutrition. Compare transmissible disease.

parts per billion (ppb) Number of parts of a chemical found in 1 billion parts of a particular gas, liquid, or solid.

parts per million (ppm) Number of parts of a chemical found in 1 million parts of a particular gas, liquid, or solid. 

parts per trillion (ppt) Number of parts of a chemical found in 1 trillion parts of a particular gas, liquid, or solid.

pathogen Organism that produces disease. persistence How long a pollutant stays in the air, water, soil, or body. See also inertia. 

poison Chemical that in one dose kills exactly 50% of the animals (usually rats and mice) in a test population (usually 60 to 200 animals) within a 14-day period. See median lethal dose.

Pollution prevention Device or process that (1) prevents a potential pollutant from forming or entering the environment or (2) sharply reduces the amount entering the environment. Compare pollution cleanup.

ppb See parts per billion. 

ppm See parts per million. 

ppt See parts per trillion. 

Precautionary principle When there is scientific uncertainty about potentially serious harm from chemicals or technologies, decision makers should act to prevent harm to humans and the environment. See pollution prevention. 

probability Mathematical statement about how likely it is that something will happen. 

response Amount of health damage caused by exposure to a certain dose of a harmful substance or form of radiation. See dose, dose-response curve, median lethal dose.

risk Probability that something undesirable will result from deliberate or accidental exposure to a hazard. See risk analysis, risk assessment, risk-benefit analysis, risk management.

risk analysis Identifying hazards, evaluating the nature and severity of risks (risk assessment), using this and other information to determine options and make decisions about reducing or eliminating risks (risk management), and communicating information about risks to decision makers and the public (risk communication).

risk assessment Process of gathering data and making assumptions to estimate short- and longterm harmful effects on human health or the environment from exposure to hazards associated with the use of a particular product or technology. See riskbenefit analysis. 

Risk communication Communicating information about risks to decision makers and the public. See risk, risk analysis, risk-benefit analysis.

risk management Using risk assessment and other information to determine options and make decisions about reducing or eliminating risks. See risk, risk analysis, risk-benefit analysis, risk communication.

risk-benefit analysis Estimate of the short- and long-term risks and benefits of using a particular product or technology. See risk assessment.

Synergistic interaction Interaction of two or more factors or processes so the combined effect is greater than the sum of their separate effects.

teratogen Chemical, ionizing agent, or virus that causes birth defects. Compare carcinogen, mutagen.

toxic chemical Chemical that is fatal to humans in low doses or fatal to more than 50% of test animals at stated concentrations. Most are neurotoxins, which attack nerve cells. See carcinogen, hazardous chemical, mutagen, teratogen.

toxicity Measure of how harmful a substance is. 

toxicology Study of the adverse effects of chemicals on health. 

Transmissible disease Disease caused by living organisms (such as bacteria, viruses, and parasitic worms) that can spread from one person to another by air, water, food, or body fluids (or in some cases by insects or other organisms). Compare nontransmissible disease.