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  • A poison is any agent capable of producing a deleterious response in a biological system.

  • A mechanistic toxicologist identifies the cellular, biochemical, and molecular mechanisms by which chemicals exert toxic effects on living organisms.

  • Toxicogenomics permits identification and protection of genetically susceptible individuals from harmful environmental exposures, and customizes drug therapies based on their individual genetic makeup.

  • A descriptive toxicologist is concerned directly with toxicity testing, which provides information for safety evaluation and regulatory requirements.

  • A regulatory toxicologist both determines from available data whether a chemical poses a sufficiently low risk to be marketed for a stated purpose and establishes standards for the amount of chemicals permitted in ambient air, industrial atmospheres, and drinking water.

  • Selective toxicity means that a chemical produces injury to one kind of living matter without harming another form of life even though the two may exist in intimate contact.

  • The individual or “graded” dose–response relationship describes the response of an individual organism to varying doses of a chemical.

  • A quantal dose–response relationship characterizes the distribution of responses to different doses in a population of individual organisms.

  • Hormesis, a “U-shaped” dose–response curve, results with some xenobiotics that impart beneficial or stimulatory effects at low doses but adverse effects at higher doses.

  • Descriptive animal toxicity testing assumes that the effects produced by a compound in laboratory animals, when properly qualified, are applicable to humans, and that exposure of experimental animals to toxic agents in high doses is a necessary and valid method of discovering possible hazards in humans.

Toxicology is the study of the adverse effects of chemical, biological, or physical agents on living organisms and the environment. These toxic substances include naturally occurring harmful chemicals, or toxins, as well as foreign substances called xenobiotics. Toxins are poisons that originate from plants and microbial organisms and include venoms released by animals in order to injure predators. By comparison, xenobiotics include a variety of synthetic chemicals with different intended purposes. Generally, such toxic chemicals are referred to as toxicants, rather than toxins, because they are not produced by biological systems.

Toxic chemicals may also be classified in terms of physical state (gas, dust, liquid, size); chemical stability or reactivity (explosive, flammable, corrosive); general chemical structure (aromatic amine, halogenated hydrocarbon, etc.); or ability to cause significant toxicity (extremely toxic, very toxic, slightly toxic, etc.). Classification of toxic chemicals based on their biochemical mechanisms of action (e.g., alkylating agent, cholinesterase inhibitor, and endocrine disruptor) is usually more informative than classification by general terms such as irritants and oxidizers. However, more descriptive categories such as air pollutants, occupation-related exposures, and acute and chronic poisons may be useful to associate toxic chemicals that result in similar adverse events or are encountered under particular conditions.

Virtually every known chemical has the potential to produce injury or death if it is present in a sufficient quantity. Table 2–1 shows the dose of chemicals needed ...

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