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Any toxic substance used to kill animals or plants that damage crops or ornamental plants or that are hazardous to the health of domestic animals or humans. All pesticides act by interfering with the target species' normal metabolism. They are often classified by the type of organism they are intended to control (e.g., insecticide, herbicide, fungicide). Some inadvertently affect other organisms in the environment, either directly by their toxic effects or via elimination of the target organism.
This entry comes from Encyclopædia Britannica Concise. For the full entry on pesticide, visit Britannica.com.