Ecologic A term referring to the general environment. Ecotoxicity The toxic effects on environmental organisms other than humans. ED50 Effective dose 50%.  The estimated dose that causes some specific effect (usually desirable) for 50% of the population. ED99 Effective dose 99%.  The estimated dose that causes some specific effect (usually desirable) for 99% of the population. Edema The retention of fluid in an organ or in the body. Effluent The discharge of waste from a plant or other source into the environment. Embryo An early stage of the development of the unborn offspring in which cell differentiation proceeds rapidly along with the formation of the major organs.  In humans this stage occurs from about 3 weeks until 8-9 weeks after conception. Embryotoxic The harmful effects of a substance on the developing embryo. Environmental Fate The fate of a substance following its release into the environment.  It includes the movement and persistence of the substance. Enzyme A protein which serves as a catalyst for chemical reactions in cells. Enzyme Activation The increase in levels of an enzyme as the result of stimulation by another chemical substance. Enzyme Inhibitor A substance which causes a decrease in levels of an enzyme. EPA Environmental Protection Agency. A federal agency responsible for regulation of most chemicals that can enter the environment.  The EPA administers the following acts: Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the Toxic Substances Control Act (TSCA), the Resource Conservation and Recovery Act (RCRA), the Safe Drinking Water Act (SDWA), Clean Air Act (CAA), and the Comprehensive Environmental Response, Compensation and Liabilities Act (CERCLA) ( Superfund Act). Epidemiology The study of the relative characteristics of exposed and nonexposed human populations for the purpose of detecting harmful effects. Epidermis The outer layer of the skin. Excretion A process whereby substances (or metabolites) are eliminated from the body. Exposure Contact with a foreign substance, usually by inhalation, ingestion, or skin contact. Exposure Assessment The analysis or estimation of the intensity, frequency, and duration of human exposures to an agent. Exposure Dose The amount of a substance in the environment to which a person is subjected.