Science Terms Definitions - E

Ecological Impact - The total effect of an environmental change, natural or man-made, on the community of living things.

Ecological Indicator - A characteristic of the environment that, when measured, quantifies magnitude of stress, habitat characteristics, degree of exposure to a stressor, or ecological response to exposure. The term is a collective term for response, exposure, habitat, and stressor indicators.

Ecological Risk Assessment - The application of a formal framework, analytical process, or model to estimate the effects of human action(s) on a natural resource and to interpret the significance of those effects in light of the uncertainties identified in each component of the assessment process. Such analysis includes initial hazard identification, exposure and dose response assessments, and risk characterization.

Ecology - The science dealing with the relationship of all living things with each other and with their environment.

Ecosystem - The interacting system of a biological community and its nonliving surroundings.

Ecosystem Structure - Attributes related to instantaneous physical state of an ecosystem; examples include species population density, species richness or evenness, and standing crop biomass.

Ecotone - A habitat created by the juxtaposition of distinctly different habitats; an edge habitat; or an ecological zone or boundary where two or more ecosystems meet.

Effect - A biological change caused by an exposure.

Effective Half-life - The time required for a radionuclide contained in a biological system, such as a human or an animal, to reduce its activity by one-half as a combined result of radioactive decay and biological elimination.

Efficacy - A measure of the probability and intensity of beneficial effects.

Effluent - Waste material discharged into the environment, treated or untreated. Generally refers to surface water pollution.

ELCR (excess lifetime cancer risk) - Potential carcinogenic effects that are characterized by estimating the probability of cancer incidence in a population of individuals for a specific lifetime from projected intakes (and exposures) and chemical-specific dose-response data (i.e., slope factors). By multiplying the intake by the slope factor, the ELCR result is a probability.

Electromagnetic Radiation - A traveling wave motion resulting from changing electric or magnetic fields. Familiar electromagnetic radiation ranges from x-rays (and gamma rays) of short wavelength, through the ultraviolet, visible, and infrared regions, to radar and radio waves of relatively long wave length.

Electron - An elementary particle carrying 1 unit of negative electric charge. Its mass is 1/1837 that of a proton.

Element - One of the 103 known chemical substances that cannot be broken down further without changing its chemical properties. Some examples include hydrogen, nitrogen, gold, lead, and uranium.

EMBAM (Environmental Management Benefit Assessment Matrix) - A management tool to evaluate and categorize EM activities based on the risks associated with the activities of each project.

Emission - Like effluent but used in regard to air pollution.

Emission Rate - The amount of pollutant emitted per unit of time.

Endangered Species - Animals, birds, fish, plants, or other living organisms threatened with extinction by man-made or natural changes in their environment. Requirements for declaring a species endangered are contained in the Endangered Species Act.

Endangerment Assessment - A study to determine the nature and extent of contamination at a site on the National Priorities List and the risks posed to public health or the environment. EPA or the state conducts the study when a legal action is to be taken to direct potentially responsible parties to clean up a site or pay for it. An endangerment assessment supplements a remedial investigation.

Enforceable Requirements - Conditions or limitations in permits issued under the Clean Water Act, Section 402 or 404 that, if violated, could result in the issuance of a compliance order or initiation of a civil or criminal action under federal or applicable state laws. If a permit has not been issued, the term includes any requirement which, in the Regional Administrator's (RA) judgment, would be included in the permit when issued. Where no permit applies, the term includes any requirement which the RA determines is necessary for the best practical waste treatment technology to meet applicable criteria.

Enforcement - EPA, state, or local legal actions to obtain compliance with environmental laws, rules, regulations, or agreements and/or obtain penalties or criminal sanctions for violations. Enforcement procedures may vary, depending on the requirements of different environmental laws and related implementing regulations. Under CERCLA, for example, EPA will seek to require potentially responsible parties to clean up a Superfund site, or pay for the cleanup, whereas under the Clean Air Act the agency may invoke sanctions against cities failing to meet ambient air quality standards that could prevent certain types of construction or federal funding. In other situations, if investigations by EPA and state agencies uncover willful violations, criminal trials and penalties are sought.

Enforcement Decision Document (EDD) - A document that provides an explanation to the public of EPA's selection of the cleanup alternative at enforcement sites on the National Priorities List. Similar to a Record of Decision.

Enrichment - The addition of nutrients (e.g., nitrogen, phosphorus, carbon compounds) from sewage effluent or agricultural runoff to surface water, greatly increases the growth potential for algae and other aquatic plants.

Entomb - A method of decommissioning in which radioactive contaminants are encased in a structurally long-lived material, such as concrete. The entombment structure is appropriately maintained, and continued surveillance is carried out until the radioactivity decays to a level permitting decommissioning and ultimate unrestricted release of the property.

Environment - Water, air, land, and all plants and man and other animals living therein, and the interrelationships which exist among them.

Environmental Assessment - An environmental analysis prepared pursuant to the National Environmental Policy Act to determine whether a federal action would significantly affect the environment and thus require a more detailed environmental impact statement.

Environmental Audit - An independent assessment of the current status of a party's compliance with applicable environmental requirements or of a party's environmental compliance policies, practices, and controls.

Environmental Equity - Equal protection from environmental hazards of individuals, groups or communities regardless of race, ethnicity, or economic status.

Environmental Exposure - Human exposure to pollutants originating from facility emissions. Threshold levels are not necessarily surpassed, but low level chronic pollutant exposure is one of the most common forms of environmental exposure.

Environmental Impact Appraisal - An environmental review supporting a negative declaration, i.e., the action is not a major Federal action significantly affecting the environment. It describes a proposed EPA action, its expected environmental impact, and the basis for the conclusion that no significant impact is anticipated.

Environmental Impact Statement - A document required of Federal agencies by the National Environmental Policy Act for major projects or legislative proposals. They provide information for decision makers on the positive and negative effects of the undertaking, and list alternatives to the proposed action, including taking no action. For example, an environmental impact assessment report, prepared by an applicant for an NPDES permit to discharge as a new source, identifies and evaluates the environmental impacts of the applicant's proposed source and feasible alternatives.

Environmental Pathway - All routes of transport by which a toxicant can travel from its release site to human populations including air, food chain, and water. The connected set of environmental media through which a potentially harmful substance travels from source to receptor.

Environmental Protection Agency (EPA) - Created in 1970, the EPA is responsible for working with state and local governments to control and prevent pollution in areas of solid and hazardous waste, pesticides, water, air, drinking water, and toxic and radioactive substances.

Epidemiology - The study of the distribution and dynamics of diseases and injuries in human populations. Specifically, the investigation of the possible causes of a disease and its transmission.

Estuary - Regions of interaction between rivers and near-shore ocean waters, where tidal action and river flow mix fresh and salt water. Such areas include bays, mouths of rivers, salt marshes, and lagoons. These brackish water ecosystems shelter and feed marine life, birds, and wildlife.

Evaporation Ponds - Areas where sewage sludge is dumped and dried.

Exposure - Contact of an organism with a chemical, radiological, or physical agent. Exposure is quantified as the amount of the agent available at the exchange boundaries of the organism (e.g.; skin, lungs, gut) and available for absorption.

Exposure Assessment - The process of measuring or estimating the intensity, frequency, and duration of human exposures to an agent currently present in the environment or of estimating hypothetical exposures that might arise from the release of new chemicals into the environment.

Exposure Concentration - The concentration of a chemical or other pollutant representing a health threat in a given environment.

Exposure Indicator - A characteristic of the environment measured to provide evidence of the occurrence or magnitude of a response indicator's exposure to a chemical or biological stress.

Exposure Level - The amount (concentration) of a chemical at the absorptive surfaces of an organism.

External Radiation Dose - The dose from sources of radiation located outside the body. This is most often from gamma rays, though beta rays can contribute to dose in the skin and other relatively superficial tissues.

Extra Risk - The added risk to that portion of the population that is not included in measurement of background tumor rate.