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Early Life Stage test
An early life stage (ELS) test is a chronic toxicity test using sensitive early life stages like embryos or larvae to predict the effects of toxicants on organisms.〔McKim JM. 1985. Early life stage toxicity tests. In Rand GM (1995). Fundamentals of Aquatic Toxicology: Effects, Environmental Fate, and Risk Assessment (2nd ed.). Boca Raton: CRC Press. pp 974–1010. ISBN 1-56032-091-5.〕 ELS tests were developed to be quicker and more cost-efficient than full life-cycle tests, taking on average 1-5 months to complete compared to 6-12 months for a life-cycle test. They are commonly used in aquatic toxicology, particularly with fish. Growth and survival are the typically measured endpoints, for which a Maximum Acceptable Toxicant Concentration (MATC) can be estimated. ELS tests allow for the testing of fish species that otherwise could not be studied due to length of life, spawning requirements, or size. ELS tests are used as part of environmental risk assessments by regulatory agencies including the U.S. Environmental Protection Agency (EPA) and Environment Canada, as well as the Organisation for Economic Co-operation and Development (OECD).〔(Technical Overview of Ecological Risk Assessment Analysis Phase: Ecological Effects Characterization. ) US EPA.〕〔Organisation for Economic Co-operation and Development. 1992. Guideline 210: Fish early-life stage toxicity test. ''OECD Guidelines for the Testing of Chemicals''. Paris, France.〕
==Development==
ELS tests were adapted from full life-cycle toxicity tests, chronic tests that expose an organism to a contaminant for its entire life-cycle. These are widely considered to be the best tests for estimating long-term "safe" concentrations of toxicants in aquatic organisms. The first full life-cycle tests on fish were developed for the fathead minnow (''Pimephales promelas''),〔Mount DI, Stephan CE. 1967. A method for establishing acceptable limits for fish-Malathion and the butoxyethanol ester of 2,4-D. ''Trans Am Fish Soc'' 96:185-193.〕〔Benoit DA, Puglisi FA, Olson DL. 1982. A fathead minnow (''Pimephales promelas'') early life stage toxicity test method evaluation and exposure to four organic chemicals. ''Environ Pollution Series A, Ecological and Biological'' 28:189-197.〕 and later for bluegill (''Lepomis macrochirus''), brook trout (''Salvelinus fontinalis''), flagfish (''Jordanella floridae''), and sheepshead minnow (''Cyprinodon variegatus'').〔Hansen DJ, Parrish PR, Schimmel SC, Goodman LR. 1978. Life-cycle toxicity test using sheepshead minnows (''Cyprinodon variegatus''). ''Bioassay Procedures for the Ocean Disposal Permit Program'', EPA-600/9-78-010.〕 While useful, full life-cycle tests require a high number of test organisms and extensive exposure time in the lab, especially for vertebrates. Typically, life-cycle tests take 6-12 months for fathead minnow and 30 months for brook trout.
Following the passage of the Toxic Substances Control Act (TSCA) in the United States in 1976, there was an increased need for quicker, more efficient vertebrate toxicity tests. The EPA was now required to assess the environmental effects of new chemicals before they could be commercially produced. Less costly and time-intensive tests were needed to evaluate a multitude of new chemicals. Researchers began developing toxicity tests that focused on early life stages, since these have been shown to be more sensitive to environmental stressors than later life stages. Many critical events occur in a short period of time in the early stages of development.〔McKim JM. 1977. Evaluation of tests with early life stages of fish for predicting long-term toxicity. ''J Fish Res Board Can'' 34:1148–1154.〕 If a stressor disrupts developmental events (including their timing), it could result in adverse effects that reduce the organism's chances of survival. Meta-analysis has found that early life-cycle portions of full life-cycle tests usually estimate an MATC within a factor of 2 of full life-cycle estimates in saltwater and freshwater fish. In 83% of 72 tests, the ELS portion resulted in the same MATC as the full life-cycle estimate, and the remaining 17% were within a factor of 2.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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