Chronic toxicity test
(2) Chronic toxicity test means a method used to determine the concentration of a substance in water that produces an adverse effect on a test organism over an extended period of time. In this test guideline, mortality and reproduction (and optionally, growth) are the criteria of toxicity. (3) EC50 means that experimentally derived concentration of test substance in dilution water that is calculated to affect 50 percent of a test population during continuous exposure over a specified period of time. In this guideline, the effect measured is immobilization. (4) Ephippium means a resting egg which develops under the carapace in response to stress conditions in daphnids. (5) Flow-through means a continuous or intermittent passage of test solution or dilution water through a test chamber or culture tank with no recycling. (6) Immobilization means the lack of movement by daphnids except for minor activity of the appendages. (7) Loading means the ratio of daphnid biomass (grams, wet weight) to the volume (liters) of test solution in a test chamber at a point in time or passing through the test chamber during a specific interval. (8) MATC (Maximum Acceptable Toxicant Concentration) means the maximum concentration at which a chemical can be present and not be toxic to the test organism. (9) Renewal system means the technique in which test organisms are periodically transferred to fresh test solution of the same composition.