§ 797.1930 Mysid shrimp acute toxicity test.
(a) Purpose. This guideline is intended for use in developing data on the acute toxicity of chemical substances and mixtures (“chemicals”) subject to environmental effects test regulations under the Toxic Substances Control Act (TSCA) (Pub. L. 94–469, 90 Stat. 2003, 15 U.S.C. 2601 et seq.). This guideline prescribes a test using mysid shrimp as test organisms to develop data on the acute toxicity of chemicals. The United States Environmental Protection Agency (EPA) will use data from these tests in assessing the hazard of a chemical to the aquatic environment.
(b) Definitions. The definitions in section 3 of the Toxic Substances Control Act (TSCA) and in part 792—Good Laboratory Practice Standards of this chapter, apply to this test guideline. The following definitions also apply to this guideline.
(1) “Death” means the lack of reaction of a test organism to gentle prodding.
(2) “Flow-through” means a continuous or an intermittent passage of test solution or dilution water through a test chamber or a holding or acclimation tank, with no recycling.
(3) “LC50” means that experimentally derived concentration of test substance that is calculated to kill 50 percent of a test population during continuous exposure over a specified period of time.
(4) “Loading” means the ratio of test organisms biomass (grams, wet weight) to the volume (liters) of test solution in a test chamber.
(5) “Retention chamber” means a structure within a flow-through test chamber which confines the test organisms, facilitating observation of test organisms and eliminating loss of organisms in outflow water.
(6) “Static system” means a test chamber in which the test solution is not renewed during the period of the test.
(c) Test procedures—(1) Summary of the test. In preparation for the test, test chambers are filled with appropriate volumes of dilution water. If a flow-through test is performed, the flow of dilution water through each chamber is adjusted to the rate desired. The test substance is introduced into each test chamber. In a flow-through test, the rate at which the test substance is added is adjusted to establish and maintain the desired concentration of test substance in each test chamber. The test is started by randomly introducing mysids acclimated in accordance with the test design into the test chambers. Mysids in the test chambers are observed periodically during the test, the dead mysids removed and the findings recorded. Dissolved oxygen concentration, pH, temperature, salinity, the concentration of test substance, and other water quality characteristics are measured at specified intervals in test chambers. Data collected during the test are used to develop concentration-response curves and LC50 values for the test substance.
(2) [Reserved]
(3) Range-finding test. (i) A range-finding test should be conducted to determine:
(A) Which life stage (juvenile or young adult) is to be utilized in the definitive test.
(B) The test solution concentrations for the definitive test.
(ii) The mysids should be exposed to a series of widely spaced concentrations of test substance (e.g., 1, 10, 100 mg/l, etc.), usually under static conditions.
(iii) This test should be conducted with both newly hatched juvenile (<24 hours old) and young adult (5 to 6 days old) mysids. For each age class (juvenile or young adult), a minimum of 10 mysids should be exposed to each concentration of test substance for up to 96 hours. The exposure period may be shortened if data suitable for the purpose of the range-finding test can be obtained in less time. The age class which is most sensitive to the test substance in the range-finding test shall be utilized in the definitive test. When no apparent difference in sensitivity of the two life stages is found, juveniles shall be utilized in the definitive test. No replicates are required, and nominal concentrations of the chemical are acceptable.