5.1 Mysids are an important component of both the pelagic and epibenthic community. They are preyed upon by many species of fish, birds, and larger invertebrate species, and they are predators of smaller crustaceans and larval stages of invertebrates. In some cases, they feed upon algae. Mysids are sensitive to both organic and inorganic toxicants ( 1 ) . ³ The ecological importance of mysids, their wide geographical distribution, ability to be cultured in the laboratory, and sensitivity to contaminants make them appropriate acute toxicity test organisms.

5.2 An acute toxicity test is conducted to obtain information concerning the immediate effects of a short-term exposure to a test material on a test organism under specified experimental conditions. An acute toxicity test provides data on the short-term effects that are useful for comparisons to other species but does not provide information on delayed effects.

5.3 Results of acute toxicity tests can be used to predict acute effects likely to occur on aquatic organisms in field conditions except that mysids might avoid exposure when possible.

5.4 Results of acute toxicity tests might be used to compare the acute sensitivities of different species and the acute toxicities of different test materials, and to study the effects of various environmental factors on results of such tests.

5.5 Results of acute toxicity tests might be an important consideration when assessing the hazards of materials to aquatic organisms (see Guide E1023 ) or when deriving water quality criteria for aquatic organisms ( 2 ) .

5.6 Results of acute toxicity tests might be useful for studying biological availability of, and structure activity relationships between test materials.

5.7 Results of acute toxicity tests will depend, in part, on the temperature, quality of the food, condition of test organisms, test procedures, and other factors.

1.1 This guide describes procedures for obtaining data concerning the adverse effects of a test material (not food) added to marine and estuarine waters on certain species of marine and estuarine mysids during 96 h of continuous exposure. Juvenile mysids used in these tests are taken from cultures shortly after release from the brood and exposed to varying concentrations of a toxicant in static or flow-through conditions. These procedures will be useful for conducting toxicity tests with other species of mysids, although modifications might be necessary.

1.2 Modifications of these procedures might be justified by special needs or circumstances. Although using appropriate procedures is more important than following prescribed procedures, results of tests conducted using unusual procedures are not likely to be comparable to results of many other tests. Comparisons of results obtained using modified and unmodified versions of these procedures might provide useful information concerning new concepts and procedures for conducting acute tests with other species of mysids.

1.3 The procedures given in this guide are applicable to most chemicals, either individually or in formulations, commercial products, and known or unknown mixtures. With appropriate modifications these procedures can be used to conduct acute tests on factors such as temperature, salinity, and dissolved oxygen. These procedures can also be used to assess the toxicity of potentially toxic discharges such as municipal wastes, oil drilling fluids, produced water from oil well production, and other types of industrial wastes.

1.4 Results of acute toxicity tests with toxicants experimentally added to salt and estuarine waters should usually be reported in terms of a LC50 (median lethal concentration).

1.5 This guide is arranged as follows:

1.6 The values stated in SI units are to be regarded as the standard.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 7 .