5.1 Tests with algae provide information on the toxicity of test materials to an important component of the aquatic biota and might indicate whether additional testing ( 1 ) ⁴ is desirable.

5.2 Algae are ubiquitous in aquatic ecosystems, where they incorporate solar energy into biomass, produce oxygen, function in nutrient cycling and serve as food for animals. Because of their ecological importance, sensitivity to many toxicants, ready availability, ease of culture, and fast growth rates (rendering it possible to conduct a multi-generation test in a short period of time), algae are often used in toxicity testing.

5.3 Results of algal toxicity tests might be used to compare the sensitivities of different species of algae and the toxicities of different materials to algae and to study the effects of various environmental factors on results of such tests.

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

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

5.6 Results of algal toxicity tests will depend on the temperature, composition of the growth medium, and other factors. These tests are conducted in solutions that contain concentrations of salts, minerals, and nutrients that greatly exceed those in most surface waters. These conditions may over- or under-estimate the effects of the test material if discharged to surface waters.

1.1 This guide covers procedures for obtaining laboratory data concerning the adverse effects of a test material added to growth medium on growth of certain species of freshwater and saltwater microalgae during a static exposure. These procedures will probably be useful for conducting short-term toxicity tests with other species of algae, although modifications might be necessary. Although the test duration is comparable to an acute toxicity test with aquatic animals, an algal toxicity test of short duration (72, 96 or 120 h) allows for examination of effects upon multiple generations of an algal population and thus should not be viewed as an acute toxicity test.

1.2 Other 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. Comparison of results obtained using modified and unmodified versions of these procedures might provide useful information concerning new concepts and procedures for conducting toxicity tests with microalgae.

1.3 These procedures are applicable to many chemicals, either individually or in formulations, commercial products, or known mixtures. With appropriate modifications, these procedures can be used to conduct tests on temperature, and pH and on such materials as aqueous effluents (see also Guide E1192 ), leachates, oils, particulate matter, sediments, and surface waters. Static tests might not be applicable to materials that are highly volatile, are rapidly biologically or chemically transformed in aqueous solutions, or are removed from test solutions in substantial quantities by the test vessels or organisms during the test. However, practical flow-through test procedures with microalgae have not been developed.

1.4 Results of tests using microalgae should usually be reported in terms of the 96-h (or other time period) IC50 (see 3.2.5 ) based on reduction in growth. In some situations, it might only be necessary to determine whether a specific concentration unacceptably affects the growth of the test species or whether the IC50 is above or below a specific concentration.

1.5 This guide is arranged as follows:

1.6 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 hazard statements are given in Section 7 .