Determining the Acute Aquatic Toxicity Criterion - Procedure for Combinations of Substances

Section 302 Section 302.621  Determining the Acute Aquatic Toxicity Criterion - Procedure for Combinations of Substances An AATC for any combination of substances (including effluent mixtures) must be determined by the following toxicity testing procedures: a)         Not more than 50% of test organisms from the most sensitive species tested may exhibit mortality or immobility after a 48-hour test for invertebrates or a 96-hour test for fish. b)         Three resident or indigenous species of ecologically diverse taxa must be tested initially.  If resident or indigenous species are not available for testing, non-resident species may be used if the non-resident species is of the same family or genus and has a similar habitat and environmental tolerance.