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.

(Source:  Amended at 47 Ill. Reg. 4437, effective March 23, 2023)