Section 302.612  Determining the Acute Aquatic Toxicity Criterion for an Individual Substance - General Procedures

a)         A chemical-specific Acute Aquatic Toxicity Criterion (AATC) is calculated using procedures specified in Sections 302.615 and 302.618 if acute toxicity data are available for at least five resident or indigenous species from five different North American genera of freshwater organisms, including representatives of the following taxa:

1)         Representatives of two families in the Class Osteichthyes (Bony Fish).

2)         The family Daphnidae.

3)         A benthic aquatic macroinvertebrate.

4)         A vascular aquatic plant or a third family in the Phylum Chordata that may be from the Class Osteichthyes.

b)         If data are not available for resident or indigenous species, data for 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. The procedures of Section 302.615 must be used to obtain an AATC for individual substances whose toxicity is unaffected by ambient water quality characteristics.  The procedures of Section 302.618 must be used if the toxicity of a substance is dependent upon some other water quality characteristic.

c)         If data are not available that meet the requirements of subsection (a), an AATC is calculated by obtaining at least one EC-50 or LC-50 value from both a daphnid species and either fathead minnow or bluegill.  If there are data available for any other North American freshwater species, they must also be included.  An AATC is calculated by dividing the lowest Species Mean Acute Value (SMAV), as determined according to Section 302.615, by 10.

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