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Water: Water Quality Standards Academy

Deriving the CMC: Step 1—Calculate the Genus Mean Acute Values

Aquatic Life Criteria

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Basic Course: Supplemental Topics

Often, available verified data include multiple toxicity tests for a species. In such cases, the species data are pooled and averaged to provide a geometric mean of the species toxic concentration, or Species Mean Acute Value (SMAV).

Similarly, if data from several species in a single genus are available, the SMAVs are pooled to calculate a geometric mean of the genus toxic concentration, or Genus Mean Acute Value (GMAV).

Key Point. If data exist for only one species, the SMAV for that species becomes the GMAV.

Sample calculations of a SMAV (using short-term toxicity data) and GMAV are presented below.

Species Mean Acute Value (SMAV)
Daphnia magna EC50 25 µg/L
Daphnia magna EC50 30 µg/L
Daphnia magna EC50 35 µg/L
Daphnia magna EC50 28 µg/L
SMAV = 29 µg/L
Genus Mean Acute Value (GMAV)
Daphnia magna 29 µg/L
Daphnia pulex 38 µg/L
Daphnia ambigua 42 µg/L
GMAV = 36 µg/L

Note: Totals for both are rounded down.

For informational purposes only–Not official statements of EPA policy.

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