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Water: Water Quality Standards Academy

Preparation for Deriving the CCC: Assessing Chronic Effects Data

Aquatic Life Criteria

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Basic Course: Supplemental Topics

Chronic tests are performed at sub-lethal toxin concentrations and measure effects on, for instance, growth of individuals or their reproductive capability. Assessing the quality and completeness of collected data includes screening for validity based on the same criteria used on data compiled for deriving the CMC. Regarding chronic values, for example, concentrations of the test chemical should have been measured at appropriate times during the test to verify consistency of exposure.

Two effect levels are identified in chronic effects testing:

  • No observed adverse effect concentration (NOAEC). The concentration at which no observable effect occurs (e.g., no statistically significant reduction in growth).
  • Lowest observed adverse effect concentration (LOAEC). The lowest concentration at which effects occur (e.g., statistically significant reduction in growth).

In general, the chronic criterion is derived from the geometric mean of these two effect levels. In some cases (e.g., for ammonia), the EC20 from chronic tests—based on concentration-effect regression analyses—is used.

Illustration. View graphic showing overview of ALC derivation. Proceed to the Illustration. » (Note: This link launches a pop-up window.)

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

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