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Water: Water Quality Standards Academy


Aquatic Life Criteria

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Basic Course: Supplemental Topics

  • Aquatic life criteria are estimates of concentrations of pollutants in ambient water that—if not exceeded—are expected to protect fish, invertebrates, and other aquatic life from unacceptable adverse effects associated with short-term (acute) or long-term (chronic) exposure (e.g., mortality, reduced reproduction).
  • EPA develops nationally recommended aquatic life criteria based on the latest scientific knowledge to provide guidance to States and Tribes for developing numerical and narrative criteria for their water quality standards.
  • An acute aquatic life criterion (termed the Criterion Maximum Concentration) is applied as a limit on the 1-hour average concentration of a particular chemical (or other material) in the environment. The chronic aquatic life criterion (termed the Criterion Continuous Concentration) is applied as a limit on the chemical’s 4-day average concentration in the environment. Aquatic life exposure to the chemical should not exceed either the CMC or the CCC more than once every 3 years on average.
  • To develop a CMC for a particular chemical, the EPA guidelines require that acceptable acute values be available for at least eight families with a specified taxonomic diversity. For the CCC, if available chronic toxicity test data are insufficient to meet minimum requirements for the standard approach, an alternative is to calculate ratios from studies in which both acute and chronic tests have been conducted simultaneously for the same species.
  • In some locations, the nationally recommended aquatic life criteria may be considered under- or overprotective if the species at a site have different sensitivities than those included in the national criteria data set. In general, EPA approves site-specific criteria if they are supportive of the designated uses established in the State/Tribe’s water quality standards and the criteria are based on sound scientific rationales.

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

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