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Water: Water Quality Standards Academy

Preparation for Deriving the CMC: Collecting Effects Data

Aquatic Life Criteria

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Basic Course: Supplemental Topics

In the course of selecting a chemical for developing aquatic life criteria, EPA reviews the availability of needed data. Then to start the actual criteria development process, the data are collected and assessed for quality and completeness.

The derivation of criteria relies on two types of values from toxicity tests:

  • Median lethal concentration (LC50). A specific concentration of a chemical that has been found to be lethal to 50 percent of individuals in a group of aquatic organisms exposed for 48 to 96 hours.
  • Median effective concentration (EC50). A specific concentration of a chemical that has been found to cause a particular effect in 50 percent of individuals in a group of aquatic organisms exposed over a given time period (e.g., weeks or years).

For calculating the CMC, the 1985 Guidelines require that acceptable acute values be available for at least eight families with a specified taxonomic diversity in order to address a wide variety of the organisms constituting an aquatic animal community. These minimum requirements include:

Data on three vertebrates:

  • Salmonid fish (e.g., trout, salmon),
  • Fish from a family other than salmonidae (e.g., bass, fathead minnow),
  • Species from a third chordate family (e.g., salamander, frog), and

Data on five invertebrates:

  • Planktonic crustacean (e.g., daphnia),
  • Benthic crustacean (e.g., crayfish),
  • Insect (e.g., stonefly, mayfly),
  • Species from a phylum other than Chordata or Arthropoda (i.e., rotifer, annelid [worm], or mollusk [e.g., mussel, snail]), and
  • Species from another order of insect or a fourth phylum (e.g., an insect or mollusk not already represented above).
keypoint1
Key Point. Where toxicity data are available for multiple life stages of the same species (e.g., eggs, juveniles, adults), the 1985 Guidelines require that the data from the most sensitive life stage be used. This ensures that an individual of that species can survive an exposure at any time during its life and thus have the opportunity to produce a succeeding generation.

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

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