Science Upgrades Ammonia Criteria; EPA Seeks Comment

On Dec. 30, 2009, the U.S. Environmental Protection Agency published in the Federal Register a Draft Update of the 1999 Ambient Water Quality Criteria for Ammonia – Freshwater that reflects new scientific knowledge.

Ammonia is toxic to aquatic life at low concentrations. EPA has incorporated in the draft criteria dataset new toxicity data on larval and juvenile freshwater mussels, which are more sensitive than the aquatic organisms represented in the dataset for the 1999 ammonia criteria.

Since freshwater mussels are not present nationwide in all waters, EPA is recommending in the draft criteria update a short-term (acute) criterion for waters with mussels present, and another criterion for waters without mussels. Similarly, the recommended long-term (chronic) criterion includes one value applied to waters with mussels, another criterion to apply to waters without mussels, and a third chronic criterion value to apply to waters without mussels but with early life stages of fish present.

EPA is accepting scientific views on the draft updated criteria document for 60 days from Federal Register publication. For more information visit

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