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Water: Ammonia

Aquatic Life Criteria - Ammonia 1999 Update

Fact Sheet: December 1999

The U.S. Environmental Protection Agency (EPA) is publishing a 1999 Update of Ambient Water Quality Criteria for Ammonia (1999 Ammonia Update). The 1999 Ammonia Update contains EPA's most recent freshwater aquatic life criteria for ammonia, superseding all previous EPA recommended freshwater criteria for ammonia. The 1999 Ammonia Update pertains only to fresh waters. It does not change or supersede the EPA's aquatic life criterion for ammonia in salt water, published in Ambient Water Quality Criteria for Ammonia (Saltwater) in 1989.


Under the Clean Water Act, EPA is required to publish and periodically update ambient water quality criteria. These criteria reflect the latest scientific knowledge on the effects of water pollutants on public health and welfare, aquatic life, and recreation. These criteria guide states, territories, and authorized tribes in developing water quality standards and ultimately provide a basis for controlling discharges or releases of pollutants into our nation's waterways.

Ambient water quality criteria are based solely on data and scientific judgments on the relationship between pollutant concentrations and the effects on aquatic life, human health, and the environment. These criteria do not reflect consideration of economic impacts or the technological feasibility of reducing chemical concentrations in ambient water.

1999 Ammonia Update

The 1999 Update of Water Quality Criteria for Ammonia incorporates comments received from the 1998 Update. The 1999 Update contains EPA's most recent freshwater aquatic life criteria for ammonia and supersedes all previous freshwater aquatic life ammonia criteria. The new criteria reflect recent research and data since 1984, and are a revision of several elements in the 1984 Criteria, including the pH and temperature relationship of the acute and chronic criteria and the averaging period of the chronic criterion.

As a result of these revisions, the acute criterion for ammonia is now dependent on pH and fish species, and the chronic criterion is dependent on pH and temperature. At lower temperatures, the dependency of the chronic criterion is also dependent on the presence or absence of early life stages of fish. The temperature dependency in the 1999 Update results in a gradual increase in the criterion as temperature decreases, and a criterion that is more stringent, at temperatures below 15 C, when early life stages of fish are expected to be present. EPA's recommendations in the 1999 Update represent a change from both the 1984 chronic criterion, which was dependent mainly on pH, and from the 1998 Update, in which the chronic criterion was dependent on pH and the presence of early life stages of fish.

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