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Hardness-Dependent Metals Aquatic Life Criteria

The toxicity of a metal to an aquatic organism can vary based on many different factors, including route of exposure to the metal, type and form of the metal and the physical/chemical characteristics of the water where the exposure takes place. Oregon's aquatic life criteria for certain metals are based on water hardness. Generally, as hardness increases, the toxicity of metals decreases. The calculator below provides acute and chronic criteria for certain metals based on water hardness.

For chromium hardness-dependent aquatic life criteria analysis and implementation recommendations, see the parameter-specific lists on the Standards for Toxic Pollutants page.

Acute cadmium criterion

On Jan. 10, 2017, EPA signed a final rule to promulgate an acute freshwater aquatic life criteria for cadmium for Oregon into federal regulations. The new federal acute hardness-based criterion for cadmium changes the hardness-based equation coefficients for the acute cadmium criterion and establishes new default hardness values by region. Note that the acute cadmium criterion is effective in Oregon, but is not reflected in Oregon's state toxics standards. See metals calculator above.


James McConaghie
Water Quality Standards Program Coordinator