x>EPA
United States
Environmental Protection
Agency
Office of Water
MC 4304T
820-F-13-013
August 2013
Aquatic Life Ambient Water Quality Criteria for
Ammonia - Freshwater (2013)
Summary
EPA has published national recommended
ambient water quality criteria for the protection
of aquatic life from the toxic effects of
ammonia, a constituent of nitrogen pollution.
These recommended criteria will help States,
Territories, and authorized Tribes update their
water quality standards with concentration levels
for ammonia in surface waters at or below which
aquatic organisms will be protected, if not
exceeded more frequently than once every three
years on average. Acute and chronic criteria
were developed to protect organisms from both
immediate effects, such as mortality, and longer-
term effects on reproduction, growth and
survival, respectively.
EPA's final Aquatic Life Ambient Water Quality
Criteria for Ammonia - Freshwater (2013)
incorporate scientific views received on EPA's
2009 draft updated ammonia criteria and
supersede EPA's previously recommended 1999
ammonia criteria.
What are national recommended aquatic life
ambient water quality criteria?
Ambient water quality criteria for the protection
of aquatic life are numeric concentrations of
pollutants, with specific associated duration and
frequency information, in surface waters that are
protective of aquatic life designated uses. Under
Clean Water Act section 304(a), EPA is required
to develop and publish water quality criteria that
reflect the latest scientific knowledge. Water
quality criteria are based solely on data and
scientific judgments about the relationship
between pollutant concentrations and potential
environmental and human health effects. EPA's
recommended water quality criteria are not
rules, nor do they automatically become part of a
state's water quality standards. States must adopt
into their standards water quality criteria that
protect the designated uses of the water bodies
within their area. These can include
scientifically defensible site-specific criteria that
are different from EPA's national recommended
criteria, as long as the site-specific criteria are
protective of the designated use. Water quality
criteria are not effective under the Clean Water
Act until they have been adopted into a state's
water quality standards and approved by EPA.
What is ammonia?
Ammonia is one of several forms of nitrogen
that exist in aquatic environments. Unlike other
forms of nitrogen, which can cause nutrient
over-enrichment of a water body at elevated
concentrations and indirect effects on aquatic
life, ammonia causes direct toxic effects on
aquatic life.
Ammonia is produced for commercial fertilizers
and other industrial applications. Natural sources
of ammonia include the decomposition or
breakdown of organic waste matter, gas
exchange with the atmosphere, forest fires,
animal and human waste, and nitrogen fixation
processes.
How does ammonia enter surface waters?
Ammonia can enter the aquatic environment via
direct means such as municipal effluent
discharges and the excretion of nitrogenous
wastes from animals, and indirect means such as
nitrogen fixation, air deposition, and runoff from
agricultural lands.
How does ammonia affect aquatic life?
When ammonia is present in water at high
enough levels, it is difficult for aquatic
organisms to sufficiently excrete the toxicant,
leading to toxic buildup in internal tissues and
blood, and potentially death. Environmental
factors, such as pH and temperature, can affect
ammonia toxicity to aquatic animals.
-------
What is the history of EPA's development of
ammonia criteria?
EPA first published ammonia criteria for the
protection of aquatic life in 1976. The criteria
were then updated in 1985 and 1999 to reflect
scientific information available at that time. The
1999 recommended aquatic life criteria for
ammonia were based on the most sensitive
endpoints known at the time: the acute criterion
was based on salmonid fish toxicity information,
and the chronic criterion was based on bluegill
sunfish early life stage toxicity.
In 2003, EPA became aware of new toxicity
studies indicating the relative sensitivity of
freshwater mussels to ammonia and began to
update the 1999 criteria to reflect this new
information. In 2009, following external peer
review, EPA published draft recommended
ammonia criteria, for waters with and without
mussels. Since the publication of the draft 2009
ammonia criteria, additional toxicity testing has
validated information on the effects of ammonia
on sensitive freshwater gill-breathing snail
species. In April 2013, EPA finalized the
updated ammonia criteria that are applicable
nationally, taking into account the latest toxicity
information for freshwater species, including
unionid mussels and gill-breathing snails. The
2013 criteria incorporate scientific views
received on the draft (2009) ammonia criteria
and supersede EPA's previously recommended
1999 criteria.
What are the 2013 recommended water
quality criteria for ammonia?
EPA recommends an acute criterion magnitude
of 17 mg Total Ammonia Nitrogen (TAN) per
liter at pH 7 and 20°C for a one-hour average
duration, not to be exceeded more than once
every three years on average. EPA recommends
a chronic criterion magnitude of 1.9 mg TAN/L
at pH 7 and 20°C for a 30-day average duration,
not to be exceeded more than once every three
years on average. In addition, the highest four-
day average within a 30-day period should not
exceed 2.5 times the chronic criterion magnitude
(e.g. 1.9 mg TAN/L x 2.5 = 4.8 mg TAN/L at
pH 7 and 20°C) more than once in three years on
average.
How do the 2013 criteria compare to the
previously recommended 1999 criteria and
the draft 2009 criteria?
The 2013 ammonia criteria recommendations
take into account the latest freshwater toxicity
information for ammonia, including toxicity
studies for sensitive unionid mussels and gill-
breathing snails. These new criteria are based on
robust toxicity data available for 69 genera
(acute) and 16 genera (chronic). The updated
criteria magnitudes are more stringent than the
previously recommended 1999 criteria
magnitudes (see Table 1). The duration
components of the 1999, 2009 and 2013 criteria
remain the same - a one-hour average duration
for the acute criterion and 30-day average
duration for the chronic criterion. The frequency
component for the acute and chronic criteria
remains once in three years on average.
Table 1. Comparison of past and current EPA-
recommended aquatic life water quality criteria
magnitudes for ammonia. Criteria magnitudes
are expressed as total ammonia nitrogen (mg
TAN/L) at pH 7 and 20°C.
Criterion
Duration
Acute
(1-hour
average)
Chronic
(30-day
rolling
average)
1999
Criteria
24
4.5*
2009
Draft
Updated
Criteria
19
0.91*
2013
Final
Updated
Criteria
17
1.9*
*Not to exceed 2.5 times the criterion
continuous concentration as a 4-day average
within a 30-day period.
Criteria frequency: Not to be exceeded more
than once in three years on average.
-------
Additional EPA Resources
EPA has developed three supporting documents
to aid states considering adoption of the 2013
recommended ammonia criteria.
Flexibilities for States Applying EPA's Ammonia
Criteria Recommendations provides an
overview of a number of implementation
approaches available for state consideration,
including the recalculation procedure for site-
specific criteria derivation, variances, revisions
to designated uses, dilution allowances, and
compliance schedules. The document describes
how each of these flexibilities fits within a
state's water quality standards adoption and
implementation processes.
EPA has also developed a Revised Deletion
Process for the Site-Specific Recalculation
Procedure for Aquatic Life Criteria that
describes a recalculation procedure and includes
a spreadsheet that may be used to derive site-
specific water quality criteria for the protection
of aquatic life in order to best reflect the
organisms that reside at a specific site.
A third document, which EPA expects to publish
in 2013, Technical Support Document for
Conducting and Reviewing Freshwater Mussel
Studies for the Development of Site-specific
Water Quality Criteria for Ammonia, will help
states determine if sensitive freshwater mussels
are present in their waters. Commonly-used
mussel sampling methods will be described and
an overview will be provided of various study
approaches, considerations, and limitations,
including real-life examples.
How to View the Criteria Document and
Supporting Information
EPA has established an official public docket for
this action under Docket ID No. EPA-HQ-OW-
2009-0921, accessed at www.regulations.gov.
You may also download the document and
supporting information from
http://water.epa.gov/scitech/swguidance/standar
ds/criteria/aqlife/ammonia/index.cfm.
For More Information
Contact Lisa Huff by telephone at (202) 566-
0787, by email at huff.lisa@epa.gov. or by mail
at U.S. EPA, MC: 4304T, 1200 Pennsylvania
Ave., N.W., Washington, D.C. 20460.
------- |