ii ¦ ¦ , .	Office of Water
United States				
EPA 822-F-19-001
v>EPA Environmental Protection
Agency	May 2019
Recommended Human Health Recreational Ambient
Water Quality Criteria or Swimming Advisories for
Microcystins and Cylindrospermopsin
Summary
EPA has released national recommendations for the
Human Health Recreational Ambient Water Quality
Criteria or Swimming Advisories (AWQC/SA) for
Microcystins and Cylindrospermopsin. These
recommended AWQC/SA accurately reflect the
latest scientific knowledge on the potential human
health effects from recreational exposure to these
two cyanotoxins. Primary contact recreation is
protected in water bodies at or below the
recommended concentrations of microcystins and
cylindrospermopsin.
These recommendations are intended as guidance
to states, territories and authorized tribes to
consider when developing water quality standards.
Alternatively, these recommendations can be used
as the basis of swimming advisories for notification
purposes in recreational waters to protect the
public. States, territories and authorized tribes may
also wish to consider using these recommendations
as both water quality criteria and swimming
advisory values.
Background
Cyanobacteria, commonly called blue-green algae,
are naturally-occurring photosynthetic bacteria
found in freshwater and marine ecosystems. Under
certain environmental conditions, such as elevated
levels of nutrients, warmer temperatures, still
water, and plentiful sunlight, cyanobacteria can
rapidly multiply to form harmful algal blooms
(HABs). HABs have been reported in ambient waters
in all states. As the cyanobacteria multiply, some of
the cells can produce toxic compounds, known as
cyanotoxins, which can be harmful to human and
animal health. Microcystins and cylindrospermopsin
are two types of toxins produced by cyanobacteria.
During a HAB, the toxin concentration can rapidly
increase and may become elevated before a visible
bloom is observed. Elevated cyanotoxin concentrations
in surface waters can persist after the bloom fades, so
human exposures can occur even after the visible signs
of a bloom are gone or have moved downstream.
Exposure to elevated-levels of microcystins can
potentially lead to liver damage; the kidneys and liver
appear to be the primary target organs for
cylindrospermopsin toxicity.
What are EPA's recommendations?
The recommended AWQC/SA for microcystins and
cylindrospermopsin consist of three components-
magnitude, duration and frequency—that are
considered protective of human health in recreational
waters. In developing these recommendations, EPA
incorporated the existing peer-reviewed and published
science on the adverse human health effects of these
toxins, recreation-specific exposure parameters from
the peer-reviewed scientific literature and EPA's
Exposure Factors Handbook using established criteria
methodologies. EPA derived these recommended
values based on children's recreational exposures
because children can be more highly exposed
compared to other age groups. The recommendations
are also protective of older age groups.
Water quality criteria recommendations are intended
as guidance in establishing new or revised water
quality standards. They are not regulations themselves.
States and authorized tribes have the discretion to
adopt other scientifically-defensible water quality
criteria that differ from these recommendations. For
use as swimming advisories, EPA envisions states and
authorized tribes applying these recommendations in a
similar manner as is currently done in their
recreational water advisory programs.

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The recommended magnitude for both toxins is
shown in the following table:
Table. Recommended magnitude for cyanotoxins.
Microcystins
Cylindrospermopsin
8 l-ig/L
15 M-g/L
Duration and Frequency:
For both cyanotoxins, the recommended duration
and frequency depend on their application as a
water quality criterion or a swimming advisory.
For application as a recreational water quality
criterion, EPA recognizes that a single exceedance of
the recommended magnitude does not necessarily
indicate that the designated use is not attained. The
recommended frequency and duration support the
identification of a trend or pattern of elevated
cyanotoxins that can be used to inform the
evaluation of a waterbody. EPA recommends states
use 10-day assessment periods, not a rolling 10-day
period, over the course of a recreation season to
evaluate ambient water body condition and
recreational use attainment. The 10-day period links
the water body assessment period to the adverse
health effects observed from ingestion of the toxins
over short-term exposures. If toxin concentrations
are higher than the criterion magnitude during a 10-
day assessment period, then that event should be
considered an excursion from the recreational
criteria. EPA recommends that when more than
three excursions occur within a recreational season
and that pattern reoccurs in more than one year, it is
an indication the water quality has been or is
becoming degraded and a water body may not be
supporting the recreational use. EPA expects states
and authorized tribes to indicate the number of years
the pattern of degradation can occur and not impair
the recreational use.
As a basis for issuing a swimming advisory, EPA
recommends the magnitude not be exceeded on any
single day. This is consistent with the goal of a
swimming advisory to provide prompt information to
people who wish to use the water body for
recreation. EPA also recommends that any
exceedance of the recommended magnitude result
in a swimming advisory being issued until the toxin
concentration falls below the recommended magnitude.
Communicating risk to the public
In 2017, EPA released an online communications toolbox
to support states, tribes, territories, and local
governments in developing, as they deem appropriate,
their own risk communication materials about
cyanobacterial blooms. It includes editable press release
templates, social media posts and other quick
references.
EPA has also released infographics that states and
communities can use to communicate basic information
about HABs to the public. The infographics highlight how
a HAB might affect both people and animals, and provide
helpful information concerning how to identify and
respond to a potential bloom. Two downloadable and
printable versions of the infographic are available on the
EPA's Cyanobacterial HABs website; one as a more
detailed poster for display and another as an abbreviated
handout. State, tribal and local governments may also
customize the infographics by adding local information
such as a logo, website address, email address and/or
telephone number.
Where can I find more information?
EPA has published the recommended AWQC/SA
document, support documents and the Federal Register
Notice online in the public docket (Docket ID No. EPA-
HQ-OW-2016-0715), which can be accessed via the
Agency's Recreational Water Quality Criteria website.
You can also contact John Ravenscroft (202) 566-1101 or
Lesley D'Anglada (202) 566-1125 for more information.

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