Algal Toxins in Drinking Water: EPA Health Advisories
link to page 1 
Updated August 18, 2015
Algal Toxins in Drinking Water: EPA Health Advisories
On June 17, 2015, the Environmental Protection Agency
§300g-1(b)(1)(F)). Health advisories include non-
(EPA) issued drinking water health advisories for two algal
enforceable guideline values for contaminants in drinking
toxins to help water providers address threats to drinking
water (based on non-cancer health effects) and often
water supplies from harmful algal blooms (HABs).
include values for different exposure durations: one day, 10
days, several years, and lifetime. Advisories also provide
Blue-green algae (cyanobacteria) occur naturally in marine
technical guidance on identifying, measuring, and treating
and fresh water and can produce numerous potent algal
contaminants in drinking water.
toxins (cyanotoxins). Exposure to cyanotoxins can cause a
range of adverse health effects, from rashes to severe illness
On June 17, 2015, EPA issued several resource documents
and, rarely, death. A confluence of conditions—including
related to HABs, including drinking water health advisories
warm water temperatures, excess nutrients (mainly nitrogen
for microcystins and cylindrospermopsin (80 Federal
and phosphorus) and strong sunlight—can trigger explosive
Register 34637). Because of insufficient health effects data,
growth of cyanobacteria, creating harmful algal blooms.
EPA was unable to issue an advisory for anatoxin-a.
These HABs can contaminate drinking water supplied from
surface water or groundwater directly influenced by surface
The advisories include levels for the cyanotoxins in
water. Further, HABs appear to be increasing. EPA’s 2009
drinking water at or below which adverse health effects are
National Lakes Assessment found microcystins, one of the
not expected to occur based on short-term (10-day)
more common and potentially harmful cyanotoxins, to be
exposures (Table 1). They also include information on
present in one-third of lakes surveyed nationwide.
analytical methods that water providers can use to test for
the presence and concentrations of the toxins and treatment
In August 2014, microcystins produced by a bloom in Lake
techniques to remove them from drinking water.
Erie contaminated a water system serving Toledo, Ohio,
and surrounding areas for several days. No federal drinking
EPA also issued Recommendations for Public Water
water standards were available for managing this or other
Systems to Manage Cyanotoxins in Drinking Water, a
cyanotoxins, nor were rapid and sufficiently specific
technical document to help water providers develop
analytical methods available to meet the needs of water
cyanotoxin management strategies (e.g., determining when
providers faced with quickly identifying, measuring, and
and how to monitor and treat water and when and how to
removing the toxins to ensure the safety of water supplies.
notify the public and officials at different toxin levels).
As a trigger for taking action, water managers used the state
guideline of 1 microgram per liter (µg/L) for microcystin-
Table 1. Cyanotoxin Health Advisory Levels
LR (one of the more common and harmful variants of
10-day exposures, micrograms per liter (µg/L)
microcystin). The immediate problem was resolved;
however, this and other incidents added urgency to EPA’s
Microcystins
Cylindrospermopsin
efforts to assess cyanotoxin risks to public water supplies.
Children less
0.3
0.7
than 6 years old
EPA has been conducting research on several common
cyanotoxins—microcystins, cylindrospermopsin, and
Ages 6 and older
1.6
3.0
anatoxin-a—and evaluating them for possible regulation
Source: EPA, 2015 Drinking Water Health Advisories for Two
under the Safe Drinking Water Act (SDWA). The agency
Cyanobacterial Toxins, Fact Sheet, http://water.epa.gov/drink/
has also worked to validate analytical methods to enable the
standards/hascience.cfm#micro.
measurement of these cyanotoxins in water at lower
Notes: EPA recommends utilities issue “do not drink, do not boil”
concentrations and with greater accuracy and precision.
notices when toxins exceed values for ages 6 and older. Targeted
However, technical challenges and information gaps on the
toxins’ health effects and occurrence have thus far
notification for sensitive groups is suggested when toxin levels exceed
the lower value but not the higher value. EPA worked with Health
prevented EPA from determining whether the cyanotoxins
Canada to develop health advisories. The World Health Organization
meet the criteria for regulation under the SDWA.
(WHO) issued a provisional drinking water guideline for microcystin-
LR of 1 µg/L in 1998. Ohio and Oregon use this same guideline level.
In light of the impacts of the Lake Erie HAB and the
Minnesota set a guidance level of 0.04 µg/L. Seventeen countries have
increasing frequency of HABs nationwide, EPA set a goal
adopted microcystin-LR guidelines ranging from 1.0 µg/L to 1.5 µg/L.
to issue health advisories for the three types of cyanotoxins
ahead of the 2015 summertime algal bloom season.
Drinking Water Health Advisories
While broadly supporting EPA efforts, the American Water
The SDWA authorizes EPA to issue health advisories for
Works Association has noted technical, policy, and cost
contaminants that are not regulated under the act (42 U.S.C.
issues with the recommendations document and has asked
https://crsreports.congress.gov
Algal Toxins in Drinking Water: EPA Health Advisories
EPA to classify the document as “economically significant”
Environment and the Economy Subcommittee of the House
and to reissue it after allowing public review and comment.
Energy and Commerce Committee held a hearing on
One issue concerns the feasibility of using two advisory
microcystins in drinking water; the full committee reported
levels for each toxin, each with different risk management
H.R. 212, amended, and the House passed H.R. 212. The
recommendations. Another of the issues concerns the
Senate passed H.R. 212 on August 5, 2015, without
effectiveness of certain recommended testing methods
amendment, and the President signed the bill into law on
(http://www.awwa.org/legislation-regulation.aspx).
August 7 (P.L. 114-45). The law requires EPA to include in
the strategic plan steps and schedules for EPA to assess
Federal Drinking Water Standards
health risks of algal toxins in drinking water, publish a list
The SDWA authorizes EPA to regulate and set enforceable
of toxins likely to pose risks and summarize their health
standards for drinking water contaminants and lays out a
effects, determine whether to issue health advisories,
process for doing so. First, EPA is required to regularly
publish guidance on feasible methods to identify and
prepare contaminant candidate lists (CCLs) that identify
measure the algal toxins in water, recommend feasible
contaminants that may require regulation. In 1998, EPA
treatment methods, etc. Further, P.L. 114-45 requires the
included cyanobacteria and their toxins as candidates for
Government Accountability Office to report on federal
regulation on the first list (CCL 1). EPA’s 2009 list (CCL
HAB-related expenditures for FY2010 through FY2014.
3) and draft CCL 4 include the cyanotoxins microcystin-
LR, anatoxin-a, and cylindrospermopsin.
Related bills, the Safe and Secure Drinking Water Act of
2015 (H.R. 243 and S. 462), were introduced to direct EPA
EPA then must make regulatory determinations for at least
to publish a microcystins health advisory within 90 days of
five listed contaminants every five years. To make a
enactment. These bills would also require EPA to report
determination to regulate, the Administrator must find that
annually to Congress—until EPA made a regulatory
(1) the contaminant may have adverse health effects, (2) it
determination for microcystins—on the status of the
occurs (or is likely to occur) in public water supplies at
determination and efforts promote testing and treatment.
levels and frequencies of concern, and (3) its regulation
presents a meaningful opportunity to reduce health risks.
HABs Prevention
Water providers and others have urged actions to reduce the
EPA reports that current scientific understanding of the risk
formation of HABs so that communities are not faced with
of exposures to low levels of cyanotoxins is too uncertain to
the resulting health risks and costs. Beyond drinking water
support setting standards. Further, information on the
impacts, HABs can harm pets, wildlife, and livestock;
frequency and levels of occurrence of the cyanotoxins in
contaminate fish; halt recreational activities; and cause
public water supplies is limited. To gather occurrence data,
other economic losses. Nutrients play a key role in the
the SDWA directs EPA to administer a monitoring program
development of HABs, and major nutrient sources include
for unregulated contaminants. EPA plans to issue its fourth
agricultural runoff, discharges from sewage treatment
Unregulated Contaminant Monitoring Rule (UCMR 4) in
plants, and storm-water runoff from lawns and streets.
2017 to require public water systems to monitor for 30
Reducing nutrient loading of waterways would help reduce
unregulated contaminants for the period 2017-2021. The
HABs. Strategies include changing fertilizer and manure
UMCR 4 is expected to include the three cyanotoxins.
management practices, increasing sewage treatment to
remove phosphorus, controlling storm-water runoff, and
The complexity of cyanobacteria and their toxins impedes
setting limits on point-source discharges to surface waters.
regulatory control. EPA reports that a single cyanobacteria
species can produce multiple toxins or no toxins, while
Among other federal actions, the U.S. Department of
different species can produce the same toxins. Further, a
Agriculture has targeted funds for conservation activities to
single toxin can have numerous “sub-species.” (Researchers
improve conditions in Lake Erie. (See CRS Report R43919,
have identified more than 80 variants of microcystins.)
Nutrients in Agricultural Production: A Water Quality
Cyanotoxins can occur outside or inside cells; in the latter
Overview.) Funding has also been provided through the
case, if the cell walls break, more toxins are released. This
Great Lakes Restoration Initiative. Similarly, Clean Water
complexity also poses testing and treatment challenges.
Act (CWA), Section 319, authorizes EPA to provide state
Although effective treatment options are available, water
grants to help address nonpoint pollution sources (e.g.,
providers must be able to identify toxins accurately to select
runoff from farmland and streets). Further, under CWA
appropriate treatment method(s), because the wrong
Section 304, EPA is developing water quality criteria for
treatment can cause some bacteria to release more toxins.
these toxins for recreational waters. States could use the
criteria to develop water quality standards and set discharge
Congressional Actions
limits in permits for pollutants that contribute to HABs.
The 114th Congress has acted to address cyanotoxins in
drinking water. H.R. 212 and S. 460 (the Drinking Water
Mary Tiemann, Specialist in Environmental Policy
Protection Act) were introduced to require EPA to submit
to Congress a detailed plan to assess and manage risks of
IF10269
algal toxins in public water supplies. In February 2015, the
https://crsreports.congress.gov
Algal Toxins in Drinking Water: EPA Health Advisories
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF10269 · VERSION 4 · UPDATED
Updated August 18, 2015
Algal Toxins in Drinking Water: EPA Health Advisories
On June 17, 2015, the Environmental Protection Agency
§300g-1(b)(1)(F)). Health advisories include non-
(EPA) issued drinking water health advisories for two algal
enforceable guideline values for contaminants in drinking
toxins to help water providers address threats to drinking
water (based on non-cancer health effects) and often
water supplies from harmful algal blooms (HABs).
include values for different exposure durations: one day, 10
days, several years, and lifetime. Advisories also provide
Blue-green algae (cyanobacteria) occur naturally in marine
technical guidance on identifying, measuring, and treating
and fresh water and can produce numerous potent algal
contaminants in drinking water.
toxins (cyanotoxins). Exposure to cyanotoxins can cause a
range of adverse health effects, from rashes to severe illness
On June 17, 2015, EPA issued several resource documents
and, rarely, death. A confluence of conditions—including
related to HABs, including drinking water health advisories
warm water temperatures, excess nutrients (mainly nitrogen
for microcystins and cylindrospermopsin (80 Federal
and phosphorus) and strong sunlight—can trigger explosive
Register 34637). Because of insufficient health effects data,
growth of cyanobacteria, creating harmful algal blooms.
EPA was unable to issue an advisory for anatoxin-a.
These HABs can contaminate drinking water supplied from
surface water or groundwater directly influenced by surface
The advisories include levels for the cyanotoxins in
water. Further, HABs appear to be increasing. EPA’s 2009
drinking water at or below which adverse health effects are
National Lakes Assessment found microcystins, one of the
not expected to occur based on short-term (10-day)
more common and potentially harmful cyanotoxins, to be
exposures (Table 1). They also include information on
present in one-third of lakes surveyed nationwide.
analytical methods that water providers can use to test for
the presence and concentrations of the toxins and treatment
In August 2014, microcystins produced by a bloom in Lake
techniques to remove them from drinking water.
Erie contaminated a water system serving Toledo, Ohio,
and surrounding areas for several days. No federal drinking
EPA also issued Recommendations for Public Water
water standards were available for managing this or other
Systems to Manage Cyanotoxins in Drinking Water, a
cyanotoxins, nor were rapid and sufficiently specific
technical document to help water providers develop
analytical methods available to meet the needs of water
cyanotoxin management strategies (e.g., determining when
providers faced with quickly identifying, measuring, and
and how to monitor and treat water and when and how to
removing the toxins to ensure the safety of water supplies.
notify the public and officials at different toxin levels).
As a trigger for taking action, water managers used the state
guideline of 1 microgram per liter (µg/L) for microcystin-
Table 1. Cyanotoxin Health Advisory Levels
LR (one of the more common and harmful variants of
10-day exposures, micrograms per liter (µg/L)
microcystin). The immediate problem was resolved;
however, this and other incidents added urgency to EPA’s
Microcystins
Cylindrospermopsin
efforts to assess cyanotoxin risks to public water supplies.
Children less
0.3
0.7
than 6 years old
EPA has been conducting research on several common
cyanotoxins—microcystins, cylindrospermopsin, and
Ages 6 and older
1.6
3.0
anatoxin-a—and evaluating them for possible regulation
Source: EPA, 2015 Drinking Water Health Advisories for Two
under the Safe Drinking Water Act (SDWA). The agency
Cyanobacterial Toxins, Fact Sheet, http://water.epa.gov/drink/
has also worked to validate analytical methods to enable the
standards/hascience.cfm#micro.
measurement of these cyanotoxins in water at lower
Notes: EPA recommends utilities issue “do not drink, do not boil”
concentrations and with greater accuracy and precision.
notices when toxins exceed values for ages 6 and older. Targeted
However, technical challenges and information gaps on the
toxins’ health effects and occurrence have thus far
notification for sensitive groups is suggested when toxin levels exceed
the lower value but not the higher value. EPA worked with Health
prevented EPA from determining whether the cyanotoxins
Canada to develop health advisories. The World Health Organization
meet the criteria for regulation under the SDWA.
(WHO) issued a provisional drinking water guideline for microcystin-
LR of 1 µg/L in 1998. Ohio and Oregon use this same guideline level.
In light of the impacts of the Lake Erie HAB and the
Minnesota set a guidance level of 0.04 µg/L. Seventeen countries have
increasing frequency of HABs nationwide, EPA set a goal
adopted microcystin-LR guidelines ranging from 1.0 µg/L to 1.5 µg/L.
to issue health advisories for the three types of cyanotoxins
ahead of the 2015 summertime algal bloom season.
Drinking Water Health Advisories
While broadly supporting EPA efforts, the American Water
The SDWA authorizes EPA to issue health advisories for
Works Association has noted technical, policy, and cost
contaminants that are not regulated under the act (42 U.S.C.
issues with the recommendations document and has asked
https://crsreports.congress.gov
Algal Toxins in Drinking Water: EPA Health Advisories
EPA to classify the document as “economically significant”
Environment and the Economy Subcommittee of the House
and to reissue it after allowing public review and comment.
Energy and Commerce Committee held a hearing on
One issue concerns the feasibility of using two advisory
microcystins in drinking water; the full committee reported
levels for each toxin, each with different risk management
H.R. 212, amended, and the House passed H.R. 212. The
recommendations. Another of the issues concerns the
Senate passed H.R. 212 on August 5, 2015, without
effectiveness of certain recommended testing methods
amendment, and the President signed the bill into law on
(http://www.awwa.org/legislation-regulation.aspx).
August 7 (P.L. 114-45). The law requires EPA to include in
the strategic plan steps and schedules for EPA to assess
Federal Drinking Water Standards
health risks of algal toxins in drinking water, publish a list
The SDWA authorizes EPA to regulate and set enforceable
of toxins likely to pose risks and summarize their health
standards for drinking water contaminants and lays out a
effects, determine whether to issue health advisories,
process for doing so. First, EPA is required to regularly
publish guidance on feasible methods to identify and
prepare contaminant candidate lists (CCLs) that identify
measure the algal toxins in water, recommend feasible
contaminants that may require regulation. In 1998, EPA
treatment methods, etc. Further, P.L. 114-45 requires the
included cyanobacteria and their toxins as candidates for
Government Accountability Office to report on federal
regulation on the first list (CCL 1). EPA’s 2009 list (CCL
HAB-related expenditures for FY2010 through FY2014.
3) and draft CCL 4 include the cyanotoxins microcystin-
LR, anatoxin-a, and cylindrospermopsin.
Related bills, the Safe and Secure Drinking Water Act of
2015 (H.R. 243 and S. 462), were introduced to direct EPA
EPA then must make regulatory determinations for at least
to publish a microcystins health advisory within 90 days of
five listed contaminants every five years. To make a
enactment. These bills would also require EPA to report
determination to regulate, the Administrator must find that
annually to Congress—until EPA made a regulatory
(1) the contaminant may have adverse health effects, (2) it
determination for microcystins—on the status of the
occurs (or is likely to occur) in public water supplies at
determination and efforts promote testing and treatment.
levels and frequencies of concern, and (3) its regulation
presents a meaningful opportunity to reduce health risks.
HABs Prevention
Water providers and others have urged actions to reduce the
EPA reports that current scientific understanding of the risk
formation of HABs so that communities are not faced with
of exposures to low levels of cyanotoxins is too uncertain to
the resulting health risks and costs. Beyond drinking water
support setting standards. Further, information on the
impacts, HABs can harm pets, wildlife, and livestock;
frequency and levels of occurrence of the cyanotoxins in
contaminate fish; halt recreational activities; and cause
public water supplies is limited. To gather occurrence data,
other economic losses. Nutrients play a key role in the
the SDWA directs EPA to administer a monitoring program
development of HABs, and major nutrient sources include
for unregulated contaminants. EPA plans to issue its fourth
agricultural runoff, discharges from sewage treatment
Unregulated Contaminant Monitoring Rule (UCMR 4) in
plants, and storm-water runoff from lawns and streets.
2017 to require public water systems to monitor for 30
Reducing nutrient loading of waterways would help reduce
unregulated contaminants for the period 2017-2021. The
HABs. Strategies include changing fertilizer and manure
UMCR 4 is expected to include the three cyanotoxins.
management practices, increasing sewage treatment to
remove phosphorus, controlling storm-water runoff, and
The complexity of cyanobacteria and their toxins impedes
setting limits on point-source discharges to surface waters.
regulatory control. EPA reports that a single cyanobacteria
species can produce multiple toxins or no toxins, while
Among other federal actions, the U.S. Department of
different species can produce the same toxins. Further, a
Agriculture has targeted funds for conservation activities to
single toxin can have numerous “sub-species.” (Researchers
improve conditions in Lake Erie. (See CRS Report R43919,
have identified more than 80 variants of microcystins.)
Nutrients in Agricultural Production: A Water Quality
Cyanotoxins can occur outside or inside cells; in the latter
Overview.) Funding has also been provided through the
case, if the cell walls break, more toxins are released. This
Great Lakes Restoration Initiative. Similarly, Clean Water
complexity also poses testing and treatment challenges.
Act (CWA), Section 319, authorizes EPA to provide state
Although effective treatment options are available, water
grants to help address nonpoint pollution sources (e.g.,
providers must be able to identify toxins accurately to select
runoff from farmland and streets). Further, under CWA
appropriate treatment method(s), because the wrong
Section 304, EPA is developing water quality criteria for
treatment can cause some bacteria to release more toxins.
these toxins for recreational waters. States could use the
criteria to develop water quality standards and set discharge
Congressional Actions
limits in permits for pollutants that contribute to HABs.
The 114th Congress has acted to address cyanotoxins in
drinking water. H.R. 212 and S. 460 (the Drinking Water
Mary Tiemann, Specialist in Environmental Policy
Protection Act) were introduced to require EPA to submit
to Congress a detailed plan to assess and manage risks of
IF10269
algal toxins in public water supplies. In February 2015, the
https://crsreports.congress.gov
Algal Toxins in Drinking Water: EPA Health Advisories
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF10269 · VERSION 4 · UPDATED