The phrase “Harmful Algae Bloom” (HAB) has
recently come to the forefront of lake management. Even before the Toledo water
crisis made national news this summer, blue-green algae and cyanotoxins were
gracing headlines across the Northeastern United States. In the summer of 2013,
the Connecticut Department of Public Health (DPH) issued new guidelines to
address HABs as a human health concern. The development of state
recommendations was expedited by widespread media coverage of a particular
blue-green algae bloom in 2012. News
of ‘toxic lake water’ is never
well-received by lake users, particularly when limited information is coming
from local media sources, instead of directly from the municipality or health
department. Complicated science is easily botched. Then, all of a sudden, a
billowing cloud of distorted details transforms into a public panic: the fear
of the unknown. By referencing scientific publications and credible
web-sources, this article hopes to dissipate any accumulated haze.
Blue-green algae basics…
Algae and
phytoplankton are terms that describe a large group of microscopic
photosynthetic organisms that inhabit both fresh and salt water environments.
Blue-green algae, now known as cyanobacteria,
make up one group of phytoplankton that typically occur in varying numbers
throughout water bodies in Connecticut. Blue-green algae utilize the sun’s
energy, carbon dioxide, and water to produce their own food. The end-product of
this process is oxygen, the life-sustaining compound that jumpstarted evolution
and made way for an explosion of life on Earth. We can thank oceanic
cyanobacteria for much of the oxygen we breathe today, and it is common
knowledge among the scientific community that the oldest cyanobacteria fossils
date back to 3.5 billion years! It’s no wonder that these amazing colonies of
cells are equipped with highly evolved adaptations enabling them to survive in
almost every environment on the planet [3].
In addition
to light, cyanobacteria also require naturally occurring nutrients (i.e.
nitrogen and phosphorus) in order to carry out cellular processes required for
growth and replication. Humans accelerate algae and cyanobacteria growth in
lakes by increasing nutrients, a process called eutrophication [3]. Anthropogenic, or human-related, sources of
nutrients to lakes include domestic and agricultural waste, septic leachate,
road run-off, and lawn fertilizers. It is because of this heightened
availability of nutrients in lakes that blue-green algae are able to reach
extremely high cell densities, referred to as a ‘bloom’ [4,6].
Many cyanobacteria
species can form gas vesicles within their cells that allow them to regulate
their vertical position in the water column. This adaptation may enable
cyanobacteria to out-compete other species of algae that do not have this
adaptive advantage. When cyanobacteria cells float to the surface, they are
subjected to wind movement, which can then concentrate cells into thick scums
along the shoreline. Though a scum does not necessarily mean that there are
cyanotoxins present, it is usually a good indicator that cell densities are high
enough that potential toxins may pose a significant health threat. The World
Health Organization (WHO) published a diagram to illustrate the accumulation of
cyanobacterial cells [7].
The complicated nature of
toxin-producing cyanobacteria and what it means for you!
There are
over one-hundred species of known toxin producing cyanobacteria. Understanding
species dynamics in lakes, along with toxicological effects relevant to humans,
is a daunting task that employs life-long researchers around the world.
Microcystin should not be a novel word to lake
residents, but the associated technical language may be off-putting to those
less scientifically inclined. Microcystin is one type of toxin produced by
numerous cyanobacterial species at varying levels. To further complicate
things, microcystin is not the only type of cyanotoxin that affects human
activity in lakes [3].
Brace
yourself for the slew of consonants that are sure to tie anyone’s tongue:
anatoxins, cylindrospermopsins, saxitoxins, nodularins (a select few relevant
to Connecticut lakes, courtesy of GreenWater Laboratories, FL). Like
microcystin, each type of toxin listed poses a unique health risk to humans and
pets, largely through contact and drinking water. Exposure to cyanotoxins may
result in skin irritation, vomiting, diarrhea, or in severe instances, damage
to the liver and nervous system. There is an extensive amount of research in
the area of cyanotoxins, and our knowledge of this field is continually
expanding with new scientific discovery.
Management based on what we know so
far…
In a previous issue of the
newsletter, CFLer Dr. George Knoecklein, spelled out the HAB guidelines
provided by the US Environmental Protection Agency (EPA) based on the WHO’s
findings. The following table outlines the Probability of Acute Health Effects
due to cyanobacteria in recreational water.
Relative Probability of Acute Health Effects
|
Cyanobacteria (cell/mL)
|
Microcystin-LR (µg/L)
|
Chlorophyll-a (µg/L)
|
Low
|
<20,000
|
<10
|
<10
|
Moderate
|
20,000-100,000
|
10-20
|
10-50
|
High
|
100,000-10,000,000
|
20-2,000
|
50-5,000
|
Very High
|
>10,000,000
|
>2,000
|
>5,000
|
Referring to
the EPA “Acute Health Effects” table, it seems as though a cyanobacteria count
of 20,000-100,000 cells/mL would be consistent with 10-20µg/L of
microcystin-LR. However, based on field experience and testing of CT lake
water, these two do not always match up. Numerous blue-green algae bloom samples from CT have yielded <1µg/L
of microcystin-LR, despite cell numbers vastly greater than 20,000 cell/mL.
Similarly, a series of scum samples taken just a few feet apart measured
7.8µg/L and 29.0µg/L microcystin-LR – while no toxins were detected about fifty
feet away (Greenwater Lab results, FL). If you sit scratching your head
at these differences, think back to the way wind can concentrate cells into
coves and along shorelines.
While much
of the off-shore lake water may pose a low probability of acute health effects,
there are bound to be areas where cyanobacteria cells conglomerate, and where
toxins may be present at dangerous levels [6,7]. Then, you may recall how there
are numerous species of cyanobacteria that produce varying levels of the toxin
microcystin. It is important for a professional with cyanobacteria taxonomy
expertise to determine which species make up the particular bloom at the time
of sample collection. Observation under a microscope will determine if there
are toxin-producing species present. It is important to note, however, that
because cyanobacteria replicate so quickly, a bloom may consist of relatively
benign species one day, and could be dominated by harmful species just days later.
At the time of the 2012 CFL
newsletter, Connecticut had not yet developed state guidelines. Since then, the
CT DPH has put together their guidance on HABs, based largely on the WHO
findings and Vermont’s existing recommendations. Because counting cyanobacteria
cells and waiting for toxin testing takes time and money, Connecticut has
adopted a visual rank category system that can be used to post a beach during a
cyanobacteria bloom. For a better understanding of the CT DPH guidelines, the
recommendations are interpreted and broken down into a chronological sequence
below.
Step 1. Make initial visual surveillance and determine Category based on
the provided table [1].
Visual
Rank Category
|
Observations
|
Category
1
|
Visible
material is not likely cyanobacteria or the water is generally clear.
|
Category
2
|
Cyanobacteria
present in low numbers. There are visible small accumulations, but water is
generally clear.
|
Category
3
|
Cyanobacteria
present in high numbers. Scums may or may not be present. Water is discolored
throughout. Large areas affected. Color assists to rule out sediment and
other algae.
|
“The initial
method for surveillance is visual and based on a Categorization scheme
developed and implemented by the State of Vermont [5].” “Reports
or complaints from the public or staff require confirmation. Confirmation can
be facilitated by consulting someone with prior field experience…a professional
Limnologist,” [1]. Validation
is important because, to an unfamiliar eye, filamentous algae and surface-growing
aquatic plants, like duckweed and watermeal, could all be mistaken for
blue-green algae.
Step 2. Once a visual assessment has
been made, the local health department is responsible for following up with
cell counts and/or toxin testing to make a determination on the course of
action based on the table below [1].
Observations
|
Notifications
|
Further
Monitoring
|
Public
Posting
|
Visual
Rank Category 1
|
Not needed
|
No change
|
Not needed
|
Visual
Rank Category 2, or blue-green algae cells >20,000/mL -
<100,000/mL
|
Notify CT
DPH, CT DEEP
|
Increase
regular visual surveillance until conditions change.
|
Not needed
|
Visual
Rank Category 3, or blue-green algae cells >100,000/mL
|
Update/inform
CT DPH & CT DEEP and expand risk communication efforts.
|
Collect
samples for analysis and/or increase frequency of visual assessment.
|
POSTED
BEACH CLOSURE: If public has beach access, alert water users that a
blue-green algae bloom is present. POST ADVISORY: At other impacted access
points.
|
Step 3. Monitor algae conditions weekly
to determine change in Category.
Step 4. End advisory when conditions are
favorable for at least two successive and representative observational rounds
one week apart.
To end an
advisory and lift a beach posting, the DPH states that, “The
recommended protocol for termination may be based on visual observations over
time, or a combination of this taken in concert with laboratory data.” Lifting a posting may be justified if
either, “Visual assessment remains at the
Category 1 condition for at least two successive and representative
observational rounds one week apart,” or
“Cell count results of the water column indicate that blue-green algal cell
abundance has markedly decreased over at least two successive and
representative sampling rounds one week apart and is below 70,000 cells per
ml.” [1].
Additional
advisories may be necessary to effectively contact all recreational lake users.
For instance, many homeowners draw water from their lake for washing dishes and
showering. If there is a Visual Rank Category 2 or 3 at the town beach, there
may be areas around the lake with much higher concentrations of cyanobacteria
cells, including personal intake pump locations. Homeowners need to ‘be in the
know’ to make their own visual assessments when deciding to use lake water for
an evening shower. Even more importantly, there are people who draw lake water
in CT to filter and drink (WHO
recommends <1µg/L microcystin for drinking water). Most water
purification systems do not affect cyanotoxins and it may be necessary for
residents to bring in bottled drinking water at certain times of the year.
Education and awareness are the tools to combat blue-green algae blooms!
The CT DPH states that their toxin threshold suggestion
is <15µg/L, which may or may not correspond to the cell numbers in the
guidance tables. There is currently no way to definitively explain when, or if,
the cells will be producing toxins [4]. Overall, the WHO, EPA, and CT DPH have
all provided their guidance on dealing with blue-green algae blooms. Cell
numbers and toxin thresholds are set as recommendations based on previous years
of research. These recommendations could change in the future as new science
unveils more detail into the nature of ‘why
and when’ specific cyanobacteria produce toxins. For now, it is best for
residents to become active stewards for lake health by taking responsibility
for lowering nutrient inputs to stymie algae and cyanobacteria growth. As the
going HAB slogan says, “When in doubt, stay
out!”
Citations:
Connecticut Department of Health (CT DPH) and Department of Energy and Environmental Protection (DEEP) 2013. Guidance to Local Health Departments for Blue-green Algae Blooms in
Recreational Freshwaters.
Fogg,
G.E., Stewart, W.P., and Walsby, A.E.
1973. The Blue-Green Algae.
Academic Press, London and New York.
Paerl,
H.W. and Fulton, R.S. 2006. Ecology of
Harmful Cyanobacteria. Ecological Studies, Vol. 189. Springer- Verlag
Berlin Heidelberg.
Vermont
Department of Health. 2008. Cyanobacteria (Blue-green Algae) Guidance for Vermont
Communities.
World
Health Organization (WHO). 1999. Toxic Cyanobacteria in Water: A guide to their
public health consequences, monitoring and management. Geneva: E & FN Spon.
World
Health Organization, 2003. Guidelines for
Safe Recreational Water Environments. Vol. 1 Coastal and Freshwaters,
Chapter 8. Geneva.
