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Harmful Algal Blooms: Guidance for Cyanobacteria
To date, neither the U.S. Environmental Protection Agency (EPA) nor the U.S. Centers for Disease Control and Prevention (CDC) has issued official regulatory or health-based standards for safe levels of cyanobacteria or toxins in recreational waters or drinking water.
In June 2015, the EPA issued drinking water health advisory guidelines for microcystins and cylindrospermopsin. EPA has identified draft recommended concentrations of cyanotoxins to protect human health while swimming or participating in other recreational activities in and on the water. In the absence of U.S. national standards, the Utah Department of Health (DOH) and Utah Department of Environmental Quality (DEQ) have provisionally adopted cyanobacteria health guidelines based on those outlined by the World Health Organization (WHO).
The World Health Organization (WHO) has developed guideline values for recreational waters that take into account the severity and probability of health effects at three different levels of cyanobacteria cell counts.
A low probability for adverse health effects is expected when cyanobacteria cell counts are between 20,000 and 100,000 cells/mL. At this level, providing information to recreational users is considered sufficient.
A moderate probability for adverse health effects is expected when cyanobacteria cell counts are between 100,000 and 10,000,000 cells/mL. Restricting bathing at beaches and public education campaigns may be appropriate when cyanobacteria counts are at this level.
A high probability for adverse health effects is expected when cyanobacteria cell counts are greater than 10,000,000 cells/mL, or there are cyanobacteria scums at bathing areas. The WHO reports that animal poisonings and human illnesses related to cyanobacteria are usually accompanied by the presence of scum material at the water surface, and that ongoing observation of beaches is necessary to assess the existence of high-risk exposures.
Many cyanobacteria species of concern form clumps, spheres, and/or coils of intertwined cells. Therefore, it is often problematic to quantify cell counts using routine laboratory protocols. It may not be possible in some cases to compare cell densities from any particular lake or pond sample to the guidelines provided by the WHO regarding human risk from exposure to cyanobacteria. Because certain species, such as those within Cylindrospermopsis, are not prone to form surface scums when cell counts are high, the WHO guidance for defining high levels of risk is less informative for these species than for others. It is also likely that there is some variation in the degree to which different species of cyanobacteria contribute to skin rashes.
DOH and DEQ recommend that local health departments (LHDs) use the table below and the accompanying decision algorithm when determining the appropriate level of health risk and public health action for a given waterbody. In the algorithm, red arrows indicate increasing potential hazard of harmful algal blooms and blue arrows indicate decreasing hazard. As shown in table below and in the algorithm, if an LHD receives reports of human or animal illness or death that is plausibly linked to cyanobacteria, an immediate public health advisory is recommended. Once an advisory is issued, we recommend at least two weeks of measurements indicating that the hazard has passed before removing the advisory.
The relationship between the cell counts in the table below and other potential measures such as toxin concentrations that are used to assess hazardous algal blooms are shown in Appendix A, Table A-1. In some situations, results for several of these measures may be available. Without any additional site-specific information, the highest level of public health advisory supported by any of the different measures shown in Table A-1 is recommended in order to be as protective of public health as possible.
Links are available to examples of CAUTION, WARNING, and DANGER signs that the public may encounter:
- Harmful Algal Bloom Warning Sign (pdf, English & Spanish)
- Harmful Algal Bloom Danger Sign (pdf, English)
- Harmful Algal Bloom Danger Sign (pdf, Spanish)
The Department of Health (DOH) and Department of Environmental Equality (DEQ) recommend a three-tier approach to HAB notifications. For information pertaining to local health department (LHD) actions at each tier and the types of information that are considered to substantiate that action, please view the Utah Harmful Algal Blooms and Human Health Guidance for Local Health Departments (pdf).
The recommended standard operating procedure (SOP) for collecting samples for HABs and HAB toxins are described in the Division of Water Quality’s Standard Operating Procedure for collection of Phytoplankton Samples during Harmful Algal Blooms. Excerpts from the SOP:
Guidance for Fish and Wildlife Mortality Sampling
The recommended standard operating procedure (SOP) for collecting samples for carcasses of fish and wildlife associated with a HAB event are described in the USFWS and DWQ Guidance for Fish and Wildlife Mortality Sampling (pdf).
Some studies have shown that cyanotoxins can accumulate in fish to some degree in natural waters with high toxin levels. It is known that the body concentrations of cyanotoxins in fish are greatest in organs and fatty tissue, with the lowest concentrations found in the muscle tissue (Zhang et al., 2009). While there have been no confirmed reports of cyanotoxin-related human health effects related to fish consumption, there are few data on cyanotoxins in lakes, fish, or shellfish to adequately base judgments regarding this health risk.
UDOH and UDEQ recommend carefully cleaning and thoroughly cooking fish harvested from waters where cyanobacteria are present. This includes removing skin and fatty deposits from the fish and rinsing the meat in clean water before cooking.
References and More Information
- Photo Gallery of Green and Blue-green Algae, Utah Department of Health
- Photo Gallery of Green and Blue-green Algae (New York State Department of Environmental Conservation)
- Zhang D, Xie P, Liu Y, Qiu T, 2009. Transfer, distribution and bioaccumulation of microcystins in the aquatic food web in Lake Taihu, China, with potential risks to human health.
- The Science of the Total Environment [2009, 407(7):2191-2199]
- WHO (2003) Guidelines for Safe Recreational Waters Volume 1 - Coastal and Fresh Waters
- US EPA Contaminant Candidate List (CCL) and Regulatory Determinations
- US EPA Creating a Cyanotoxin Target List for the UCMR (PDF) (17 pp, 110K; About PDF)
- WHO Blue-green algae toxins: Microcystin-LR in Drinking-water
- WHO (1999) Toxic blue-green algae in water: A guide to their public health consequences, monitoring and management