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Anatoxin-a is a neurotoxin produced by certain species of cyanobacteria (formerly referred to as blue-green algae). Cyanobacteria are sometimes found in surface water when conditions favor growth and formation of algal blooms.

People can be exposed to anatoxin-a by:

  • ingesting fish or shellfish from waters containing anatoxin-a;
  • having direct skin contact with water containing anatoxin-a through bathing, showering, swimming or wading;
  • breathing airborne anatoxin-a while boating, waterskiing or recreating in waters with anatoxin-a present; or
  • consuming drinking water containing anatoxin-a.
Drinking water treatment generally removes intact cyanobacterial cells and low levels of cyanotoxins from source waters, but during a severe algal bloom, some anatoxin-a may escape treatment.


Information on the effects of anatoxin-a on humans is limited. However, drinking water with high levels of anatoxin-a has been found to damage the nervous system. Symptoms include muscle twitching, loss of coordination and seizures. Laboratory testing on animals show that ingesting high levels of anatoxin-a can cause death from respiratory paralysis.
The best way to know if anatoxin-a is in your source water or treated drinking water is to contact your water utility or state public health agency. Depending on the source of your water, climate and potential for nutrient pollution, your utility may or may not monitor for anatoxin-a and other cyanotoxins. Some sources are more likely to be at risk from anatoxin-a than others. For example, if your water comes from groundwater sources, it’s not likely to contain anatoxin-a.
Currently there are no federal regulatory standards or guidelines for anatoxin-a. However, a few states (Minnesota, Ohio and Vermont) have drinking water standards for it. In 2015, the U.S. Environmental Protection Agency conducted a review of available information on its health effects, and found the data inadequate to develop a health advisory for anatoxin-a at that time.

The Safe Drinking Water Act (SDWA) requires EPA to publish a list of substances that could potentially be of concern and warrant further study, known as the Contaminant Candidate List (CCL), and anatoxin-a is on the list. In 2015, EPA submitted a report to Congress committing to collecting additional information on anatoxin-a.

Under the SDWA, EPA is also required once every five years to issue a new list of up to 30 unregulated contaminants to be monitored by public water systems. This is known as the Unregulated Contaminant Monitoring Rule. Anatoxin-a is included in the fourth round of UCMR (UCMR4). Testing for UCMR4 starts in January 2018 and will continue through December 2020. The data from this nationwide monitoring will inform and support EPA’s decisions on regulatory actions to protect public health.

Typically, groundwater wells are not expected to contain cyanotoxins such as anatoxin-a. However, if your well is affected by surface water it could contain anatoxin-a. If your well is influenced by surface water then you should take additional steps to address several potential contaminants. EPA has information available on their private drinking water well page. Your local health department is another reliable source of information regarding steps you should consider.
If you are concerned about anatoxin-a in your drinking water you may consider purchasing a home treatment device. However, there is limited information on the effectiveness of at-home treatment devices on removing anatoxin-a from drinking water. There are some organizations currently developing certification standards to test residential treatment devices to evaluate how well they remove anatoxin-a and other cyanotoxins from drinking water. These standards are projected to be published soon. To make a well-informed and cost-effective decision, consider:
  • Checking with your water system or consumer confidence report to learn about the amount of anatoxin-a and other cyanotoxins in your water, and
  • Identifying a device that has been independently certified to remove anatoxin-a.

If you decide to use a home treatment device, be sure to follow manufacturer instructions for proper care and maintenance of the device.

Bottled water in the United States is regulated by the U.S. Food and Drug Administration and is required to meet standards equal to EPA’s tap water standards. There are also individual state standards to consider. In most cases, you must contact the bottled water manufacturer for information about anatoxin-a levels.