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Harmful Algal Blooms – Special Sampling and Response Actions

If you become concerned that an algae bloom may be toxic, water systems in Wyoming or EPA R8 Tribal Lands can call the EPA Region 8 Helpline at 1-(800) 227-8917 for assistance (specify Drinking Water – harmful algal blooms).

Background on Harmful Algae in Surface Waters

Some common algae toxins are microcystin, cylindrospermopsin, anatoxin and saxitoxin. The LD50 (individual dose required to kill 50% of the population) for cobra venom is 20 µg/kg, but for saxitoxin the LD50 is only 10 µg/kg. Saxitoxin is more toxic than cobra venom! Saxitoxin is a potent neurotoxin that blocks the flow of sodium in the nerve cells leading to numbness, paralysis and death. Microcystins are the most common algae toxins; they have an LD50 of 50 µg/kg and are liver toxins that cause cells to shrink, which causes blood to spill into the liver and can quickly lead to death.

The algae that produce toxins are not algae at all, but actually photosynthetic bacteria called cyanobacteria. Cyanobacteria, common to freshwater and marine ecosystems, can under certain conditions (high nutrient concentrations and high light intensity) form scums or blooms at the surface of a water body. These blooms can produce toxic compounds (or “cyanotoxins”) that are harmful to the environment, animals and human health. Winds and water currents can transport cyanobacterial blooms within proximity to drinking water intakes at treatment plants that, if not removed during treatment, can cause odor, taste and color problems in treated drinking water and can be harmful to human health.

Microcystins were found in the finished water at Toledo, Ohio in August of 2014. In response to this and similar events, in June of 2015 EPA published 10-day health advisories for microcystins (0.3 ppb for children under 6, and 1.6 ppb for all others) and cylindrospermopsin (0.7 ppb for children under 6, and 3.0 ppb for all others). For more information on the health advisories, see Drinking Water Health Advisory Documents for Cyanobacterial Toxins.

Some PWSs have experienced treatment challenges from algae for decades. What’s changed? The conditions that favor algae which produce toxins are both presence of nutrients (nitrogen (N) and phosphorous (P)) and high temperatures. Concentrations of N and P in surfaces waters are increasing, and records show temperatures continue to rise, leading to more frequent algae blooms.

Not every algae bloom has toxins in it. In algae blooms, the majority of the bloom can be cyanobacteria (~60 to 90 %), but of the blooms tested world-wide only about 59% produce toxins. It is currently unknown what environmental conditions trigger cyanobacteria to produce toxins. Therefore, one bloom may be toxic and the next one may not be, or this entire years’ blooms may be diatoms and the next years’ blooms may be toxic. You may not detect toxins when the bloom is going through its rapid growth phase, but may detect toxins during the die off phase, or vice versa. It is the episodic nature of toxin production that makes it very challenging to predict when to test.

It gets trickier. If you wanted to test for toxins and are looking for a visual bloom to trigger testing you may not find a bloom during a particular time of day. Cyanobacteria have air vacuoles in them that allows them to float to the level where the highest concentration of nutrients are located. Sometimes, there may be no visible indication of a bloom from the surface, yet toxins are being produced.

What to Do if Your System Has Indicators of an Algal Bloom – Region 8 Strategy:

The best strategy is to stay vigilant and to track either the visual progress of a bloom, treatment changes (diurnal pH swings of the raw water, taste and odor, shortened filter runs, etc.) or direct measurements like algae identification or cell counts. To assist you, EPA Region 8 developed a Harmful Algal Bloom Response Strategy that is based upon Ohio’s strategy, the state with the most experience dealing with HABs.

In the strategy, the first step we recommend is that the raw water be tested with a test strip (which we can provide) to see if toxins are present. If toxins are present, EPA’s Regional Lab may be able to assist with testing of the raw and finished water at no cost to you. See the Laboratory List for Harmful Algal Bloom Toxins for a partial list of labs that will accept samples for toxin analysis.

If toxins are found in the raw water, we will work with you to determine how best to optimize your treatment for toxin removal. The toxins are held within the cells so the treatment strategy is focused on removing whole cells, and not breaking apart the cell walls. Adding copper sulfate or an algaecide to actively break up the algae bloom may fix the filter clogging problem, but if the cyanobacteria happen to be producing toxins then the algaecide is going to lyse the algae cells and release those toxins. Toxins are smaller and much more difficult to remove through treatment than the whole algae cells.

Do not add an algaecide without consultation, and testing first for toxins! If toxins are not present, then it is safe to add the algaecide. If there are toxin levels found in the finished water, testing should be conducted as often as possible. If toxins are detected over the health advisory levels, then public notice needs to be conducted.

Please contact Bob Clement at 303-312-6653 or clement.robert@epa.gov if you have any questions.