Microcystins: A Toxic Threat to Drinking Water

Cyanobacteria Microcystin NSF ANSI 53
Algal bloom in a lake, caused by blue-green algae, Microcystis.

Blue-green algae (cyanobacteria) comprises the oldest known fossils and date back more than 3.5 billion years, but these freshwater organisms are still prominent today. Cyanobacteria, primordial in their structure and behavior, share a world with complex animals shaped by billions of years of adaptation beyond their conception. Therefore, it should come as no surprise that harm transfers between the two groups. One such way is through the production of microcystins.

To address this issue, NSF/ANSI 53-2021: Drinking Water Treatment Units – Health Effects—the American National Standard for the materials, design, and performance of drinking water treatment systems designed to reduce specific health-related contaminants in water supplies—underwent some revisions associated with microcystins.

What are Microcystins?

Microcystins are toxins released by cyanobacteria (under the genus Microcytis), a type of unicellular bacteria known as “blue-green algae” due to its photosynthetic and aquatic nature. Cyanobacteria, however, is not related to other organisms we call algae, but they do form visible colonies on the surface of stagnant freshwater.

Interestingly, cyanobacteria releases microcystins when conditions are favorable for algal blooms.  When algal blooms form, cyanobacteria degrade, leading to cell death or lysis, and many release microcystins. These hepatotoxins (liver toxins) can persist for weeks and even months.

Health Effects of Microcystins

Microcystins can be harmful to human life. Direct exposure to the skin can produce a rash, hives, or skin blisters. Swallowing water containing microcystin can lead to gastrointestinal symptoms, including stomach pain, nausea, vomiting, diarrhea, severe headaches, and fever. Even inhaling small droplets of water containing the toxin can lead to irritated eyes and nose, cough, and sore throat, as well as chest pain and asthma-like symptoms.

Most significantly, as it is a hepatotoxin, exposure to a large amount of microcystin can cause liver damage.

However, there are relatively few documented cases of severe human health effects due to microcystins, and there are no known human fatalities resulting from exposure to the toxin. It has, however, been known to kill livestock and pets that drink affected waters, and fish and bird deaths have been reported in persistent cyanobacteria blooms.

Where Microcystin Occurs

Cyanobacteria can be present in any freshwater body. Algae blooms have significantly influenced the Great Lakes area, the world’s largest freshwater system. Lake Erie, which suffered significant blooms between 1960 and 1980, is seeing a resurgence in algal blooms. In fact, the world currently is seeing frequent algal blooms, and it will likely continue this trend due to several environmental factors. This is certainly problematic for the populations of people that get their drinking water from the affected bodies of water.

Aerial image of Willowick Ohio and Lake Erie

The biggest reason is agricultural runoff introducing hefty loads of nitrogen and phosphorus into fresh and saltwater systems, accelerating algal blooms. Phosphorus in particular is a noteworthy culprit for the production of microcystin, as it not only supports algal blooms that, in turn, help to degrade cyanobacteria, but it also directly helps the blue-green algae multiply.

Warm water and temperate weather also help cyanobacteria populations increase. Invasive species, two in particular—zebra and quagga mussels, exacerbate the problem due to their dislike of microcystis. By selectively feeding on other phytoplankton species, these two species of mussels inadvertently help cyanobacteria thrive. With the current state of environmental issues, such as climate change and the rise of invasive species, microcystins are likely to emerge in greater numbers than in recent history.

NSF/ANSI 53-2021

With the presence of cyanobacteria and the microcystin hepatotoxins, there is a clear need to safeguard drinking water supplies, specifically in the areas susceptible to blue-green algae blooms. For this reason (and others), NSF/ANSI 53-2021 establishes guidelines for treatment systems designed to reduce microcystins in public water supplies.

NSF/ANSI 53-2021: Drinking Water Treatment Units – Health Effects is available on the ANSI Webstore.

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