CYANOBACTERIA AND CYANOTOXINS IN WATER
Over the past decade, cyanobacteria blooms have emerged as an important issue in the water and wastewater industry. Tory Colling, Scientist, explains what water professionals ought to know about cyanobacteria and cyanotoxins in water:
1. What are cyanotoxins?
Cyanotoxins are produced by some species of cyanobacteria or as commonly known as blue-green algae. These toxins are typically stored inside the cells, but when cyanobacteria cells degrade, the toxins are released.
Cyanobacteria are microscopic bacteria that have some plant-like characteristics. They are commonly called “algae blooms” in the media.
2. Where are they found?
Cyanobacteria naturally occur in freshwater. In fact, they contribute oxygen in our atmosphere. When conditions are favourable, such as warm temperatures and nutrient-rich, shallow and stagnant waters, cyanobacteria can form blooms. Cyanobacteria blooms are made up of densely-populated cells that form discoloured water, which is often described as pea soup or spilt paint with an oily appearance.
Certain cyanobacteria can produce by-products, known as cyanotoxins. When these cyanobacteria cells form a bloom, large amounts of cyanotoxins can be detected.
3. What are the health concerns?
Health concerns can range from liver toxins, neurotoxins, tumor-promoting effects or skin irritation. There are different types of cyanotoxins and each type has different health concerns. The most common cyanotoxin is called microcystin. Microcystin is a liver toxin and can cause tumor-promoting effects.
4. What are some strategies to control cyanotoxins?
Reducing nutrient inputs to source water or effective reservoir/watershed management are long-term strategies to control cyanobacteria and cyanotoxins.
5. How can cyanotoxins be removed from drinking water?
For larger municipal systems, combining effectively operated drinking water treatment processes can provide a multiple barrier to remove intact cells or released cyanotoxins. Some drinking water treatment processes, such as coagulation, flocculation and sedimentation or flotation, are capable of removing intact cyanobacteria cells. While other drinking water treatment processes, such as chlorination or ozonation, are capable of degrading released cyanotoxins, provided there is enough disinfectant concentration and contact time with the disinfectant.
Some very small or private drinking water systems may only rely on point-of-entry (POE) drinking water treatment units. If these private drinking water systems suspect a bloom in the water supply, it is recommended to contact the local health unit and use an alternative water source. Very limited POE treatment units are certified to specifically remove cyanotoxins. However, in 2019, the National Sanitation Foundation (NSF)/American National Standards Institute (ANSI) updated NSF/ANSI Standard 53 to include a protocol to test activated carbons filters to reduce microcystins.