How Water Is Tested for Cyanotoxins Using Enzyme-Linked Immunosorbent Assay (ELISA)

When conditions are just right​—such as found on warm, sunny days in the summer​—small organisms called blue-green algae (or “cyanobacteria”) grow and may multiply rapidly in oceans, lakes, rivers, ponds, and other bodies of water.

As they eat, reproduce, and die, some of these cyanobacteria may produce and release different types of cyanotoxins, which can make people sick if they drink the water. By regularly testing water samples for the presence of these cyanotoxins, water quality specialists can make decisions about treating the water to reduce or remove the toxins, or advise the community when it may not be safe to drink or play in the water.

​How ELISA works

One reliable method experts often use to test water for the presence of cyanotoxins is called enzyme-linked immunosorbent assay, abbreviated ELISA (pronounced “ee-LIE-zuh”). Here is how it works.



Step 1

A water sample is collected, and a small part of the sample is placed into a vial.



Step 2

First the vial of water is completely frozen using a cryogenic freezer at −78°C (−108°F). Then the water is thawed by placing it in a 35°C (95°F) water bath.



​Step 3

The water sample is frozen and thawed three times to rupture (or “lyse”) any algae cells. Algae cells must be lysed this way to release any cyanotoxins they contain before the amount of toxins in the water can be measured.



​Step 4

The vial is placed on a rack in the cyanotoxin automated assay system (CAAS). This equipment adds a variety of chemicals to the water sample and lets it sit during incubation periods.



​Step 5

Finally, to calculate how much toxin (if any) is in the water, the CAAS measures how much blue light (at 450 nanometers) the water absorbs. The higher the absorbance reading of 450 nm light is, the lower the concentration of toxins is. If there is a lower absorbance of light, it indicates a higher concentration of toxins in the water.

​Useful test results



Step 6

Test result data are sent to water quality staff at the City, who review and track the data. If test results show high levels of cyanotoxins are in the source water above the treatment facility, more water samples are taken from other locations in the drinking water distribution system to be tested.



​Step 7

If cyanotoxin levels in samples taken from within the drinking water distribution system are at or above one of the Environmental Protection Agency’s advisory levels, a water advisory is issued.



​Step 8

Water quality specialists also use the data to make adjustments to the water treatment process, such as increasing chlorination or diluting the water from other sources that do not contain harmful blue-green algae.


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