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.

Water sample bottle and CAAS

As part of a rigorous water quality monitoring program, skilled City of Salem Public Works employees collect, track, and test water samples from various locations in the watershed, water treatment facility at Geren Island, and water distribution system. Microcystin and Cylindrospermopsin are two types of cyanotoxins caused by blue-green algae (or “cyanobacteria”) that the City can test for at its in-house lab using enzyme-linked immunosorbent assay (ELISA).

Lab technician preparing samples

A City of Salem certified lab technician prepares water samples for testing using a cyanotoxin automated assay system (CAAS) at its in-house lab. This specialized equipment allows the City to use enzyme-linked immunosorbent assay (ELISA) to test the water for any concentration of cyanotoxins by measuring how much blue light the water will absorb. Results are sent to water quality staff who review, track, and use the data to make decisions about drinking water treatment.

​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.


Hands pouring water sample into vial

The enzyme-linked immunosorbent assay (ELISA) testing that the City of Salem performs in its in-house lab is the recommended testing method under Oregon’s new rules adopted June 29, 2018, by Oregon Health Authority.

Water samples in freezer

Before water samples can be accurately tested for the presence of cyanotoxins, the samples must be frozen and thawed three times to rupture (or “lyse”) any blue-green algae cells the water may contain. A cryogenic freezer is part of the City of Salem’s ELISA equipment at its in-house lab. By using an in-house lab, the City can receive and share test results as quickly as possible.

Lab technician preparing samples

A lab technician prepares water samples to test for the presence of any cyanotoxins. As of June 2018, the City of Salem is one of only two organizations in Oregon that have equipment to run enzyme-linked immunosorbent assay (ELISA) testing.

Rack of samples in CAAS

Carefully labeled samples are loaded into the cyanotoxin automated assay system (CAAS) at the City of Salem lab. The equipment will use enzyme-linked immunosorbent assay (ELISA) to test the water for any cyanotoxins that may have been produced by blue-green algae that grow during the summer in the North Santiam River and Detroit Lake watersheds.

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