Detection Methods for Cyanotoxins
There is a diverse range of rapid screen tests and laboratory methods available to detect and identify cyanobacteria cells and cyanotoxins in water. These methods can vary greatly in their degree of sophistication and the information they provide. These methods include:
- Enzyme–linked immunosorbent assays (ELISA)
- Protein phosphatase inhibition assay (PPIA)
- Reversed-phase high performance liquid chromatographic methods (HPLC) combined with mass spectrometric (MS, MS/MS) or ultraviolet/photodiode array detectors (UV/PDA).
- Liquid chromatography/mass spectrometry (LC/MS)
- Conventional polymerase chain reaction (PCR), quantitative real–time PCR (qPCR) and microarrays/DNA chips
Many of these methods have been developed to analyze for microcystins and its congeners, however, relatively little work has been done on methods for detection of other toxins, including anatoxins and cylindrospermopsins. Saxitoxins are the exception, as they also occur widely in the marine environment and many methods have been developed for their detection in shellfish.
EPA developed the following methods for the detection of cyanotoxins in drinking water and ambient freshwater:
- Method 544: Determination of Microcystins and Nodularin in Drinking Water
- Method 545: Determination of Cylindrospermopsin and Anatoxin-a in Drinking Water
- Method 546: Determination of Total Microcystins and Nodularins in Drinking and Ambient Waters
- Method for Determination of Cylindrospermopsin and Anatoxin-a in Ambient Freshwaters
- Method for Determination of Microcystins and Nodularin in Ambient Freshwaters
The table below describes the methods available for cyanotoxin measurement in freshwater. Commercially available Enzyme-Linked Immunosorbent Assay (ELISA) test kits are one of the more commonly utilized cyanotoxin testing methods, since they do not require expensive equipment or extensive training to run. Semi-quantitative field screening ELISA kits are available for the presence or absence of cyanotoxins. If cyanotoxins are detected by a field screening kit, repeat analysis is recommended using either a quantitative ELISA test or one of the other analytical methods identified in the table below.
More precise, more quantitative ELISA test kits are available for microcystins/nodularins (including ADDA-ELISA), saxitoxin, anatoxin-a, and cylindrospermopsin. Although they provide rapid results, ELISA kits generally have limitations in selectivity and are not congener specific. In addition, the ability of ELISA to recognize different variants or congeners of cyanotoxins can vary quantitatively due to different cross-reactivities. The microcystins/nodularins (ADDA) kit is based on the ADDA structure within the microcystin molecule and is designed to detect over 100 microcystin congeners identified to date (but cannot distinguish between congeners).
Methods that utilize liquid chromatography combined with mass spectrometry (LC/MS) can precisely and accurately identify specific microcystin congeners for which standards are available. LC/MS methods have also been designed to minimize matrix interference. At this time there are only standards for a limited number of the known microcystin congeners. If congener-specific information is needed, an LC/MS (ion-trap, TOF, tandem mass spectrometry) method should be considered. HPLC-PDA methods are less selective than LC/MS methods and the quantitation is more problematic due to lower selectivity and to sample matrix interference. However, when analytical toxin standards are available for confirmation, they could provide a measure of resolution of the congeners present.
The following table describes the methods available for cyanotoxin measurement in freshwater.
|Protein Phosphatase Inhibition Assays (PPIA)||No||No||Yes|
|Enzyme-Linked Immunosorbent Assays
|Gas Chromatography with Flame
Ionization Detection (GC/FID)
|Gas Chromatography with Mass
|Liquid Chromatography / Ultraviolet-
Visible Detection (LC/UV or LC/PDA)
|Liquid Chromatography/Fluorescence (LC/FL)||Yes||No||No||Yes|
|Liquid Chromatography Combined with Mass Spectrometry|
|Liquid Chromatography Ion Trap Mass||Yes||Yes||Yes||Yes|
|Liquid Chromatography Time-of-Flight
Mass Spectrometry (LC/TOF MS)
|Liquid Chromatography Single
Quadrupole Mass Spectrometry (LC/MS)
|Liquid Chromatography Triple
Quadrupole Mass Spectrometry (LC/MS/MS)
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