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Comparative measurement of microcystins in diverse surface waters using ADDA-ELISA, LC-MS/MS, and MMPB techniques
Citation:
Sanan, T. AND D. Lytle. Comparative measurement of microcystins in diverse surface waters using ADDA-ELISA, LC-MS/MS, and MMPB techniques. Presented at SETAC World Congress 2016, Orlando, FL, November 06 - 10, 2016.
Impact/Purpose:
This work is part of StRAP 4.01 A and 4.01 D.
Description:
The measurement of microcystins, cyanotoxins associated with cyanobacterial blooms which are increasingly prevalent in inland waters, is complicated by the diversity of congeners which have been observed in the environment. At present, more than 150 microcystin congeners have been identified, and this poses a significant challenge to analytical methods intended to assess human health risks in surface and drinking water systems. The most widely employed analytical method at present is the ADDA-ELISA technique which is potentially sensitive to all microcystins, but it is primarily intended as a semi-quantitative method, and questions have been raised regarding the potential for cross-reactivity and false positives. LC-MS/MS methods targeting specific congeners, such as US EPA Method 544, are intended for use as a secondary confirmation following a positive ELISA response, but these techniques can target only those congeners for which commercial standards are available. Accordingly, they not suitable for ascertaining the safety of a given water sample, given the potential for omitting unknown microcystin congeners which might be present.An alternative approach involves oxidative transformation of microcystins to a common product, 2-methyl-3-methoxy-4-phenylbutyric acid, or MMPB. Measuring MMPB by LC-MS/MS can potentially provide a metric for the sum of all microcystin congeners present in a sample, subject to the efficiency and overall yield of conversion. The present study discusses the results from the application of the MMPB method, applied in conjunction with ADDA-ELISA and individual congener measurement using LC-MS/MS, to measure microcystins in bloom-impacted surface water samples obtained from multiple sites across the United States. Results of toxin measurements will be compared between sites and analytical techniques, and optimized conditions for the MMPB procedure will be presented.
