Cyanotoxin Analysis: Round Robin Testing and Comparison of Commercially Available Standards

Drinking Water
Oral Presentation

Prepared by Y. Guo1, B. Vanderford2, A. Eaton3, G. Di Giovanni1, A. Jia1, M. Prescott1, W. Li1
1 - Metropolitan Water District of Southern California, 700 Moreno Avenue, La Verne, CA, 91750, United States
2 - Southern Nevada Water Authority, River Mountains Water Treatment Facility, 1299 Burkholder Boulevard, Henderson, NV, 89015, United States
3 - Eurofins Eaton Analytical (Retired), 750 Royal Oaks Drive, Suite 100, Monrovia, CA, 91016, United States


Contact Information: yguo@mwdh2o.com; 909-392-7108

ABSTRACT

Three groups of cyanotoxins—microcystins (MCs), anatoxin-a (ANTX), and cylindrospermopsin (CYL)—are included in the U.S. Environmental Protection Agency (EPA) Fourth Unregulated Contaminant Monitoring Rule. EPA has set non-regulatory 10-day health advisories at 0.3 µg/L for MCs and 0.7 µg/L for CYL in treated drinking water for children younger than six years of age. The health advisories for older children and adults are 1.6 µg/L for MCs and 3 µg/L for CYL. EPA has also set guidelines for recreational waters at 8 µg/L for MCs and 15 µg/L for CYL. Two commonly used methods for cyanotoxins in water are an enzyme-linked immunosorbent assay (ELISA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). This presentation will discuss findings from two inter-laboratory round-robin evaluations to compare results from different methods and laboratories. For the first round, three sample matrices (reagent water, raw water, and finished drinking water) were used, and MCs, ANTX, and CYL at varying concentrations were evaluated. For the second round, two cyanobacterial bloom samples were analyzed by participating laboratories. ELISA kits from the same lot and LC-MS/MS calibration standards were provided to participating laboratories to minimize variability. After excluding outliers using the Grubb’s test, relative standard deviations of ELISA results for MCs were 5%-51% for the first round robin (n=11) and 5%-34% for the second (n=15). Results showed that some of the differences between fortified concentrations and reported values could be attributed to differences between ELISA and LC-MS/MS methods as well as standards from different vendors used for the analyses. Further evaluation of 85 commercially available standards showed that MC standards had substantial concentration differences between vendors and sometimes between lots. Responses varied by as much as 50% for some of the MC variants. These findings will help support water utilities with regards to cyanotoxin monitoring and data interpretation.