Citation:

Woodruff, P., M. McNeely, T. Sanan, AND N. Dugan. Analysis of microcystins in alum water treatment sludges: holding times, temperatures, linearity of response, and sensitivity to pre-coagulation cell titers. ENVIRONMENTAL TECHNOLOGY. Selper LIMITED, London, Uk, , 1-14, (2024). https://doi.org/10.1080/09593330.2024.2349263

Impact/Purpose:

The goals of this project were to begin the process of quantifying:  (1) recovery, as measured by the ELISA assay, of microcystin-LR from alum drinking water treatment sludges at different holding times and temperatures; (2) ELISA assay linearity of response for microcystin-LR in a range of alum sludges; and (3) ELISA and LC/MS/MS recovery of microcystins from alum sludges derived from waters spiked pre-coagulation with toxin-producing cells of Microcystis aeruginosa.  With these results in hand, the drinking water community will be able to make a more educated decision as to whether or not to use the ELISA assay as a tool for monitoring cyanobacterial toxin concentrations in their source waters and treatment facilities.  It is anticipated that this information will be of use to drinking water treatment practicioners, consulting engineers, state primacy agency personnel, and EPA regional office personnel.

Description:

The ELISA assay is a potential tool to screen for dissolved or cell bound microcystins in drinking water treatment plant sludges.  In order to evaluate this potential more thoroughly, a series of experiments were performed to: (1) evaluate the impacts of storage times and temperatures on microcystin-LR recovery from alum sludges by ELISA as a function of pre-coagulation turbidities and natural organic matter (NOM) concentrations; (2) examine the linearity of ELISA responses as a function of pre-coagulation turbidities and NOM concentrations in thickened sludges spiked with 0.5 to 4 µg/L microcystin-LR;  (3) examine the ability of the ELISA and LC/MS/MS to detect microcystins in thickened sludges generated by coagulating waters of differing turbidities and NOM concentrations spiked prior to coagulation with 10^2 to 10^6 cells/mL of toxin producing Microcystis aeruginosa.  Microcystin recovery efficiencies ranged from 85% to 125% across the range of 12 storage time and temperature combinations with recovery efficiencies in 7 of the 12 combinations falling into the 90% to 110% range.  Linear models fit ELISA responses in all four thickened sludge compositions with R^2 values ≥ 0.95 and F statistics ≥ 120.  Simple freeze/thaw/centrifugation processing combined with ELISA analysis resulted in detection of microcystins in thickened sludges derived from pre-coagulation cell suspensions of 102 – 106 cells/mL. In addition, the relationships between toxin concentrations in sludges and the original cell titers were linear, and these results were confirmed by LC/MS/MS.

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