Analysis of microcystins in alum water treatment sludges: holding times, temperatures, linearity of response, and sensitivity to pre-coagulation cell titers.

ELISA assays are a potential tool to screen for dissolved or cell bound microcystins in drinking water treatment sludges. In order to evaluate this potential more thoroughly, experiments were performed in alum sludges to: (1) evaluate the impacts of sample storage times, temperatures, and sludge composition on spiked microcystin-LR recovery by ELISA; (2) examine the linearity of ELISA responses to spiked microcystin-LR as a function of sludge composition; and (3) examine the sensitivity ELISA and LC/MS/MS to five different concentrations of microcystin-producing cyanobacteria entrained in sludges of two different compositions. During storage experiments, 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. During the linearity experiments, linear models fit ELISA responses in all sludge compositions with R2 values ≥ 0.95. During the sensitivity studies, simple freeze/thaw/centrifugation processing combined with ELISA or LC/MS/MS analyses 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 regardless of analytical method.

Assessing residential activity in a home plumbing system simulator: monitoring the occurrence and relationship of major opportunistic pathogens and phagocytic amoebas.

Opportunistic premise plumbing pathogens (OPPPs) have been detected in buildings' plumbing systems causing waterborne disease outbreaks in the United States. In this study, we monitored the occurrence of OPPPs along with free-living amoeba (FLA) and investigated the effects of residential activities in a simulated home plumbing system (HPS). Water samples were collected from various locations in the HPS and analyzed for three major OPPPs: Legionella pneumophila, nontuberculous mycobacterial species (e.g., Mycobacterium avium, M. intracellulare, and M. abscessus), and Pseudomonas aeruginosa along with two groups of amoebas (Acanthamoeba and Vermamoeba vermiformis). A metagenomic approach was also used to further characterize the microbial communities. Results show that the microbial community is highly diverse with evidence of spatial and temporal structuring influenced by environmental conditions. L. pneumophila was the most prevalent pathogen (86% of samples), followed by M. intracellulare (66%) and P. aeruginosa (21%). Interestingly, M. avium and M. abscessus were not detected in any samples. The data revealed a relatively low prevalence of Acanthamoeba spp. (4%), while V. vermiformis was widely detected (81%) across all the sampling locations within the HPS. Locations with a high concentration of L. pneumophila and M. intracellulare coincided with the highest detection of V. vermiformis, suggesting the potential growth of both populations within FLA and additional protection in drinking water. After a period of stagnation lasting at least 2-weeks, the concentrations of OPPPs and amoeba immediately increased and then decreased gradually back to the baseline. Furthermore, monitoring the microbial population after drainage of the hot water tank and partial drainage of the entire HPS demonstrated no significant mitigation of the selected OPPPs. This study demonstrates that these organisms can adjust to their environment during such events and may survive in biofilms and/or grow within FLA, protecting them from stressors in the supplied water.