Comparative Assessment of Physical and Chemical Cyanobacteria Cell Lysis Methods for Total Microcystin-LR Analysis

ABSTRACT: Standardization and validation of alternative cell lysis methods used for quantifying total cyanotoxins is needed to improve laboratory response time goals for total cyanotoxin analysis. In this study, five cell lysis methods (i.e., probe sonication, microwave, freeze-thaw, chemical lysis with Abraxis QuikLyseTM, and chemical lysis with copper sulfate) were assessed using laboratory-cultured Microcystis aeruginosa (M. aeruginosa) cells. Methods were evaluated for destruction of cells (as determined by optical density of the sample) and recovery of total microcystin-LR (MC-LR) using three M. aeruginosa cell densities (i.e., 1 × 105 cells/mL (low-density), 1 × 106 cells/mL (medium-density), and 1 × 107 cells/mL (high-density)). Of the physical lysis methods, both freeze-thaw (1 to 5 cycles) and pulsed probe sonication (2 to 10 min) resulted in >80% destruction of cells and consistent (>80%) release and recovery of intracellular MC-LR. Microwave (3 to 5 min) did not demonstrate the same decrease in optical density (80% intracellular MC-LR. Abraxis QuikLyseTM was similarly effective for intracellular MC-LR recovery across the different M. aeruginosa cell densities. Copper sulfate (up to 500 mg/L Cu2+) did not lyse cells nor release intracellular MC-LR within 20 min. None of the methods appeared to cause degradation of MC-LR. Probe sonication, microwave, and Abraxis QuikLyseTM served as rapid lysis methods (within minutes) with varying associated costs, while freeze-thaw provided a viable, low-cost alternative if time permits

Impact of Hydrogen Peroxide and Copper Sulfate on the Delayed Release of Microcystin

Algicides, like hydrogen peroxide and copper sulfate, are commonly applied to recreational waters and drinking water sources to mitigate cyanobacterial blooms. In this work, the effects of hydrogen peroxide and copper sulfate were evaluated in two natural bloom samples (collected from Canadian and American waterbodies) and one lab-cultured Microcystis aeruginosa suspended in Colorado River water. Five algicide to dissolved organic carbon (DOC) dose ratios were evaluated during an initial exposure period of 24 h. One dose ratio (0.4 H2O2:DOC or 0.25 CuSO4:DOC) was then evaluated during stagnation after quenching (hydrogen peroxide) or extended exposure (copper sulfate) for up to 96 or 168 h. During the initial hydrogen peroxide exposure, the CA bloom had no release of intracellular microcystins (MCs) and the USA bloom only released MC at 4 H2O2:DOC. The reverse occurred with copper sulfate, where the CA bloom released MCs at 0.6 CuSO4:DOC but the USA bloom had no detectable extracellular MCs. Extracellular MC was released from the lab-cultured Microcystis at the lowest hydrogen peroxide and copper sulfate doses. In the hydrogen peroxide stagnation experiment, intracellular MC decreased in the USA bloom after 168 h despite the low dose applied. Similarly, the extended copper sulfate exposure led to intracellular MC decreases in both bloom samples after 168 h, despite showing no impact during the initial 24 h monitoring period. The lab-cultured Microcystis was again less resistant to both algicides, with releases observed after less than 2 h of stagnation or exposure. The damage to cells as measured by pigments during these experiments did not match the MC data, indicating that blooms with depressed pigment levels can still be a risk to nearby drinking water sources or recreational activities. These results provide insight on the timeline (up to one week) required for monitoring the potential release of MCs after algicide application

Tailored Synthesis of Photoactive TiO₂ Nanofibers and Au/TiO₂ Nanofiber Composites: Structure and Reactivity Optimization for Water Treatment Applications

Titanium dioxide (TiO₂) nanofibers with tailored structure and composition were synthesized by electrospinning to optimize photocatalytic treatment efficiency. Nanofibers of controlled diameter (30–210 nm), crystal structure (anatase, rutile, mixed phases), and grain size (20–50 nm) were developed along with composite nanofibers with either surface-deposited or bulk-integrated Au nanoparticle cocatalysts. Their reactivity was then examined in batch suspensions toward model (phenol) and emerging (pharmaceuticals, personal care products) pollutants across various water qualities. Optimized TiO₂ nanofibers meet or exceed the performance of traditional nanoparticulate photocatalysts (e.g., Aeroxide P25) with the greatest reactivity enhancements arising from (i) decreasing diameter (i.e., increasing surface area), (ii) mixed phase composition [74/26 (±0.5) % anatase/rutile], and (iii) small amounts (1.5 wt %) of surface-deposited, more so than bulk-integrated, Au nanoparticles. Surface Au deposition consistently enhanced photoactivity by 5- to 10-fold across our micropollutant suite independent of their solution concentration, behavior that we attribute to higher photocatalytic efficiency from improved charge separation. However, the practical value of Au/TiO₂ nanofibers was limited by their greater degree of inhibition by solution-phase radical scavengers and higher rate of reactivity loss from surface fouling in nonidealized matrixes (e.g., partially treated surface water). Ultimately, unmodified TiO₂ nanofibers appear most promising for use as reactive filtration materials because their performance was less influenced by water quality, although future efforts must increase the strength of TiO₂ nanofiber mats to realize such applications