Solvent choice influences final toxicity results in Thamnocephalus platyurus bioassay when exposed to microcystin -LR.

Cyanobacterial blooms present a threat to many waterbodies around the world used for drinking water and recreational purposes. Toxicology tests, such as the Thamnotoxkit-F which uses the cladoceran T. platyurus, have been employed to assess the health hazards that these blooms may pose to the public. However, reported median lethal concentrations (LC50) of microcystin -LR to T. platyurus vary significantly from one study to the next. The variation in solvent type and concentrations used to dissolve microcystin -LR in preparation for toxicity experiments may be contributing to the variations in LC50 values found in the literature. The primary goal of this study was to determine what solvents and their corresponding concentrations can be used for microcystin -LR testing using T. platyurus without artifactually impacting LC50 values. All toxicity testing was completed using glassware as polystyrene containers have been shown to sorb microcystin. Microcystin -LR LC50 values for T. platyurus were determined using United States Environmental Protection Agency (US EPA) moderately hard standard freshwater as a control for comparison with systems that were prepared using dimethyl sulfoxide or methanol to dissolve microcystin -LR. Low levels of dimethyl sulfoxide (2%) or methanol (1%) did not impact LC50 values of microcystin -LR to T. platyurus compared to US EPA moderately hard standard freshwater diluted in microcystin -LR. However, higher levels of dimethyl sulfoxide (4%) and methanol (1.4% and 4%) did lower the LC50 for microcystin -LR to T. platyurus, consistent with the toxicity of these solvents to T. platyurus when dosed in the absence of microcystin -LR. Researchers need to report the type and concentrations of solvents used in toxicity tests using cyanotoxins in order to ensure that results can be intercompared appropriately. Furthermore, researchers need to use caution when using organic solvents such as dimethyl sulfoxide or methanol to ensure that these solvents are not causing significant mortality in toxicity testing.

Impact of bloom events on dissolved organic matter fluorophore signatures in Ohio waters.

Due to the increase in severe cyanobacterial blooms in drinking water sources and recreational waters across the globe, inexpensive and reliable methods of detecting oncoming blooms are needed. Cyanobacterial blooms can contribute substantially to the bulk chromophoric dissolved organic matter pool. Thus, the fluorescence signature of organic matter derived from these blooms may be an indicator of upcoming blooms. Water samples from five sites around Ohio were collected regularly between February and October 2017. A PARAFAC model was developed to determine if these protein-like fluorophores could be linked to bloom biomass and whether they were absent in dissolved organic matter from oligotrophic waters. One reference site at an oligotrophic reservoir was included to confirm the lack of protein-like fluorophores in the absence of a bloom event. We found that an increase in tryptophan-like and tyrosine-like fluorophores occurs before the increase in chlorophyll a levels, associated with bloom biomass, in some Ohio waters affected by cyanobacterial blooms; however, protein-like fluorophores are not correlated with levels of the cyanotoxin, microcystin. The excitation and emission wavelengths of these fluorophores (tryptophan-like: 239/341 nm, tyrosine-like: 248/306 nm) may be used to monitor impending blooms in waters heavily impacted by cyanobacteria but may not be applicable to waters receiving treated wastewater discharges.

Diethyl phenylene diamine (DPD) oxidation to measure low concentration permanganate in environmental systems.

Permanganate has been used traditionally in drinking water treatment for its oxidation properties and ease of use. The concentration of permanganate in treatment conditions is low and difficult to detect. A colorimetric method using diethylphenylene diamine (DPD) oxidation to measure low levels (i.e., less than 6 µM) of permanganate in water was developed and applied to quantify permanganate scavenging by dissolved organic matter (DOM). Manganese dioxide (MnO2) particles were shown to interfere with DPD oxidation; however, particles were removed effectively using 0.1 µm PVDF filters prior to reaction with DPD. DOM and complexed-Mn(III) were concluded to not interfere with the DPD reaction. The DPD method was validated by obtaining the second-order rate constant for permanganate reaction with phenol (1.7 ±â€¯0.2 M-1 s-1), and comparing to the rate constant obtained independently by monitoring phenol degradation (i.e., UPLC-UV) (1.6 ±â€¯0.2 M-1 s-1). Permanganate reaction with DOM isolate samples did not follow pseudo-first order kinetics. Faster reaction rates were observed with higher ionic strength (1 mM versus 5 mM carbonate). No change in reaction rates with pH was observed at lower ionic strength (1 mM); while at higher ionic strength, the reaction rate was faster at pH 7 than at pH 10. In contrast, linear kinetics were observed for permanganate reaction with DOM in filtered whole water samples. These samples showed similar trends with pH and ionic strength as for DOM isolates. The presented method is valid to quantify permanganate reaction rates with organic contaminants or with natural scavengers.