Freshwater Cyanotoxins Research Articles

Influence of environmental factors on cyanobacterial biomass and microcystin concentration in the Dau Tieng Reservoir, a tropical eutrophic water body in Vietnam

Cyanobacterial blooms can be harmful to environmental and human health due to the production of toxic secondary metabolites, known as cyanotoxins. Microcystins (MCs), one of the most widespread class of cyanotoxins in freshwater, have been found to be positively correlated with cyanobacterial biomass as well as with nitrogen and phosphorus concentrations in temperate lakes. However, in tropical water bodies, cyanobacterial density and cyanotoxin correlation to environmental factors is not fully understood. In the present study, we examined the effects of total nitrogen and total phosphorus (TP) concentrations among other environmental parameters on cyanobacterial community structure and MC concentrations in the Dau Tieng reservoir, a tropical, eutrophic water body in Southern Vietnam. Cyanobacterial biomass and MC content were monitored monthly from March 2012 to February 2013, when MCs were present in the Dau Tieng Reservoir. The highest concentrations of intracellular MCs were found in September and February when cyanobacteria biomass reached maximum values, with 2.50 and 2.13 μg MC.L–1 , respectively. Principle component analysis and redundancy analysis showed that MC concentration was positively correlated with the biomass of the cyanobacterial order Chroococcales, whereas TP was the primary abiotic factor influencing cyanobacterial biomass and MC concentrations in the Dau Tieng Reservoir. In addition, Bayesian model average analysis was used to construct a prediction model of MCs using cyanobacterial biomass and environmental variables revealing a suite of useful predictive factors for MCs in the Dau Tieng Reservoir, including water temperature, TP and the biomass of Chroococcales.

A validated UPLC–MS/MS method for the surveillance of ten aquatic biotoxins in European brackish and freshwater systems

Over the past few decades, there has been an increased frequency and duration of cyanobacterial Harmful Algal Blooms (HABs) in freshwater systems globally. These can produce secondary metabolites called cyanotoxins, many of which are hepatotoxins, raising concerns about repeated exposure through ingestion of contaminated drinking water or food or through recreational activities such as bathing/swimming. An ultra-performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS) multi-toxin method has been developed and validated for freshwater cyanotoxins; microcystins-LR, -YR, -RR, -LA, -LY and -LF, nodularin, cylindrospermopsin, anatoxin-a and the marine diatom toxin domoic acid. Separation was achieved in around 9min and dual SPE was incorporated providing detection limits of between 0.3 and 5.6ng/L of original sample. Intra- and inter-day precision analysis showed relative standard deviations (RSD) of 1.2–9.6% and 1.3–12.0% respectively. The method was applied to the analysis of aquatic samples (n=206) from six European countries. The main class detected were the hepatotoxins; microcystin-YR (n=22), cylindrospermopsin (n=25), microcystin-RR (n=17), microcystin-LR (n=12), microcystin-LY (n=1), microcystin-LF (n=1) and nodularin (n=5). For microcystins, the levels detected ranged from 0.001 to 1.51μg/L, with two samples showing combined levels above the guideline set by the WHO of 1μg/L for microcystin-LR. Several samples presented with multiple toxins indicating the potential for synergistic effects and possibly enhanced toxicity. This is the first published pan European survey of freshwater bodies for multiple biotoxins, including two identified for the first time; cylindrospermopsin in Ireland and nodularin in Germany, presenting further incentives for improved monitoring and development of strategies to mitigate human exposure.

Rapid quantitative analysis of microcystins in raw surface waters with MALDI MS utilizing easily synthesized internal standards

The freshwater cyanotoxins, microcystins (MCs), pose a global public health threat as potent hepatotoxins in cyanobacterial blooms; their persistence in drinking and recreational water has been associated with potential chronic effects in addition to acute intoxications. Rapid and accurate detection of the over 80 structural congeners is challenged by the rigorous and time consuming clean up required to overcome interference found in raw water samples. MALDI-MS has shown promise for rapid quantification of individual congeners in raw water samples, with very low operative cost, but so far limited sensitivity and lack of available and versatile internal standards (ISs) has limited its use. Two easily synthesized S-hydroxyethyl-Cys(7)-MC-LR and -RR ISs were used to generate linear standard curves in a reflectron MALDI instrument, reproducible across several orders of magnitude for MC-LR, -RR and -YR. Minimum quantification limits in direct water samples with no clean up or concentration step involved were consistently below 7 μg/L, with recoveries from spiked samples between 80 and 119%. This method improves sensitivity by 30 fold over previous reports of quantitative MALDI-TOF applications to MCs and provides a salient option for rapid throughput analysis for multiple MC congeners in untreated raw surface water blooms as a means to identify source public health threats and target intervention strategies within a watershed. As demonstrated by analysis of a set of samples from Uruguay, utilizing the reaction of different MC congeners with alternate sulfhydryl compounds, the m/z of the IS can be customized to avoid overlap with interfering compounds in local surface water samples.

Evidence for a Novel Marine Harmful Algal Bloom: Cyanotoxin (Microcystin) Transfer from Land to Sea Otters

“Super-blooms” of cyanobacteria that produce potent and environmentally persistent biotoxins (microcystins) are an emerging global health issue in freshwater habitats. Monitoring of the marine environment for secondary impacts has been minimal, although microcystin-contaminated freshwater is known to be entering marine ecosystems. Here we confirm deaths of marine mammals from microcystin intoxication and provide evidence implicating land-sea flow with trophic transfer through marine invertebrates as the most likely route of exposure. This hypothesis was evaluated through environmental detection of potential freshwater and marine microcystin sources, sea otter necropsy with biochemical analysis of tissues and evaluation of bioaccumulation of freshwater microcystins by marine invertebrates. Ocean discharge of freshwater microcystins was confirmed for three nutrient-impaired rivers flowing into the Monterey Bay National Marine Sanctuary, and microcystin concentrations up to 2,900 ppm (2.9 million ppb) were detected in a freshwater lake and downstream tributaries to within 1 km of the ocean. Deaths of 21 southern sea otters, a federally listed threatened species, were linked to microcystin intoxication. Finally, farmed and free-living marine clams, mussels and oysters of species that are often consumed by sea otters and humans exhibited significant biomagnification (to 107 times ambient water levels) and slow depuration of freshwater cyanotoxins, suggesting a potentially serious environmental and public health threat that extends from the lowest trophic levels of nutrient-impaired freshwater habitat to apex marine predators. Microcystin-poisoned sea otters were commonly recovered near river mouths and harbors and contaminated marine bivalves were implicated as the most likely source of this potent hepatotoxin for wild otters. This is the first report of deaths of marine mammals due to cyanotoxins and confirms the existence of a novel class of marine “harmful algal bloom” in the Pacific coastal environment; that of hepatotoxic shellfish poisoning (HSP), suggesting that animals and humans are at risk from microcystin poisoning when consuming shellfish harvested at the land-sea interface.

Ct values required for degradation of microcystin-LR by free chlorine

Recently, there has been increased interest in microcystin-LR and other fresh water cyanotoxins because of their toxicity and occurrence throughout the world. Although previous studies have shown that free chlorine can degrade microcystin-LR, there are insufficient data to develop the contact times and free chlorine doses that achieve targeted levels of microcystin-LR degradation. Furthermore, there are insufficient microcystin-LR degradation data that would allow for the development of feasible microcystin-LR criteria or standards. To systematically develop this critical information, a total of 34 batch chlorination experiments were performed at different pH values, chlorine doses, and toxin concentrations. For all conditions, Ct (C = chlorine concentration, t = contact time) values required for degradation of microcystin-LR were calculated and safety factors were estimated. Twenty seven of the 34 experiments were conducted with reagent-grade water and seven of the 34 experiments were conducted with natural waters. At all pH values tested, the degradation of microcystin-LR increased with increasing Ct . For Ct values usually observed in drinking water treatment, a 1-log degradation of microcystin-LR in reagent-grade water was observed only at pH 6.0. The results also suggest that the Ct values obtained from reagent-grade water experiments are appropriate for application to natural waters that have been subjected to conventional coagulation, flocculation, sedimentation, and filtration prior to chlorine addition.