Biotic and abiotic factors affect microcystin-LR concentrations in water/sediment interface (original) (raw)
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Contribution of sediments in the removal of microcystin-LR from water
""Microcystins are produced by several species of cyanobacteria and can harm aquatic organisms and human beings. Sediments have the potential to contribute to the removal of dissolved microcystins from the water body through either adsorption to sediment particles or biodegradation by the sediment’s bacterial community. However, the relative contribution of these two removal processes remains unclear and little is known about the significance of sediment’s overall contribution. To study this, changes in the concentration of microcystin-LR (MCLR) in the presence of sediment, sediment with microbial inhibitor, and non-sterile lake water were quantified in a laboratory experiment. Our results show that, in the presence of sediment, MCLR concentration decreased significantly in an exponential way without a lag phase, with an average degradation rate of 9 mg d-1 in the first 24 h. This indicates that sediment can contribute to the removal of MCLR from the water immediately and effectively. Whilst both, the biodegradation and adsorption ability of the sediment contributed significantly to the removal of MCLR from the water body, biodegradation was shown to be the dominant removal process. Also, the sediment’s ability to degrade MCLR from the water was shown to be faster than the biodegradation through the bacterial community in the water. The present study emphasizes the importance of sediments for the removal of microcystins from a water body. This will be especially relevant in shallow systems where the interaction between the water and the sediment is naturally high. Our results are also useful for the application of sediments to remove microcystins at water treatment facilities.""
Journal of Great Lakes Research, 2019
Microcystin-LR (MC-LR) is a cyclic hepatotoxin produced by cyanobacteria, including Microcystis sp. and Planktothrix sp. Harmful algal blooms (HABs) in Lake Erie have become a major human health concern in recent years, highlighted by the August 2014 city of Toledo, Ohio, municipal water “do not drink” order that affected nearly 500,000 residents for 3 days. Given that microcystin degrading bacteria have been reported from HAB-affected waters around the world, we hypothesized that MC-LR degrading bacteria could be isolated from Lake Erie. To test this hypothesis, 13 water samples were collected from various Lake Erie locations during the summers of 2014 and 2015, MC-LR was continuously added to each water sample for 3 to 5 weeks to enrich for MC-LR-degrading bacteria, and MC-LR was quantitated over time. Whereas MC-LR was relatively stable in sterile-filtered lake water, robust MC-LR degradation (up to 19 ppb/day) was observed in some water samples. Following the MC-LR selection process, 67 individual bacterial isolates were isolated from MC-LR degrading water samples and genotyped to exclude potential human pathogens, and MC-LR degradation by smaller groups of bacterial isolates (e.g., groups of 22 isolates, groups of 11 isolates, etc.) was examined. Of those smaller groups, selected groups of four to five bacterial isolates were found to degrade MC-LR into non-toxic forms and form robust biofilms on siliconized glass tubes. Taken together, these studies support the potential use of isolated bacterial isolates to remove MC-LR from drinking water.
Microcystin Elimination During Sediment Contact
Environmental Science & Technology, 2010
Microcystins (MCYSTs) are a group of structurally similar toxic peptides produced by cyanobacteria ("blue-green algae") which occur frequently in surface waters worldwide. Reliable elimination is necessary when using these waters as drinking water sources. Bank filtration and artificial groundwater recharge utilize adsorption and degradation processes in the subsurface, commonly through sand and gravel aquifers, for the elimination of a wide range of substances during drinking water (pre-) treatment. To obtain parameters for estimating whether MCYST breakthrough is likely in field settings, we tested MCYST elimination in laboratory experiments (batch experiments, column experiments) under a range of conditions. Adsorption coefficients (k d -values) obtained from batch studies ranged from 0.2 mL/g for filter sand to 11.6 mL/g for fine grained aquifer materials with 2% fine grains (<63 µm) and 0.8% organic matter. First order degradation rates in column studies reached 1.87 d -1 under aerobic conditions and showed high variations under anoxic conditions (<0.01-1.35 d -1 ). These results show that, next to sediment texture, redox conditions play an important role for MCYST elimination during sediment passage. Biodegradation was identified as the dominating process for MCYST elimination in sandy aquifer material.
Ecotoxicology and environmental safety, 2017
Cyanobacterial blooms and cyanotoxins occur in freshwater lakes and reservoirs all over the world. Bacterial degradation of microcystins (MC), hepatotoxins produced by several cyanobacterial species, has also been broadly documented. However, information regarding MC biodegradation in European water bodies is very limited. In this paper, the occurrence and identification of MC biodegradation products was documented for 21 European lakes and reservoirs, many of which have well-documented cyanobacterial bloom histories. Varying cyanobacterial abundance and taxonomical composition were documented and MC producers were found in all the analysed samples. Planktothrix agardhii was the most common cyanobacterial species and it formed mass occurrences in four lakes. MC biodegradation was observed in 86% of the samples (18 out of 21), and four products of dmMC-LR decomposition were detected by HPLC and LC-MS methods. The two main products were cyclic dmMC-LR with modifications in the Arg-Asp...
Ecological Indicators, 2018
The frequent occurrence and accumulation of microcystins (MCs) in freshwater systems pose serious threats to the drinking water safety and health of human beings. However, determining the overall toxicity and environmental risks from MC exposure is complex because of the variety of MC analogues and their respective toxicities. To address this issue, we conducted a survey of particulate (intracellular) and dissolved (extracellular) MC in Lake Taihu from 14 sampling sites in the northern part of the lake, and 32 stations throughout the entire lake, over a 16-month period. We propose a novel indicator, total MC-LR concentration (TLR), defined as the total concentration of MC-LR after transforming other MC variants (i.e., MC-RR and MC-YR) to an equivalent toxicity of MC-LR. Intracellular concentrations of TLR (iTLR) were usually observed, with the maximum values in July and October 2013 corresponding to periods of peaks in phytoplankton biomass. In contrast, extracellular concentrations of TLR (eTLR) were highest in May and June 2014. These differences in temporal patterns exhibited by LR, TLR, and TMC between intracellular and extracellular MC may be attributed to the influence of environmental variables. In addition, the distribution of iTLR and eTLR in the entire lake showed clear spatial heterogeneity. MC concentrations were greatest in the northern part of the lake during warm months, especially in Meiliang Bay. Based on the strong linear relationships between TLR and the concentration of chlorophyll-a (Chl-a), as well as TLR and the cell density of cyanobacteria, we propose not-to-exceed safety thresholds for Chl-a of 21.28 μg/L in the northern lake and 23.26 μg/L in the whole lake, which are paired with safety thresholds for cyanobacterial cell densities of 2.21 × 10 8 cells/L and 1.15 × 10 8 cells/L, respectively. The application of this newly proposed indicator, TLR, may contribute to better evaluation of overall MC toxicity and provide guidance on recommended limits for Chl-a concentration and cyanobacterial cell density in other freshwater ecosystems.
Harmful Algae, 2020
Microcystins (MCs) are among the predominant cyanotoxins that are primarily degraded by heterotrophic bacteria in various freshwater environments, including Lake Erie, a Laurentian Great Lake. However, despite the prevalence of MCs in Lake Erie basins, our knowledge about the taxonomic diversity of local MC-degrading bacteria is largely limited. The current study obtained thirty-four MC-degrading bacterial pure isolates from Lake Erie surface water and characterized their taxonomical and phenotypic identities as well as their MC-degradation rates under different pH, temperature, availability of organic substrates and with other MC-degrading isolates. Obtained MC-degrading isolates included both Gram-positive (18 isolates of Actinobacteria and Firmicutes) and Gram-negative bacteria (16 isolates of Gamma-proteobacteria); and 7 of these isolates were motile, and 13 had the capacity to form biofilms. In general, MC-degradation rates of the isolates were impacted by temperature and pH but insensitive to the presence of cyanobacterial exudates. At the optimal temperature (30-35°C) and pH (7-8), individual isolates degraded MC-LR, the most abundant MC isomer, at an average of 0.20 µg/mL/hr. With additions of cyanobacterial exudates, only Pseudomonas sp. LEw-2029, a non-motile biofilm maker, showed increased MC degradation (0.25 µg/mL/hr). Five out of nine tested dual culture mixtures showed rises in MC degradation rates than their corresponding monocultures; the highest rate reached 0.40 µg/mL/hr for the pair LEw-(1132 + 2029). PCR amplification of mlrA genes yielded negative results for all isolates; subsequent enzyme assay-Mass Spectrum analysis identified no product associated with the mlr gene-based MC degradation pathway. Collectively, our results demonstrated that a diversity of indigenous Lake Erie bacteria can degrade MCs via a novel mlr-independent pathway. Obtained MC degraders, especially Pseudomonas sp. LEw-2029, may serve as candidates for the development of biological filters to remove cyanotoxins in water treatment systems.
The importance of lake sediments as a pathway for microcystin dynamics in shallow eutrophic lakes
Microcystins are toxins produced by cyanobacteria. They occur in aquatic systems across the world and their occurrence is expected to increase in frequency and magnitude. As microcystins are hazardous to humans and animals, it is essential to understand their fate in aquatic systems in order to control health risks. While the occurrence of microcystins in sediments has been widely reported, the factors influencing their occurrence, variability, and spatial distribution are not yet well understood. Especially in shallow lakes, which often develop large cyanobacterial blooms, the spatial variability of toxins in the sediments is a complex interplay between the spatial distribution of toxin producing cyanobacteria, local biological, physical and chemical processes, and the re-distribution of toxins in sediments through wind mixing. In this study, microcystin occurrence in lake sediment, and their relationship with biological and physicochemical variables were investigated in a shallow, eutrophic lake over five months. We found no significant difference in cyanobacterial biomass, temperature, pH, and salinity between the surface water and the water directly overlying the sediment (hereafter ‘overlying water’), indicating that the water column was well mixed. Microcystins were detected in all sediment samples, with concentrations ranging from 0.06 to 0.78 µg equivalent microcystin-LR/g sediments (dry mass). Microcystin concentration and cyanobacterial biomass in the sediment was different between sites in three out of five months, indicating that the spatial distribution was a complex interaction between local and mixing processes. A combination of total microcystins in the water, depth integrated cyanobacterial biomass in the water, cyanobacterial biomass in the sediment, and pH explained only 21.1% of the spatial variability of microcystins in the sediments. A more in-depth analysis that included variables representative of processes on smaller vertical or local scales, such as cyanobacterial biomass in the different layers and the two fractions of microcystins, increased the explained variability to 51.7%. This highlights that even in a well-mixed lake, local processes are important drivers of toxin variability. The present study emphasises the role of the interaction between water and sediments in the distribution of microcystins in aquatic systems as an important pathway which deserves further consideration.
Toxicon, 2010
The presence of microcystin-LR -degrading bacteria in an active anthracite biofilter and in Lake Mead, Nevada was investigated. Four bacterial isolates from enrichment culture were identified using 16S rRNA analysis. Microcystin biodegradation tests were performed with both, the enrichment cultures and the respective isolates, using microcystin alone and acetate as carbon sources. A newly recognized microcystin-degrading bacterium, Morganella morganii, was isolated from the biofilter and from Lake Mead. The results of the biodegradation tests indicated that addition of a carbon source (acetate), significantly repressed the degradation of microcystin-LR. The findings of this study inform on the prevalence of microcystin-degrading bacteria in the environment indicating bioaugmentation may not be needed, if biofiltration is used to remove microcystin from waters. The results also imply that, in a biofilter, biodegradable naturally organic matter (NOM) and microcystin will compete and therefore lower toxin removals are likely in waters with higher NOM content. The feasibility of removing microcystin by biofiltration depends on the toxin concentration and the concentration of biodegradable carbon sources in the biofilter.
Toxicon, 2015
Adsorption of mixtures of cyanotoxins onto sediment as a dominant mechanism in the elimination of cyanotoxins from the aqueous phase has not been extensively investigated. The aim of this study was to investigate adsorption and desorption behavior of six microcystins including microcystin (MC)-LR, RR, YR, LY, LW and LF and cylindrospermopsin (CYN) on natural sediment. Freundlich and Langmuir isotherms could be fitted for MC-LR, RR, YR and CYN. Sorption kinetics showed immediate rapid adsorption for all cyanotoxins: CYN, MCLW and MCLF were adsorbed 72.6%, 56.7% and 55.3% respectively within 2 h. Results of desorption experiments demonstrated that less than 9% of cyanotoxins desorbed from sediment within 96 h. Adsorption of cyanotoxins onto three fractionated sediments particles, clayesilt (<75 mm), find sand (75e315 mm) and coarse sand (315e2000 mm) demonstrated that adsorption capacity of coarse sand fraction for all the tested cyanotoxins was less than 4% of the clayesilt fraction. Results of this study revealed that there is a potential for cyanotoxins to accumulate in the sediments of lakes, as well as in drinking water treatment plants. Monitoring programs must consider cyanotoxins in the particulate phase to avoid largely underestimating toxin concentrations following their release from blooms.