Fate of the cyanotoxin cylindrospermopsin in sediments (original) (raw)
Related papers
Toxicon, 2010
Recent results show that cylindrospermopsin is more frequent and widespread in surface waters than previously assumed. Studies on the fate of CYN in sediments are lacking, but this is important if these resources are used for drinking-water production via sediment passage. Therefore, the aim of our study was to determine a) CYN retention in two sandy sediments as a function of flow rate, CYN concentration, the presence of DOM and the content of fines (1% and 4%, respectively) and b) the influence of sediment preconditioning and DOM composition of the water (aquatic DOM versus DOM released from lysed cells) on CYN degradation. Retention of CYN proved negligible under the investigated conditions. Degradation in virgin sediments showed the highest lag phases (20 days). Preconditioned sediments showed no lag phase. The presence of aquatic DOM yielded highest degradation rates (k 1 ¼ 0.46 and 0.49 day À1 ) without a lag phase. Readily available organic carbon sources were preferentially metabolized and hence induced a lag phase. Thus, the presence and composition of DOM in the water proved important for both CYN degradation rates in preconditioned sediments and for the lag phase. Cylindrospermopsin degradation took place solely in the sediment and not in the water body.
Water Research, 2012
Sand filtration Cyanobacterial toxin Sediment preconditioning a b s t r a c t One possible consequence of increasing water temperatures due to global warming in middle Europe is the proliferation of cylindrospermopsin-producing species from warmer regions. This may lead to more frequent and increased cylindrospermopsin (CYN) concentrations in surface waters. Hence, efficient elimination of CYN is important where contaminated surface waters are used as a resource for drinking water production via sediment passage. Sediments are often characterized by a lack of oxygen and low temperature (i.e. approx. 10 C). The presence of dissolved organic carbon (DOC) is not only known to enhance but also to retard contaminant degradation by influencing the extent of lag phases. So far CYN degradation has only been investigated under oxic conditions and at room temperature. Therefore, the aim of our experiments was to understand CYN degradation, focusing on the effects of i) anoxic conditions, ii) low temperature (i.e. 10 C) in comparison to room temperature (23 AE 4 C) and iii) DOC on lag phases. We used two natural sandy sediments (virgin and preconditioned) and surface water to conduct closed-loop column experiments. Anoxic conditions either inhibited CYN degradation completely or retarded CYN breakdown in comparison to oxic conditions (T 1/2 (oxic) ¼ 2.4 days, T 1/2 (anoxic) ¼ 23.6 days). A decrease in temperature from 20 C to 10 C slowed down degradation rates by a factor of 10. The presence of DOC shortened lag phases in virgin sediments at room temperature but induced a lag phase in preconditioned sediments at 10 C, indicating potential substrate competition. These results show that information on physico-chemical conditions in sediments is crucial to assess the risk of CYN breakthrough. ª
Environmental Toxicology, 2008
The cyanotoxin cylindrospermopsin (CYN) is produced by several species of cyanobacteria and can be persistent in drinking waters supplies, which is of major concern to water authorities because of its potential to severely compromise human health. Consequently, there is a need to fully understand the persistence of CYN in water supplies, in particular, to determine whether this toxin is readily degraded by endemic aquatic organisms. This study provides insights into the environmental factors that can influence the biodegradation of this toxin in Australian drinking water supplies. Biodegradation of CYN was only evident in water supplies that had a history of toxic Cylindrospermopsis raciborskii blooms. In addition, lag periods were evident prior to the onset of biodegradation; however, repeated exposure of the endemic organisms to CYN resulted in substantial decreases in the lag periods. Furthermore, the concentration of CYN was shown to influence biodegradation with a near linear relationship (R 2 of 0.9549) existing between the biodegradation rate and the initial CYN concentration. Temperature was also shown to affect the biodegradation of CYN, which is important since CYN is now being detected in more temperate climates. The presence of copper-based algicides inhibited CYN degradation, which has significant implications since copper-based algicides are commonly used to control cyanobacterial growth in water bodies. The results from this study indicate that the biodegradation of CYN in natural water bodies is a complex process that can be influenced by many environmental factors, some of which include CYN concentration, temperature, and the presence of copper-based algicides.
Biotic and abiotic factors affect microcystin-LR concentrations in water/sediment interface
Microbiological Research, 2020
Harmful cyanobacterial blooms are increasingly common in aquatic environments. This can lead to higher concentrations of cyanotoxins, such as microcystins (MCs), posing a great risk to diverse organisms, including humans. MCs are among the most commonly reported cyanotoxins in freshwater environments worldwide, where they may have different fates. MCs can adsorb to suspended particles into the water column and deposit onto the sediment where they can be affected by physical factors (e.g. winds in shallow lakes causing sediment resuspension) or biological factors (e.g. biodegradation). Here we focused on the conditions of a coastal shallow lagoon contaminated by MCs aiming to estimate the return of pre-existing MCs from the sediment to the water column, to evaluate the adsorption of dissolved MC-LR to the sediment and to verify the occurrence of biodegradation. In experiments with sediment, desorption and adsorption were tested under the influence of temperature, pH and aeration, reproducing conditions observed in the lagoon. MC-desorption was not detected under the tested conditions. Spiking MC-LR into lagoon water samples in the presence of sediment resulted in a 50 % reduction of soluble MC-LR concentration in control conditions (25°C, pH 8.0, no aeration). Increasing temperature (45°C) or introducing aeration further stimulated MC-LR removal from the water. Biodegradation was observed in sediment samples and interstitial water (even with tetracycline). The composition of the bacterial community differed in sediment and interstitial water: major phyla were Chloroflexi, Proteobacteria, Firmicutes, and OP3. From the assigned OTUs, we identified genera already described as MC degrading bacteria. Thus, the sediment is a key factor influencing the fate of MC-LR in this shallow coastal lake contributing to stable adsorption and biodegradation.
Degradation of microcystin in sediments at oxic and anoxic, denitrifying conditions
Water Research, 2003
The potent toxin microcystin is frequently released during cyanobacterial blooms in eutrophic waters and may impose a risk to human health, when surface water is used for drinking water. For removal of microcystin in surface waters, infiltration through sediment is commonly used. In the present study, mineralization of 14 C-labelled microcystin (accumulation of 14 CO 2 ) and concentration changes (protein phosphatase inhibition assay) demonstrated that indigenous microorganisms in the sediment of a water recharge facility were capable of degrading microcystin. At oxic or microaerophilic (o2% O 2 ) conditions, microcystin added to sediment slurries at 70 mg l À1 was reduced to o20 mg l À1 in 1-2 weeks, and less than 3 mg l À1 after 7 weeks. At anoxic conditions (o0.3% O 2 ) and with addition of nitrate, the degradation was significantly stimulated, reducing microcystin from 100 to o20 mg l À1 within 1 day. The simultaneous production of N 2 O in the samples suggests that the microcystin degradation was coupled to dissimilative nitrate reduction (denitrification). Since aquifers and sediments beneath drinking water reservoirs often are anoxic, nitrate respiration may be an important process in removal and detoxification of microcystin. r
Journal of Soils and Sediments, 2020
Purpose Cyanobacterial blooms pose a serious threat to aquatic environmental health and have emerged as a primary issue in the recovery of eutrophic lakes. In order to comprehensively establish the effects of cyanobacterial blooms on nutrients in the aquatic environment, nutrient migration and transformation were studied in freshwater and sediments during cyanobacterial bloom decomposition. Materials and methods Cyanobacteria and sediments were collected from Zhushan Bay, in Taihu Lake, and the process of cyanobacterial decomposition was simulated in the laboratory. The focus of this research was to assess the effects of cyanobacterial decomposition on physicochemical parameters and nutrient concentrations in water, the vertical distribution of nutrients in sediments. We also determined the moisture content (ΔC w) and organic matter content (ΔOM) in surface sediments. Correlations were assessed between cyanobacterial decomposition and nutrient concentrations in water, with ΔC w and ΔOM in surface sediments simultaneously analyzed. Results and discussion In the water column, electric conductivity (Ec) was found to significantly increase, while dissolved oxygen (DO) and oxidation reduction potential (ORP) rapidly reduced. In addition, pH initially decreased and then increased, while ultraviolet light (UV 254) exhibited an opposite trend, which was related to the release and degradation of organic matter during the decomposition of cyanobacteria. Other nutrient concentrations were found to increase gradually with time, with the exception of nitrate nitrogen (NO 3 −-N), indicating that nutrients undergo temporal transitions between forms during cyanobacterial decomposition. Cyanobacterial decomposition causes ΔOM and ΔC w to increase in surface sediment layers, affecting the vertical distribution of nutrient species in the sediment. The water-sediment interface nutrient flux intensity was ranked in the order total nitrogen (TN) > ammonia nitrogen (NH 4 +-N) > NO 3 −-N > total phosphorus (TP), which was related to the settlement of cyanobacterial debris during cyanobacterial decomposition. Good binomial relationships (R 2 > 0.90, p < 0.05) were found between cyanobacterial density and nutrient concentrations in the waterbody, as well as between cyanobacterial density and ΔOM or ΔC w in the surface sediment. Conclusions Cyanobacterial decomposition affected various water quality parameters, leading to nutrient migration and transformation in the water-sediment interface, providing nutrients to drive cyanobacterial bloom development.
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.
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.
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.""