Influence of Microcystis sp. and freshwater algae on pH: Changes in their growth associated with sediment

Effects of Cadmium and Nickel Mixtures on Multiple Endpoints of the Microalga Raphidocelis subcapitata

It is crucial to investigate the effects of mixtures of contaminants on aquatic organisms, because they reflect what occurs in the environment. Cadmium (Cd) and nickel (Ni) are metals that co-occur in aquatic ecosystems, and information is scarce on their joint toxicity to Chlorophyceae using multiple endpoints. We evaluated the effects of isolated and combined Cd and Ni metals on multiple endpoints of the chlorophycean Raphidocelis subcapitata. The results showed that Cd inhibited cell density, increased reactive oxygen species (ROS) production (up to 308% at 0.075 mg L-1 of Cd), chlorophyll a (Chl a) fluorescence (0.050-0.100 mg L-1 of Cd), cell size (0.025-0.100 mg L-1 of Cd), and cell complexity in all concentrations evaluated. Nickel exposure decreased ROS production by up to 25% at 0.25 mg L-1 of Ni and Chl a fluorescence in all concentrations assessed. Cell density and oxygen-evolving complex (initial fluorescence/variable fluorescence [F0/Fv]) were only affected at 0.5 mg L-1 of Ni. In terms of algal growth, mixture toxicity showed antagonism at low doses and synergism at high doses, with a dose level change greater than the median inhibitory concentration. The independent action model and dose-level-dependent deviation best fit our data. Cadmium and Ni mixtures resulted in a significant increase in cell size and cell complexity, as well as changes in ROS production and Chl a fluorescence, and they did not affect the photosynthetic parameters. Environ Toxicol Chem 2024;43:1855-1869. © 2024 SETAC.

Glyphosate-environmental variables interaction: How does it affect the parasite Chordodes nobilii?

The worldwide used herbicide Glyphosate can interact with environmental variables, but there is limited information on the influence of environmental stressors on its toxicity. Environmental changes could modify glyphosate effects on non-target organisms, including parasites such as gordiids. The freshwater microscopic larvae of the gordiid Chordodes nobilii are sensitive to several pollutants and environmental variables, but their combined effect has not been evaluated yet. The aim of this study was to evaluate the impact of temperature, pH and exposure time on the toxicity of Glyphosate to C. nobilii larvae. A protocol was followed to evaluate the infectivity of larvae treated with factorial combinations of concentration (0 and 0.067 mg/L), exposure time (24 and 48 h), temperature (18, 23 and 28 °C), and pH (7, 8 and 9). The reference values were 23 °C, pH 8 and 48 h. The interaction effect on the infectivity of gordiid larvae was assessed post-exposure using Aedes aegyptii larvae as host. Results were evaluated using GLMM, which does not require data transformation. The modeling results revealed three highly significant triple interactions. Glyphosate toxicity varied depending on the combination of variables, with a decrease being observed after 24 h-exposure at pH 7 and 23 °C. Glyphosate and 28 °C combination led to slightly reduced infectivity compared to temperature alone. This study is the first to report the combined effects of glyphosate, temperature, pH and time on a freshwater animal. It demonstrates that a specific combination of factors determines the effect of glyphosate on a non-target organism. The potential use of C. nobilli as a bioindicator is discussed. In the context of global warming and considering that the behavioral manipulation of terrestrial hosts by gordiids can shape community structure and the energy flow through food webs, our results raise concerns about possible negative effects of climate change on host-parasite dynamics.

Enhancing water quality prediction for fluctuating missing data scenarios: A dynamic Bayesian network-based processing system to monitor cyanobacteria proliferation

Tackling the impact of missing data in water management is crucial to ensure the reliability of scientific research that informs decision-making processes in public health. The goal of this study is to ascertain the root causes associated with cyanobacteria proliferation under major missing data scenarios. For this purpose, a dynamic missing data management methodology is proposed using Bayesian Machine Learning for accurate surface water quality prediction of a river from Limia basin (Spain). The methodology used entails a sequence of analytical steps, starting with data pre-processing, followed by the selection of a reliable dynamic Bayesian missing value prediction system, leading finally to a supervised analysis of the behavioral patterns exhibited by cyanobacteria. For that, a total of 2,118,844 data points were used, with 205,316 (9.69 %) missing values identified. The machine learning testing showed the iterative structural expectation maximization (SEM) as the best performing algorithm, above the dynamic imputation (DI) and entropy-based dynamic imputation methods (EBDI), enhancing in some cases the accuracy of imputations by approximately 50 % in R2, RMSE, NRMSE, and logarithmic loss values. These findings can impact how data on water quality is being processed and studied, thus, opening the door for more reliable water management strategies that better inform public health decisions.

Characterization of phosphate solubilizing bacteria in the sediments of eutrophic lakes and their potential for cyanobacterial recruitment

Microbes may induce endogenous phosphorus (P) migration from lacustrine sediment. This study focused on the role of phosphate-solubilizing bacteria (PSB) disturbance in affecting the sediment P release and further contributing to cyanobacterial recruitment in Meiliang Bay, Lake Taihu. Gluconic acid was the main mechanism of phosphate solubilizing by PSB. The dominant PSB (Burkholderia) isolated from eutrophic lake sediments was used as a representative to investigate the effects of disturbance on endogenous P release using diffusive gradients in thin films (DGT) and high-resolution dialysis (HR-Peeper). The results show that soluble reactive phosphorus (SRP) and iron (Fe (II)) concentrations could reach 0.51 mg L-1 and 33.56 mg L-1 in pore water, respectively. And the sediment DGT-P and DGT-Fe were relatively reduced by PSB. Subsequent the chlorophyll a (Chl a) concentrations reached peaks of 344.8 μg L-1 in overlying water. The abundance of the dominant PSB (Burkholderia-Caballeronia-Paraburkholderia) were significantly associated with Chl a (P < 0.05) and algal effective state phosphorus (AAP) (P < 0.05), respectively. PSB mainly regulates AAP leaching to pore water and then diffusing across the sediment-water interface to the overlying water, producing the effect of cyanobacteria recruitment. The results provide new insights into early management of cyanobacterial resuscitation in a large eutrophic lake.

Changes in microcystin concentration in Lake Taihu, 13 years (2007-2020) after the 2007 drinking water crisis

Since the 2007 water crisis occurred in Lake Taihu, substantial measures have been taken to restore the lake. This study evaluates the effectiveness of these restoration activities. We examined the physicochemical parameters and the distribution of microcystin and Microcystis in both the water column and sediment during the bloom period of May 2020 to October 2020. The mean value of extracellular and intracellular microcystin content was 0.12 μg L-1 and 16.26 μg L-1, respectively. The mean value of microcystin in sediment was 172.02 ng g-1 and peaked in August. The concentration in the water and sediment was significantly lower than the historical average concentration. The abundance of toxigenic Microcystis and total Microcystis in the water column ranged from 2.61 × 102 to 2.25 × 109 copies·L-1 and 8.28 × 105 to 2.76 × 109 copies·L-1, respectively. The proportion of toxic Microcystis in the sediment ranging from 31.2% to 19.12%. The highest and lowest region was Meiliang Bay and Grass-algae type zone, respectively. The copy number of the 16S rRNA gene was 1-4 orders of magnitude higher than that of mcyA gene in populations of Microcystis, indicating that non-toxic Microcystis was the dominant form in the majority of the lake. The abundance of toxic Microcystis in the water column was positively correlated with total phosphorus, PO43--P and pH, while the water temperature played distinct role to the distribution of toxic Microcystis in sediment. Our research indicated phosphorus remains a key factor influencing the toxic Microcystis and microcystins in the water column. pH played distinct roles in the distribution of microcystins in sediment and water column. The increasing water temperature is a threat. Explicit management actions and policies, which take into account nutrient concentrations, pH, and increasing temperatures, are necessary to understand and control the distribution of microcystin and Microcystis in Lake Taihu.

Fundamental alteration of cellular biochemicals from attached microalgae onto palm kernel expeller waste upon optimizing the growth environment in forming adhesion complex

Changing the growth environment for microalgae can overall lead to the fundamental alteration in cellular biochemicals whilst attaching onto palm kernel expeller (PKE) waste to form adhesion complex in easing harvesting at stationary growth phase. This study had initially optimized the PKE dosage, light intensity and photoperiod in maximizing the attached microalgal productivity being attained at 0.72 g/g day. Lipid content increased progressively from pH 3 to pH 11, with the highest value observed at pH 11. Meanwhile, in terms of protein and carbohydrate contents, the highest values were obtained by cultivation medium of pH 5 with 9.92 g and 17.72 g, respectively followed by pH 7 with 9.16 g and 16.36 g, respectively. Moreover, the findings also suggested that the low pH mediums utilized polar interactions in the formation of complexes between PKE and microalgae, whereas at higher pH levels, the non-polar interactions became more significant. The work of attachment was thermodynamically favourable towards the attachment formation with values greater than zero which was also aligned with the microscopic surface topography, i.e., revealing a clustering pattern of microalgae colonizing the PKE surface. These findings contribute to comprehensive understanding of optimizing growth condition and harvesting strategy of attached microalgae in attaining the cellular biochemical components, facilitating the development of efficient and sustainable bioresource utilization.

Effect of butachlor on Microcystis aeruginosa: Cellular and molecular mechanisms of toxicity

The rapid development of agriculture increases the release of butachlor into aquatic environments. As a dominant species causing cyanobacterial blooms, Microcystis aeruginosa (M. aeruginosa) can produce microcystin and poses threats to aquatic ecosystems and human health. However, the impact of butachlor on M. aeruginosa remains unclarified. Therefore, the physiochemical responses of M. aeruginosa to butachlor were investigated, and the relevant underlying molecular mechanism was highlighted. There were no significant changes (P > 0.05) in the growth and physiology of M. aeruginosa at the low concentrations of butachlor (0-0.1 mg/L), which evidenced a high level of butachlor tolerance in Microcystis aeruginosa. For the high concentrations of butachlor (4-30 mg/L), the inhibition of photosynthetic activity, disruption of cell ultrastructure, and oxidative stress were dominant toxic effects on M. aeruginosa. Additionally, the impaired cellular integrity and lipid peroxidation may be attributed to the substantial elevations of extracellular microcystin-LR concentration. Downregulation of genes associated with photosynthesis, energy metabolism, and oxidative stress was inferred to be responsible for the growth suppression of M. aeruginosa in 30 mg/L butachlor treatment. The upregulation of gene sets involved in nitrogen metabolism may illustrate the specific effort to sustain the steady concentration of intracellular microcystin-LR. These findings dissect the response mechanism of M. aeruginosa to butachlor toxicity and provide valuable reference for the evaluation of potential risk caused by butachlor in aquatic environments.

Effects of overwintering cyanobacteria on phosphorus and iron regeneration across the sediment-water interface: A pilot simulation experiment

Cyanobacterial blooms are a major environmental problem in eutrophic reservoirs in China. Algal cells can migrate to the sediment surface in winter and maintain biological activity, which could further affect the cycling process of sediment phosphorus (P) and iron (Fe). In this study, a pilot simulation experiment was conducted to investigate the effect of overwintering cyanobacteria (Owc) on P and Fe regeneration across the sediment-water interface (SWI). Owc esterase activity ranged from 16.4 to 26.6 nmol (FDA)/(L·h), with a fluctuating increasing trend within the incubation time. Compared with the control (no Owc), Owc treatment increased the redox potential value (Eh) at the SWI but slightly decreased the pH during the first stage of this experiment (0-24 d); however, the Eh at the SWI under Owc treatment decreased to 50.9 % of that of the control on day 90. The Fe(II) could rapidly oxidized to Fe (oxyhydro)oxides and combine with phosphate in high Eh environments, and Owc inhibited P and Fe release at the SWI within 24 days; however, the continuous decrease in Eh resulted in the reduction of Fe(III). Thus, the Fe concentration measured via diffusive gradients in thin films in the Owc-treated interstitial water gradually increased to 1.92 times that of the control, promoting the release of Fe and P across the SWI. For 13 days after Owc addition, the amount of mobile P in the sediment was significantly higher than that in the control, and it gradually decreased from day 24 to 90, with the lowest being approximately 74.1 % of the amount in the control. The reactive Fe concentration in the sediment showed a similar variation trend. These results indicate that mobile P and reactive Fe in the sediment could be the main sources of regeneration across the SWI in the presence of Owc.

Application and validation of a biotic ligand model for calculating acute toxicity of lead to Moina dubia in lakes of Hanoi, Vietnam

It is increasingly being recognized that biotic ligand models (BLMs) can successfully predict the toxicity of divalent metals toward aquatic biota applied to temperate freshwater ecosystems. However, studies on the eutrophic lakes in tropical regions toward native tropical organisms, including Moina, are relatively limited. In this study, Moina dubia, the native organism of the Hanoi eutrophic urban lakes, were used in toxicological studies of lead (Pb); 24-h EC₅₀ value of Pb was 523.19 µg/L under optimal living conditions for M. dubia in the laboratory. The constant binding of Pb²⁺ on M. dubia surface sites (log K_PbBL = 2.38) was significantly low. Other stability constants were obtained under experiments as logK_CaBL = 2.48, logK_MgBL = 2.80, logK_NaBL = 2.35, logK_KBL = 2.49, and logK_HBL = 3.026. A BLM was developed to calculate the acute toxicity (EC₅₀-24 h) of lead on M. dubia based on the condition of the urban lakes of Hanoi. Validation with toxicity data in synthetic medium showed a coefficient determination of 79.16% and a mean absolute percentage error (MAPE) of 10.2%, while the validation with the toxicity data with natural water medium from 11 Hanoi lakes showed a coefficient determination of 73.7% and a MAPE of 13.66%. The BLM worked well with water at a pH of 7.0 to 8.0, but failed with water at a pH above 8.0. Eutrophic conditions proved to have a significant effect on the toxicity of lead on local zooplankton.

The proliferation rule of Microcystis aeruginosa under different initial pH conditions and its influence on the pH value of the environment

This study investigated the characteristics of the proliferation process of Microcystis aeruginosa and its changes to environmental pH values under different initial pH values and different initial inoculation densities. The results showed that although the initial pH value or the initial inoculation density was different, the pH values of the culture systems fluctuated up and down throughout the proliferation of M. aeruginosa, both on a daily and hourly time scale, and then tended to stabilize around the same value of 10.0 at the end of proliferation. The optimal pH value for the proliferation of M. aeruginosa was 9.55. This study creatively proposes that the period when the environmental pH value starts to rise rapidly toward 9.0 could be selected as an early warning period for a cyanobacterial outbreak, and the environmental pH value could be adjusted to below 8.0 to delay the outbreak. These results provide a scientific basis for further understanding the mechanism of cyanobacterial blooms and formulating pH-based control strategies.

Effects of light and water disturbance on the growth of Microcystis aeruginosa and the release of algal toxins

Eutrophication of water constitutes a serious threat to global water quality. Light intensity and water disturbance are important factors affecting the growth of algae and the release of algal toxins. In this study, algal growth indicators, algal enzyme systems, and algal toxin release in Microcystis aeruginosa under different light intensities and water disturbances were determined. The results showed that 2500 lx and 120 rpm were the optimal conditions for the growth of M. aeruginosa. The growth of algal cells was inhibited by high light intensity and high water disturbance. However, the optimal conditions for algal growth were not favorable conditions for the release of algal toxin. The highest concentration of microcystin-LR (MC-LR), observed at 4500 lx and 80 rpm, was 198.1 μg/L, whereas the highest single cell toxin production reached up to 10.49 × 10^-9  μg/cell at 7000 lx and 120 rpm. Redundancy analysis results showed that the concentration of MC-LR was positively correlated with algal cell density and antioxidant enzyme activities (superoxide dismutase, catalase, peroxidase, and malondialdehyde [MDA]) and negatively correlated with the total nitrogen and total phosphorus consumption rates and MDA. Single cell toxin production was negatively correlated with algal cell density and antioxidant enzyme activity but positively correlated with MDA content. PRACTITIONER POINTS: There was an optimal water disturbance condition for algae growth affected by the light intensity. Optimal conditions for algae cell growth are not necessarily the optimal conditions for algal toxin release. Enzyme indicators have correlation with the release of algae toxins and the growth of algae cells.

Anthocyanins, Phenolic Compounds, and Antioxidants from Extractions of Six Eucalyptus Species

The leaves of Eucalyptus have multiple biological activities such as antimicrobial, antiseptic, antioxidant, and antifungal. A Soxhlet extraction, SLE, and HD were used to obtain extracts from the leaves of six Eucalyptus species, E. globulus, E. oblicua, E. pavaflora, E. camaldulensis, E. viminalis, and E. nitens, and to study their antioxidant capacity. Solvents such as acetone, dichloromethane, ethanol, hexane, methanol, and water were used to study how polarity influences extraction yields. The SLE method achieved higher or similar yields, depending on the species and its composition, than the Soxlet method at a temperature of 50 °C. The highest yields were obtained with E. viminalis with methanol (42.5 wt.%), the highest phenolic content was obtained with E. nitens with methanol (124.17 mg GAE/g of extract), and the highest anthocyanin levels obtained were with E. nitens with hexane (5.05 mg CC/g of extract). E. nitens obtained almost five times more phenolic content than E. globulus; therefore, it is the most promising species. The high content of the compounds analysed confirm the good potential of these species to obtain value-added compounds. Our results demonstrate that the differences in the extract contents depend on the polarity of the solvents used. In addition, the use of these species will reduce the residue in the forest, which is greatly beneficial.

Remote Detection of Cyanobacterial Blooms and Chlorophyll-a Analysis in a Eutrophic Reservoir Using Sentinel-2

Harmful cyanobacterial blooms have been one of the most challenging ecological problems faced by freshwater bodies for more than a century. The use of satellite images as a tool to analyze these blooms is an innovative technology that will facilitate water governance and help develop measures to guarantee water security. To assess the viability of Sentinel-2 for identifying cyanobacterial blooms and chlorophyl-a, different bands of the Sentinel-2 satellite were considered, and those most consistent with cyanobacteria analysis were analyzed. This analysis was supplemented by an assessment of different indices and their respective correlations with the field data. The indices assessed were the following: Normalized Difference Water Index (NDWI), Normalized Differences Vegetation Index (NDVI), green Normalized Difference Vegetation Index (gNDVI), Normalized Soil Moisture Index (NSMI), and Toming’s Index. The green band (B3) obtained the best correlating results for both chlorophyll (R2 = 0.678) and cyanobacteria (R2 = 0.931). The study by bands of cyanobacteria composition can be a powerful tool for assessing the physiology of strains. NDWI gave an R2 value of 0.849 for the downstream point with the concentration of cyanobacteria. Toming’s Index obtained a high R2 of 0.859 with chlorophyll-a and 0.721 for the concentration of cyanobacteria. Notable differences in correlation for the upstream and downstream points were obtained with the indices. These results show that Sentinel-2 will be a valuable tool for lake monitoring and research, especially considering that the data will be routinely available for many years and the images will be frequent and free.

Harvesting freshwater algae with tannins from the bark of forest species: Comparison of methods and pelletization of the biomass obtained

Toxic cyanobacteria growth rates have increased in recent decades due to climate change and human activities. Microalgae, with their ability to produce a large amount of biomass, are considered as a source of energy that can be used to produce biofuels. The aim of this study is to test four different microalgae harvesting methods (sedimentation, coagulation-flocculation, pH variation, and centrifugation) in order to find which is best suited to the A Baxe reservoir, which has been suffering from cyanobacterial blooms in recent years. Centrifugation proved the most efficient method (85.74%-1790 RCF), but it can induce cell rupture. Natural sedimentation and pH variation obtained similar results at 49.36% and 49.02% respectively. Although all four methods have advantages, our results reveal that coagulation-flocculation, using 10 mg/L of Pinus pinaster, results in a removal efficiency of 68.10%, making it the most suitable method, though with 20 mg/L the performance was lower (66.03%). To minimise environmental waste, the microalgae removed were then transformed into pellets to be used as biofuel, with a higher heating value (HHV) of 21,196.96 ± 1602.33 kJ/kg. The pellets obtained from the microalgae residue did not meet all the requirements for use as biofuels, but microalgae biomass could be mixed with other sources and therefore looks like a promising option for the future.