Cell surfaces properties of and were characterised with spectroscopic, chemical and physicochemical methods. According to previous studies, , a picocyanobacteria, is more sensitive to copper than the other phytoplanktonic species such as a chlorophycea. An experimental study was carried out to determine the cell wall characteristics of both species. The cell surface of . presented a lower hydrophobic character and a more negative surface charge over a larger pH range than for . , according to hydrophobicity and zeta potentials measurements. By combining infrared spectroscopy data and potentiometric titrations, the total concentration of functional groups determined for . (1.60 × 10 mol/g), as well as the number of carboxyl groups, was higher than for the . ones (0.22 × 10 mol/g). The differences in surface properties, as shown by chemical, physicochemical and spectroscopic measurements would justify the differences in sensitivities to copper ions up-take between the two specimens.
Algal blooms are a seasonal problem in eutrophic water bodies, and novel approaches to algal removal are required. The effect of hydrodynamic cavitation (HC) on the removal of was investigated using a laboratory scale device. Samples treated by HC were subsequently grown under illuminated culture conditions. The results demonstrated that a short treatment with HC could effectively settle naturally growing without breaking cells. Algal cell density and chlorophyll-a of a sample treated for 10 min were significantly decreased by 88% andv 94%, respectively, after 3 days culture. Various HC operating parameters were investigated, showing that inhibition of growth mainly depended on treatment time and pump pressure. Electron microscopy confirmed that sedimentation of algae was attributable to the disruption of intracellular gas vesicles. Damage to the photosynthetic apparatus also contributed to the inhibition of algal growth. Free radicals produced by the cavitation process could be as an indirect indicator of the intensity of HC treatment, although they inflicted minimal damage on the algae. In conclusion, we suggest that HC represents a potentially highly effective and sustainable approach to the removal of algae from water systems.
A cheap and biodegradable modifier, cationic starch (CS), was used to turn local soils into effective flocculants for ( ) removal. The isoelectric point of soil particles was remarkably increased from pH 0.5 to 11.8 after modification with CS, which made CS modified soil particles positively charged and obtain algal flocculation ability. At the soil concentration of 100 mg/L, when the CS modifier was 10 mg/L, 86% of cells were removed within 30 min. Lower or higher CS dosage led to limited algal removal. About 71% and 45% of cells were removed within 30 min when CS was 5 mg/L and 80 mg/L, respectively. This is because only part of algal cells combined with CS modified soil particles through charge neutralization at low dosage, while flocs formed at high CS dosage were positively charged which prevents further aggregation among the flocs. The floc stability was quantified by a floc breakage index under applied shear force. Algal flocs formed at acid and alkaline conditions were more prone to be broken than those at the neutral condition. The cost and biodegradability concerns may be largely reduced through the use of CS modified local soils. For field applications, other practical issues (e.g., re-suspension) should be further studied by jointly using other methods.
The performance of UV-activated persulfate (UV/PS) technology as preoxidation process to enhance removal by subsequent coagulation-sedimentation was firstly evaluated. The results demonstrate that UV/PS preoxidation could successfully promote coagulation of algae cells through the effective neutralization of zeta potential, which was caused by the changes of cell morphology, size distribution and surface properties after simultaneous UV irradiation and formed reactive species (i.e. SO and HO ) oxidation. Since excessive oxidation would cause cell rupture along with the release of organics, which could deteriorate coagulation efficiency, optimal PS dose (60 mg/L) and UV dose (375 mJ/cm ) were proposed to exist in this study. The concentrations of extracellular algal organic matter (AOM) sharply increased by 48.2% during the preoxidation period, while gradually decreased in the following coagulation and sedimentation. Most of the concerned disinfection by-products (DBPs) monotonically decreased or followed fluctuant reduction with increasing PS doses, whereas the trichloromethane, trichloroacetic acid and dichloroacetonitrile persistently increased, which was inferred to be related to the variation of AOM. This study suggests that UV/PS might be a potential pretreatment process to assist coagulation on the removal of algae.
The enantioselective effects of chiral herbicides on aquatic organisms have received increasing attention. As one kind of freshwater algae responsible for most algal blooms, Microcystis aeruginosa can produce hepatotoxic microcystin and cause serious health concerns for drinking water. Thus, the effects of chiral herbicides on M. aeruginosa are of vital significance but poorly understood, especially as the structures of chiral herbicides become more complex. In this study, the enantioselective effects of four metolachlor enantiomers based on carbon center and axis chirality on M. aeruginosa were investigated for the first time at an enantiomeric level. The results of the investigation into algal growth inhibition, chlorophyll a content, and cell integrity indicated that (S)-metolachlor [(S)-Met] was significantly more toxic than any other isomer. The toxicity ranking of different enantiomers at the highest concentration (15 mg/L) against M. aeruginosa was (S)-Met > (alpha R,1'S)-Met > (alpha S,1'S)-Met > (alpha S,1'R)-Met > (alpha R,1'R)-Met, with (alpha S,1'S)-Met and (alpha R,1'S)-Met displaying a synergistic effect. Additionally, the Fe distribution in M. aeruginosa presented distinct enantioselectivity, which may contribute to the enantioselective toxicity of metolachlor. Furthermore, metolachlor upregulated the expression of genes mcyD and mcyH in an enantioselective manner, indicating that this herbicide can potentially promote the synthesis and efflux of microcystin, thus aggravating agricultural water contamination to different extents. Overall, this study will help to understand the ecotoxicity of metolachlor at a deeper level and provide theoretical insights into the enantioselective behaviors of metolachlor.
Cyanobacteria blooms in source waters have become a worldwide issue for drinking water production. UV-activated persulfate (UV/PS) technology was firstly applied to remove cultivated ( ) in bench scale. The presence of persulfate significantly enhanced both cytoclasis and algal organic matter mineralization compared with UV-C inactivation alone. Around 98.2% of algal cells were removed after UV/PS process treatment for 2 h at a dosage of PS being 1500 mg/L (approximately 6 mM). Both sulfate and hydroxyl radicals were proven to contribute to the removal of algae and the loss of cell integrity. The cultivated in death growth phase were found to be more vulnerable to UV/PS treatment than those growing in log phase, thus a significant lower dosage of PS is needed to achieve the desired removal efficiency. This study suggested a novel application of UV/PS process in the removal of algae in source waters due to the high degradation efficiency of both algal cells and their derived organic matter.
This is the first study investigating the toxicity of nanoparticles (NPs) to algae in the presence of dissolved organic matter (DOM). Suwannee river fulvic acid (SRFA), a type of DOM, could significantly increase the toxicity of CuO NPs to prokaryotic alga Microcystis aeruginosa. Internalization of CuO NPs was observed for the first time in the intact algal cells using high resolution transmission electron microscopy (HRTEM), and the cell uptake was enhanced by SRFA. A fast Fourier transformation (FFT)/inversed FFT (IFFT) process revealed that a main form of intracellular NPs was Cu2O, and an intracellular environment may reduce CuO into Cu2O. The internalization behavior alone did not seem to pose a hazard to membrane integrity as shown from the flow cytometry data. Elevated CuO nanotoxicity by SRFA was related to a combination of a lesser degree of aggregation, higher Cu2+ release, and enhanced internalization of CuO NPs.
The frequent outbreaks of cyanobacteria bloom are often accompanied by the generation and release of reduced phosphorus species (e.g., phosphine), which raises interesting questions regarding their potential algae-related effects. To clarify the physiological and biochemical responses of cyanobacteria to phosphine, was treated with different concentrations of phosphine. Net photosynthetic rate, total antioxidant capacity (T-AOC), catalase (CAT) activity, and the concentrations of chlorophyll , carotenoid and total protein were investigated and scanning electron microscopy (SEM) was conducted to elucidate the physiological and biochemical responses of to phosphine. The results showed that phosphine was beneficial to the growth of algal cells after acclimatized to the treatment of phosphine, and treatment with 2.48 × 10 mg/L phosphine had a greater positive effect on the growth and reproduction of than 7.51 × 10 mg/L phosphine, in which most algal cells were smooth and flat on day 16. Treatment with the high concentration of phosphine (7.51 × 10 mg/L) for 16 d reduced T-AOC, CAT activity, net photosynthetic rate, and the concentrations of chlorophyll , carotenoid and total protein of to the minimums, resulting in the lysis and death of cells, which indicates phosphine has a toxic effect on the growth of algal cells. However, the high concentration of phosphine (7.51 × 10 mg/L) had a greater positive effect on the growth of cells than the lower two (7.51 × 10 mg/L and 2.48 × 10 mg/L) from 3 d to 12 d. Our findings provide insight into how phosphine potentially affects the growth of cells and the important roles of elevated phosphine on the outbreak of cyanobacteria bloom.
Combined toxicity of spiramycin and amoxicillin was tested in The respective 50% effective concentrations (EC ) expressed in toxic unit (TU) values were 1.25 and 1.83 for spiramycin and amoxicillin mixed at 1:7 and 1:1, suggesting an antagonistic interaction at the median effect level. Deviations from the prediction of concentration addition (CA) and independent action (IA) models further indicated that combined toxicity of two antibiotics mixed at 1:1 varied from synergism to antagonism with increasing test concentration. Both the EC of 0.86 (in TU value) and the deviation from two models manifested a synergistic interaction between spiramycin and amoxicillin mixed at 7:1. At an environmentally relevant concentration of 800 ng L , combined effect of mixed antibiotics on algal growth changed from stimulation to inhibition with the increasing proportion of higher toxic component (spiramycin). Chlorophyll-a content and expression levels of , , and varied in a similar manner as growth rate, suggesting a correlation between algal growth and photosynthesis under exposure to mixed antibiotics. The stimulation of microcystin-production by mixed antibiotics was related with the elevated expression of . The mixture of two target antibiotics with low proportion of spiramycin (<50%) could increase the harm of to aquatic environments by stimulating algal growth and production and release of microcystin-LR at their current contamination levels.
An important objective in understanding harmful phytoplankton blooms is determining how environmental factors influence the toxicity of bloom-forming species. We examined how nutrients and grazers (dreissenid mussels) affect the production of microcystin (a liver toxin) by the cyanobacterium , via a combination of field and laboratory experiments, and field observations in Lake Erie. The field experiment revealed no effect of mussel density on microcystin quota (particulate microcystin per unit biomass). In contrast, in both field and laboratory experiments, nitrogen-limited conditions led to substantially reduced microcystin quota relative to phosphorus-limited or nutrient-saturated conditions. In the field experiment, microcystin per unit of gene was strongly reduced under nitrogen-limited conditions, indicating a phenotypic response. Results from a seasonal survey in the western basin of Lake Erie revealed a similar negative influence of nitrogen limitation (as indexed by nitrate concentration) on microcystin quota. Our results are consistent with stoichiometric considerations in that the cell quota of a nitrogen-rich secondary metabolite, microcystin, was reduced disproportionately under nitrogen limitation.