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Zero-valent nano-iron particles (nZVI) are increasingly present in freshwater aquatic environments due to their numerous applications in environmental remediation. However, despite the broad benefits associated with the use and development of nZVI nanoparticles, the potential risks of introducing them into the aquatic environment need to be considered. Special attention should be focused on primary producer organisms, the basal trophic level, whose impact affects the rest of the food web. Although there are numerous acute studies on the acute effects of these nanoparticles on photosynthetic primary producers, few studies focus on long-term exposures. The present study aimed at assessing the effects of nZVI on growth rate, photosynthesis activity, and reactive oxygen activity (ROS) on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa. Moreover, microcystin production was also evaluated. These parameters were assessed on both organisms singly exposed to 72 h-effective nZVI concentration for 10% maximal response for 28 days. The results showed that the cell growth rate of S. armatus was initially significantly altered and progressively reached control-like values at 28 days post-exposure, while M. aeruginosa did not show any significant difference concerning control values at any time. In both strains dark respiration (R) increased, unlike net photosynthesis (Pn), while gross photosynthesis (Pg) only slightly increased at 7 days of exposure and then became equal to control values at 28 days of exposure. The nZVI nanoparticles generated ROS progressively during the 28 days of exposure in both strains, although their formation was significantly higher on green algae than on cyanobacteria. These data can provide additional information to further investigate the potential risks of nZVI and ultimately help decision-makers make better informed decisions regarding the use of nZVI for environmental remediation. [Display omitted] • Short-term exposures to nZVI decreased freshwater microalgae growth. • nZVI-IC 10 did not affect the M. aeruginosa exponential growth rate at 28-d. • The S. armatus growth recovered after nZVI-IC 10 7-d exposure. • The initial effect on photosynthetic activity decreased after 28 days of exposure. • ROS increased in both species during 28 days of exposure to nZVI-IC 10. [ABSTRACT FROM AUTHOR]

The use of allelochemicals has been proved an environmentally friendly and promising method to control harmful algal blooms. This study was conducted to explore the application potential of Ailanthus altissima ( A. altissima ) extracts in Microcystis aeruginosa ( M. aeruginosa ) control for the first time. Four treatments with A. altissima extractions (25 mg L −1 , 50 mg L −1 , 100 mg L −1 , and 200 mg L −1 respectively) and a control group were built to investigate the effects of A. altissima on the growth, cellular microstructure and cell viability, physiological changes, and release of extracellular matters. Results showed that the cell density of M. aeruginosa was effectively inhibited by A. altissima extract, and the inhibition rates were dose-dependent within 5 d. Especially for the treatment with 200 mg L −1 of extract, the inhibitory rates remains above 90% after 5 d exposure. In addition, A. altissima effectively decreased the amount of extracellular cyanotoxin microcystins and destroyed the photosynthesis-related structure of algae cell during the experimental period. The results demonstrated the A. altissima extracts can be used as an effective and safe algicide to control algal blooms. However, it must be noted that specific compounds responsible for algicidal effect should be isolated and identified to explore inhibition mechanism of A. altissima in future study. [ABSTRACT FROM AUTHOR]

Removals of extracellular organic matter (EOM) derived from cyanobacterium M. aeruginosa and humic acid (HA) in single-component and bi-component systems and the interactions during the coagulation-ultrafiltration (C–UF) process were investigated in this study. In a single-component system, only 23% EOM could be removed by alum at dose as high as 6 mg/L, which induced serious membrane fouling in the following UF process. Interestingly, higher EOM removal efficiency was achieved (increase by about 20%) with the existence of HA and EOM-HA achieved less decline of permeate flux compared with individual EOM C–UF process. Zeta potential and Fourier transform infrared spectroscopy analysis indicated that the interactions of HA and EOM can strengthen charge neutralization and reduce CH 2 chemical bonds, which had a positive effect on the coagulation process. In addition, EOM-HA floc had a more open and looser structure than EOM floc, which was more favorable in the UF process. The extended Derjaguin–Landau–Verwey–Overbeek theory indicated that the acid–base interaction energy was mainly reduced, thereby alleviating membrane fouling. The study showed this beneficial interaction between the HA and EOM would enhance the EOM removal efficacy by coagulation and release the membrane fouling caused by EOM. Image 1 • Co-existence of EOM and HA improved the EOM and HA removal efficiency. • Charge neutralization ability was strengthened and CH 2 bonds was reduced. • The existence of HA reduced the membrane fouling of EOM. • EOM-HA floc had a more open and looser structure than EOM floc. • The interactions of HA and EOM mainly reduced the acid–base interaction energy. [ABSTRACT FROM AUTHOR]

The frequent outbreaks of cyanobacterial blooms which caused serious societal and economic loss have become a worldwide problem. Interactions between toxic cyanobacteria and heterotrophic bacteria competitors play a pivotal role in the formation of toxic cyanobacterial bloom, but the underlying mechanisms of interactions between them await further research. The antagonist activity of Pseudomonas grimontii (P.grimontii) was confirmed by reduction in chlorophyll a concentration of Microcystis aeruginosa (M. aeruginosa) in an infected culture for a 7d period. The initial concentration of P.grimontii affected the M. aeruginosa activity significantly. When the 10% (V/V) concentration of P.grimontii A01 and P.grimontii A14 cultures were infected, the reduction of M. aeruginosa reached to 91.81% and 78.25% after 7 days, respectively. While a 0.1% (v/v) concentration of P.grimontii A01 and P.grimontii A14 cultures were infected, the M. aeruginosa increased 31.13% and 16.67 % occurred, respectively. The content of reactive oxygen species (ROS) and malondialdehyde (MDA) increased with increasing of P.grimontii fermentation liquid, indicating the M. aeruginosa underwent oxidative stress. Using matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) imaging mass spectrometry (IMS) profiling of co-cultures of M. aeruginosa and its antagonist P.grimontii , we revealed novel interspecies allelopathic interactions and compete molecule. We showed the spatial secondary metabolites may mediate the interactions in which P.grimontii inhibits growth of M. aeruginosa. Additionally, we revealed how M. aeruginosa feedback to the P.grimontii , which stimulates secondary metabolites such as [D-Asp3]-microcystin-LR released by M. aeruginosa. IMS method highlights the significance of allelopathic interactions between a widely distributed toxic cyanobacteria and its bacteria competitors. • Molecular-specific mass spectrometry imaging in situ metabolomics on cyanobacteria. • Investigation of M. aeruginosa - P. grimontii interaction effects. • High spatial resolution elucidation of metabolites distribution in specific localizations. [ABSTRACT FROM AUTHOR]