The effect of oxytetracycline on physiological and enzymatic defense responses in aquatic plant species Egeria densa,Azolla caroliniana,and Taxiphyllum barbieri

Oxytetracycline is an antibiotic widely employed in aquaculture to control and treat bacterial diseases of fish. Due to ineffective wastewater treatment, antibiotic residues from fish ponds are directly released into surface and groundwater affecting the environment. The Green Liver System® is a sustainable and cost-effective water treatment based on the ability of aquatic plants to biotransformation xenobiotics. To expand the application range of this system, Egeria densa, Azolla caroliniana, and Taxiphyllum barbieri were tested in response to oxytetracycline exposure. The aquatic plants were exposed to 0.5, 2.0, 5.0, and 25 μg/L oxytetracycline (n = 4) for 24 h in order to analyze the physiological responses (photosynthetic pigment contents and hydrogen peroxide formation -- H₂O₂), the biotransformation process (activity of glutathione S-transferase), and the antioxidant defense (glutathione reductase; peroxidase; and catalase) responses. There were no statistical differences in the photosynthetic pigment contents and H₂O₂ level between the treatment and control groups in the three aquatic plant species. It can be concluded that oxytetracycline does not provoke physiological damage to the tested species within 24 h of exposure. Nevertheless, the antioxidant defense mechanism was activated. Peroxidase and catalase were the most prominent antioxidant enzymes in the three plant species, whereas glutathione S-transferase activity was significantly increased in A. caroliniana and T. barbieri.     

Physiological responses of Cladophora glomerata to cyanotoxins: a potential new phytoremediation species for the Green Liver Systems

Due to increased pollution of potable water sources as a consequence of eutrophication and anthropogenic xenobiotics, sustainable water purification is an essential concern. Therefore, the Green Liver System, a natural, economic and sustainable water purification system employing the biotransformation capabilities of aquatic plants, was developed. To expand the capacities and applications of this system, new aquatic plants are continually evaluated for their potential to remediate various aquatic pollutants. In this study, the potential of Cladophora glomerata to internalize cyanotoxins, microcystins (MCs) and anatoxin-a, and consequently its ability to cope with the subsequent oxidative stress associated with toxin-uptake were investigated. C. glomerata was able to take up all three of the tested MC congeners as well as anatoxin-a, similarly to previous toxin internalizations reported for aquatic plants such as Ceratophyllum demersum, Myriophyllum spicatum and Hydrilla versiculata. The antioxidative stress defense of C. glomerata proved to efficiently endure the toxin-uptake with no adverse effects. Subsequently, the uptake potential of C. glomerata was investigated at lab-scale by exposure to the three MC congeners and anatoxin-a collectively. After a period of seven days, 95–97% of the MCs and 100% of anatoxin-a were removed from the exposure media. C. glomerata therefore, is a suitable candidate to be incorporated in future Green Liver Systems.     

Rise of toxic cyanobacterial blooms in temperate freshwater lakes: causes,correlations and possible countermeasures

The progressive degradation of surface freshwater quality due to the mass proliferation of toxic cyanobacterial blooms is of growing global concern. The occurrence of cyanobacterial blooms is not a new phenomenon. However, a global increase in the frequency, duration, and distribution of toxic cyanobacterial blooms could be observed in the past decades. Evidence suggests that this trend might be attributed to a complex interplay of direct and indirect anthropogenic influences. The underlying causes and interrelations for this development have not been fully clarified. Nonetheless, all evidence points to the fact that mitigation of toxic cyanobacterial blooms will be a key challenge of the twenty-first century. This review addresses the underlying causes for the increased incidence of toxic cyanobacteria in temperate freshwater lakes and attempts to reveal possible reciprocities between bloom promoting factors. Selected approaches for the prevention of toxic cyanobacterial blooms as well as the mitigation of their potential negative impacts on humans will be presented.     

Mycoremediation of diclofenac using Mucor hiemalis

Diclofenac (DCF) is a pharmaceutical drug widely found in the aquatic environment, where it represents a persistent, anthropogenic hazard to all biota. Owing to the reported inefficiency of water treatment strategies to remove pharmaceuticals, the present study aimed to investigate the ability of the aquatic fungus Mucor hiemalis to take up and accumulate DCF. Cultures of M. hiemalis were exposed to varying concentrations of DCF (10, 25 and 50 µg/L) over a period of 144 h. In the presence of M. hiemalis, DCF concentrations in the media decreased by 95% within 24 h. This early removal was most likely due to extracellular metabolism of DCF, as low proportions of the pharmaceutical were found in the mycelium of the fungus, thereby excluding bioaccumulation as the main mode of removal. However, adsorption of DCF onto the surface of the M. hiemalis pellets cannot be excluded. Our study provides the first report of DCF remediation using M. hiemalis and is the first successful step towards a feasible and inexpensive bioremediation technique for DCF.     

Temporal variability of zooplankton biomass (ATP content and dry weight) in the St. Lawrence Estuary: Advective phenomena during neap tide

In order to assess the temporal variability of living zooplankton in a tidal estuary, the ATP content and dry weight of mixed zooplankton populations (mainly copepods) were measured during a period of 175 h at an anchor station in the Upper St. Lawrence Estuary. Vertical tows were made every 30 min. Hourly vertical profiles of the current speed and direction, temperature and salinity were also obtained during the experiment. A strong tidal influence was found in all series. Maxima and minima of the ATP content (living biomass) and the dry weight (total biomass) were correlated with low and high water slacks. The serial autocorrelation and cross-correlation showed, in both series a 12 to 13-h cycle, and the ATP:dry weight ratio showed a significant 24-h cycle. The cross-correlation with the Kendall τ was used to detect the relationship between biological components and physical indices (stratification and Ri). It is suggested that the proportion of living zooplankton biomass in the Upper St. Lawrence Estuary is most likely the result of a combination of diurnal migration and longitudinal advection.