Toxicological effects of cypermethrin to marine phytoplankton in a co-culture system under laboratory conditions

Oxidative stress in Arthrospira platensis by two organophosphate pesticides

Although it is known that organophosphate insecticides are harmfull to aquatic ecosystems, oxidative damages caused by Dimethoate and Chlorpyrifos are not studied on Arthrospira platensis Gomont. In this study, various Chlorpyrifos (0-150 µg mL-1) and Dimethoate (0-250 µg mL-1) concentrations were added to the culture medium in laboratory to evaulate growth rate, chlorophyll-a content and antioxidant parameters of A. platensis. Optical Density (OD560) and chlorophyll-a decreased compared to the control for seven days in both pesticide applications. Superoxide dismutase (SOD) activity increased at 50 µg mL-1 Chlorpyrifos concentration but it decreased at all concentrations. Although Ascorbate peroxidase (APX) and glutathione reductase (GR) activities increased with Chlorpyrifos application, they did not change with Dimethoate application. Malondialdehyde (MDA) amount decreased at 150 µg mL-1 Chlorpyrifos concentration but it increased in Dimethoate application. The H2O2 content were increased in both applications. Proline decreased in 50 and 75 µg mL-1 Chlorpyrifos concentrations and increased at 150 µg mL-1 concentration, while it increased at 25 µg mL-1 Dimethoate concentration. The results were tested at 0.05 significance level. These pesticides inhibit A. platensis growth and chlorophyll-a production and cause oxidative stress. The excessive use may affect the phytoplankton and have negative consequences in the aquatic ecosystem.

Toxicity effects of disinfection byproduct chloroacetic acid to Microcystis aeruginosa: Cytotoxicity and mechanisms

Chlorine-based disinfectants are widely used for disinfection in wastewater treatment. The mechanism of the effects of chlorinated disinfection by-products on cyanobacteria was unclear. Herein, the physiological effects of chloroacetic acid (CAA) on Microcystis aeruginosa (M. aeruginosa), including acute toxicity, oxidative stress, apoptosis, production of microcystin-LR (MC-LR), and the microcystin transportation-related gene mcyH transcript abundance have been investigated. CAA exposure resulted in a significant change in the cell ultrastructure, including thylakoid damage, disappearance of nucleoid, production of gas vacuoles, increase in starch granule, accumulation of lipid droplets, and disruption of cytoplasm membranes. Meanwhile, the apoptosis rate of M. aeruginosa increased with CAA concentration. The production of MC-LR was affected by CAA, and the transcript abundance of mcyH decreased. Our results suggested that CAA poses acute toxicity to M. aeruginosa, and it could cause oxidative damage, stimulate MC-LR production, and damage cell ultrastructure. This study may provide information about the minimum concentration of CAA in the water environment, which is safe for aquatic organisms, especially during the global coronavirus disease 2019 pandemic period.

Effects of suspended particles in the Jinjiang River Estuary on the physiological and biochemical characteristics of Microcystis flos-aquae

The effects of different concentrations (100, 150, 200, 250 mg/L) and different particle sizes (0-75 μm, 75-120 μm, 120-150 μm, 150-500 μm) on the soluble protein content, superoxide dismutase (SOD) and catalase (CAT) activity, malondialdehyde (MDA) content, chlorophyll a (Chla) content, and photosynthetic parameters of Microcystis flos-aquae were studied, and the mechanism of the effect of suspended particulate matter on the physiology and biochemistry of Microcystis flos-aquae was discussed. The results showed that the soluble protein content of Microcystis flos-aquae did not change noticeably after being stressed by suspended particles of different concentrations/diameters. The SOD activity of Microcystis flos-aquae first increased and then decreased with increasing suspended particulate matter concentrations. The SOD activity of Microcystis flos-aquae reached 28.03 U/mL when the concentration of suspended particulate matter was 100 mg/L. The CAT activity of Microcystis flos-aquae increased with increasing concentrations of suspended particles and reached a maximum value of 12.45 U/mg prot in the 250 mg/L concentration group, showing a certain dose effect. Small particles had a more significant effect on SOD, CAT, and MDA in Microcystis flos-aquae than large particles. The larger the concentration was and the smaller the particle size was, the stronger the attenuation of light and the lower the content of Chla. Both the maximum quantum yield of PSII (Fv/Fm) and the potential photosynthetic activity of PSII (Fv/F₀) of Microcystis flos-aquae increased at first and then decreased under different concentrations/sizes of suspended particles. The relative electron transfer rate gradually returned to a normal level over time. There was no significant difference in the initial slope (α) value between the treatment group and the control group, and the maximum photo synthetic rate (ETRmax) and the semilight saturation (I_k) decreased.

Ecotoxicological effects of DBPs on freshwater phytoplankton communities in co-culture systems

Intensive disinfection of wastewater during the COVID-19 pandemic might elevate the generation of toxic disinfection byproducts (DBPs), which has triggered global concerns about their ecological risks to natural aquatic ecosystems. In this study, the toxicity of 17 DBPs typically present in wastewater effluents on three representative microalgae, including Scenedesmus sp. (Chlorophyta), Microcystis aeruginosa (Cyanophyta), and Cyclotella sp. (Bacillariophyta) was investigated. The sensitivities of the three microalgae to DBPs varied greatly from species to species, indicating that DBPs may change the structure of phytoplankton communities. Later, co-cultures of these phytoplankton groups as a proxy of ecological freshwater scenario were conducted to explore the impacts of DBPs on phytoplankton community succession. M. aeruginosa became surprisingly dominant in co-cultures, representing over 50% after dosing with monochloroacetic acid (MCAA, 0.1-10 mg/L). The highest proportion of M. aeruginosa was 70.3% when exposed to 2 mg/L MCAA. Although Scenedesmus sp. dominated in monochloroacetonitrile (MCAN) exposure, M. aeruginosa accounted for no less than 30% even at 40 mg/L MCAN. In this study, DBPs disrupted the original inter-algal relationship in favor of M. aeruginosa, suggesting that DBPs may contribute to the outbreak of cyanobacterial blooms in aquatic ecosystems.

Single and Combined Effects of Cypermethrin and UVR Pre-Exposure in the Microalgae Phaeodactylum Tricornutum

Coastal marine microalgae are exposed to anthropogenic pollutants, including pesticides from aquaculture/agriculture/household uses. Some microalgae species, such as Phaeodactylum tricornutum, can induce and accumulate UV-absorbing compounds (UACs) upon ultraviolet radiation (UVR) exposure to prevent deleterious effects. Tolerance mechanisms activated by natural stressors might also protect organisms from anthropogenic stressors. This work assesses the effects of the insecticide cypermethrin (Cyp) and UVR in the marine microalgae P tricornutum. Considering the pro-oxidant properties of both stressors and UACs' induction in P tricornutum, lethal and sublethal effects of Cyp were tested in cultures with and without UVR acclimation. After a 24-h exposure to 10 μg L^-1 of technical Cyp or culture medium, UACs, growth, glutathione-S-transferase activity (GST), sulfhydryl groups (SH-g), and lipid peroxidation (LPO) were analyzed. Results showed differences in terms of growth between Cyp and Cyp + UVR pre-exposure. UACs' content was induced after UVR acclimation and diminished after 24 h of growth in control and UVR pre-treated cultures, while levels remained constant under Cyp exposure. A single Cyp exposure exerted GST induction, SH-g depletion, and LPO increments. In UVR-acclimatized treatments, oxidative stress responses showed similar or more pronounced effects than the single chemical exposure, suggesting a potential additive effect of the UVR acclimation. The contrasting effects of Cyp + UVR observed between growth and biochemical responses suggest different compensatory mechanisms that need to be further investigated. Also, it highlights the need to include both lethal and sublethal endpoints to understand microalgae's tolerance and its significance in the multiple stressors' context.

Microbial co-culturing strategies for the production high value compounds, a reliable framework towards sustainable biorefinery implementation - an overview

The microbial co-cultures or consortia are a natural set of microorganisms formed from different species or the same species but different strains, in which members can interact with each other. The co-culture systems have wide variety of technological applications such as the production of foods, treatment of wastewater, removal of toxic substances, environmental recovery, and all these without the need to work in sterile conditions. Therefore, the need of understanding communication mechanisms between cell-to-cell within co-culture will allow to construct and to program their biological behavior from the use of complex substrates to produce biocompounds. The technology of co-culture systems enables the development of biorefinery platforms to obtain biofuels, and high value compounds through biomass transformation by sustainable process. This review focuses on understanding the roles of consortia microbial to design and built co-culture systems to produce high value compounds in terms a sustainable biorefinery.

Removal of harmful alga, Chattonella marina, by recyclable natural magnetic sphalerite

Fish-killing harmful algal blooms (HABs) of Chattonella marina causes serious hazards and risks to fish farming and environment throughout the world. At present, it is necessary to explore cost-effective and recyclable materials for controlling C. marina blooms to reduce the cost and control the potential side effect to the environment. A novel earth-abundant natural magnetic sphalerite (NMS) for removing C. marina was systematically investigated, including the effect of NMS dosage, temperature, pH and salinity on algal removal efficiency. Algal cells could be rapidly removed by NMS (1-2g/L) through adsorption and physical interaction. The algal destruction process was enhanced under the following reaction conditions: temperature>25°C, salinity>30 ppt and pH value<7.5. The reusability of magnetic recycled NMS and effect of light irradiation on algal cell removal were also determined. NMS exhibited excellent stability after repeated algal cell removal, and the efficiency was further enhanced by light illumination. The current study suggested that using NMS to control C. marina blooms could be a novel promising strategy, which is cost-effective, stable, and easy for recycling.

Bacterial growth efficiency in a partly eutrophicated bay of South China Sea: Implication for anthropogenic impacts and potential hypoxia events

Bacterial metabolism plays a dual role [bacterial production (BP) and bacterial respiration (BR)] in the aquatic ecosystem and potentially leads to hypoxia in the coastal eutrophic area. Bacterial growth efficiency (BGE) is an important index showing the contribution of bacterial metabolism to marine biological production and carbon budget in the pelagic ecosystem. In this study, the spatial and seasonal variety as well as diurnal variation dynamics of BGE and associated ecological characteristics were investigated in a partly eutrophicated subtropical bay (the Daya Bay) located in the northern South China Sea. Furthermore, the relationship between bacterial metabolism and potential hypoxia event was analyzed. The average BGE was 0.14 and 0.22 in summer and winter, respectively, which was lower than the mean value ever reported in other coastal and estuarine waters. The diurnal variations of BGE and BP were widely fluctuated in the Daya Bay, with approximately 3-8 fold variation of BP and 2-3 fold variation of BR in different seasons, suggesting the importance of short-term ecological dynamics on evaluating the long-term ecological processes in the coastal waters. BR was the predominant contributor to the bacterial carbon demand; however, the variation of BGE was controlled by BP in both seasons. BGE was always high in the near-shore waters with higher eutrophic level and more active BP and BR. The bacterial metabolism could deplete dissolved oxygen (DO) in the Daya bay within about 9 days when the water body was enclosed and photosynthesis was prohibited. Therefore, low DO concentration and potential hypoxia was more likely to be found in the near-shore waters of the Daya Bay in summer, since the water was stratified and enclosed with poor water exchange capacity in this area. While in winter, hypoxia seldom occurred due to vertical mixing throughout the water column. Further biological-physical coupling research is recommended to find out the detailed formation mechanism of hypoxia in the bay, and to predict the potential hypoxia events and their environmental impacts in the future.

Seasonal succession of phytoplankton community and its relationship with environmental factors of North Temperate Zone water of the Zhalong Wetland, in China

A data set of phytoplankton community and environmental parameters in a hydrological integrity period, i.e. a poor water term, a medium term and a rich water term of North Temperate Zone climate, was analyzed in order to describe seasonal variation of phytoplankton community and its relationship with environmental variables in the Zhalong Wetland of China. The algal population of the Zhalong Wetland was not abundant, with a mean density of 5.08 × 10(7) cell/L (ranged from 4.54 × 10(7) cell/L in a poor term to 5.56 × 10(7) cell/L a medium term). However, its diversity was essentially limited to Cryptophyta, Bacillariophyta, Chlorophyta, Euglenophyta being the group with highest densities. There were considerable seasonal variations in phytoplankton composition. In general, the dominance of Bacillariophyceae was found in a medium term, which was higher than the other period (p < 0.05). The rich water period also showed Bacillariophyceae and Chlorophyta dominance while the phytoplankton was dominated by Cryptophyta erosa in a poor water term. 10 environmental variables, which were significant (p < 0.05) during the studied periods in one-way analysis of covariance, were selected to explore the relationship between phytoplankton structure and environmental factors by canonical correspondence analysis (CCA). The results of the CCA applied to the environmental factors indicated that water temperature (WT) and ammonia (NH3-N) significantly influenced the phytoplankton community (p < 0.05; Monte Carlo test of first constrained axis). Besides WT and NH3-N, the most discriminate physic-chemical variables were nitrite (NO2-N), suspend solid, nitrate (NO3-N), silicon dioxide (SiO2) and all the 10 physical-chemical parameters had a higher marginal effect and λA in the series of constrained CCAs though they were not significant.

Competition increases toxicant sensitivity and delays the recovery of two interacting populations

We investigated how persistent competitive pressure alters toxicant sensitivity and recovery from a pesticide pulse at community level. Interacting populations of Daphnia (Daphnia magna) and Culex larvae (Culex pipiens molestus) were pulse-exposed (48 h) to the pyrethroid fenvalerate. The abundance and biomass of the populations were monitored by non-invasive image analysis. Shortly after exposure, Daphnia showed a concentration-response relationship with the toxicant with an LC₅₀ of 0.9 μg/L. Culex larvae were slightly less sensitive with an LC₅₀ of 1.7 μg/L. For both species, toxicant sensitivity increased with the population biomass of the respective species before exposure, which is explained by intraspecific competition. Several weeks after exposure to the highest treatment concentration of 1 μg/L, the slight differences in sensitivity between the two species were amplified to contrasting long-term effects due to interspecific competition: high interspecific competition impaired the recovery of Daphnia. Subsequently, Culex larvae profited from the slow recovery of Daphnia and showed an increased success of emergence. We conclude that, in natural systems where competition is present, such competitive processes might prolong the recovery of the community structure. Hence, natural communities might be disturbed for a longer period by toxic exposure than predicted from single-species tests alone.