The influence of salinity on the toxicity of selected sulfonamides and trimethoprim towards the green algae Chlorella vulgaris

Effects of sulfamonomethoxine and trimethoprim co-exposures at different environmentally relevant concentrations on microalgal growth and nutrient assimilation

In aquaculture around the world, sulfamonomethoxine (SMM), a long-acting antibiotic that harms microalgae, is widely employed in combination with trimethoprim (TMP), a synergist. However, their combined toxicity to microalgae under long-term exposures at environmentally relevant concentrations remains poorly understood. Therefore, we studied the effects of SMM single-exposures and co-exposures (SMM:TMP=5:1) at concentrations of 5 μg/L and 500 μg/L on Chlorella pyrenoidosa within one aquacultural drainage cycle (15 days). Photosynthetic activity and N assimilating enzyme activities were employed to evaluate microalgal nutrient assimilation. Oxidative stress and flow cytometry analysis for microalgal proliferation and death jointly revealed mechanisms of inhibition and subsequent self-adaptation. Results showed that exposures at 5 μg/L significantly inhibited microalgal nutrient assimilation and induced oxidative stress on day 7, with a recovery to levels comparable to the control by day 15. This self-adaptation and over 95 % removal of antibiotics jointly contributed to promoting microalgal growth and proliferation while reducing membrane-damaged cells. Under 500 μg/L SMM single-exposure, microalgae self-adapted to interferences on nutrient assimilation, maintaining unaffected growth and proliferation. However, over 60 % of SMM remained, leading to sustained oxidative stress and apoptosis. Remarkably, under 500 μg/L SMM-TMP co-exposure, the synergistic toxicity of SMM and TMP significantly impaired microalgal nutrient assimilation, reducing the degradation efficiency of SMM to about 20 %. Consequently, microalgal growth and proliferation were markedly inhibited, with rates of 9.15 % and 17.7 %, respectively, and a 1.36-fold increase in the proportion of cells with damaged membranes was observed. Sustained and severe oxidative stress was identified as the primary cause of these adverse effects. These findings shed light on the potential impacts of antibiotic mixtures at environmental concentrations on microalgae, facilitating responsible evaluation of the ecological risks of antibiotics in aquaculture ponds.

Enhancing bioremediation potential of microalgae Chlorella vulgaris and Scenedesmus acutus by NaCl for pyrene degradation

Microalgae are increasingly recognized as promising organisms for bioremediation of organic pollutants. This study investigates the potential of enhancing the bioremediation efficiency of pyrene (PYR), a polycyclic aromatic hydrocarbon (PAH), through NaCl induced physiological and biochemical alterations in two microalgae species, Chlorella vulgaris and Scenedesmus acutus. Our findings reveal significant improvement in PYR removal when these microalgae were cultivated in the presence of 0.1% NaCl where PYR removal increased from 54 to 74% for C. vulgaris and from 26 to 75% for S. acutus. However, it was observed that NaCl induced stress had varying effects on the two species. While C. vulgaris exhibited increased PYR removal, it experienced reduced growth and biomass production, as well as lower photosynthetic efficiency when exposed to PYR and PYR + NaCl. In contrast, S. acutus displayed better growth and biomass accumulation under PYR + NaCl conditions, making it a more efficient candidate for enhancing PYR bioremediation in the presence of NaCl. In addition to assessing growth and biochemical content, we also investigated stress biomarkers, such as lipid peroxidation, polyphenol and proline contents. These findings suggest that S. acutus holds promise as an alternative microalgae species for PYR removal in the presence of NaCl, offering potential advantages in terms of bioremediation efficiency and ecological sustainability. This study highlights the importance of understanding the physiological and biochemical responses of microalgae to environmental stressors, which can be harnessed to optimize bioremediation strategies for the removal of organic pollutants like PYR.

The effects of carbon nitrogen ratio and salinity on the treatment of swine digestion effluent simultaneously producing bioenergy by microalgae biofilm

In order to remove high concentrations of ammonia nitrogen (NH4+-N) and refractory sulfamethazine (SM2) from swine digestion effluent, different carbon/nitrogen (C/N) ratios and salinity were used to determine the effects of pollutants removal in the microalgae biofilm system. Microalgae biofilm treatment under optimal environmental conditions in synthetic swine digestion effluent were C/N ratio of 20 and salinity of 140 mM. In order to make the actual swine digestion effluent discharge up to the standard, three different two-cycle treatments (suspended microalgae, microalgae biofilm, microalgae biofilm under the optimal conditions) were studied. The results showed that after two-cycle treatment with microalgae biofilm under the optimal conditions, the actual swine digestion effluent levels of total nitrogen (TN), NH4+-N, total phosphorus (TP), chemical oxygen demand (COD), SM2 were 22.65, 9.32, 4.11, 367.28, and 0.99 mg L-1, respectively, which could satisfy the discharge standards for livestock and poultry wastewater in China. At the same time, first-order kinetic simulation equations suggested a degradation half-life of 4.85 d for SM2 under optimal conditions in microalgae biofilm, and microbial community analysis indicated that the dominant genus was Halomonas. Furthermore, 35.66% of lipid, 32.56% of protein and 18.44% of polysaccharides were harvested after two-cycle in microalgae biofilm treatment under optimal environmental conditions. These results indicated that the regulation of C/N and salinity in microalgae biofilm for the treatment of swine digestion effluent was a high-efficiency strategy to simultaneously achieve wastewater treatment and bioenergy production.

Effect of salinity on the toxicity of diclofenac, ibuprofen and naproxen toward cyanobacterium Synechocystis salina

Aquatic species are continuously exposed to pharmaceuticals and changeable water conditions simultaneously, which can induce changes in the toxicity of pollutants. Cyanobacterium are an organism for which less ecotoxicological tests have been performed compared to green algae. In this study, we decided to check how selected non-steroidal anti-inflammatory drugs (NSAID) affect the grow of Synechocystis salina, picocyanobacterium isolated from the Baltic Sea, with salinity as potential modulator of toxicity. S. salina was exposed to diclofenac (DCF), ibuprofen (IBF) and naproxen (NPX) (nominal 100 mg L-1) in BG11 medium and sea salt supplemented BG11 medium (38 PSU) over 96 h in continuous light at 23 °C. No acute toxicity was found in both tested salinity levels. The comparable grow rate in exposed culture compared to control culture over 4 days indicate lack of stress for several generations which need to be overcome with substantial energy consumption. S. salina was found to be halotolerant and can be species for ecotoxicology test where salinity in an additional stressor. Furthermore, resistant of S. salina to target NSAIDs provide a competitive advantage over other phytoplankton species.

Removal of Antibiotics Using an Algae-Algae Consortium (Chlorella protothecoides and Chlorella vulgaris)

The intensive use of antibiotics (for human, veterinary, and agricultural purposes) has steadily increased over the last 30 years. Large amounts of antibiotic residues are released into aquatic systems, mostly due to inefficient wastewater treatment. Conventional wastewater treatments are not designed to remove emerging contaminants (such as antibiotics) from wastewater. Therefore, algae treatment (phycoremediation) has emerged as a promising choice for cost-effective, eco-friendly, and sustainable wastewater treatment. For this reason, we investigated the removal performance of a well-established algal consortia (Chlorella protothecoides and Chlorella vulgaris) used in passive wastewater treatment ponds (Mosselbay, South Africa). Five antibiotics (sulfamethoxazole, amoxicillin, trimethoprim, ofloxacin, and clarithromycin) were selected for their ubiquity and/or low removal efficiency in conventional wastewater treatment plants (WWTPs). For each antibiotic, two concentrations were used: one environmentally relevant (10 ppb) and another 10 times higher (100 ppb), tested in triplicate and collected at two-time points (7 and 10 days). The algae remained viable over the exposure period (which is similar to the retention time within maturation ponds) and exhibited the capacity to remove sulfamethoxazole (77.3% ± 3.0 and 46.5% ± 5.3) and ofloxacin (43.5% ± 18.9 and 55.1% ± 12.0) from samples spiked with 10 and 100 ppb, respectively. This study demonstrates the potential and innovation of algal remediation for contaminants in a developing country context, where minimal infrastructure is available.

Two novel superoxide dismutase genes (CuZnSOD and MnSOD) in the toxic marine dinoflagellate Alexandrium pacificum and their differential responses to metal stressors

Superoxide dismutase (SOD) is an important antioxidant enzyme that is involved in the first line of defense against reactive oxygen species (ROS) within cells. Herein, we determined two novel CuZnSOD and MnSOD genes from the toxic marine dinoflagellate Alexandrium pacificum (designated as ApCuZnSOD and ApMnSOD) and characterized their structural features and phylogenetic affiliations. In addition, we examined the relative gene expression and ROS levels following exposure to heavy metals. ApCuZnSOD encoded 358 amino acids (aa) with two CuZnSOD-conserved domains. ApMnSOD encoded 203 aa that contained a mitochondrial-targeting signal and a MnSOD signature motif but missed an N-terminal domain. Phylogenetic trees showed that ApCuZnSOD clustered with other dinoflagellates, whereas ApMnSOD formed a clade with green algae and plants. Based on the 72-h median effective concentration (EC₅₀), A. pacificum showed toxic responses in the order of Cu, Ni, Cr, Zn, Cd, and Pb. SOD expression levels dramatically increased after 6 h of Pb (≥6.5 times) and 48 h of Cu treatment (≥3.9 times). These results are consistent with the significant increase in ROS production in the A. pacificum exposed to Pb and Cu. These suggest that the two ApSODs are involved in the antioxidant defense system but respond differentially to individual metals.

Study of the Phytoextraction and Phytodegradation of Sulfamethoxazole and Trimethoprim from Water by Limnobium laevigatum

Phytoremediation is an environmentally friendly and economical method for removing organic contaminants from water. The purpose of the present study was to use Limnobium laevigatum for the phytoremediation of water from sulfamethoxazole (SMX) and trimethoprim (TRI) residues. The experiment was conducted for 14 days, in which the loss of the pharmaceuticals in water and their concentration in plant tissues was monitored. Determination of SMX and TRI was conducted using liquid chromatography coupled with tandem mass spectrometry. The results revealed that various factors affected the removal of the contaminants from water, and their bioaccumulation coefficients were obtained. Additionally, the transformation products of SMX and TRI were identified. The observed decrease in SMX and TRI content after 14 days was 96.0% and 75.4% in water, respectively. SMX removal mainly involved photolysis and hydrolysis processes, whereas TRI was mostly absorbed by the plant. Bioaccumulation coefficients of the freeze-dried plant were in the range of 0.043-0.147 for SMX and 2.369-2.588 for TRI. Nine and six transformation products related to SMX and TRI, respectively, were identified in water and plant tissues. The detected transformation products stemmed from metabolic transformations and photolysis of the parent compounds.

Salinity fluctuation influences the toxicity of 1-octyl-3-methylimidazolium chloride ([C8mim]Cl) to a marine diatom Phaeodactylum tricornutum

In this work, a marine diatom (Phaeodactylum tricornutum) was exposed to 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl) for 96 h at three different salinities (25, 35, and 45 ‰) for investigating their interactive effects. Results showed that values of EC₁₀ and EC₅₀ at 96 h of exposure were 0.29, 1.06, 2.01 μg L^-1 and 7.21, 7.71, 7.25 mg L^-1 when the salinities were 25, 35, and 45 ‰, respectively, meaning that salinity fluctuation affected the toxicity of [C₈mim]Cl to this diatom. Changes in chlorophyll a contents and chlorophyll fluorescence parameters suggested that [C₈mim]Cl and salinity fluctuation had a significant interactive effect on the algal photosynthesis. In addition, soluble protein content and activities of antioxidant enzymes in algal cells changed significantly. Increased malondialdehyde contents indicated that the combined stresses could induce excessive production of reactive oxygen species leading to oxidative damage to the algal cells.

Antibiotic Toxicity Isolated and as Binary Mixture to Freshwater Algae Raphidocelis subcapitata: Growth Inhibition, Prediction Model, and Environmental Risk Assessment

Antibiotics in aqueous environments can have extremely adverse effects on non-targeted organisms. However, many research projects have only focused on the toxicological evaluation of individual antibiotics in various environments. In the present work, individual and binary mixture toxicity experiments have been conducted with the model organism Raphidocelis subcapitata (R. subcapitata), and a mixture concentration-response curve was established and contrasted with the estimated effects on the basis of both the concentration addition (CA) and the independent action (IA) models. In addition, different risk assessment methods were used and compared to evaluate the environmental risk of binary mixtures. The toxic ranking of the selected antibiotics to R. subcapitata was erythromycin (ERY) > sulfamethoxazole (SMX) > sulfamethazine (SMZ). In general, the conclusion of this study is that the adverse effects of binary mixtures are higher than the individual antibiotics. The CA model and RQSTU are more suitable for toxicity prediction and risk assessment of binary mixtures. This study reveals the potential ecological risks that antibiotics and their mixtures may pose to water ecosystems, thus providing scientific information for environmental quality regulation.

Updated knowledge, partitioning and ecological risk of pharmaceuticals and personal care products in global aquatic environments

Over the last few decades, the occurrence of pharmaceuticals and personal care products (PPCPs) in aquatic environments has generated increasing public concern. In this review, data on the presence of PPCPs in environmental compartments from the past few years (2014-2022) are summarized by carrying out a critical survey of the partitioning among water, sediment, and aquatic organisms. From the available articles on PPCP occurrence in the environment, in Web of Science and Scopus databases, 185 articles were evaluated. Diclofenac, carbamazepine, caffeine, ibuprofen, ciprofloxacin, and sulfamethoxazole were reported to occur in 85% of the studies in at least one of the mentioned matrices. Risk assessment showed a moderate to high environmental risk for these compounds worldwide. Moreover, bioconcentration factors showed that sulfamethoxazole and trimethoprim can bioaccumulate in aquatic organisms, while ciprofloxacin and triclosan present bioaccumulation potential. Regarding spatial distribution, the Asian and European continents presented most studies on the occurrence and effects of PPCPs on the environment, while Africa and Asia are the most contaminated continents. In addition, the impact of COVID-19 on environmental contamination by PPCPs is discussed.

Can Chemical Toxicity in Saltwater Be Predicted from Toxicity in Freshwater? A Comprehensive Evaluation Using Species Sensitivity Distributions

Species sensitivity distributions (SSDs) play an important role in ecological risk assessment. Estimating SSDs requires toxicity data for many species, but reports on saltwater species are often limited compared to freshwater species. This limitation can constrain informed management of saltwater quality for the protection of marine ecosystems. We investigated the relationships between the parameters (i.e., mean and standard deviation [SD]) of freshwater and saltwater log-normal SSDs to determine how accurately saltwater toxicity could be estimated from freshwater toxicity test data. We estimated freshwater and saltwater SSDs for 104 chemicals with reported acute toxicity data for five or more species and compared their means, SDs, and hazardous concentrations for 5% of the species (HC5) derived from the acute SSDs. Standard major axis regression analyses generally showed that log-log relationships between freshwater and saltwater SSD means, SDs, and HC5 values were nearly 1:1. In addition, the ratios of freshwater-to-saltwater SSD means and HC5 values for most of the 104 chemicals fell within the range 0.1-10. Although such a strong correlation was not observed for SSD SDs (r²  < 0.5), differences between freshwater and saltwater SSD SDs were relatively small. These results indicate that saltwater acute SSDs can be reasonably estimated using freshwater acute SSDs. Because the differences of the means and SDs between freshwater and saltwater SSDs were larger when the number of test species used for SSD estimation was lower (i.e., five to seven species in the present study), obtaining toxicity data for an adequate number of species will be key to better approximation of a saltwater acute SSD from a freshwater acute SSD for a given chemical. Environ Toxicol Chem 2022;41:2021-2027. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Enhanced sulfonamides removal via microalgae-bacteria consortium via co-substrate supplementation

Both co-cultivation and co-substrate addition strategies have exhibited massive potential in microalgae-based antibiotic bioremediation. In this study, glucose and sodium acetate were employed as co-substrate in the cultivation of microalgae-bacteria consortium for enhanced sulfadiazine (SDZ) and sulfamethoxazole (SMX) removal. Glucose demonstrated a two-fold increase in biomass production with a maximum specific growth rate of 0.63 ± 0.01 d^-1 compared with sodium acetate. The supplementation of co-substrate enhanced the degradation of SDZ significantly up to 703 ± 18% for sodium acetate and 290 ± 22% for glucose, but had almost no effect on SMX. The activities of antioxidant enzymes, including peroxidase, superoxide dismutase and catalase decreased with co-substrate supplementation. Chlorophyll a was associated with protection against sulfonamides and chlorophyll b might contribute to SDZ degradation. The addition of co-substrates influenced bacterial community structure greatly. Glucose enhanced the relative abundance of Proteobacteria, while sodium acetate improved the relative abundance of Bacteroidetes significantly.

Microplastics decrease the toxicity of sulfamethoxazole to marine algae (Skeletonema costatum) at the cellular and molecular levels

Microplastics (MPs) and sulfamethoxazole (SMX) are ubiquitous in various aquatic environments, but little is known about their joint toxicity mechanism on marine organisms. This study investigated the individual and joint toxicity of SMX and five MPs, including polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS) and bioplastic polylactic acid (PLA), on Skeletonema costatum. The inhibition rates (IR) of the single MPs systems (50 mg/L) followed the order of PP > PE > PLA > PS > PET, while the addition of 0.3 mg/L SMX significantly decreased the toxicity of PP, PE and PLA in the joint system due to the "shelter" effect from MPs adsorption. As for the PS and SMX joint system, the malondialdehyde (MDA), reactive oxygen species (ROS) levels and superoxide dismutase (SOD) activity were higher than those of the other joint systems. The metabolomic results showed that SMX downregulated glycerophospholipid and amino acid metabolism. PS caused the downregulation of glycerophospholipids, carbohydrates and amino acid via the hetero-aggregation with algae. The co-exposure of SMX and PS alleviated the perturbation of alanine, aspartate and glutamate metabolism of algae compared with SMX. These findings enhance our understanding of the potential mechanisms of the MPs and organic pollutants joint toxicity in the marine environment.

Persistence, environmental hazards, and mitigation of pharmaceutically active residual contaminants from water matrices

Pharmaceutical compounds are designed to elicit a biological reaction in specific organisms. However, they may also elicit a biological response in non-specific organisms when exposed to ambient quantities. Therefore, the potential human health hazards and environmental effects associated with pharmaceutically active compounds presented in aquatic environments are being studied by researchers all over the world. Owing to their broad-spectrum occurrence in various environmental matrices, direct or indirect environmental hazardous impacts, and human-health related consequences, several pharmaceutically active compounds have been categorized as emerging contaminants (ECs) of top concern. ECs are often recalcitrant and resistant to abate from water matrices. In this review, we have examined the classification, occurrence, and environmental hazards of pharmaceutically active compounds. Moreover, because of their toxicity and the inefficiency of wastewater treatment plants to remove pharmaceutical pollutants, novel wastewater remediation technologies are urgently required. Thus, we have also analyzed the recent advances in microbes-assisted bioremediation as a suitable, cost-effective, and eco-friendly alternative for the decontamination of pharmaceutical pollutants. Finally, the most important factors to reach optimal bioremediation are discussed.

Occurrence of antibiotics in waters, removal by microalgae-based systems, and their toxicological effects: A review

Global antibiotics consumption has been on the rise, leading to increased antibiotics release into the environment, which threatens public health by selecting for antibiotic resistant bacteria and resistance genes, and may endanger the entire ecosystem by impairing primary production. Conventional bacteria-based treatment methods are only moderately effective in antibiotics removal, while abiotic approaches such as advanced oxidation and adsorption are costly and energy/chemical intensive, and may cause secondary pollution. Considered as a promising alternative, microalgae-based technology requires no extra chemical addition, and can realize tremendous CO₂ mitigation accompanying growth related pollutants removal. Previous studies on microalgae-based antibiotics removal, however, focused more on the removal performances than on the removal mechanisms, and few studies have concerned the toxicity of antibiotics to microalgae during the treatment process. Yet understanding the removal mechanisms can be of great help for targeted microalgae-based antibiotics removal performances improvement. Moreover, most of the removal and toxicity studies were carried out using environment-irrelevant high concentrations of antibiotics, leading to reduced guidance for real-world situations. Integrating the two research fields can be helpful for both improving antibiotics removal and avoiding toxicological effects to primary producers by the residual pollutants. This study, therefore, aims to build a link connecting the occurrence of antibiotics in the aquatic environment, the removal of antibiotics by microalgae-based processes, and the toxicity of antibiotics to microalgae. Distribution of various categories of antibiotics in different water environments were summarized, together with the antibiotics removal mechanisms and performances in microalgae-based systems, and the toxicological mechanisms and toxicity of antibiotics to microalgae after either short-term or long-term exposure. Current research gaps and future prospects were also analyzed. The review could provide much valuable information to the related fields, and provoke interesting thoughts on integrating microalgae-based antibiotics removal research and toxicity research on the basis of environmentally relevant concentrations.

Interactive effects of polymethyl methacrylate (PMMA) microplastics and salinity variation on a marine diatom Phaeodactylum tricornutum

Until now, knowledge about the interactive effects of microplastics and environmental factors on primary producers is quite limited. In this work, a marine diatom (Phaeodactylum tricornutum) was exposed to polymethyl methacrylate (PMMA) microplastics at different salinities (25, 35, and 45‰) for 10 days in order to study their interactive effects. Results showed that growth of P. tricornutum was negatively affected by PMMA microplastics and salinity variation with a minimum EC₅₀ value of 91.75 mg L^-1. Photosynthetic activity of P. tricornutum was also inhibited by the two factors, and their interactive effects on chlorophyll fluorescence parameters (F_v/F_m and Φ_PSII) were significant. In the algal cells, soluble protein accumulated, activities of two antioxidant enzymes changed, and malondialdehyde (MDA) content increased when this diatom was exposed to the microplastics at different salinities. These data would help to evaluate the risks of microplastics to primary producers under different environmental factors.

Phycoremediation integrated approach for the removal of pharmaceuticals and personal care products from wastewater - A review

Pharmaceuticals and personal care products (PPCPs) are of emerging concerns because of their large usage, persistent nature which promised their continuous disposal into the environment, as these pollutants are stable enough to pass through wastewater treatment plants causing hazardous effects on all the organisms through bioaccumulation, biomagnification, and bioconcentration. The available technologies are not capable of eliminating all the PPCPs along with their degraded products but phycoremediation has the advantage over these technologies by biodegrading the pollutants without developing resistant genes. Even though phycoremediation has many advantages, industries have found difficulty in adapting this technology as a single-stage treatment process. To overcome these drawbacks recent research studies have focused on developing technology that integrated phycoremediation with the commonly employed treatment processes that are in operation for treating the PPCPs effectively. This review paper focuses on such research approaches that focused on integrating phycoremediation with other technologies such as activated sludge process (ASP), advanced oxidation process (AOP), Up-flow anaerobic sludge blanket reactor (UASBR), UV irradiation, and constructed wetland (CW) with the advantages and limitations of each integration processes. Furthermore, augmenting phycoremediation by co-metabolic mechanism with the addition of sodium chloride, sodium acetate, and glucose for the removal of PPCPs has been highlighted in this review paper.

Evaluation of growth and biochemical responses of freshwater microalgae Chlorella vulgaris due to exposure and uptake of sulfonamides and copper

Sulfonamides (SAs) and heavy metals are frequently detected together in livestock wastewater. In this study, evaluations regarding their potentially adverse effects on microalgae and according removals were investigated. Results showed that the growth of C. vulgaris was inhibited by SAs and Cu. There was an obvious recovery period in photosynthetic activity (Fv/Fm), indicating that the damage to the photosystem of microalgae was reversible. The co-existence of SAs and Cu significantly affected the biochemical characteristics, including the activities of antioxidant enzyme and the contents of photosynthetic pigments, proteins and polysaccharides. The addition of Cu obviously promoted the removal efficiencies of SMZ, SMX and SMM, which might be ascribed to the bridging effect of Cu in the bioadsorption of SAs. This study is conducive to understand the changes in the biochemical responses of microalgae under the combined impacts of SAs and Cu, and provides a new insight for the simultaneous removals.

Azithromycin induces dual effects on microalgae: Roles of photosynthetic damage and oxidative stress

Antibiotics are frequently detected in aquatic ecosystems, posing a potential threat to the freshwater environment. However, the response mechanism of freshwater microalgae to antibiotics remains inadequately understood. Here, the impacts of azithromycin (a broadly used antibiotic) on microalgae Chlorella pyrenoidosa were systematically studied. The results revealed that high concentrations (5-100 μg/L) of azithromycin inhibited algal growth, with a 96-h half maximal effective concentration of 41.6 μg/L. Azithromycin could weaken the photosynthetic activities of algae by promoting heat dissipation, inhibiting the absorption and trapping of light energy, impairing the reaction centre, and blocking electron transfer beyond Q_A. The blockage of the electron transport chain in the photosynthetic process further induced the generation of reactive oxygen species (ROS). The increases in the activities of superoxide dismutase, peroxidase and glutathione played important roles in antioxidant systems but were still not enough to scavenge the excessive ROS, thus resulting in the oxidative damage indicated by the elevated malondialdehyde level. Furthermore, azithromycin reduced the energy reserves (protein, carbohydrate and lipid) and impaired the cellular structure. In contrast, a hormesis effect on algal growth was found when exposed to low concentrations (0.5 and 1 μg/L) of azithromycin. Low concentrations of azithromycin could induce the activities of the PSII reaction centre by upregulating the mRNA expression of psbA. Additionally, increased chlorophyll b and carotenoids could improve the absorption of light energy and decrease oxidative damage, which further contributed to the increase in energy reserves (protein, carbohydrate and lipid). The risk quotients of azithromycin calculated in this study were higher than 1, suggesting that azithromycin could pose considerable ecological risks in real environments. The present work confirmed that azithromycin induced dual effects on microalgae, which provided new insight for understanding the ecological risk of antibiotics.

Current progress in electrochemical anodic-oxidation of pharmaceuticals: Mechanisms, influencing factors, and new technique

Various pharmaceuticals have been detected in natural water and wastewater bodies, causing threats to water ecosystem and human health. Although electrochemical anodic-oxidation (EAO) has been shown to be efficient for pharmaceuticals degradation from aqueous solution, it still has a distinct need to apply EAO technology for pharmaceuticals removal rationally. This review provides the most recent progress on the mechanisms, influencing factors, and new technique of EAO for pharmaceuticals degradation. The mechanism and superiority of EAO were analyzed. Major influencing factors (e.g., electrode materials, electrochemical reactor, applied current density, anode-cathode distance, electrolyte type and concentration, initial solution pH value, and initial pharmaceuticals concentration) were discussed on the removal of pharmaceuticals. The latest development of reactive electrochemical membranes (REM) was regarded as an emerging EAO technique, and it was also highlighted. This work revealed that the EAO of pharmaceuticals has extraordinary application prospects in the field of water and wastewater treatment.

Environmental risk assessment and bioaccumulation of pharmaceuticals in a large urbanized estuary

We screened for the presence of 66 different pharmaceutical residues in surface waters and in multiple invertebrate and fish species of the Tejo estuary to produce an environmental risk assessment of individual pharmaceuticals and their mixtures, as well as evaluate the bioaccumulation of pharmaceuticals in one of Europe's largest estuarine systems. Sixteen pharmaceutical residues, from seven therapeutic classes, were detected in estuarine waters, with environmental mixture concentrations ranging from 42 to 1762 ng/L. Environmental risk assessment via the determination of risk quotients, demonstrated high ecological risk for the antibiotic amoxicillin and angiotensin II receptor blockers irbesartan and losartan. Moderate risk was estimated for antidepressants, antiepileptics, anxiolytics and beta-blockers, but the risk quotient of the accumulated mixture of compounds was over 380-fold higher than the no risk threshold, driven by antibiotics and angiotensin II receptor blockers. In biota, higher risk therapeutic groups were found in higher concentrations, with nine pharmaceutical residues detected, including six antibiotics and two neuroactive compounds, and maximum tissue concentrations up to 250 μg/kg. Bioaccumulation was species- and compound-specific, with only two compounds found simultaneously in water and biota, likely a result of the complex dynamics and fate of pharmaceuticals in estuarine waters. Nonetheless, higher detection frequencies were observed in species living directly on or just above the substrate (i.e. benthic and demersal species), underpinning the importance of habitat use, as well the potential role of sediment and diet based routes for pharmaceutical uptake. Ultimately, results support urgent action on managing the impact of pharmaceuticals in coastal environments, striving for improved monitoring schemes tailored to the dynamic nature and ecological diversity of estuaries and coastal ecosystems.

Sulfamethoxazole-Altered Transcriptomein Green Alga Raphidocelis subcapitata Suggests Inhibition of Translation and DNA Damage Repair

Occurrence of sulfonamide antibiotics has been reported in surface waters with the exposures ranging from < 1 ng L^–1 to approximately 11 μg L^–1, which may exert adverse effects on non-target algal species, inhibiting algal growth and further hindering the delivery of several ecosystem services. Yet the molecular mechanisms of sulfonamide in algae remain undetermined. The aims of the present work are: (1) to test the hypothesis whether sulfamethoxazole (SMX) inhibits the folate biosynthesis in a model green alga Raphidocelis subcapitata; and (2) to explore the effects of SMX at an environmentally relevant concentration on algal health. Here, transcriptomic analysis was applied to investigate the changes at the molecular levels in R. subcapitata treated with SMX at the concentrations of 5 and 300 μg L^–1. After 7-day exposure, the algal density in the 5 μg L^–1 group was not different from that in the controls, whereas a marked reduction of 63% in the high SMX group was identified. Using the adj p < 0.05 and absolute log₂ fold change > 1 as a cutoff, we identified 1 (0 up- and 1 downregulated) and 1,103 (696 up- and 407 downregulated) differentially expressed genes (DEGs) in the 5 and 300 μg L^–1 treatment groups, respectively. This result suggested that SMX at an environmentally relevant exposure may not damage algal health. In the 300 μg L^–1 group, DEGs were primarily enriched in the DNA replication and repair, photosynthesis, and translation pathways. Particularly, the downregulation of base and nucleotide excision repair pathways suggested that SMX may be genotoxic and cause DNA damage in alga. However, the folate biosynthesis pathway was not enriched, suggesting that SMX does not necessarily inhibit the algal growth via its mode of action in bacteria. Taken together, this study revealed the molecular mechanism of action of SMX in algal growth inhibition.

Review of aquatic toxicity of pharmaceuticals and personal care products to algae

Pharmaceuticals and Personal Care Products (PPCPs) have been frequently detected in the environment around the world. Algae play a significant role in aquatic ecosystem, thus the influence on algae may affect the life of higher trophic organisms. This review provides a state-of-the-art overview of current research on the toxicity of PPCPs to algae. Nanoparticles, contained in personal care products, also have been considered as the ingredients of PPCPs. PPCPs could cause unexpected effects on algae and their communities. Chlorophyta and diatoms are more accessible and sensitive to PPCPs. Multiple algal endpoints should be considered to provide a complete evaluation on PPCPs toxicity. The toxicity of organic ingredients in PPCPs could be predicted through quantitative structure-activity relationship model, whereas the toxicity of nanoparticles could be predicted with limitations. Light irradiation can change the toxicity through affecting algae and PPCPs. pH and natural organic matter can affect the toxicity through changing the existence of PPCPs. For joint and tertiary toxicity, experiments could be conducted to reveal the toxic mechanism. For multiple compound mixture toxicity, concentration addition and independent addition models are preferred. However, there has no empirical models to study nanoparticle-contained mixture toxicity. Algae-based remediation is an emerging technology to prevent the release of PPCPs from water treatment plants. Although many individual algal species are identified for removing a few compounds from PPCPs, algal-bacterial photobioreactor is a preferable alternative, with higher chances for industrial applications.

Combined Effects of Sulfamethoxazole and Erythromycin on a Freshwater Microalga, Raphidocelis subcapitata: Toxicity and Oxidative Stress

This study investigated the environmental effects of two familiar emerging contaminants, sulfamethoxazole (SMX) and erythromycin (ERY), and their mixture (10:1 w/w) using a green microalga, R. subcapitata. The cell density, pigment content, and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) glutathione peroxidase (GSH-Px), and glutathione S-transferase (GST) were analyzed. The calculated EC₅₀ values of SMX, ERY, and their mixture after 96 h were 0.49, 0.044, and 0.06 mg/L, respectively. High concentrations of antibiotics lead to a decrease in chlorophyll a and total carotenoid content, affecting the ability to photosynthesize ROS scavenging capacity. This may be a factor leading to the inhibition of algal growth. When R. subcapitata was exposed to SMX and the mixture, SOD and CAT increased to resist oxidative damage, while the activities of GSH and GST decreased, suggesting that this algae’s antioxidant system was unbalanced due to oxidative stress. R. subcapitata reduced the ERY-induced ROS by increasing the activities of SOD, GSH, and GST. The difference in the contents of nonenzymatic antioxidants and enzyme antioxidants in R. subcapitata indicated the antioxidant mechanisms to SMX and ERY were not identical. This study provides insights into the oxidative stress process in R. subcapitata under different antibiotics.

Global variation in freshwater physico-chemistry and its influence on chemical toxicity in aquatic wildlife

Chemical pollution is one of the major threats to global freshwater biodiversity and will be exacerbated through changes in temperature and rainfall patterns, acid-base chemistry, and reduced freshwater availability due to climate change. In this review we show how physico-chemical features of natural fresh waters, including pH, temperature, oxygen, carbon dioxide, divalent cations, anions, carbonate alkalinity, salinity and dissolved organic matter, can affect the environmental risk to aquatic wildlife of pollutant chemicals. We evidence how these features of freshwater physico-chemistry directly and/or indirectly affect the solubility, speciation, bioavailability and uptake of chemicals [including via alterations in the trans-epithelial electric potential (TEP) across the gills or skin] as well as the internal physiology/biochemistry of the organisms, and hence ultimately toxicity. We also show how toxicity can vary with species and ontogeny. We use a new database of global freshwater chemistry (GLORICH) to demonstrate the huge variability (often >1000-fold) for these physico-chemical variables in natural fresh waters, and hence their importance to ecotoxicology. We emphasise that a better understanding of chemical toxicity and more accurate environmental risk assessment requires greater consideration of the natural water physico-chemistry in which the organisms we seek to protect live.

Brazilian silverside, Atherinella brasiliensis (Quoy & Gaimard,1825) embryos as a test-species for marine fish ecotoxicological tests

The fish embryo test (FET) is an alternative to the classic freshwater toxicity test used to assess environmental hazards and risks to fish. This test has been standardized and adopted by the Organization for Economic and Cooperation and Development (OECD). As salinity may affect the substances’ toxicity, we describe the development of an alternative euryhaline test species for embryonic ecotoxicological tests: the Brazilian silverside Atherinella brasiliensis (Quoy & Gaimard, 1825). This species is broadly distributed along the coast of South America and is able to inhabit a broad range of environmental and saline conditions. Ours is the first study on the maintenance of a native South American species for natural reproduction and the generation of embryos for tests. The embryos used are transparent and possess fluorescent cells which have only been seen in a few species and which may be used as markers, making it an alternative assessment tool for the lethal and sublethal substances in marine and estuarine environments. We provide a detailed description and analysis of embryonic development under different salinities and temperatures. The embryos and larvae developed in similar ways at different salinities, however as temperatures increased, mortality also increased. We considered the effects of the reference toxicants Zn²⁺ and SDS using a protocol similar to the FET that was standardized for zebrafish. Brazilian silverside embryos are as sensitive as freshwater, or euryhaline fish, to the surfactant but are more resistant to metals prior to hatching. We were able to show the advantages of the Brazilian silverside as a model for a marine fish embryo test (FETm) with high levels of reproducibility and little contaminated waste.

Quantitative characterization of toxicity interaction within antibiotic-heavy metal mixtures on Chlorella pyrenoidosa by a novel area-concentration ratio method

Toxicity interaction, synergism and antagonism, may occur when multiple pollutants are exposed to the environment simultaneously, which limits the utility of some standard models to assess toxicity hazards and risks. The development and application of models which can provide an insight into the combined toxicity of pollutants becomes necessary. Therefore, a novel model, area-concentration ratio (ACR) method, was developed to characterize the toxicity interaction within mixtures of three aminoglycoside antibiotics (AGs), kanamycin sulfate (KAN), paromomycin sulfate (PAR), tobramycin (TOB) and one heavy metal copper (Cu) in this study. The inhibition toxicity of single contaminants and mixtures designed by direct equilibration ray method and uniform design ray method to Chlorella pyrenoidosa (C. pyrenoidosa) was determined by the microplate toxicity analysis (MTA). The results showed that the novel method ACR could be used for quantitative characterization of combined toxicity. According to the ACR, all the binary AG antibiotic mixture systems display obvious synergism and weak antagonism. The addition of the heavy metal Cu into binary AG antibiotic mixtures can obviously change toxicity interaction, but toxicity interaction changing trend varies greatly in different ternary mixture systems. Toxicity interaction in the six mixture systems has component concentration-ratio dependence. ACR can be suggested as an effective novel method to quantitatively characterize toxicity interaction when assessing the hazards and risks of the combined pollution.

The Toxic Effects of Antibiotics on Freshwater and Marine Photosynthetic Microorganisms: State of the Art

Antibiotic residues have been commonly detected worldwide in freshwater, estuarine, and marine ecosystems. The review summarizes the up-to-date information about the toxic effects of over 60 antibiotics on nontarget autotrophic microorganisms with a particular focus on marine microalgae. A comprehensive overview of the available reports led to the identification of significant knowledge gaps. The data on just one species of freshwater green algae (Raphidocelis subcapitata) constitute 60% of the total information on the toxicity of antibiotics, while data on marine species account for less than 14% of the reports. Moreover, there is a clear knowledge gap regarding the chronic effects of antibiotic exposure (only 9% of studies represent exposition time values longer than 7 days). The review summarizes the information on different physiological endpoints, including processes involved in photosynthesis, photoprotective and antioxidant mechanisms. Currently, the hazard assessment is mostly based on the results of the evaluation of individual chemicals and acute toxicity tests of freshwater organisms. Future research trends should involve chronic effect studies incorporating sensitive endpoints with the application of environmentally relevant concentrations, as well as studies on the mixture effects and combined environmental factors influencing toxicity.

Ofloxacin induces etiolation in Welsh onion leaves

Antibiotic pollution has become an important global issue, and ofloxacin (OFL) is widely used worldwide. However, little is known about the potential adverse effects of OFL on plants. We assessed the toxic effects of OFL on Welsh onion and explored its toxicity mechanism. The leaf pigment content increased in 0.1 mg/L of OFL but decreased in a dose-dependent manner (0.5-2 mg/L OFL) until leaf etiolation. The ultrastructure of leaves showed that the treatment of 2 mg/L OFL produced significant toxicity. Furthermore, photosynthetic and fluorescence parameters were negatively affected by OFL treatment. The photosynthetic electron transport chain was significantly inhibited by OFL treatment, especially between Q_A and Q_B. The hydrogen peroxide and malondialdehyde content also increased with OFL concentration, indicating that antioxidant enzymes' role in antibiotic response is limited. In conclusion, OFL can damage chloroplasts by promoting ROS accumulation, which results in the etiolation of Welsh onion leaves.

Modeling the relationship between emerging and persistent organic contaminants in water, sediment and oysters from a temperate lagoon

The concentrations of emerging and persistent organic contaminants (EPOC) in oysters (C_O) from Aveiro Lagoon are represented as a function of their concentrations in water (C_W) and sediment (C_S) using linear and generalized additive models (LM, GAM). Additionally, four sampling seasons, octanol/water partition coefficients (K) and type of EPOC (pyrethroids, flame-retardants, musks, UV filters, polycyclic aromatic hydrocarbons, others) are included in the models. The probabilities of detection of EPOC in water, sediment and oysters are analyzed by GAM. The behavior of contaminants in water is determined by K with a clear seasonal trend. Sediments are reservoirs for hydrophobic compounds with less seasonal variation. Seasonal changes are found for C_O, the last being determined additively both by C_W and hydrophobicity from one side and by C_S and type of contaminants from the other side. The seasonal change of EPOC concentration in water, sediment and oysters is specific for each contaminant type.

Nanocolloids, but Not Humic Acids, Augment the Phytotoxicity of Single-Layer Molybdenum Disulfide Nanosheets

Engineered nanomaterials (ENMs), especially transition metal dichalcogenide (TMDC), have received great attention in recent years due to their advantageous properties and applications in various fields and are inevitably released into the environment during their life cycle. However, the effect of natural nanocolloids, widely distributed in the aquatic environment, on the environmental transformation and ecotoxicity of ENMs remains largely unknown. In this study, the effects of natural nanocolloids were compared to humic acid on the environmental transformation and ecotoxicity of single-layer molybdenum disulfide (SLMoS₂), a representative TMDC. SLMoS₂ with nanocolloids or humic acid (HA) enhanced their dispersion and Mo ion release in deionized water. Nanocolloids induced growth inhibition, reactive oxygen species (ROS) elevation, and cell permeability. Low-toxicity SLMoS₂ combined with nanocolloids will enhance the above adverse effects. SLMoS₂-nanocolloids induced serious damage (cell distortion and deformation), SLMoS₂ internalization, and metabolic perturbation on Chlorella vulgaris (C. vulgaris). In contrast, the addition of HA induced the growth promotion and lower ROS level, inhibited the internalization of SLMoS₂, and mitigated metabolic perturbation on C. vulgaris. This work provides insights into the effect of natural nanocolloids on the behaviors and biological risks of ENMs in aquatic environments, deserving substantial future attention.

Acute effects of CH3NH3PbI3 perovskite on Scenedesmus obliquus and Daphnia magana in aquatic environment

CH₃NH₃PbI₃ is one of the most widely studied and most promising photoelectric conversion materials for large-scale application. However, once it is discharged into the aquatic environment, it will release a variety of lethal substances to the aquatic organisms. Herein, two typical aquatic pollution indicators, Scenedesmus obliquus (a typical phytoplankton) and Daphnia magna (a typical zooplankton), were used to assess the acute effects of CH₃NH₃PbI₃ perovskite on aquatic organisms. The results showed that, when the initial CH₃NH₃PbI₃ perovskite level (CPL) was 40 mg L^-1 or higher, the growth of S. obliquus would be remarkably inhibited with significant decreases of chlorophyll content and protein content. And when the CPL was over 5 mg L^-1, the survival of D. magna would be notably threatened. Specifically, the 72 h EC-50 of CH₃NH₃PbI₃ perovskite to S. obliquus was calculated as 37.21 mg L^-1, and the 24 h LC-50 of this perovskite to D. magna adults and neonates were calculated as 37.53 mg L^-1 and 18.55 mg L^-1, respectively. Moreover, remarkably solution pH declination and large amounts of lead bio-accumulation was observed in the both acute experiments, which could be the main reasons causing the above acute effects. Considering the strong acute effects of these CH₃NH₃PbI₃ perovskite materials and their attractive application prospect, more attentions should be paid on their harmness to the environment.

Environmental risk dynamics of pesticides toxicity in a Mediterranean micro-estuary

Pesticides are potentially toxic to aquatic systems, even at low concentration, depending on their individual ecotoxicological properties and their mixture composition. Thus, to evaluate possible ecological stress due to pesticide load, a thorough assessment of the potential toxicity of pesticide mixtures is required. Here we report water discharge and quality data of an eastern Mediterranean micro-estuary (Alexander stream), targeting the temporal distribution of a pesticide mixture. Over 150 water samples were collected during 2 hydrological years representing base-flow and flood conditions. On average, each water sample contained 34 and 45 different pesticides with peak concentrations of 1.4 μg L^-1 of Imidacloprid and 55 μg L^-1 of Diuron during base-flow and flood events, respectively. Pesticide mixtures were potentially toxic to benthic invertebrates and algae during flood events, surpassing the toxicity benchmark with medians of 110% and 155%, respectively. The herbicide Diuron and the insecticide Imidacloprid were the main pesticides responsible for the high potential toxicity during flood events. The falling limb of the flood hydrographs was found to inflict the highest stress on the estuarine environment due to elevated toxicity combined with prolonged residence time of the water. Examination of the potential chronic toxicity of single compounds showed continuous stress for plants, algae, amphibians, crustaceans, insects and fish from nine pesticides. Our data show that the ecosystem of the Alexander micro-estuary is under a continuous chronic stress with acute peaks in potential toxicity during flood events and the period that follows them. We propose that analyzing a small set of flood-tail samples is needed for the evaluation of small estuarine ecosystems risk during the rainy season. From a management perspective, we suggest better control of application practices for Diuron in the watershed to minimize the stress to the estuarine ecosystem.

Ecological Risk Dynamics of Pharmaceuticals in Micro-Estuary Environments

Micro-estuarine ecosystems have a surface area <1 km² and are abundant in Mediterranean regions. As a result of their small size, these systems are particularly vulnerable to the effects of chemical pollution. Due to the fluctuating flow conditions of base flow dominated by treated wastewater effluents and flood events transporting rural and urban non-point-source pollution, micro-estuaries are under a dynamic risk regime, consequently struggling to provide ecological services. This 2 year study explored the occurrence and risks of pharmaceutical contamination in the Alexander micro-estuary in Israel. Pharmaceuticals were detected in all samples (n = 280) at as high as 18 μg L^-1 in flood events and 14 μg L^-1 in base flow. The pharmaceutical mixture composition was affected by flow conditions with carbamazepine dominating the base flow and caffeine dominating flood events. The median annual risk quotients for fish, crustaceans, and algae were 19.6, 5.2, and 4.5, respectively, indicating that pharmaceuticals pose a high risk to the ecosystem. Ibuprofen, carbamazepine, and caffeine contributed most to the risk quotients. The current work highlights that micro-estuary ecosystems, like the Alexander estuary, are continuously exposed to pharmaceuticals and most likely to other pollutants, placing these ecologically important systems under an elevated risk in comparison to the more frequently studied large estuarine systems.

Insights into the effect of cerium oxide nanoparticle on microalgal degradation of sulfonamides

Nanoparticles have been commercially used worldwide; however, there is a lack of information of their environmental impacts and ecotoxicity. In this study, the effect of cerium oxide nanoparticle (CeO₂NP) on a green microalga Scenedesmus obliquus, and microalgal biodegradation of four sulfonamides (sulfamethazine, sulfamethoxazole, sulfadiazine, and sulfamethoxazole) was investigated. There is insignificant inhibition of microalgal growth induced by CeO₂NP; however, it substantially influenced the expression of genes involved in key cellular metabolic activities of S. obliquus. For example, genes involved in photosynthetic activity (psbA) and energy production (ATPF0C) were downregulated with exposure to CeO₂NP. The low concentrations of CeO₂NP improved microalgal degradation of sulfonamides. This may be because of the upregulated genes encoding hydrogenase and oxidoreductase. The exploration of this study has provided a new understanding of the environmental impacts of CeO₂NP on microalgae-based biotechnologies for treatment of wastewater containing emerging organic contaminants.

Ecotoxicological effects of sulfonamides and fluoroquinolones and their removal by a green alga (Chlorella vulgaris) and a cyanobacterium (Chrysosporum ovalisporum)

In recent years, antibiotic pollution has become worse, especially in China. In this study, the ecotoxicological effects of four frequently used antibiotics with different lipophilic degrees (log Kow) (sulfadiazine (SD), sulfamethazine (SM2), enrofloxacin (ENR), and norfloxacin (NOR)) at four concentrations of 1, 5, 20, and 50 mg L^-1 were examined using batch cultures of green alga Chlorella vulgaris and cyanobacterium Chrysosporum ovalisporum for 16 days based on changes in chlorophyll fluorescence parameters (chl a, Fv/Fm, and ΦPSII) and responses of the antioxidant system. Besides, the antibiotics removal efficiencies of the two microalgae were investigated. Sulfonamides (SD and SM2) had no significant inhibitory effect on the growth of C. ovalisporum, but had an inhibitory effect on C. vulgaris, whereas fluoroquinolones (ENR and NOR) significantly inhibited C. ovalisporum. The activities of superoxide dismutase, catalase, and glutathione reductase suggested that C. vulgaris was more tolerant to these antibiotics than C. ovalisporum. The increased malondialdehyde level in both algae indicated their tolerance against antibiotics. When compared with C. ovalisporum, C. vulgaris presented better capacity to remove antibiotics. In summary, the four antibiotics exerted time- or concentration-dependent ecotoxicological effects on the microalgae examined, whereas the microalgae could remove the antibiotics based on the log Kow of the antibiotics. The findings of this study contribute to effective understanding of the ecotoxicological effects of antibiotics and their removal by microalgae.

Occurrence and toxicity of antibiotics in the aquatic environment: A review

In recent years, antibiotics have been used for human and animal disease treatment, growth promotion, and prophylaxis, and their consumption is rising worldwide. Antibiotics are often not fully metabolized by the body and are released into the aquatic environment, where they may have negative effects on the non-target species. This review examines the recent researches on eight representative antibiotics (erythromycin, trimethoprim, sulfamethoxazole, tetracycline, oxytetracycline, ofloxacin, ciprofloxacin, and amoxicillin). A detailed overview of their concentrations in surface waters, groundwater, and effluents is provided, supported by recent global human consumption and veterinary use data. Furthermore, we review the ecotoxicity of these antibiotics towards different groups of organisms, and assessment of the environmental risks to aquatic organisms. This review discusses and compares the suitability of currently used ecotoxicological bioassays, and identifies the knowledge gaps and future challenges. The risk data indicate that selected antibiotics may pose a threat to aquatic environments. Cyanobacteria were the most sensitive organisms when using standard ecotoxicological bioassays. Further studies on their chronic effects to aquatic organisms and the toxicity of antibiotic mixtures are necessary to fully understand the hazards these antibiotics present.

Evaluation of physiological changes induced by the fluoroquinolone antibiotic ciprofloxacin in the freshwater macrophyte species Lemna minor and Lemna gibba

The worldwide increase in the consumption of antibiotics is becoming a concern for the scientific community, since the presence of their residues in the wild poses specific challenges, especially in ecotoxicological terms. Currently, antibiotics are used for a wide range of purposes, being used against bacterial diseases but also as growth promoters. As a result, their environmental presence can affect wild organisms, especially those from the aquatic environment. This scenario leads to the need of characterizing the toxicity of antibiotics, especially towards non-target organisms. In this study we selected two species of aquatic macrophytes, Lemna minor and Lemna gibba, which are standard plant species inscribed in ecotoxicological testing guidelines. In this work we characterized the toxic effects of the quinolone antibiotic ciprofloxacin (in levels of 0.005, 0.013, 0.031, 0.078, and 0.195 mg/L), focusing on its potential toxicity towards photosynthetic mechanisms, and pro-oxidant effects. These objectives were attained by measuring the concentrations of chlorophyll a and b, and carotenoids levels. The determination of the quantum yield allowed assessing the effects of ciprofloxacin on the photochemical efficiency of the Photosystem II (PSII). The pro-oxidant effects induced by ciprofloxacin were evaluated by measuring oxidative stress biomarkers, such as catalase activity, and also by determining lipoperoxidation levels. The obtained results showed no differences in terms of the content of both chlorophylls a and b, or any change in the photochemical efficiency of the PSII; however, the global carotenoids content of L. gibba were significantly decreased. The activity of the anti-oxidant enzyme catalase was also significantly increased in L. minor. L. gibba showed a decrease in lipid peroxidation levels, but only for the two lowest concentrations of ciprofloxacin. The global set of data shows the activation of the anti-oxidant defensive system of both plant species, a response that was likely activated by the pro-oxidant character of ciprofloxacin. Our data demonstrate the interference of this therapeutic compound at different levels of plant metabolism, at ecologically relevant concentrations. In fact, the obtained results are of ecological relevance since they illustrate deleterious effects that may compromise the physiology of aquatic non-target plant species.

Effects of commonly used therapeutic drugs, paracetamol, and acetylsalicylic acid, on key physiological traits of the sea snail Gibbula umbilicalis

Over time, the consumption of pharmaceutical drugs has highly augmented, directly contributing for an increase of the discharges of these substances into sewage water due to excretion, and their direct release to the environment, with or without adequate treatment. Considering that part of the sewage water is dumped into rivers and seas, this is the major source of contamination of the aquatic environment. Paracetamol and acetylsalicylic acid are among the most worldwide consumed pharmaceutical drugs, frequently found in wastewater discharges and consequently in the aquatic environment in considerable amounts, posing ecotoxicity concerns especially towards aquatic non-target species. Thus, it is important to study the ecotoxicological implications that these drugs might pose to organisms from aquatic environments. The objective of this study was to assess the toxic effects of these two compounds on key biochemical features (antioxidant defenses and damage, metabolism, and cholinergic neurotoxicity) of the marine snail species Gibbula umbilicalis after an acute (96 h) exposure, simulating pulses of contamination. In order to understand the effects that those drugs have on this species, the biochemical biomarkers analyzed were the activities of catalase (CAT), glutathione-S-transferases (GSTs), cholinesterases (ChEs), and the levels of lipid peroxidation (TBARS). After acute exposure to paracetamol, catalase activity decreased significantly in organisms exposed to both highest concentrations; no significant alterations were observed for glutathione-S-transferases activity; TBARS concentration decreased significantly in organisms exposed to the intermediate and both highest concentrations, and cholinesterase activity increased significantly in animals exposed to the lowest concentration. However, after acute exposure to acetylsalicylic acid, catalase activity increased significantly; no significant alterations were observed for glutathione-S-transferases activity, and TBARS concentrations and cholinesterase activity increased. This set of data shows that G. umbilicalis is highly responsive to the presence of the tested drugs, and may thus be a promising species to serve as test organism in future marine ecotoxicological testing. The adoption of this species may broaden the offer of highly ecologically representative test organisms to be included in biomonitoring projects of the coastal and marine environment. Furthermore, it is possible to suggest that both drugs may pose significant deleterious effects of pro-oxidative origin to the physiology of the selected species, with potential adverse ecological consequences, even after short periods of exposure. The absence of neurotoxicity showed that despite being able to trigger antioxidant mechanisms, both drugs did not affect neurotransmission.

Combined effects of erythromycin and enrofloxacin on antioxidant enzymes and photosynthesis-related gene transcription in Chlorella vulgaris

Multiple antibiotics are simultaneously detected in aquatic environment, so it is extremely important to study the combined effects of their mixtures. In this study, we investigated the toxic effects of erythromycin (ERY) and enrofloxacin (ENR), added individually or in combination, on Chlorella vulgaris and explored the toxic mechanisms. Results showed that the 96 h-EC₅₀ values of ERY, ENR and ERY-ENR mixture to C. vulgaris were 85.7, 124.5 and 39.9 μg L^-1 respectively, and combined toxicity assessment found that joint effect of the two antibiotics was synergism, which was proven by the chlorophyll content in algae. Antioxidant defense system and photosynthesis were involved in toxic mechanisms and the results revealed that both the activities of antioxidant enzymes, and the malondialdehyde (MDA) and glutathione (GSH) contents increased in antibiotic treatments. In addition, the increase was more significant in joint exposure treatment, which implied that the antioxidant defense system was synergistically affected. RT-PCR showed that ERY and ENR upregulated the transcript abundance of psaB, psbC and chlB at low concentrations and the transcription abundance was synergistically increased in combined treatment. Therefore, the risk of the toxicity of antibiotics to aquatic organisms in real environment both at organismal and molecular level increases as a result of their combined presence.

Degradation of sulfadimethoxine by permanganate in aquatic environment: Influence factors, intermediate products and theoretical study

The excess sulfadimethoxine (SDM) in the environment could lead to antibiotic resistance by microorganisms and may do harm to many aquatic organisms. In this work, the removal of SDM by potassium permanganate (KMnO₄) was comprehensively studied. The influence of various factors, including the pH, oxidant doses, and temperature, on SDM removal were investigated. The optimal reaction conditions were determined to be pH 5.0, T = 25 °C and [KMnO₄]₀ = 200 μmol L^-1. Anions (Cl^-, SO₄^2-, HCO₃^2-, and NO₃^-) and cations (K⁺, Ca²⁺, Mg²⁺, and NH₄⁺) had no significant influence on the removal of SDM. However, H₂PO₄^- improved the efficiency of SDM removal by KMnO₄. Humic acid (0-10 mg L^-1) promoted the removal of SDM, which was attributed to the generation of in situ MnO₂. Meanwhile, the degradation of SDM in various water matrices was studied, and the removal order was ultrapure water > Jiuxiang river water ≈ synthetic water > secondary clarifier effluent. According to ten intermediate products identified and a frontier electron densities (FED) calculation, several pathways were proposed that involve the oxidation of amidogen, the cleavage of CS and SN bonds, and an oligomerization reaction. The predicted toxicity assessment indicated that most of the degradation products were not harmful to aquatic organisms except SDM dimers (connection by HNNH), suggesting that byproducts, such as dimers, formed during the oxidation of SDM and other sulfonamides should be taken into consideration. In sum, KMnO₄ has the potential to remove SDM from the aquatic environment.

Effect of PHRs and PCPs on Microalgal Growth, Metabolism and Microalgae-Based Bioremediation Processes: A Review

In this review, the effect of pharmaceuticals (PHRs) and personal care products (PCPs) on microalgal growth and metabolism is reported. Concentrations of various PHRs and PCPs that cause inhibition and toxicity to growths of different microalgal strains are summarized and compared. The effect of PHRs and PCPs on microalgal metabolism (oxidative stress, enzyme activity, pigments, proteins, lipids, carbohydrates, toxins), as well as on the cellular morphology, is discussed. Literature data concerning the removal of PHRs and PCPs from wastewaters by living microalgal cultures, with the emphasis on microalgal growth, are gathered and discussed. The potential of simultaneously bioremediating PHRs/PCPs-containing wastewaters and cultivating microalgae for biomass production in a single process is considered. In the light of reviewed data, the feasibility of post-bioremediation microalgal biomass is discussed in terms of its contamination, biosafety and further usage for production of value-added biomolecules (pigments, lipids, proteins) and biomass as a whole.

Combined effects of sulfamethazine and sulfamethoxazole on a freshwater microalga, Scenedesmus obliquus: toxicity, biodegradation, and metabolic fate

This study investigated the environmental effects of two common emerging contaminants, sulfamethazine (SMZ) and sulfamethoxazole (SMX), and their mixture using a green microalga, Scenedesmus obliquus. The calculated EC₅₀ values of SMZ, SMX, and their mixture (11:1 wt/wt) after 96 h were 1.23, 0.12, and 0.89 mg L^-1, respectively. The toxicity of the mixture could be better predicted using a concentration addition model than an independent action model. The risk quotients of SMZ, SMX, and their mixture were >1 during the experiment, indicating their high potential risks on aquatic microorganisms. Despite their toxicity, S. obliquus exhibited 17.3% and 29.3% removal of 0.1 mg L^-1 and 0.2 mg L^-1 after 11 days of cultivation. The changes of SMZ and SMX removal were observed when combined, which showed a significantly improved removal of SMZ (up to 3.4 folds) with addition of SMX (0.2 mg L^-1). The metabolic pathways of SMZ and SMX were proposed according to mass spectroscopic analysis, which showed six metabolites of SMX and seven intermediates of SMZ, formed as a result of ring cleavage, hydroxylation, methylation, nitrosation, and deamination.

Removal of sulfapyridine by ferrate(VI): efficiency, influencing factors and oxidation pathway

The removal of sulfapyridine (SPY) by ferrate(VI) in aqueous solutions under a broad range of reaction conditions, including ferrate(VI) dosage, solution pH, natural organic matter and coexisting inorganic ions, was systematically investigated and the oxidation pathway of SPY by ferrate(VI) was deeply explored. Results showed that 500 µg/L of SPY was efficiently decomposed (86%) within 1 min by 5 mg/L ferrate(VI) at pH 5.6. The increment in ferrate(VI) dosage was surely favorable for SPY removal. The best SPY degradation was achieved at pH 5.6, under or above which the removal decreased. The introduction of inorganic ions in solutions retarded SPY removal. Ten oxidation intermediates were identified and the cleavages of C-S and S-N bonds might be the primary ways of SPY oxidation by ferrate(VI).

Identification of the pollutants' removal and mechanism by microalgae in saline wastewater

This study investigated the growth dynamics of a freshwater and marine microalgae with supported biochemical performance in saline wastewater, the pollutants assimilation by a developed method, and the mechanism of salinity's effect to pollutants assimilation. Maximal biomass yield was 400-500 mg/L at 0.1-1% salinity while the TOC, NO₃^--N, PO₄^3--P were eliminated 39.5-92.1%, 23-97.4% and 7-30.6%, respectively. The biomass yield and pollutants removal efficiencies reduced significantly when salinity rose from 0.1 to 5%. The freshwater Chlorella vulgaris performed its best with a focus on TOC removal at 0.1% salinity. The marine Chlorella sp. was prominent for removing NO₃^--N at 0.1-1% salinity. Through the developed method, the freshwater C. vulgaris competed to the marine microalgae referring to pollutants assimilation up to 5% salinity. This study unveiled the mechanism of salinity's effect with evidence of salt layer formation and salt accumulation in microalgae.

Effect of elevated benzophenone-4 (BP4) concentration on Chlorella vulgaris growth and cellular metabolisms

Benzophenone-4 (BP4), as the raw material of common sunscreen products, usually shows strong eco-toxicity and endocrine-disrupting activity in aquatic animals. However, the potential adverse effect of BP4 on aquatic vegetation is still unclear. In order to evaluate the inhibitory effect of BP4 on phytoplankton, wild and acclimated Chlorella vulgaris was used as representative aquatic plant cells and experimental studies were conducted on the characteristics of its growth and cellular metabolisms upon exposure to elevated BP4 concentrations (1, 5, 10, 20, 50, and 100 mg L^-1). C. vulgaris basically appeared low sensitivity to BP4 exposure because the 96-h EC₅₀ was measured as 65.16 mg L^-1 for its wild type. The 96-h EC₅₀ of the acclimated type, which was pre-exposed to 10 mg L^-1 of BP4 and transferred twice, was 140.76 mg L^-1. By cellular response tests regarding non-enzymatic antioxidants carotenoid content, malondialdehyde (MDA), enzyme antioxidant superoxide dismutase (SOD) activity, and the photosynthetic efficiency, it was clarified that increasing exposure concentration elevated the hindrance to cellular metabolism. However, the rate of BP4 utilization as substrates for C. vulgaris growth showed a trend of decreasing with increasing BP4 concentration. The higher 96-h EC₅₀ value of the acclimated C. vulgaris to BP4 inhibition than the wild C. vulgaris showed the enhanced tolerance capability; however, the continuous stress response of acclimated type should be taken into account when using microalgae species for toxicity assessment.

Effects of five sulphonamides on duckweed (Lemna minor) after prolonged exposure time and their dependency on photoradiation

Sulphonamides (SAs) are one of the most commonly used veterinary drugs and therefore their residues are regularly found in the environment. So far scientific attention has mostly been paid to the evaluation of their acute ecotoxicological effects with data on long-term effects for non-target organisms still largely missing. Therefore, the main aim of this study was to evaluate the potential toxicities of five sulphonamides to duckweed (Lemna minor) after prolonged exposure time (14days). To elucidate whether their phytotoxic effects result from potential photodegradation products, the toxicity of standard solutions of selected sulphonamides was also investigated in a standard 7-day test but after irradiation (by keeping them under the test conditions) for the selected time (after 7 and 14days). The ecotoxicological tests were accompanied by chemical analyses to be able to link the observed effects to the concentrations and nature of the exposed compounds. The results showed a shift in the toxicity of SAs: a strong decrease in toxicity for the two most toxic sulphonamides (sulphamethoxazole and sulphadimethoxine) and a slight increase in toxicity for three other SAs (sulphadimidine, sulphathiazole, sulphamerazine) in the prolonged test. However, a decrease in the toxicity and concentration of all the SAs was observed when stock solutions were irradiated prior to the toxicity experiment, which suggests that the observed effects towards L. minor of five SAs in the prolonged test cannot be directly associated with the degradation of these compounds under the test conditions but with their different mode of toxic action towards these organisms.

Integrated toxic evaluation of sulfamethazine on zebrafish: Including two lifespan stages (embryo-larval and adult) and three exposure periods (exposure, post-exposure and re-exposure)

Persistence of antibiotics in aquatic environment may pose a risk to the non-target aquatic organisms. This study provided an integrated evaluation to analyze the toxic stress of sulfamethazine (SMZ) on zebrafish in two lifespan stages (embryo-larval and adult) and three exposure periods (exposure, post-exposure and re-exposure). Zebrafish embryos and adult zebrafish were exposed to SMZ at 0.2, 20 and 2000 μg/L, respectively. The results showed that SMZ at any given concentration inhibited the hatching of embryos at 58-96 hpf (hours post-fertilization). Our result also indicated that two major kinds of the malformation, which was induced by the antibiotic, were edema and spinal curvature. Additionally, the antibiotic stimulated the heartbeat while reduced the body length of the embryo at 72 hpf. Superoxide dismutase (SOD) activities and malondialdehyde (MDA) contents significantly increased at 120 hpf when the embryos were exposed to the lowest concentration (0.2 μg/L) of the antibiotic. On the other hand, the antibiotic induced SOD activities and MDA contents in adult zebrafish in the exposure and re-exposure periods. The MDA contents could recover while SOD activities still increased in 2 d after the exposure. Both SOD activities and MDA contents could recover in 7 d after the exposure. Levels of SOD and MDA in the re-exposure were higher than those in the first exposure. Our results suggested that SMZ had toxic effects on both embryos and adult zebrafish, and provided an integrated evaluation of the toxic effects of SMZ on zebrafish at a new perspective.

Permanganate with a double-edge role in photodegradation of sulfamethoxazole: Kinetic, reaction mechanism and toxicity

In this study, the double-edge role of permanganate in sulfamethoxazole (SMX) photodegradation with a recyclable catalyst was revealed for the first time. The role of the catalyst under different UV wavelength, the role of permanganate in the treatment process, the effects of permanganate dosage and solution pH on the removal efficiency were investigated. Moreover, the transformation products, TOC reduction and the toxicity of the treated final product to Chlorella vulgaris and Artemia salina were determined. Sole permanganate showed no effect in SMX degradation, while its introduction to the photocatalytic process doubled the reaction rate at the optimal dosage. It is interesting to find that the reaction rate showed a fluctuation trend in terms of permanganate dosage due to the summation of positive effect of permanganate oxidation and the negative effect of the formed MnO₂ at the surface of the catalyst, as well as the light attenuation due to overdosed permanganate. The determined intermediates, the higher inorganic ions release and TOC reduction provided a clue on a higher mineralization compared to SMX degradation in the same process without permanganate. Permanganate above 1 μM may pose a threat to the algae growth, therefore a good monitoring and control of residual permanganate dosage should be incorporated into the process design. A good toxicity reduction to A. salina was observed in the treated effluent; a longer detention is suggested for the complete removal of toxicity.