Evaluation of the toxicity of clozapine on the freshwater diatom Navicula sp. using the FTIR spectroscopy.

Clozapine is an often prescribed neuroactive pharmaceutical and frequently detected in the aquatic environments. However, its toxicity on low trophic level species (i.e., diatoms) and associated mechanisms are seldom reported. In this study, the toxicity of clozapine on a widely distributed freshwater diatom Navicula sp. was evaluated using the FTIR spectroscopy along with biochemical analyses. The diatoms were exposed to various concentrations of clozapine (0, 0.01, 0.05, 0.10, 0.50, 1.00, 2.00, 5.00 mg/L) for 96 h. The results revealed that clozapine reached up to 392.8 µg/g in the cell wall and 550.4 µg/g within the cells at 5.00 mg/L, suggesting that clozapine could be adsorbed extracellularly and accumulated intracellularly in diatoms. In addition, hormetic effects were displayed on the growth and photosynthetic pigments (chlorophyll a and carotenoid) of Navicula sp., with a promotive effect at concentrations less than 1.00 mg/L while an inhibited effect at concentrations over 2 mg/L. Clozapine induced oxidative stress in Navicula sp., accompanied by decreased levels of total antioxidant capacity (T-AOC) (>0.05 mg/L), in which, the activity of superoxide dismutase (SOD) (at 5.00 mg/L) was increased whereas the activity of catalase (CAT) (>0.05 mg/L) was decreased. Furthermore, FTIR spectroscopic analysis showed that exposure to clozapine resulted in accumulation of lipid peroxidation products, increased sparse ß-sheet structures, and altered DNA structures in Navicula sp. This study can facilitate the ecological risk assessment of clozapine in the aquatic ecosystems.

Cyclophosphamide alters the behaviors of adult Zebrafish via neurotransmitters and gut microbiota.

Cyclophosphamide, one of the earliest prescribed alkylating anticancer drugs, has been frequently detected in aquatic environments. However, its effects on fish behavior and associated mechanisms remain largely unknown. In this study, the behaviors, neurochemicals, and gut microbiota of adult zebrafish were investigated after 2 months of exposure to CP at 0.05, 0.5, 5, and 50 µg/L. Behavioral assays revealed that CP increased locomotion and anxiety, and decreased the cognition of zebrafish. The alteration of neurotransmitters and related gene expressions in the dopamine and gamma-aminobutyric acid pathways induced by CP may be responsible for the observed changes in locomotion and cognition of adult zebrafish. Meanwhile, CP increased the anxiety of adult zebrafish through the serotonin, acetylcholine, and histamine pathways in the brain. In addition, increased abundances of Fusobacteriales, Reyanellales, Staphylococcales, Rhodobacterals, and Patescibateria in the intestine at the CP-50 treatment were observed. The study has demonstrated that CP affects the locomotion, anxiety, and cognition in zebrafish, which might be linked with the dysfunction of neurochemicals in the brain. This study further suggests that the gut-brain axis might interact to modulate fish behaviors upon exposure to CP (maybe other organic pollutants). Further research is warranted to test this hypothesis.

Altered life history traits and transcripts of molting- and reproduction-related genes by cadmium in Daphnia magna.

Cadmium (Cd) is a non-essential element and can be toxic to aquatic organisms at low concentrations. Despite its well-known toxicity to Daphnia magna, the effects of Cd on physiological parameters (heart rate and thoracic limb activity) and molting- and reproduction-related genes are relatively understudied. In this study, D. magna were exposed to 0 (control), 25, 50 and 75 µg L-1 of Cd for 7 d and 21 d to determine the toxicity of Cd. The results showed that the Cd body burden in D. magna was significantly increased with elevated Cd concentrations, up to 13.4 µg Cd/g dry weight (dw) after exposure to 75 µg L-1 for 21 d. After 21 d of exposure, the body length and body weight of D. magna were significantly decreased in all Cd treatments compared to the control. The heart rate and thoracic limb activity were reduced by 4.3-11.7 and 5.0-10.3%, respectively. The levels of malondialdehyde (MDA) were increased by ~24-37% and the activity of catalase (CAT) was inhibited by ~50% compared to the control. The reproductive parameters (i.e., size of the first brood, the total number of offspring per female and the number of offspring per brood) were remarkably reduced, causing adverse effects on the population dynamics. In addition, the transcripts of genes (cyp314, cyp18a1, ecra, usp, hr3, cut, cht and cht3) related to the molting of D. magna were altered, whereas the transcripts of genes (vtg1, vtg2 and vmo1) related to reproduction were down-regulated. This study helps better understand the effects of Cd at different biological levels.

Transformation products of tetracyclines in three typical municipal wastewater treatment plants.

Antibiotics in the environment could undergo various processes with formation of transformation products, but little has been known about their occurrence and (eco)toxicological consequences. Here we investigated the occurrence and fate of nine transformation products of four tetracyclines (tetracycline, oxytetracycline, chlortetracycline and doxycycline) in three municipal wastewater treatment plants (WWTPs) in Guangzhou, China. The results showed the detection of all the tetracyclines and their transformation products in the WWTPs, with mean concentrations ranging from 17.8 ng/L (anhydrotetracycline) to 49.1 ng/L (oxytetracycline) in influent, 3.03 ng/L (tetracycline) to 6.94 ng/L (4-epi-chlortetracycline) in effluent, and 19.8 ng/g (isochlortetracycline) to 503 ng/g (4-epi-tertracycline) in sludge, respectively. The transformation products of tetracycline, oxytetracycline, chlortetracycline and doxycycline accounted for 73%-83%, 26%-52%, 70%-73% and 69%-74% of total concentrations, respectively. The aqueous removal rates of tetracyclines and their transformation products in the three WWTPs ranged from 18.4% (demethyl-chlortetracycline) to 93.7% (oxytetracycline). Mass balance analysis based on both aqueous and solid phase showed that their removals were mainly attributed to the sludge adsorption. Residual tetracyclines and their transformation products in the effluents would pose no obvious ecological risks to three aquatic organisms (green algae, daphnia and fish). However, 43.5% of sludge samples had high risks from these tetracyclines and transformation products, especially the compounds with poor biodegradability. The results from this study suggest that transformation products should be included in future environmental monitoring and control.

The effects of the chemotherapy drug cyclophosphamide on the structure and functioning of freshwater communities under sub-tropical conditions: A mesocosm study.

Cyclophosphamide (CP) is a chemotherapy drug which is widely used in the treatment of neoplastic diseases and have often been detected in urban and hospital wastewater, and surface waters. However, at present the effects of CP on aquatic organisms and ecosystems are poorly understood. The main objective of the present study was to assess the effect of CP on the structure and functioning of a sub-tropical freshwater ecosystem (macroinvertebrates, zooplankton and phytoplankton) at environmental relevant concentrations. CP (0, 0.5, 5 and 50 µg/L) was applied weekly to 13,600 L mesocosms over a period of four weeks followed by a one month post exposure period. CP was found to dissipate much faster than previous reported in literature and the half-dissipation times were treatment dependent, being 2.2, 21.3 and 23.6 days in the lowest, middle and highest treatments respectively. Only treatment related effects were observed on the community structure at individual samplings with zooplankton (NOECcommunity = 0.5 µg/L) responding at lower concentrations than phytoplankton (NOECcommunity = 5 µg/L) and macroinvertebrates (NOECcommunity ≥ 50 µg/L). The dissolved organic carbon concentration was consistently higher in the 2 highest treatments, indicating a potential effect on food web interactions and/or the microbial loop. At the population level, consistent adverse effects were observed for the plankton taxa Pleuroxus laevis, Dissotrocha sp. and Oscillatoria sp. at all CP concentrations (NOEC <0.5 µg/L). Additionally, at the highest CP treatments 7% of all the taxa showed a clear short-term adverse effect. Based on comparison with literature data it can be concluded that these taxa have the highest CP sensitivity ever recorded and these findings indicate a potential CP risk to aquatic ecosystems at environmental relevant concentrations.

Cyclophosphamide affects eye development and locomotion in zebrafish (Danio rerio).

Cyclophosphamide (CP) is a broad-spectrum anticancer drug and has been frequently detected in aquatic environments due to its incomplete removal by wastewater treatment facilities and slow degradation in waters. Its toxicity in fish remains largely unknown. In this study, zebrafish eggs <4 h post fertilization (hpf) were exposed to CP at the concentrations from 0.5 to 50.0 µg/L until 168 hpf, and its toxicity was evaluated by biochemical, transcriptomic, and behavioral approaches. The results showed that malformation and mortality rates increased with CP concentrations. The 7-day malformation EC50 and mortality (LC30) by CP were calculated to be 86.8 µg/L and 7.5 mg/L, respectively. Inhibited startle response (light to dark) (a minimal of 19%) and reduced swimming velocity (a minimal of 30%) were observed in the CP-exposed larvae. The thicknesses of retinal ganglion layer, inner plexiform layer, and inner nuclear layer in the retina were increased after exposure to CP. Meanwhile, exposure to CP increased karyorrhexis and karyolysis in the liver tissue. Transcriptomic analysis identified 607 differentially expressed genes (DEGs) (159 up-regulated and 448 down-regulated). A significant reduction in the transcripts of sgk1 (the FoxO pathway), jun (the MAPK pathway), and diabloa (apoptosis pathway) were observed in the CP-treated larvae. This study has demonstrated that low concentrations of CP cause malformation, reduced swimming capacity, histopathological alterations in the retina and liver tissues, and interference on transcriptional expressions of key genes associated with different pathways. The ecological risk of CP and other anticancer drugs to aquatic organisms merits future investigation.

Dietary Seleno-l-methionine Alters the Microbial Communities and Causes Damage in the Gastrointestinal Tract of Japanese Medaka Oryzias latipes.

Excess dietary seleno-l-methionine (Se-Met) induces various adverse effects in fish inhabiting the Se-contaminated environments. However, there is an extreme paucity of data on the effects of excess dietary Se-Met on the microbiota in the gastrointestinal (GI) tract in fish. In this study, Japanese medaka Oryzias latipes (three months old) were fed the Se-Met enriched diets at environmentally relevant concentrations: 2.90 (Control: (C), 6.69 (L), 11.89 (M), and 27.05 (H) µg Se/g dw) for 60 d. Histopathological, high throughput sequencing, and biochemical approaches were used to investigate the alterations in histology and microbial communities of the GI tract, enzymatic activity, and transcripts of closely related genes. The results showed that the fish weight was reduced at ∼13% from the L and H treatments. Decreased height and thickness of villus in the GI tract were observed in the H treatment. Meanwhile, the level of D-lactate and activity of diamine oxidase (DAO), protease, and lipase were inhibited in the H treatment. The transcripts of the genes related to the inflammation (i.e., IL-1ß and IL-8) were elevated, while those of the genes related to the intestinal barrier (i.e., cdh1, ZO-1, ocln, and cldn7) were inhibited in the H treatment. In addition, alpha diversity at the genus level was higher in the L treatment than the control, and the composition of the microbial community was altered by dietary Se-Met. Furthermore, 5 genera (Rhodobacter, Cloacibacterium, Bdellovibrio, Shinella, and Aeromonas) exhibited the largest variation in abundance among treatments. This study has demonstrated that excess dietary Se-Met inhibits growth, causes hispathological damage to the GI tract, and alters the composition of the microbial community in Oryzias latipes.

Imidacloprid treatments induces cyanobacteria blooms in freshwater communities under sub-tropical conditions.

Imidacloprid is one of the most used neonicotinoid insecticides all over the world and is considered as a contaminant of concern due to its high toxicity potential to aquatic organisms. However, the majority of the studies that have evaluated the effects of imidacloprid on aquatic organisms were conducted under temperate conditions. In the present study, a mesocosm experiment was conducted under sub-tropical conditions to assess the effects of imidacloprid on the structure (macroinvertebrates, zooplankton and phytoplankton) and functional endpoints of an aquatic ecosystem and to compare the results with similar temperate and (sub-)tropical mesocosm studies. Imidacloprid (0, 0.03, 0.3 and 3 µg/L) was applied to 13 mesocosms weekly over a period of 4 weeks, followed by a one month recovery period. At the community level a lowest NOECcommunity of 0.03 µg/L was calculated for the zooplankton, phytoplankton and macroinvertebrate communities. The highest sensitivity to imidacloprid (NOEC < 0.03 µg/L) were observed for Gerris sp., Diaptomus sp. and Brachionus quadridentatus. Imidacloprid induced population declines of the larger zooplankton species (Diaptomus sp. and Ostracoda) resulted in increased rotifer abundances and shifted the phytoplankton community to a graze resistant gelatinous cyanobacteria dominated ecosystem. These cyanobacteria blooms occurred at all different concentrations and could pose an important public health and environmental concern. Although there are some differences in species and community sensitivity between the present and the other (sub-)topical mesocosm studies, it can be observed that all show a similar general community response to imidacloprid. Under (sub-)tropical conditions, the toxic effects of imidacloprid occur at lower concentrations than found for temperate ecosystems.

Dietary Seleno-l-Methionine Causes Alterations in Neurotransmitters, Ultrastructure of the Brain, and Behaviors in Zebrafish (Danio rerio).

Elevated concentrations of dietary selenium (Se) cause abnormalities and extirpation of fish inhabiting in Se-contaminated environments. However, its effect on fish behavior and the underlying mechanisms remain largely unknown. In this study, two-month-old zebrafish (Danio rerio) was fed seleno-l-methionine (Se-Met) at environmentally relevant concentrations (i.e., control (2.61), low (5.43), medium (12.16), and high (34.61) µg Se/g dry weight (dw), respectively, corresponding to the C, L, M, and H treatments) for 60 days. Targeted metabolomics, histopathological, and targeted transcriptional endpoints were compared to behavioral metrics to evaluate the effects of dietary exposure to Se-Met . The results showed that the levels of total Se and malondialdehyde in fish brains were increased in a dose-dependent pattern. Meanwhile, mitochondrial damages and decreased activities of the mitochondria respiratory chain complexes were observed in the neurons at the M and H treatments. In addition, dietary Se-Met affected neurotransmitters, metabolites, and transcripts of the genes associated with the dopamine, serotonin, gamma-aminobutyric acid, acetylcholine, and histamine signaling pathways in zebrafish brains at the H treatments. The total swimming distance and duration in the Novel Arm were lowered in fish from the H treatment. This study has demonstrated that dietary Se-Met affects the ultrastructure of the zebrafish brain, neurotransmitters, and associated fish behaviors and may help enhance adverse outcome pathways for neurotransmitter-behavior key events in zebrafish.

Occurrence, fate and mass loading of benzodiazepines and their transformation products in eleven wastewater treatment plants in Guangdong province, China.

Benzodiazepines (BZDs) are one of the most widely prescribed psychoactive drugs, however their persistence in the receiving environment has raised great concerns about their potential ecological risks. Here we investigated the occurrence, fate and mass loading of 17 BZDs and their 3 transformation products in 11 wastewater treatment plants (WWTPs) in Guangdong province, China. A total of 10 BZDs and 1 transformation product were found in the WWTPs influents, effluents and excess sludge, with concentrations reaching up to 44.5 ng/L (clozapine), 27.1 ng/L (oxazepam) and 62.9 ng/g (clozapine), respectively. The overall removal efficiency varied widely from negative to complete removal in these 11 WWTPs. Mass balance analysis of two representative WWTPs (WWTPA and WWTPB) with different treatment processes showed that their removals were mainly attributed to the sludge adsorption and biodegradation/biotransformation. The total usage of detected BZDs was estimated to be 185 kg/y in Guangdong province, China, while the total emission was 143 kg/y. Based on sewage epidemiology method, the total back-estimated consumption and emissions of BZDs and their transformation products in one district of Guangzhou (WWTPC service area) were 1012 mg/d/1000 people and 10.1 mg/d/1000 people, respectively. The findings from this study demonstrate the persistence of BZDs in WWTPs and also provide basis for further investigation into the potential ecological risks from this group of chemicals.