Influence of multi-walled carbon nanotubes on the effects of roxithromycin in crucian carp (Carassius auratus) in the presence of natural organic matter

Polystyrene microplastics exacerbate acetochlor-induced reproductive toxicity and transgenerational effects in zebrafish

Microplastic (MPs) can adsorb co-existing pollutants, and alter their behavior and toxicity. Meanwhile, amide herbicides like acetochlor (ACT) are widely used in agriculture, with potential endocrine-disrupting effects that raise ecological concerns. The aim of this research was to examine the effects of MPs on the reproductive endocrine disruption caused by ACT and the effects of maternal transmission. Zebrafish were employed in this study to assess the reproductive toxicity of ACT alone and in combination with polystyrene microplastics (PS-MPs) of different sizes (200 nm and 2 μm) and concentrations (0.1 and 1 mg/L) over a 63-day exposure experiment. The results indicated that ACT was concentrated in zebrafish tissues in the order: intestine > liver > gill > brain > gonad > muscle. PS-MPs increased ACT bioaccumulation, worsened gonadal damage, led to abnormalities in hormone levels, and caused disruptions in HPG axis gene expression, further exacerbating the reproductive toxicity. Maternal transfer of ACT affected offspring growth, thyroid function, and HPT axis gene expression, with nanoplastics (NPS) amplifying these adverse effects. This study offers crucial insights into the ecological hazards posed by ACT and PS-MPs, emphasizing the increased toxicity due to PS-MPs.

Unveiling combined ecotoxicity: Interactions and impacts of engineered nanoparticles and PPCPs

Emerging contaminants such as engineered nanoparticles (ENPs), pharmaceuticals and personal care products (PPCPs) are of great concern because of their wide distribution and incomplete removal in conventional wastewater and soil treatment processes. The production and usage of ENPs and PPCPs inevitably result in their coexistence in different environmental media, thus posing various risks to organisms in aquatic and terrestrial ecosystems. However, the existing literature on the physicochemical interactions between ENPs and PPCPs and their effects on organisms is rather limited. Therefore, this paper summarized the ecotoxicity of combined ENPs and PPCPs by discussing: (1) the interactions between ENPs and PPCPs, including processes such as aggregation, adsorption, transformation, and desorption, considering the influence of environmental factors like pH, ionic strength, dissolved organic matter, and temperature; (2) the effects of these interactions on bioaccumulation, bioavailability and biotoxicity in organisms at different trophic levels; (3) the impacted of ENPs and PPCPs on cellular-level biological process. This review elucidated the potential ecological hazards associated with the interaction of ENPs and PPCPs, and serves as a foundation for future investigations into the ecotoxicity and mode of action of ENPs, PPCPs, and their co-occurring metabolites.

Carbon nanotubes and nanofibers seen as emerging threat to fish: Historical review and trends

Since the discovery of the third allotropic carbon form, carbon-based one-dimensional nanomaterials (1D-CNMs) became an attractive and new technology with different applications that range from electronics to biomedical and environmental technologies. Despite their broad application, data on environmental risks remain limited. Fish are widely used in ecotoxicological studies and biomonitoring programs. Thus, the aim of the current study was to summarize and critically analyze the literature focused on investigating the bioaccumulation and ecotoxicological impacts of 1D-CNMs (carbon nanotubes and nanofibers) on different fish species. In total, 93 articles were summarized and analyzed by taking into consideration the following aspects: bioaccumulation, trophic transfer, genotoxicity, mutagenicity, organ-specific toxicity, oxidative stress, neurotoxicity and behavioral changes. Results have evidenced that the analyzed studies were mainly carried out with multi-walled carbon nanotubes, which were followed by single-walled nanotubes and nanofibers. Zebrafish (Danio rerio) was the main fish species used as model system. CNMs' ecotoxicity in fish depends on their physicochemical features, functionalization, experimental design (e.g. exposure time, concentration, exposure type), as well as on fish species and developmental stage. CNMs' action mechanism and toxicity in fish are associated with oxidative stress, genotoxicity, hepatotoxicity and cardiotoxicity. Overall, fish are a suitable model system to assess the ecotoxicity of, and the environmental risk posed by, CNMs.

Accumulation of polystyrene nanoplastics and triclosan by a model tooth-carp fish, Aphaniops hormuzensis (Teleostei: Aphaniidae)

The presence and effects of nanoplastics (NPs; <1 μm) in the aquatic environment are a growing concern. In this study, a model tooth-carp fish, Aphaniops hormuzensis, has been exposed to different concentrations of fluorescent polystyrene nanoplastics (PS-NP) in its diet (up to 5 mg kg-1) over periods of 28 d and the particle accumulation in different tissues determined. Accumulation was observed in both digestive and non-digestive organs, with concentrations greater in the gut, liver and gill (up to 400 μg kg-1 dw) than in the skin and muscle (<180 μg kg-1 dw), but no dependency on exposure time or dose was evident. The presence of the organic contaminant, triclosan (TCS), in the diet and at concentrations up to 0.5 μg kg-1 did not affect PS-NP uptake by A. hormuzensis, while TCS accumulation in the whole body increased with time (up to 10 μg kg-1) and, likewise, appeared to be unaffected by the presence of PS-NPs. These observations suggest that the two contaminants do not interact with each other or that any interactions have no impact on accumulation. The results of this study add to the growing body of evidence that NPs can be translocated by aquatic organisms after ingestion, and reveal that, for the species and conditions employed, nanoplastics are accumulated more readily than a widely used organic chemical.

How multi-walled carbon nanotubes in wastewater influence the fate of coexisting antibiotic resistant genes in the subsequent disinfection process

Wastewater treatment plants (WWTPs) are important hubs for the spread of antibiotic resistance genes (ARGs). Engineered nanoparticles, which was inevitably released to WWTPs, could change environmentally sensitive of antibiotic resistant bacteria (ARB). This would influence the fate of ARGs in subsequent disinfection process and consequent health risk. In this study, the ARGs fate of the effluent in conventional sodium hypochlorite (NaClO) disinfection process was investigated as multi-walled carbon nanotubes (MWCNTs) existed in sequencing batch reactor (SBR). The results showed the existence of MWCNTs in SBR could enhance the removal efficiency of intracellular 16S rRNA gene and intI1, extracellular intI1, sul2 and tetX in the effluent by NaClO. This is mainly due to the variation of bacterial physiological status, bacterial population structure and the activation of NaClO under the role of MWCNTs. MWCNTs in SBR could increase in membrane permeability of bacterial cells, which would be conducive to the penetration of chlorination to cytoplasm. MWCNTs in SBR also could change the bacterial population structure and induce the chlorine-sensitive bacteria; thus the potential hosts of ARGs in the effluent would be more easily inactivated by NaClO. Moreover, the residual MWCNTs in the effluent could activate NaClO to generate various free radical, which would enhance the oxidizing capacity of chlorination.

Intergenerational and biological effects of roxithromycin and polystyrene microplastics to Daphnia magna

The influence of microplastics (MPs) on transgenerational effects of pharmaceuticals are drawing growing attention, however, whether aged process will alter the carrier effects of MPs were unknown. In this study, the intergenerational toxicity of single and combined exposure of polystyrene microplastics (PS-MPs) and roxithromycin (ROX) were investigated at the environmentally related concentrations, using Daphina magna as test organism. In the presence of UV-aged PS-MPs, the survival of D. magna for maternal generation (F0) at ROX concentration of 0.1 and 10 µg/L were increased by 20% and 40%, respectively. Meanwhile, the inhibition effects of ROX on the number of offspring and intrinsic rate of natural increase were obviously moderated. All these reproductive toxicity of ROX and PS-MPs in the first offspring (F1) were further aggravated both for the single and combined exposure. And the adverse effects disappeared much easier for the single exposure compared to the co-exposure through subsequent recovery. The combined exposure resulted in the change of inhibition of ROX on the swimming velocity and acceleration of D. magna into induction, while the feeding behavior kept inhibited. The AChE activity was distinctly increased by 1.61-3.25 times for the single and combined treatments, and the induction level of UV-aged MPs was higher than that of original MPs. Oxidative stress of the single exposure of ROX and original PS-MPs was observed with obvious induction of T-AOC and SOD activity, while the significant increase of MDA content was observed for the co-exposure. Among all indicators, the biochemical biomarkers and time of first brood were attributed to a class among all indicators, indicating that the time of first brood might be the most sensitive reproductive toxicity index. These results illustrated that both maternal impacts and offspring quality need to be considered for assessment of interaction of emerging contaminants.

Migration of antibiotic resistance genes and evolution of flora structure in the Xenopus tropicalis intestinal tract with combined exposure to roxithromycin and oxytetracycline

The intestinal flora is one of the most important environments for antibiotic resistance development, owing to its diverse mix of bacteria. An excellent medicine model organism, Xenopus tropicalis, was selected to investigate the spread of antibiotic resistance genes (ARGs) in the intestinal bacterial community with single or combined exposure to roxithromycin (ROX) and oxytetracycline (OTC). Seventeen resistance genes (tetA, tetB, tetE, tetM, tetO, tetS, tetX, ermF, msrA, mefA, ereA, ereB, mphA, mphB, intI1, intI2, intI3) were detected in the intestines of Xenopus tropicalis living in three testing tanks (ROX tanks, OTC tanks, ROX + OTC tanks) and a blank tank for 20 days. The results showed that the relative abundance of total ARGs increased obviously in the tank with single stress but decreased in the tank with combined stress, and the genes encoding the macrolide antibiotic efflux pump (msrA), phosphatase (mphB) and integron (intI2, intI3) were the most sensitive. With the aid of AFM scanning, DNA was found to be scattered short chain in the blank, became extended or curled and then compacted with the stress from a single antibiotic, and was compacted and then fragmented with combined stress, which might be the reason for the variation of the abundance of ARGs with stress. The ratio of Firmicutes/Bacteroides related to diseases was increased by ROX and OTC. The very significant correlation between intI2 and intI3 with tetS (p ≤ 0.001) hinted at a high risk of ARG transmission in the intestines. Collectively, our results suggested that the relative abundance of intestinal ARGs could be changed depending on the intestinal microbiome and DNA structures upon exposure to antibiotics at environmental concentrations.

Multi-walled carbon nanotubes impact on the enantioselective bioaccumulation and toxicity of the chiral insecticide bifenthrin to zebrafish (Danio rerio)

The effects of different multi-walled carbon nanotubes on the enantioselective bioaccumulation and toxicity of the chiral pesticide bifenthrin to zebrafish were investigated in this work. The results showed that MWCNTs and MWCNTs-COOH did not affect the preferential bioaccumulation of 1R-cis-BF in zebrafish following exposure to cis-BF enantiomers for 28 days, but which increased cis-BF accumulation amount by 1.03-1.48 times. Further research demonstrated that the genes related to immunity, endocrine activity and neurotoxicity showed enantioselective expression in different zebrafish tissues, and sex-specific differences were observed. The levels of c-fos, th, syn2a, 17β-hsd and cc-chem were expressed as 1.09-2.84 times higher in females and males treated with 1R-cis-BF than in the 1S-cis-BF-treated groups. However, in the presence of MWCNTs or MWCNTs-COOH, c-fos, th, syn2a, 17β-hsd and cc-chem levels were expressed as 1.53-14.92 times higher in females and males treated with 1S-cis-BF than in 1R-cis-BF-treated groups, which indicated that enantioselective expression was altered. The effects of different types of MWCNTs on the enantioselective bioaccumulation and toxicity of BF in zebrafish have little difference. In summary, the presence of MWCNTs or MWCNTs-COOH increased the impact of BF on zebrafish. Therefore, the risks posed by coexisting nanomaterials and chiral pesticides in aquatic environments should be considered.

Migration, Transformation and Removal of Macrolide Antibiotics in The Environment: A Review

Macrolide antibiotics (MAs), as a typical emerging pollutant, are widely detected in environmental media. When entering the environment, MAs can interfere with the growth, development and reproduction of organisms, which has attracted extensive attention. However, there are few reviews on the occurrence characteristics, migration and transformation law, ecotoxicity and related removal technologies of MAs in the environment. In this work, combined with the existing relevant research, the migration and transformation law and ecotoxicity characteristics of MAs in the environment are summarized, and the removal mechanism of MAs is clarified. Currently, most studies on MAs are based on laboratory simulation experiments, and there are few studies on the migration and transformation mechanism between multiphase states. In addition, the cost of MAs removal technology is not satisfactory. Therefore, the following suggestions are put forward for the future research direction. The migration and transformation process of MAs between multiphase states (such as soil-water-sediment) should be focused on. Apart from exploring the new treatment technology of MAs, the upgrading and coupling of existing MAs removal technologies to meet emission standards and reduce costs should also be concerned. This review provides some theoretical basis and data support for understanding the occurrence characteristics, ecotoxicity and removal mechanism of MAs.

Toxicity of amine-functionalized single-carbon nanotube (NH2 f-SWCNT) to Channel Catfish (Ietalurus Punetaus): Organ pathologies, oxidative stress, inflammation, and apoptosis

The rapid development of carbon nanotubes (CNTs) in the field of fish disease control and prevention raises concerns about the toxicity and safe use in fish. This study was performed to assess the effect on histological changes, oxidative stress related markers in response to various concentrations of amine-functionalized single carbon nanotubes (NH₂ f-SWCNT) (1, 10 and 100 mg kg^-1 fish) in Channel Catfish (Ietalurus Punetaus) for up to 10 days. Moreover, pro-inflammatory cytokine genes and apoptotic genes were analyzed to obtain a better understanding of molecular mechanism of NH₂ f-SWCNT induced toxicity. As a result, intraperitoneal (i.p.) administration of NH₂ f-SWCNT caused dose-dependent and time-dependent injuries in the sampled tissues. In comparison with the control groups, decrease of catalase (CAT) activity and superoxide dismutase (SOD), and increase of malondialdehyde (MDA) and lactin dehydrogenase (LDH) were observed in all treatments. Real-time PCR assay showed inflammatory response with dose-dependent increase of tumor necrosis factor alpha (TNFα) and transient increase of interleukin 1β (IL-1β) in the liver. NH₂ f-SWCNT administration induced increase of p38 as well as caspase-3 in all treatments compared to the control groups, indicating the involvement of p38-MAPK cascade and caspase-3 cascade in liver cell apoptosis. Overall, we conclude that NH₂ f-SWCNT exert effects by direct injury and indirectly oxidative stress, resulting in inflammation and apoptosis, which provides data for understanding of the biological mechanisms underlying the toxicity of CNTs in fish.

Influence of suspended sediment on the bioavailability of benzophenone-3: Focus on accumulation and multi-biological effects in Daphnia magna

The UV-filter benzophenone-3 (BP3) tends to associate with suspended sediment (SPS) due to hydrophobicity, which could alter its toxicological effects on non-target aquatic organisms. In this study, the freshwater cladoceran Daphnia magna (D. magna) was selected as a model organism to investigate the impacts of the source and composition of SPS on the accumulation and multiple toxicological effects (from the molecular level to individual level) of BP3. Among the three components of SPS, amorphous organic carbon (AOC) and minerals promoted the body burden of BP3, while black carbon (BC) inhibited the bioaccumulation. The inhibition effects of BP3 on swimming and feeding behaviors of D. magna were also enhanced due to the presence of AOC and BC. Compared with BP3 exposure alone, higher oxidative stress and neurotoxicity were observed in the presence of SPS containing AOC, BC and minerals, corresponding to that superoxide dismutase, catalase and glutathione-S-transferase activities were further induced, and acetylcholinesterase activity was inhibited. Furthermore, BP3 induced mRNA expression levels of the endocrine system (ecdysone receptor, cytochrome P450 CYP314) and metabolic system (toxicant nuclear receptor HR96, P-glycoprotein), and the presence of SPS containing AOC, BC and minerals exhibited an enhanced effect. Combined with all endpoints, evident relationship was observed between the bioaccumulation level and the response of individual behavior and molecular biomarkers. The results demonstrated that the effects of SPS compositions on bioaccumulation and toxicological effects of organic UV-filters should be considered in aquatic environments.

Influence of multi-walled carbon nanotubes on enantioselective bioaccumulation and oxidative stress toxicity of indoxacarb in zebrafish(Danio rerio)

Carbon nanotubes (CNTs) have been widely used in various fields with the rapid development of nanotechnology. Pesticides have an irreplaceable role in agricultural production, which leads to their massive utilization and their inevitably penetrate into the aquatic environment. However, limited information is available regarding the impact of CNTs on the toxicity and enrichment of chiral compounds to organisms. Using zebrafish as a model to study whether the enantioselective bioaccumulation and oxidative stress of chiral pollutants may be altered in the presence of MWCNTs. Significant enantioselective bioaccumulation was observed in zebrafish with the preferential accumulation of R-(-)-indoxacarb during the 28-day bioaccumulation. The combined exposure of MWCNTs does not affect the enantioselectivity of zebrafish bioaccumulation, but increase the bioaccumulation amount of R-(-)-indoxacarb by 65%. Moreover, the average degradation half-life of indoxacarb enantiomers was 1.30 days. The indoxacarb causes oxidative stress toxicity in zebrafish liver and exhibited enantioselectivity, while the addition of MWCNTs did not significantly change the enantioselectivity of oxidative stress toxicity of indoxacarb, but enhanced the toxicity 20% with increased MWCNTs concentrations. This study suggests that the risk of the co-presence of nanomaterials and chiral pesticides in aquatic environments should be taken into consideration.

Effects of multi-walled carbon nanotubes on the enantioselective toxicity of the chiral insecticide indoxacarb toward zebrafish (Danio rerio)

The mass production and usage of carbon nanotubes (CNTs) have led to the inevitable release into the environment, and the effects of CNTs on the toxicity of co-existing pollutants have been well documented. However, knowledge of the effects of CNTs on the enantioselective toxicity of chiral compounds is limited. Using zebrafish as an experimental model, the enantioselective expression of the apoptosis, CYP3C and EAAT-related genes were analyzed following exposure to multi-walled carbon nanotubes (MWCNTs) (0.05 and 0.5 mg/L), rac-/R-/S-indoxacarb (0.01 mg/L), or the combination of rac-/R-/S-indoxacarb mixed with MWCNTs for 28d. Sex-specific differences were observed in both the liver and brain of zebrafish. The expression of apoptosis and CYP3C-related genes was 16.55-44.29 times higher in the livers of males treated with R-indoxacarb than in S-indoxacarb treated groups. The EAAT-related genes were expressed at 1.38-2.56 times higher levels in the brain of females treated with R-indoxacarb than in S-indoxacarb-treated groups. In the presence of MWCNTs, the expression of caspase-3, cyp3c3, cyp3c4, eaat1a, eaat1b and eaat2 in the livers of males and brains of females treated with S-indoxacarb were 1.65-15.33 times higher than in fish treated with R-indoxacarb. Based on these results, MWCNTs affected the enantioselective toxicity of indoxacarb toward zebrafish.

Antagonistic effects of multi-walled carbon nanotubes and BDE-47 in zebrafish (Danio rerio): Oxidative stress, apoptosis and DNA damage

In natural environments, organisms are often exposed to several environmental pollutants at any one time, and the potential effects of such co-exposures on human and environmental health are of considerable concern. It is thought that multi-walled carbon nanotubes (MWCNTs) may interact with other pollutants in aquatic systems and induce considerably different effects compared with exposure to a single contaminant. The objective of this study was to evaluate the potential acute combined effects of mixtures of MWCNTs and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on embryonic development stages, oxidative stress, apoptosis and DNA damage in developing zebrafish (Danio rerio). The embryos were treated with BDE-47 (5, 10, and 50 μg/L) and MWCNTs (50 mg/L), either combined or individually, for 96 h. Following exposure, BDE-47 induced significant acute toxicity, while the MWCNTs exhibited slight toxicity. When compared with BDE-47-only exposure, the inhibited growth induced by BDE-47 was weakened in the presence of MWCNTs. Similarly, the levels of oxidative stress biomarkers (reactive oxygen species, superoxide dismutase, catalase activities and malondialdehyde), apoptosis (apoptosis rate, caspase-3 and caspase-9 activities) and DNA damage (comet assay and comet olive tails) decreased in the presence of MWCNTs compared to those exposed to BDE-47 alone. These results demonstrate that MWCNTs can weaken the developmental inhibition, oxidative stress, apoptosis and DNA damage induced by BDE-47 in the early stages of zebrafish development.

Influence of roxithromycin as antibiotic residue on volatile fatty acids recovery in anaerobic fermentation of waste activated sludge

The removal of antibiotics and resistance genes in wastewater treatment plants has attracted widespread attention, but the potential role of residual antibiotics in the disposal of waste activated sludge (WAS) has not been clearly understood. In this study, the effect of roxithromycin (ROX) on volatile fatty acid (VFA) recovery from WAS anaerobic fermentation was investigated. The experimental results showed that ROX made a positive contribution to the production of VFAs. With the increase of ROX dosages from 0 to 100 mg/kg TSS, the maximum accumulation of VFAs increased from 295 to 610 mg COD/L. Mechanism studies revealed that ROX promoted the solubilization of WAS by facilitating the disruption of extracellular polymeric substances. In addition, ROX enhanced the activity of acetate kinase and inhibited the activities of α-glucosidase and coenzyme F₄₂₀, and showed a stronger inhibitory effect on methane production than the hydrolysis process, thus resulting in an increase in VFA accumulation. These findings provide a new insight for the role of antibiotics in anaerobic fermentation of WAS.

Interactive effects of roxithromycin and freshwater microalgae, Chlorella pyrenoidosa: Toxicity and removal mechanism

Roxithromycin (ROX) has received increasing concern due to its large usage, ubiquitous detection in environment and high ecotoxicology risk. This study investigated the acute and chronic effects of ROX on the growth, chlorophyll, antioxidant enzymes, and malonaldehyde (MDA) content of Chlorella pyrenoidosa, as well as the removal mechanism of ROX during microalgae cultivation. The calculated 96 h median effective concentration of ROX on yield (E_yC₅₀) and specific growth rate (E_rC₅₀) of C. pyrenoidosa was 0.81 and 2.87 mg/L, respectively. After 96 h exposure, 1.0 ~ 2.0 mg/L of ROX significantly inhibited the synthesis of chlorophyll and promoted the activities of SOD and CAT (p < 0.05). The MDA content increased with the ROX concentration increasing from 0.5 ~ 1.0 mg/L, and then decreased to 105.76% of the control exposure to 2.0 mg/L ROX, demonstrating the oxidative damage could be moderated by the upregulation of SOD and CAT activities. During the 21 d chronic exposure, low concentration of ROX (0.1 and 0.25 mg/L) showed no significant effect on the growth and chlorophyll content of algae during the first 14 d, but significantly inhibited the growth of algae and the synthesis of chlorophyll at 21 d (p < 0.05 or p < 0.01). 1.0 mg/L ROX significantly inhibited the growth of microalgae during 3 ~ 21 d and the synthesis of chlorophyll at 7 ~ 21 d. High concentration and long-term exposure of low concentration of ROX caused the SOD and CAT activities and MDA content to increase, demonstrating a higher level of oxidative damage of microalgae. During the first 14 d, abiotic removal of ROX played a more important role, contributing about 12.21% ~ 21.37% of ROX removal. After 14 d, the biodegradation of ROX by C. pyrenoidosa gradually became a more important removal mechanism, contributing about 45.99% ~ 53.30% of ROX removal at 21 d. Bio-adsorption and bioaccumulation both played minor roles in the removal of ROX during algae cultivation.

Single and combined effects of microplastics and roxithromycin on Daphnia magna

There is a rising concern about the pollution of microplastics (plastic particles < 5 mm) in water due to their physicochemical properties, especially their interaction with organic contaminants; however, such knowledge is still limited. The mass production and consumption of medication for the treatment of infectious diseases in human and animals have led to the ubiquity of antibiotics in the environment. We studied the single and joint effects of microplastics (1-μm and 10-μm polystyrene particles, PS) and roxithromycin (ROX) on Daphnia magna through the acute and sublethal toxicity tests. The 48-h median effective concentration (EC₅₀) of 1-μm and 10-μm PS to D. magna was 66.97 mg/L and 199.94 mg/L, respectively, while the value of ROX was 20.28 mg/L. Malondialdehyde (MDA) levels and the activities of four enzymatic biomarkers, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione S-transferase (GST), were further detected to assess the oxidative stress caused in D. magna caused. The results showed that 48-h exposure to PS (0.1 mg/L) or ROX (0.01 mg/L) alone activated the activities of CAT and GST and MDA levels. When compared with the ROX alone, the responses of GPx and MDA in D. magna co-exposed to 1-μm PS were significantly decreased, while co-exposure to 10-μm PS significantly decreased the responses of GST and MDA. Furthermore, the integrated biomarker response version 2 (IBRv2) analysis revealed that co-exposure to 1-μm PS and ROX led to the strongest biological responses in D. magna. Our findings underlined that microplastics should be a concern when they interact with the co-existence of pollutants in the aquatic environment.

Comparison of the accumulation and metabolite of fluoxetine in zebrafish larva under different environmental conditions with or without carbon nanotubes

Few studies have focused on the influence of environmental conditions on the bioavailability of pollutants interacted with nanomaterials in organisms. In this study, we primarily compared the influence of multiwalled carbon nanotubes (MWCNTs) on the bioavailability of fluoxetine in zebrafish (Danio rerio) larva under different environmental conditions: natural organic matter (NOM) and salinity. The results showed that fluoxetine accumulated in the larvae and then transformed into the metabolite norfluoxetine, with the metabolic rates from 2.8 to 3.5. Following co-exposure to MWCNTs, the accumulation of fluoxetine and norfluoxetine were further enhanced, suggesting a superior carrier of MWCNTs for fluoxetine, especially the functional MWCNTs. The consistent increase in the fluoxetine and norfluoxetine accumulation highlights the bioavailability of absorbed fluoxetine on MWCNTs in zebrafish larvae. The presence of NOM promoted the accumulation of fluoxetine and norfluoxetine in zebrafish, but alleviated the carrier effects of MWCNTs, acting as a natural antidote. Salinity negatively influenced the bioavailability of fluoxetine in the larvae, and further reversed the enhancements caused by MWCNTs. These findings provide a new insight into the influence of environmental conditions on the interactions between nanomaterials and pollutants in organisms.

Interactive effects of polystyrene microplastics and roxithromycin on bioaccumulation and biochemical status in the freshwater fish red tilapia (Oreochromis niloticus)

There are hundreds of thousands metric tons of microplastics (MPs) present in aquatic environments. The MPs coexist with other pollutants in water bodies, such as pharmaceuticals, and may carry and transfer them into aquatic organisms, consequently causing unpredictable ecological risks. The purpose of the present study was to evaluate the effect of the presence of polystyrene microplastics (PS-MPs) on the distribution and bioaccumulation of roxithromycin (ROX) in freshwater fish red tilapia (Oreochromis niloticus) as well as their interactive biochemical effects in red tilapia. PS-MPs were found to enhance the bioaccumulation of ROX in fish tissues compared to ROX-alone exposure. In the treatment of PS-MPs (100 μg L^-1) combined with ROX (50 μg L^-1), the highest concentrations of ROX reached 39,672.9 ± 6311.4, 1767.9 ± 277.8, 2907.5 ± 225.0, and 4307.1 ± 186.5 μg kg^-1 in gut, gills, brain, and liver, respectively. Furthermore, compared to the ROX alone, the neurotoxicity caused by ROX was alleviated due to the presence of MPs after 14 d of exposure. The activities of cytochrome P450 (CYP) enzymes [7-ethoxyresorufin O-deethylase (EROD) and 7-benzyloxy-4-trifluoromethyl-coumarin O-dibenzyloxylase (BFCOD)] in fish livers exposed to all co-exposure treatments exhibited great variability compared to ROX alone after 14 d of exposure, suggesting that the presence of MPs may affect the metabolism of ROX in tilapia. Compared with ROX alone, the superoxide dismutase (SOD) activity increased significantly, and malondialdehyde (MDA) contents decreased in the co-exposure treatments, showing that oxidative damage in situations of co-exposure to MPs and ROX was mitigated in fish livers after 14 d of exposure. Collectively, the presence of MPs could affect the fate and toxicity of other organic pollutants in fish. The results emphasize the importance to study the interactions between MPs and other organic pollutants in aquatic environments.

Accumulation, metabolite and active defence system responses of fluoxetine in zebrafish embryos: Influence of multiwalled carbon nanotubes with different functional groups

Studies on the bioavailability of organic contaminants adsorbed to nanomaterials are increasing. In this study, we investigated the interaction between fluoxetine (FLX) and three multiwalled carbon nanotubes (MWCNTs) with different functional groups in zebrafish (Danio rerio) embryos, focusing on the FLX accumulation, the formation of the metabolite norfluoxetine (NFLX), and the active defence system responses. The accumulation of FLX in zebrafish was intensified by MWCNTs (46-99%), which simultaneously facilitated the formation of the metabolite NFLX by 23-167%. The consistent enhancement revealed that the absorbed FLX is bioavailable in zebrafish. Moreover, the coexisting MWCNTs further promoted the influences of FLX on the active defence system in zebrafish (e.g. antioxidant and metabolic function), eliciting the defence function. The influences of MWCNTs on the bioavailability of FLX in zebrafish could be ordered as OH-MWCNTs > COOH-MWCNTs > pristine MWCNTs. The release of FLX from MWCNTs in biofluids may partially contribute to these significant alterations. In particular, MWCNTs themselves may also modulate the bioavailability of FLX in zebrafish by downregulating the gene expression of membrane ATP-binding cassette transporter (abcb4). These findings demonstrated that MWCNTs increased the bioavailability of FLX in zebrafish, especially the functionalized MWCNTs. The production of metabolites may be a useful bio-endpoint to evaluate the bioavailability of adsorbed contaminants on nanomaterials.

Influence of suspended sediment characteristics on the bioaccumulation and biological effects of citalopram in Daphnia magna

The influence of suspended sediment (SPS) characteristics on the bioavailability of the antidepressant citalopram (CIT) was investigated in the cladoceran Daphnia magna. The bioaccumulation, swimming behaviours, psychological indices, and oxidative stress were examined. The CIT bioaccumulation were altered in the presence of SPS, such that the body burden of CIT decreased as the concentration of SPS increased and as the organic carbon content of SPS (f_oc) increased; moreover, the body burden of CIT increased as SPS particle size increased. All the biomarker activities of D. magna were markedly induced at a CIT exposure concentration of 10 μg/L. However, the biological effects of CIT did not depend on the body burden of CIT as SPS concentration increased, while the swimming activities and oxidative stress were significantly enhanced by SPS concentration at 1 g/L. The influences of SPS particle size and f_oc on the activities of swimming and physiological indicators were mainly associated with the CIT bioaccumulation, while f_oc in SPS was more substantial than particle size. In addition, the antioxidant activities decreased as f_oc increased and were significantly strengthened at particle sizes of 30-60 μm. The impacts of different SPS characteristics on the adsorption and desorption capacity of CIT and the ingestion habits of D. magna were the main reasons for the variations in CIT body burden and biological effects. According to the results obtained in this study, the SPS characteristics should be considered in the risk assessment of contaminants in natural aquatic environments.

Influence of multiwall carbon nanotubes on the toxicity of 17β-estradiol in the early life stages of zebrafish

Due to increasing use and release, both multiwall carbon nanotubes (MWCNTs) and 17β-estradiol (E2) may co-exist and interact with each other in aquatic environments. However, little is known about their combined effects on non-target organisms, especially in the presence of other environmental factors. In this study, the interplay between MWCNTs and E2 in the early life stages of zebrafish was investigated, focusing on the alterations in estrogenic responses with and without other environmental factors. There were no significant differences in the hatchability, mortality, or physical development of zebrafish in any treatments. Compared with E2 exposure, the E2-induced estrogenic responses (vtg1, vtg3, and esr1 genes) in zebrafish were markedly reduced to baseline by the presence of MWCNTs in most cases, indicating a strong protective effect. Furthermore, this inhibitive effect was not significantly changed by the preloading of natural organic matter (NOM) on MWCNTs. Nevertheless, the addition of ammonia nitrogen in the mixtures of MWCNTs and E2 alleviated the protective effect of MWCNTs, resuscitating the E2-induced estrogenic responses in zebrafish. These findings highlight the influence of carbon nanomaterials on the bioavailability of co-contaminants in organisms. The widespread environmental factors in natural environments should also be taken into consideration when the combined toxicity of nanomaterials and contaminants is discussed.

Adsorptive removal of aqueous bezafibrate by magnetic ferrite modified carbon nanotubes

MFe₂O₄/CNTs were synthesized and successfully applied for the removal of aqueous bezafibrate. The adsorption behavior and mechanism were elucidated in detail.