Theoretical insights of the pharmaceutical compound fluoxetine in water: Role in direct photolysis and indirect photolysis by free radicals.

The frequent detection of pharmaceutical compounds in the environment has led to a growing awareness, which may pose a major threat to the aquatic environment. In this study, photodegradation (direct and indirect photolysis) of two different dissociation states of fluoxetine (FLU) was investigated in water, mainly including the determination of photolytic transition states and products, and the mechanisms of indirect photodegradation with ·OH, CO3*- and NO3*. The main direct photolysis pathways are defluorination and C-C bond cleavage. In addition, the indirect photodegradation of FLU in water is mainly through the reactions with ·OH and NO3*, and the photodegradation reaction with CO3*- is relatively difficult to occur in the water environment. Our results provide a theoretical basis for understanding the phototransformation process of FLU in the water environment and assessing its potential risk.

Theoretical explanation of direct photolysis and indirect photolysis of bendazone with •OH, •SO4-, and •CO3- in water: mechanism insights and ecotoxicity evaluation.

Bendazone (BNTE) is an herbicide and a highly concerned pollutant in aquatic environments. Understanding the photochemical behavior of BNTE in water is crucial for evaluating its photochemical conversion process in aquatic environments. This study analyzed the direct photolysis and indirect photolysis pathways of two dissociated forms of BNTE in water through density functional theory and time-dependent density functional theory method. The results show that the reaction types of indirect photolysis of BNTE with free radicals (•OH, •SO4-, and •CO3-) are OH- addition, SO4- addition, and CO3- addition. In the process of indirect photolysis of BNTE and free radicals, the photolysis of •OH and BNTE was the easiest, followed by •SO4-. In addition, the active site of BNTE reacting with •OH is C8, and the active site of BNTE reacting with •SO4- is C10. However, the photolysis effect of •CO3- on BNTE is very small, indicating that •CO3- in water plays a secondary role in the indirect photolysis of BNTE. In the direct photolysis of BNTE, N1-C6 bond breaking is difficult to occur spontaneously in the environment due to its high endothermic property and energy barrier. The direct photolysis pathway of BNTE involves the break of the N1-S2/S2-N3/N3-C12 bond. In addition, the ecological toxicity evaluation showed that toxicity of most of the degradation products were reduced, but the toxicity level was still maintained at a harmful level. Our findings provide the photochemical fate of BNTE in aquatic environments and will help to more accurately understand their photochemical conversion mechanisms in the environment.

Study on the Direct and Indirect Photolysis of Antibacterial Florfenicol in Water Using DFT/TDDFT Method and Comparison of Its Reactivity with Hydroxyl Radical under the Effect of Metal Ions.

Florfenicol (FLO) is a widely used antibacterial drug, which is often detected in the environment. In this paper, the photolysis mechanism of FLO in water was investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The focus of the study is to elucidate the direct photolysis mechanism of FLO in the water environment and the indirect photolysis of free radicals (·OH, ·NO3, and ·SO4-) as active species. The effect of metal ions Ca2+/Mg2+/Zn2+ on the indirect photolysis was also investigated. The results show that the direct photolysis of FLO involves C-C/C-N/C-S bond cleavage, the C5-S7 bond cleavage is most likely to occur, and the C17-C18 cleavage reaction is not easy to occur during the direct photodegradation of FLO. The indirect photolysis of FLO is more likely to occur in the environment than direct photolysis. The main indirect photolysis involves OH-addition, NO3-addition, and SO4-addition on benzene ring. The order of difficulty in the indirect photolysis with ·OH is C2 > C3 > C4 > C5 > C6 > C1, Ca2+ can promote the indirect photolysis with ·OH, and Mg2+/Zn2+ has a dual effect on the indirect photolysis with ·OH. In other words, Mg2+ and Zn2+ can inhibit or promote the indirect photolysis with ·OH. These studies provide important information for theoretical research on the environmental behavior and degradation mechanism of drug molecules.

The mechanism of photodegradation reaction of different dissociation forms of tetrabromobisphenol S in water with free radicals and the ecotoxicity evaluation of related products.

Tetrabromobisphenol S (TBBPS) is a widely used brominated flame retardant that has attracted environmental concern due to its abundant presence in water. The objective of this study is to systematically analyze the direct photolysis and degradation mechanisms of TBBPS in two different dissociation forms in water, as well as to evaluate their toxicological effects induced by •OH, 1O2, and •NO2 radicals. The degradation mechanism of TBBPS is investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, and the toxicity of the degradation products is assessed through toxicological studies. The results of the study indicate that the OH-addition and H-abstraction reactions are favorable pathways for •OH-induced TBBPS degradation. The H-abstraction reaction of TBBPS0 with •OH was more favorable than the •OH addition reaction. However, in the degradation of TBBPS-, the •OH addition reaction was favored over the H-abstraction reaction. Additionally, the indirect photolysis of TBBPS by 1O2 and •NO2 in water was found to be easier for TBBPS- compared to TBBPS0, with degradation mechanisms involving Br-substitution and NO2-addition reactions. The higher Ea values calculated indicate that the degradation of TBBPS by 1O2 and •NO2 in water has been a secondary reaction. The direct photolysis reaction pathway of TBBPS in water has involved the cleavage of the S1-C7 and S1-C16 bonds. For TBBPS0 in the S1/T1 states, the primary reaction pathway is the cleavage of the S1-C16 bond, while for TBBPS-, the primary reaction pathway is the cleavage of the S1-C7 bond. Furthermore, the computational toxicology results indicate a slight increase in the toxicity levels of most products, highlighting the significance of investigating the degradation byproducts of TBBPS in greater detail.

Photodegradation fate of different dissociation species of antidepressant paroxetine and the effects of metal ion Mg2+: Theoretical basis for direct and indirect photolysis.

Paroxetine (abbreviated as PXT) has been widely used as one of the standard antidepressants for the treatment of depression. PXT has been detected in the aqueous environment. However, the photodegradation mechanism of PXT remains unclear. The present study aimed to use density functional theory and time-dependent density functional theory to study the photodegradation process of two dissociated forms of PXT in water. The main mechanisms include direct and indirect photodegradation via reaction with ·OH and 1O2 and photodegradation mediated by the metal ion Mg2+. Based on the calculations, PXT and PXT-Mg2+ complexes in water are photodegraded mainly indirectly and directly. It was found that PXT and PXT-Mg2+ complexes were photodegraded by H-abstraction, OH-addition and F-substitution. The main reaction of PXT indirect photolysis is OH-addition reaction, while the main reaction of PXT0-Mg2+ complex is H-abstraction. All the reaction pathways of H-abstraction, OH-addition and F-substitution are exothermic. PXT0 reacts more readily with ·OH or 1O2 in water than PXT+. However, the higher activation energy of PXT with 1O2 indicates that the 1O2 reaction plays a minor role in the photodegradation pathway. The direct photolysis process of PXT includes ether bond cleavage, defluorination, and dioxolane ring-opening reaction. In the PXT-Mg2+ complex, the direct photolysis process occurs via a dioxolane ring opening. Additionally, Mg2+ in water has a dual effect on the direct and indirect photolysis of PXT. In other words, Mg2+ can inhibit or promote their photolytic reactions. Overall, PXT in natural water mainly undergo direct and indirect photolysis reactions with ·OH. The main products include direct photodegradation products, hydroxyl addition products and F-substitution products. These findings provide critical information for predicting the environmental behavior and transformation of antidepressants.

Computational Study of Photodegradation Process and Conversion Products of the Antidepressant Citalopram in Water.

Citalopram (CIT) is a commonly prescribed medication for depression. However, the photodegradation mechanism of CIT has not yet been fully analyzed. Therefore, the photodegradation process of CIT in water is studied by density functional theory and time-dependent density functional theory. The calculated results show that during the indirect photodegradation process, the indirect photodegradation of CIT with ·OH occurs via OH-addition and F-substitution. The minimum activation energy of C10 site was 0.4 kcal/mol. All OH-addition and F-substitution reactions are exothermic. The reaction of 1O2 with CIT includes the substitution of 1O2 for F and an addition reaction at the C14 site. The Ea value of this process is 1.7 kcal/mol, which is the lowest activation energy required for the reaction of 1O2 with CIT. C-C/C-N/C-F cleavage is involved in the direct photodegradation process. In the direct photodegradation of CIT, the activation energy of the C7-C16 cleavage reaction was the lowest, which was 12.5 kcal/mol. Analysis of the Ea values found that OH-addition and F-substitution, the substitution of 1O2 for F and addition at the C14 site, as well as the cleavage reactions of C6-F/C7-C16/C17-C18/C18-N/C19-N/C20-N are the main pathways of photodegradation of CIT.

A density functional theory/time-dependent density functional theory study of the structure-related photochemical properties of hydroxylated polybrominated diphenyl ethers and methoxylated polybrominated diphenyl ethers and metal ion effects.

As the derivatives and structural analogs of polybrominated diphenyl ethers (PBDEs), hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and methoxylated polybrominated diphenyl ethers (MeO-PBDEs) have attracted increasing concern. However, knowledge of the photochemical behaviors of OH-PBDEs and MeO-PBDEs in water is limited. Here, we used density functional theory and time-dependent density functional theory to examine the structure-related photochemical properties of OH-PBDEs and MeO-PBDEs in water and the effects of metal ions as environmental factors. Eight 6-OH-PBDEs with 1-8 bromine substituents and eight 6-MeO-PBDEs with 1-8 bromine substituents were selected for this study. The optimized geometries of the selected congeners and their complexes with metals in the lowest excited triplet state (T1) showed that one C-Br bond moderately or significantly elongated. The elongated C-Br bond in the T1 state was shown in the ortho-position for the 6-OH-PBDE congeners and the ortho-position or the meta-position for the 6-MeO-PBDE congeners. For the selected congeners, there were significant positive linear correlations between the number of bromine atoms (NBr) and the calculated average atomic charge of bromine and maximum electronic absorbance wavelength (λmax), and a negative linear correlation between the NBr and average bond dissociation energy of C-O bonds (BDEC-O). The photoreactivities of the 6-OH-PBDEs and 6-MeO-PBDEs increased with an increase in the bromination degree with or without metal ions. The calculated average atomic charge of bromine and BDEC-O of the complexes with Mg2+/Zn2+ was higher and lower than those of the corresponding monomers, respectively, indicating that the presence of Mg2+/Zn2+ increased the photoreactivity (debromination and dissociation of C-O bond) of the selected 6-OH-PBDEs and 6-MeO-PBDEs. The effects of the coordination of Mg2+/Zn2+ may be overestimated due to their missing explicit solvation shell. These results provide vital insight into the photochemical properties of OH-PBDEs and MeO-PBDEs in water.

Validation of a nomogram to predict the risk of cancer in patients with intraductal papillary mucinous neoplasm and main duct dilatation of 10 mm or less.

BACKGROUND: Intraductal papillary mucinous neoplasm (IPMN) is premalignant pancreatic lesion. International guidelines offer limited predictors of individual risk. A nomogram to predict individual IPMN malignancy risk was released, with good diagnostic performance based on a large cohort of Asian patients with IPMN. The present study validated a nomogram to predict malignancy risk and invasiveness of IPMN using both Eastern and Western cohorts. METHODS: Clinicopathological and radiological data from patients who underwent pancreatic resection for IPMN at four centres each in Eastern and Western countries were collected. After excluding patients with missing data for at least one malignancy predictor in the nomogram (main pancreatic duct diameter, cyst size, presence of mural nodule, serum carcinoembryonic antigen and carbohydrate antigen (CA) 19-9 levels, and age). RESULTS: In total, data from 393 patients who fit the criteria were analysed, of whom 265 were from Eastern and 128 from Western institutions. Although mean age, sex, log value of serum CA19-9 level, tumour location, main duct diameter, cyst size and presence of mural nodule differed between the Korean/Japanese, Eastern and Western cohorts, rates of malignancy and invasive cancer did not differ significantly. Areas under the receiver operating characteristic (ROC) curve values for the nomogram predicting malignancy were 0·745 for Eastern, 0·856 for Western and 0·776 for combined cohorts; respective values for the nomogram predicting invasiveness were 0·736, 0·891 and 0·788. CONCLUSIONS: External validation of the nomogram showed good performance in predicting cancer in both Eastern and Western patients with IPMN lesions.

ANTECEDENTES: La neoplasia mucinosa papilar intraductal (intraductal papillary mucinous neoplasm, IPMN) es una lesión pancreática premaligna. Las guías internacionales incluyen un número limitado de factores predictivos de riesgo individual. Para predecir el riesgo individual de malignidad del IPMN se ha propuesto un nomograma con un buen rendimiento diagnóstico, basado en una gran cohorte de pacientes asiáticos con IPMN. Este estudio validó el nomograma para predecir el riesgo de cáncer y de invasión de la IPMN utilizando cohortes tanto orientales como occidentales. MÉTODOS: Se recogieron datos clínico-patológicos y radiológicos de pacientes en los que se realizó una resección de páncreas por IPMN en 4 centros en países orientales y en 4 centros de países occidentales. Se excluyeron los pacientes en los que en el nomograma faltaba ≥ 1 factor(es) predictivo(s) de malignidad (diámetro del conducto pancreático principal, tamaño del quiste, presencia de nódulo mural, niveles séricos de CEA y CA19-9, y edad). RESULTADOS: En total, se analizaron datos de 393 pacientes que cumplían con los criterios de inclusión, de los cuales 265 eran de centros orientales y 128 de centros occidentales. Aunque la edad media, el sexo, el valor logarítmico del nivel sérico de CA19-9, la localización del tumor, el diámetro del conducto principal, el tamaño del quiste y la presencia de un nódulo mural difirieron entre las cohortes de Corea/Japón y las cohortes oriental y occidental, las tasas de malignidad y de cáncer invasivo no fueron significativamente diferentes. Las áreas bajo la curva operativa del receptor (area under the receiver operating curve, AUC) que mostró el nomograma para predecir la malignidad fueron: cohorte oriental: 0,745; cohorte occidental: 0,856 y cohortes combinadas: 0,776; y para predecir la invasión tumoral fueron: cohorte oriental: 0,736; cohorte occidental: 0,891, y cohortes combinadas: 0,788. CONCLUSIÓN: La validación externa del nomograma mostró un buen rendimiento en la predicción de cáncer, tanto en pacientes orientales como occidentales con lesiones IPMN.

Dissolved Organic Matter Modulates Algal Oxidative Stress and Membrane System Responses to Binary Mixtures of Nano-Metal-Oxides (nCeO2, nMgO and nFe3O4) and Sulfadiazine.

Joint biomarker responses, oxidative stress and membrane systems, were determined for nano-metal-oxides (nMeO, i.e., nCeO2, nMgO, and nFe3O4) and sulfadiazine (SDZ) exposed at relevant low concentrations to two freshwater microalgae Scenedesmus obliquus and Chlorella pyrenoidosa. The impacts of dissolved organic matter (DOM) on the joint biomarker responses were also investigated. Results indicated that the presence of SDZ significantly decreased the level of intercellular reactive oxygen species (ROS) in the algal cells exposed to each nMeO. Reduction of cell membrane permeability (CMP) and mitochondrial membrane potential (MMP) in the algal cells was observed when the algae were exposed to the mixture of SDZ and the nMeO. The degree of reduction of the ROS level, CMP, and MMP significantly went down with the addition of DOM to a certain extent. Changes in cellular oxidative stress and membrane function depended on the types of both nMeO and algal species. This contribution provides an insight into the hazard assessment of a mixture consisting of emerging contaminants and DOM, as they can coexist in the aquatic environment.

Aquatic behavior and toxicity of polystyrene nanoplastic particles with different functional groups: Complex roles of pH, dissolved organic carbon and divalent cations.

Herein we systematically examined the roles of water chemistry (pH, dissolved organic carbon (DOC), and divalent cations) and particle surface functionality that control the aqueous stability, aggregation, and toxicity of engineered nanoplastic particles in simulated natural environmental conditions. Model polystyrene latex nanoparticles (PLNPs) with three different functional groups, namely unmodified (uPLNPs), amine-modified (aPLNPs), and carboxyl-modified (cPLNPs), were investigated. Results indicate that the presence of only DOC increased the surface charge and exhibited negligible effects on the size distribution of the PLNPs in aqueous suspensions. The presence of the divalent cations (Ca2+ and Mg2+) was observed to decrease the surface charge and increase the size of the PLNPs. The coexistence of DOC and the divalent cations enhanced the extent of aggregation of the PLNPs in the water columns. The surface modification and pH were sensitive factors influencing the stability of PLNPs during long-term suspension when DOC and the divalent cations coexisted. Direct visual further testified the conclusions on the combined effects of solution and surface chemistry parameters. Furthermore, in situ transmission electron microscope observations revealed that the enhancement of PLNP aggregation in the presence of DOC and the divalent cation was caused by bridge formation. Toxicity test indicated the PLNPs exhibited acute toxicity and physical damage to Daphnia magna. The more complex the solution conditions, the more toxicity the aPLNPs and cPLNPs. Analysis of mode of toxic action implied that the PLNPs mainly caused the accumulation of oxidative damage to the gut of D. magna.

Metagenomic analysis of bacterial communities and antibiotic resistance genes in the Eriocheir sinensis freshwater aquaculture environment.

Aquaculture has attracted significant attention as an environmental gateway to the development of antibiotic resistance. The industry of Chinese mitten crab Eriocheir sinensis contributes significantly to the freshwater aquaculture industry in China. However, the situation of antibiotic resistance in the E. sinensis aquaculture environment is not known. In this study, high-throughput sequencing based metagenomic approaches were used to comprehensively investigate the structure of bacterial communities, the abundance and diversity of antibiotic resistance genes (ARGs), as well as mobile genetic elements (MGEs) in three E. sinensis aquaculture ponds in Jiangsu Province, China. The dominant phyla were Proteobacteria, Actinobacteria, and Bacteroidetes in water samples and Proteobacteria, Chloroflexi, Verrucomicrobia, and Bacteroidetes in sediment samples. Bacitracin and multidrug were predominant ARG types in water and sediment samples, respectively. There was a significant correlation between MGEs and ARGs. In particular, plasmids were the most abundant MGEs and strongly correlated with ARGs. This is the first study of antibiotic resistome that uses metagenomic approaches in the E. sinensis aquaculture environment. The results indicate that the opportunistic pathogens may acquire ARGs via horizontal gene transfer, intensifying the potential risk to human health.

Ecotoxicological effects on Scenedesmus obliquus and Danio rerio Co-exposed to polystyrene nano-plastic particles and natural acidic organic polymer.

The importance of attention to unravel the interaction of nano-plastic particles (NPs) with natural acidic organic polymer (NAOP) in freshwater environment should not be neglected. However, toxicological data available for the interaction between NPs and NAOP remain limited. Here, we investigate the toxicological effects of three model polystyrene (PS) NPs with different functional groups (unmodified, amino- and carboxyl-modified PS NPs) on two freshwater organisms of different trophic levels (Scenedesmus obliquus and Danio rerio) in the absence and presence of two classes of NAOP, namely fulvic acid and humic acid. The NAOP interaction with the NPs is shown to alter oxidative stress and disturb membrane function in S. obliquus cells to a certain extent. Combined oxidative stress responses to the NPs and NAOP in D. rerio as a function of their mixture levels showed inhibition, alleviation, and reinforce. Changes in cellular oxidative stress and membrane function depended on the concentration and types of both NPs and NAOP. Furthermore, the characterization parameters of the NPs were important for the explanation of the ecotoxicological mechanism of the NPs in the presence of NAOP. Our findings emphasized the critical role of NAOP in the fate and toxicity of plastic particles in freshwater environment.

A DFT/TDDFT study on the mechanisms of direct and indirect photodegradation of tetrabromobisphenol A in water.

Tetrabromobisphenol A (TBBPA) is the most widely used commercial brominated flame retardant. However, the mechanisms underlying the photodegradation of TBBPA remain unclear. Here we use density functional theory and time-dependent density functional theory to examine the photodegradation of the two species of TBBPA in water: TBBPA (neutral form) and TBBPA- (anionic form). The study includes direct photodegradation and indirect photodegradation of TBBPA with ·OH and 1O2. The results of the calculations indicate that indirect photodegradation of TBBPA and TBBPA- with ·OH occurs via OH-addition and Br-substitution. All of the OH-addition and Br-substitution pathways are exothermic. Indirect photodegradation of TBBPA and TBBPA- by 1O2 proceeds via H abstraction by 1O2.Ea was higher for H abstraction of TBBPA than H abstraction of TBBPA-. The mechanisms for the direct photodegradation of TBBPA and TBBPA- include debromination, C1C7/C7C13 cleavage, and cyclization. CBr cleavage was observed in the optimized geometries of TBBPA and TBBPA- at the lowest excited triplet state. However, high Ea values and an endothermic nature indicated that C1C7/C7C13 cleavage and cyclization reactions were not the main pathways. OH-adducts, Br-substitution products, H-abstraction (by 1O2) products, and debromination products were the main products of photodegradation of TBBPA. These findings provide useful information for risk assessment and pollution control of brominated flame retardants.

Algal toxicity of binary mixtures of zinc oxide nanoparticles and tetrabromobisphenol A: Roles of dissolved organic matters.

The present study investigated the impacts of dissolved organic matters (DOM) on joint toxicity involved in zinc oxide nanoparticles (ZnO NPs) and tetrabromobisphenol A (TBBPA) at relevant low-exposure concentrations (<1 mg/L). It was found that ZnO NPs in single and combined systems exhibited severe inhibition effects on a freshwater microalgae Scenedesmus obliquus. However, the presence of DOM slightly alleviated the growth inhibition toxicity induced by the binary mixtures of ZnO NPs and TBBPA. Ultrastructure analysis revealed that ZnO NPs caused structural damage to cells, including plasmolysis, membrane destruction, and the disruption of thylakoid in the chloroplast, regardless of the presence of coexisting substances. Oxidative stress biomarker quantitative analysis and in situ observations indicated that the massive accumulation of reactive oxygen species in the binary mixtures of ZnO NPs and TBBPA caused severe oxidative damage, but the presence of DOM significantly mitigated the damage.

DFT/TDDFT insights into effects of dissociation and metal complexation on photochemical behavior of enrofloxacin in water.

Elucidation of the mechanisms underlying the effects of different dissociated forms and metal ion complexation on the photochemical behavior of antibiotics in aqueous media is a key problem and requires further research. We examined the mechanism of the direct photolysis of enrofloxacin (ENRO) in different dissociated forms in water and the impact of metal ions (Mg2+) on the photolysis of ENRO using density functional theory and time-dependent density functional theory. The results showed that different dissociated forms of ENRO exhibited diverse maximum electronic absorbance wavelengths (ENRO3+ (264 nm) < ENRO- (278 nm) < ENRO0 (280 nm) < ENRO2+ (282 nm) < ENRO+ (306 nm)). The calculations of the reaction pathways and activation energies (Ea) in the photolysis of ENRO0/ENRO+/ENRO- showed that defluorination was the main reaction pathway. The removal of cyclopropane was the main reaction pathway for the direct photolysis of ENRO2+/ENRO3+. Furthermore, the presence of Mg2+ was observed to change the order of the maximum electronic absorbance wavelengths and increases the intensities of the ENRO absorbance peaks. Calculations of the photolysis reaction pathways showed that the presence of Mg2+ increased the Ea for the most direct photolysis pathways of ENRO, while its presence decreased the Ea for several partial direct photolysis pathways such as the pathway in which the piperazine ring moiety of ENRO0/ENRO3+ is damaged and the pathway in which cyclopropane is released from ENRO3+. The findings on the photolysis behavior of ENRO in water system have provided useful information on the risk assessment of antibiotics.

Toxicological assessment of multi-walled carbon nanotubes combined with nonylphenol in male mice.

Carbon nanotubes have attracted increasing attention attributable to their widespread application. To evaluate the joint toxicity of multi-walled carbon nanotubes (MWCNTs) and nonylphenol (NP), we investigated the toxicological effects of NP, pristine MWCNTs, and MWCNTs combined with NP in male mice. After exposing male mice by gavage for 5 days, intracellular superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity, as well as malondialdehyde (MDA) and glutathione (GSH) levels in tissues were determined to evaluate in vivo oxidative stress. In addition, genotoxicity was assessed by examining DNA damage in mouse liver and sperm via the comet assay, and transmission electron microscopy (TEM) was used for direct visual observations of mitochondrial damage in the liver. Results from the oxidative damage and DNA damage experiments indicate that after adsorbing NP, MWCNTs at a high dose induce oxidative lesions in the liver and cause DNA damage in mouse sperm; these data offer new insights regarding the toxicological assessment of MWCNTs.

Toxicity of mixtures of zinc oxide and graphene oxide nanoparticles to aquatic organisms of different trophic level: particles outperform dissolved ions.

Concomitant releases of various engineered nanoparticles (NPs) into the environment have resulted in concerns regarding their combined toxicity to aquatic organisms. It is however, still elusive to distinguish the contribution to toxicity of components in NP mixtures. In the present study, we quantitatively evaluated the relative contribution of NPs in their particulate form (NP(particle)) and of dissolved ions released from NPs (NP(ion)) to the combined toxicity of binary mixtures of ZnO NPs and graphene oxide nanoplatelets (GO NPs) to three aquatic organisms of different trophic levels, including an alga species (Scenedesmus obliquus), a cladoceran species (Daphnia magna), and a freshwater fish larva (Danio rerio). Our results revealed that the effects of ZnO NPs and GO NPs were additive to S. obliquus and D. magna but antagonistic to D. rerio. The relative contribution to toxicity (RCT) of the mixture components to S. obliquus decreased in the order of RCTGO NP(particle) > RCTZnO NP(particle) > RCTZnO NP(ion), while the RCT of the mixture components to D. magna and D. rerio decreased in the order of RCTZnO NP(particle) > RCTGO NP(particle) > RCTZnO NP(ion). This finding also implies that the suspended particles rather than the dissolved Zn-ions dictated the combined toxicity of binary mixtures of ZnO NPs and GO NPs to the aquatic organisms of different trophic level. The alleviation of the contribution to toxicity of the ionic form of ZnO NPs was caused by the adsorption of the dissolved ions on GO NPs. Furthermore, the ZnO NP(particle) and GO NP(particle) displayed a different contribution to the observed mixture toxicity, dependent on the trophic level of the aquatic organisms tested. The difference of the contributions between the two particulate forms was mainly associated with differences in the intracellular accumulation of reactive oxygen species. Our findings highlight the important role of particles in the ecological impact of multi-nanomaterial systems.

Dissolved organic matter and aluminum oxide nanoparticles synergistically cause cellular responses in freshwater microalgae.

This study investigated the impact of dissolved organic matters (DOM) on the ecological toxicity of aluminum oxide nanoparticles (Al2O3NPs) at a relatively low exposure concentration (1 mg L-1). The unicellular green alga Scenedesmus obliquus was exposed to Al2O3NP suspensions in the presence of DOM (fulvic acid) at various concentrations (1, 10, and 40 mg L-1). The results show that the presence of DOM elevated the growth inhibition toxicity of Al2O3NPs towards S. obliquus in a dose-dependent manner. Moreover, the combination of DOM at 40 mg L-1 and Al2O3NPs resulted in a synergistic effect. The relative contribution of Al-ions released from Al2O3NPs to toxicity was lower than 5%, indicating that the presence of the particles instead of the dissolved ions in the suspensions was the major toxicity sources, regardless of the presence of DOM. Furthermore, DOM at 10 and 40 mg L-1 and Al2O3NPs synergistically induced the upregulation of intercellular reactive oxygen species levels and superoxide dismutase activities. Analysis of the plasma malondialdehyde concentrations and the observation of superficial structures of S. obliquus indicated that the mixtures of DOM and Al2O3NPs showed no significant effect on membrane lipid peroxidation damage. In addition, the presence of both DOM and Al2O3NPs contributed to an enhancement in both the mitochondrial membrane potential and the cell membrane permeability (CMP) in S. obliquus. In particular, Al2O3NPs in the presence of 10 and 40 mg L-1 DOM caused a greater increase in CMP compared to Al2O3NPs and DOM alone treatments. In conclusion, these findings suggest that DOM at high concentrations and Al2O3NPs synergistically interrupted cell membrane functions and triggered subsequent growth inhibition toxicity.

Aqueous aggregation and stability of graphene nanoplatelets, graphene oxide, and reduced graphene oxide in simulated natural environmental conditions: complex roles of surface and solution chemistry.

Graphene-family nanomaterials (GFNs) exhibit universal applications and consequently will inevitably enter aquatic systems. However, both the fate and behavior of GFNs in aquatic environments have not been completely explored at field relevant conditions. Herein, we have systematically investigated the aqueous aggregation and stability of graphene nanoplatelets (GNPs), graphene oxide (GO), and reduced graphene oxide (RGO) under varied solution chemistry parameters (pH, divalent cations, and dissolved organic carbon (DOC)) during 21 days of incubation in simulated natural environmental conditions. Results indicate that pH values from 6 to 9 had a notable impact on the aqueous behaviors of the three GFNs. Divalent cations (Ca2+ and Mg2+) at the concentrations of 2.5 and 10 mM remarkably increased the extent of aggregation of the three GFNs and resulted in severe sedimentation, independently of surface chemical functionalization. The presence of only DOC ranging from 0.5 to 2 mg C/L significantly elevated the dispersion stability of GNPs and RGO in a dose-dependent manner, whereas no effects were observed on GO. Furthermore, DOC at the studied concentrations and surface functionality were insufficient to counterbalance the impact of the divalent cations. Direct visual and in situ observations further supported the conclusions on the effects of divalent cations or/and DOC. These findings further underline that the environmental behaviors of GFNs are controlled by the complex interplay between water chemistry parameters and GFN surface properties.