Mechanism of the Synergistic Toxicity of Ampicillin and Cefazoline on Selenastrum capricornutum.

Ampicillin (AMP) and cefazolin (CZO) are commonly used ß-lactam antibiotics which are extensively globally produced. Additionally, AMP and CZO are known to have relatively high ecotoxicity. Notably, the mix of AMP and CZO creates a synergistic effect that is more harmful to the environment, and how exposure to AMP-CZO can induce synergism in algae remains virtually unknown. To yield comprehensive mechanistic insights into chemical toxicity, including dose-response relationships and variations in species sensitivity, the integration of multiple endpoints with de novo transcriptomics analyses were used in this study. We employed Selenastrum capricornutum to investigate its toxicological responses to AMP and CZO at various biological levels, with the aim of elucidating the underlying mechanisms. Our assessment of multiple endpoints revealed a significant growth inhibition in response to AMP at the relevant concentrations. This inhibition was associated with increased levels of reactive oxygen species (ROS) and perturbations in nitrogen metabolism, carbohydrate metabolism, and energy metabolism. Growth inhibition in the presence of CZO and the AMP-CZO combination was linked to reduced viability levels, elevated ROS production, decreased total soluble protein content, inhibited photosynthesis, and disruptions in the key signaling pathways related to starch and sucrose metabolism, ribosome function, amino acid biosynthesis, and the production of secondary metabolites. It was concluded from the physiological level that the synergistic effect of Chlorophyll a (Chla) and Superoxide dismutase (SOD) activity strengthened the growth inhibition of S. capricornutum in the AMP-CZO synergistic group. According to the results of transcriptomic analysis, the simultaneous down-regulation of LHCA4, LHCA1, LHCA5, and sodA destroyed the functions of the photosynthetic system and the antioxidant system, respectively. Such information is invaluable for environmental risk assessments. The results provided critical knowledge for a better understanding of the potential ecological impacts of these antibiotics on non-target organisms.

Analysing N-nitrosamine occurrence and sources in karst reservoirs, Southwest China.

N-nitrosamines in reservoir water have drawn significant attention because of their carcinogenic properties. Karst reservoirs containing dissolved organic matter (DOM) are important drinking water sources and are susceptible to contamination because of the fast flow of various contaminants. However, it remains unclear whether N-nitrosamines and their precursor, DOM, spread in karst reservoirs. Therefore, this study quantitatively investigated the occurrence and sources of N-nitrosamines based on DOM properties in three typical karst reservoirs and their corresponding tap water. The results showed that N-nitrosamines were widely spread, with detection frequencies > 85%. Similar dominant compounds, including N-nitrosodimethylamine, N-nitrosomethylethylamine, N-nitrosopyrrolidine, and N-nitrosodibutylamine, were observed in reservoirs and tap water, with average concentrations of 4.7-8.9 and 2.8-6.7 ng/L, respectively. The average carcinogenic risks caused by these N-nitrosamines were higher than the risk level of 10-6. Three-dimensional fluorescence excitation-emission matrix modeling revealed that DOM was composed of humus-like component 1 (C1) and protein-like component 2 (C2). Fluorescence indicators showed that DOM in reservoir water was mainly affected by exogenous pollution and algal growth, whereas in tap water, DOM was mainly affected by microbial growth with strong autopoietic properties. In the reservoir water, N-nitrosodiethylamine and N-nitrosopiperidine were significantly correlated with C2 and biological indicators, indicating their endogenously generated sources. Based on the principal component analysis and multiple linear regression methods, five sources of N-nitrosamines were identified: agricultural pollution, microbial sources, humus sources, degradation processes, and other factors, accounting for 46.8%, 36.1%, 7.82%, 8.26%, and 0.96%, respectively. For tap water, two sources, biological reaction processes, and water distribution systems, were identified, accounting for 75.7% and 24.3%, respectively. Overall, this study presents quantitative information on N-nitrosamines' sources based on DOM properties in typical karst reservoirs and tap water, providing a basis for the safety of drinking water for consumers.

Toxic interactions at the physiological and biochemical levels of green algae under stress of mixtures of three azole fungicides.

Assessing the interactions between environmental pollutants and these mixtures is of paramount significance in understanding their negative effects on aquatic ecosystems. However, existing research often lacks comprehensive investigations into the physiological and biochemical mechanisms underlying these interactions. This study aimed to reveal the toxic mechanisms of cyproconazole (CYP), imazalil (IMA), and prochloraz (PRO) and corresponding these mixtures on Auxenochlorella pyrenoidosa by analyzing the interactions at physiological and biochemical levels. Higher concentrations of CYP, IMA, and PRO and these mixtures resulted in a reduction in chlorophyll (Chl) content and increased total protein (TP) suppression, and malondialdehyde (MDA) content exhibited a negative correlation with algal growth. The activity of catalase (CAT) and superoxide dismutase (SOD) decreased with increasing azole fungicides and their mixture concentrations, correlating positively with growth inhibition. Azole fungicides induced dose-dependent apoptosis in A. pyrenoidosa, with higher apoptosis rates indicative of greater pollutant toxicity. The results revealed concentration-dependent toxicity effects, with antagonistic interactions at low concentrations and synergistic effects at high concentrations within the CYP-IMA mixtures. These interactions were closely linked to the interactions observed in Chl-a, carotenoid (Car), CAT, and cellular apoptosis. The antagonistic effects of CYP-PRO mixtures on A. pyrenoidosa growth inhibition can be attributed to the antagonism observed in Chl-a, Chl-b, Car, TP, CAT, SOD, and cellular apoptosis. This study emphasized the importance of gaining a comprehensive understanding of the physiological and biochemical interactions within algal cells, which may help understand the potential mechanism of toxic interaction.

LC-QTOF/MS-based non-targeted metabolomics to explore the toxic effects of di(2-ethylhexyl) phthalate (DEHP) on Brassica chinensis L.

Di(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer known to pose health risks to humans upon exposure. Recognizing the toxic nature of DEHP, our study aimed to elucidate the response mechanisms in Brassica chinensis L. (Shanghai Qing) when subjected to varying concentrations of DEHP (2 mg kg-1, 20 mg kg-1, and 50 mg kg-1), particularly under tissue stress. The findings underscored the substantial impact of DEHP treatment on the growth of Brassica chinensis L., with increased DEHP concentration leading to a notable decrease in chlorophyll levels and alterations in the content of antioxidant enzyme activities, particularly superoxide dismutase (SOD) and peroxidase (POD). Moreover, elevated DEHP concentrations correlated with increased malondialdehyde (MDA) levels. Our analysis detected a total of 507 metabolites in Brassica chinensis L., with 331 in shoots and 176 in roots, following DEHP exposure. There was a significant difference in the number of metabolites in shoots and roots, with 79 and 64 identified, respectively (VIP > 1, p < 0.05). Metabolic pathway enrichment in Brassica chinensis L. shoots revealed significant perturbations in valine, leucine, and isoleucine biosynthesis and degradation, aminoacyl-tRNA, and glucosinolate biosynthesis. In the roots of Brassica chinensis L., varying DEHP levels exerted a substantial impact on the biosynthesis of zeatin, ubiquinone terpenoids, propane, piperidine, and pyridine alkaloids, as well as glutathione metabolic pathways. Notably, DEHP's influence was more pronounced in the roots than in the shoots, with higher DEHP concentrations affecting a greater number of metabolic pathways. This experimental study provides valuable insights into the molecular mechanisms underlying DEHP-induced stress in Brassica chinensis L., with potential implications for human health and food safety.

Synergistic removal performance and mechanism of Cd(II) and As(III) from irrigation water by iron sulfide-based porous biochar.

Since Cd(II) and As(III) have extremely opposite chemical characteristics, it is a huge challenging to simultaneously remove these two ions from aqueous solutions. Therefore, a novel iron sulfide-based porous biochar (FSB) was synthesized and used to evaluate its Cd(II) and As(III) removal performance and mechanisms. The characterization and batch experiments results indicated that FeS was successfully loaded on the surface of biochar and increased its adsorption sites. The iron sulfide-based porous biochar was very favorable for the removal of Cd(II) and As(III) in the weakly acidic environment. The maximum adsorption of Cd(II) and As(III) by FSB was 108.8 mg g-1 and 76.3 mg g-1, respectively, according to the Langmuir and Freundlich isothermal adsorption model, and the adsorption equilibrium time was 12 h and 4 h, respectively, according to the pseudo-second-order kinetic model. In the coexisting ion system, Cd(II) adsorption was suppressed by Ca2+, Mg2+, and humic acid, but enhanced by PO43- and As(III). As(III) adsorption was inhibited by PO43- and humic acid. Precipitation and complexation are the predominant adsorption mechanisms of Cd(II) and As(III), which contribute to the formation of Cd-O, Fe-O-Cd, As-O, Fe-O-As, ternary complex Cd-Fe-As, and stable compounds FeAsO4·2H2O and CdS. Therefore, The iron sulfide-based porous biochar can be an efficient and environmentally friendly candidate for the treatment of Cd(II) and As(III) co-polluted irrigation water.

Impact of agricultural activities on the occurrence of N-nitrosamines in an aquatic environment.

N-Nitrosamines, nitroso compounds with strong carcinogenic effects on humans, have been frequently detected in natural waters. In agricultural areas, there is typically a lack of drinking water treatment processes and distribution systems. As a result, residents often consume groundwater as drinking water which may contain N-nitrosamines, necessitating the investigation of the occurrence, sources, and carcinogenic risk of N-nitrosamines within the groundwater of agricultural areas. This study identified eight N-nitrosamines in groundwater and river water in the Jianghan Plain, a famous agricultural region in central China. N-Nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosomorpholine (NMOR), N-nitrosopyrrolidine (NPYR), and N-nitrosodi-n-butylamine (NDBA) were detected in groundwater, with NDMA being the main compound detected (up to 52 ng L-1). Comparable concentrations of these N-nitrosamines were also found in river water. From laboratory experiments, we found a tremendous potential for the formation of N-nitrosamines in groundwater. Principal component analysis and multiple linear regression analysis results showed that the primary sources of N-nitrosamines in groundwater were the uses of nitrogen fertilizers and pesticides carrying specific N-nitrosamines such as NPYR. The average total carcinogenic risk values of detected N-nitrosamines were higher than the acceptable risk level (10-5), suggesting a potential carcinogenic risk of groundwater. Further research is urgently needed to minimize N-nitrosamine levels in the groundwater of agricultural areas, particularly in those where pesticides and fertilizers are heavily used.

Occurrence and transport of N-nitrosamines in the urban water systems of the Pearl River Delta, southern China.

The discharge of substantial amounts of N-nitrosamines-contained wastewater into receiving rivers can significantly deteriorate water quality, as these carcinogenic compounds can be easily transported into groundwater and drinking water systems. This study investigated the distribution of eight species of N-nitrosamines in river water, groundwater, and tap water located in the center of the Pearl River Delta (PRD), China. The results showed that three major N-nitrosamines, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosodibutylamine (NDBA), with concentrations of up to 64 ng/L, were observed in river water, groundwater, and tap water, whereas the other compounds occurred sporadically. In river water and groundwater, high concentrations of NDMA, NDEA, N-nitrosomorpholine (NMOR), and NDBA were found in industrial and residential lands as compared to agricultural lands owing to the influence of various human activities. The primary sources of N-nitrosamines in river water were industrial and domestic wastewater, and the infiltration of river water was responsible for the high levels of N-nitrosamines in groundwater. Among the target N-nitrosamines, NDEA and NMOR with long biodegradation half-lives (>4 days) and low LogKow values (<1) displayed the highest potential for groundwater. N-nitrosamines in groundwater and tap water pose significant potential cancer risks to residents, especially children, and juveniles, with lifetime cancer risks of over 10-4, necessitating advanced water treatments for drinking water and critical controls on primary industrial discharge in urban areas.

Toxicity interactions of azole fungicide mixtures on Chlorella pyrenoidosa.

It is acknowledged that azole fungicides may release into the environment and pose potential toxic risks. The combined toxicity interactions of azole fungicide mixtures, however, are still not fully understood. The combined toxicities and its toxic interactions of 225 binary mixtures and 126 multi-component mixtures on Chlorella pyrenoidosa were performed in this study. The results demonstrated that the negative logarithm 50% effect concentration (pEC50 ) of 10 azole fungicides to Chlorella pyrenoidosa at 96 h ranged from 4.23 (triadimefon) to 7.22 (ketoconazole), while the pEC50 values of the 351 mixtures ranged from 3.91 to 7.44. The high toxicities were found for the mixtures containing epoxiconazole. According to the results of the model deviation ratio (MDR) calculated from the concentration addition (MDRCA ), 243 out of 351 (69.23%) mixtures presented additive effect at the 10% effect, while the 23.08% and 7.69% of mixtures presented synergistic and antagonistic effects, respectively. At the 30% effect, 47.29%, 29.34%, and 23.36% of mixtures presented additive effects, synergism, and antagonism, respectively. At the 50% effect, 44.16%, 34.76%, and 21.08% of mixtures presented additive effects, synergism, and antagonism, respectively. Thus, the toxicity interactions at low concentration (10% effect) were dominated by additive effect (69.23%), whereas 55.84% of mixtures induced synergism and antagonism at high concentration (50% effect). Climbazole and imazalil were the most frequency of components presented in the additive mixtures. Epoxiconazole was the key component induced the synergistic effects, while clotrimazole was the key component in the antagonistic mixtures.

Occurrence and mass loads of N-nitrosamines discharged from different anthropogenic activities in Desheng River, South China.

N-nitrosamines are widespread in various bodies of water, which is of great concern due to their carcinogenic risks and harmful mutagenic effects. Livestock rearing, domestic, agricultural, and industrial wastewaters are the main sources of N-nitrosamines in environmental water. However, information on the amount of N-nitrosamines these different wastewaters contribute to environmental water is scarce. Here, we investigated eight N-nitrosamines and assessed their mass loadings in the Desheng River to quantify the contributions discharged from different anthropogenic activities. N-nitrosodimethylamine (NDMA) (< 1.6-18 ng/L), N-nitrosomethylethylamine (NMEA) (< 2.2 ng/L), N-nitrosodiethylamine (NDEA) (< 1.7-2.4 ng/L), N-nitrosopyrrolidine (NPYR) (< 1.8-18 ng/L), N-nitrosomorpholine (NMOR) (< 2.0-3.5 ng/L), N-nitrosopiperidine (NPIP) (< 2.2-2.5 ng/L), and N-nitrosodi-n-butylamine (NDBA) (< 3.3-16 ng/L) were detected. NDMA and NDBA were the dominant compounds contributing 89% and 92% to the total N-nitrosamine concentrations. The mean cumulative concentrations of N-nitrosamines in the livestock rearing area (26 ± 11 ng/L) and industrial area (24 ± 4.8 ng/L) were higher than those in the residential area (16 ± 6.3 ng/L) and farmland area (15 ± 5.1 ng/L). The mean concentration of N-nitrosamines in the tributaries (22 ng/L) was slightly higher than that in the mainstem (17 ng/L), probably due to the dilution effect of the mainstem. However, the mass loading assessment based on the river's flow and water concentrations suggested the negligible mass emission of N-nitrosamines into the mainstem from tributaries, which could be due to the small water flow of tributaries. The average mass loads of N-nitrosamines discharged into the mainstem were ranked as the livestock rearing area (742.7 g/d), industrial area (558.6 g/d), farmland area (93.9 g/d), and residential areas (83.2 g/d). In the livestock rearing, residential, and industrial area, NDMA (60.9%, 53.6%, and 46.7%) and NDBA (34.6%, 33.3%, and 44.9%) contributed the most mass loads; NDMA (23.4%), NDEA (15.8%), NPYR (10.1%), NPIP (12.8%), and NDBA (37.8%) contributed almost all the mass loads in the farmland area. Photodegradation amounts of NDMA (0.65 ~ 5.25 µg/(m3·day)), NDBA (0.37 ~ 0.91 µg/(m3·day)), and NDEA (0 ~ 0.66 µg/(m3·day)) were also calculated according to the mass loading. Quantifying the contribution of different anthropogenic activities to the river will provide important information for regional river water quality protection. Risk quotient (RQ) values showed the negligible ecological risks for fish, daphnid, and green algae.

Degradation Characteristics and Remediation Ability of Contaminated Soils by Using ß-HCH Degrading Bacteria.

Three degradation strains that can utilize ß-Hexachlorocyclohexanes (ß-HCH) as the sole carbon source were isolated from the soil substrate of constructed wetland under long-term ß-HCH stress, and they were named A1, J1, and M1. Strains A1 and M1 were identified as Ochrobactrum sp. and strain J1 was identified as Microbacterium oxydans sp. by 16S rRNA gene sequence analysis. The optimum conditions for degradation with these three strains, A1, J1, and M1, were pH = 7, 30 °C, and 5% inoculum amount, and the degradation rates of 50 µg/L ß-HCH under these conditions were 58.33%, 51.96%, and 50.28%, respectively. Degradation characteristics experiments showed that root exudates could increase the degradation effects of A1 and M1 on ß-HCH by 6.95% and 5.82%, respectively. In addition, the degradation bacteria A1 and J1 mixed in a ratio of 1:1 had the highest degradation rate of ß-HCH, which was 69.57%. An experiment on simulated soil remediation showed that the compound bacteria AJ had the best effect on promoting the degradation of ß-HCH in soil within 98 d, and the degradation rate of ß-HCH in soil without root exudates was 60.22%, whereas it reached 75.02% in the presence of root exudates. The addition of degradation bacteria or degradation bacteria-root exudates during soil remediation led to dramatic changes in the community structure of the soil microorganisms, as well as a significant increase in the proportion of aerobic and Gram-negative bacterial groups. This study can enrich the resources of ß-HCH degrading strains and provided a theoretical basis for the on-site engineering treatment of ß-HCH contamination.

Endocrine Disruption of Propylparaben in the Male Mosquitofish (Gambusia affinis): Tissue Injuries and Abnormal Gene Expressions of Hypothalamic-Pituitary-Gonadal-Liver Axis.

Propylparaben (PrP) is a widely used preservative that is constantly detected in aquatic environments and poses a potential threat to aquatic ecosystems. In the present work, adult male mosquitofish were acutely (4d) and chronically (32d) exposed to environmentally and humanly realistic concentrations of PrP (0, 0.15, 6.00 and 240 µg/L), aimed to investigate the toxic effects, endocrine disruption and possible mechanisms of PrP. Histological analysis showed time- and dose-dependent manners in the morphological injuries of brain, liver and testes. Histopathological alterations in the liver were found in 4d and severe damage was identified in 32d, including hepatic sinus dilatation, cytoplasmic vacuolation, cytolysis and nuclear aggregation. Tissue impairments in the brain and testes were detected in 32d; cell cavitation, cytomorphosis and blurred cell boundaries appeared in the brain, while the testes lesions contained spermatogenic cell lesion, decreased mature seminal vesicle, sperm cells gathering, seminiferous tubules disorder and dilated intercellular space. Furthermore, delayed spermatogenesis had occurred. The transcriptional changes of 19 genes along the hypothalamus-pituitary-gonadal-liver (HPGL) axis were investigated across the three organs. The disrupted expression of genes such as Ers, Ars, Vtgs, cyp19a, star, hsd3b, hsd17b3 and shh indicated the possible abnormal steroidogenesis, estrogenic or antiandrogen effects of PrP. Overall, the present results provided evidences for the toxigenicity and endocrine disruptive effects on the male mosquitofish of chronic PrP exposure, which highlights the need for more investigations of its potential health risks.

Integration of Zeolite Membrane Bioreactor With Granular Sludge-Based Anammox in High-Efficiency Nitrogen Removal From Iron Oxide Red Wastewater.

Acquisition of stable nitritation and efficient anammox play a crucial role in partial nitritation (PN) combined with anammox for nitrogen removal from ammonium-rich wastewater. Due to the limitation of ammonia-oxidizing bacteria (AOB) enrichment and nitrite-oxidizing bacteria (NOB) control in traditional membrane biological reactor (MBR), it can result in a lower nitrite production rate (NPR) and unstable PN, eventually reducing the nitrogen removal rate (NRR) via PN-anammox. In this study, we developed a zeolite membrane biological reactor (ZMBR) to enhance the PN of iron oxide red wastewater (IORW), in which the biofilm derived from the zeolite surface can provide free ammonia (FA)-containing microenvironment for AOB enrichment and NOB inhibition. The results showed that ZMBR can tolerate a higher influent nitrogen loading rate (NLR) of 2.78 kg/(m3⋅day) in comparison to the traditional MBR [2.02 kg/(m3⋅day)] and the NPR in ZMBR and traditional MBR were 1.39 and 0.96 kg/(m3⋅day), respectively. The mass concentration ratio of NO 2 - -N/ NH 4 + -N ranged from 1.05 to 1.33 in ZMBR, suggesting a suitable condition for nitrogen removal via anammox. Subsequently, the domesticated granular sludge obtained from a paper-making wastewater treatment was used as the carrier of anammox bacteria to remove nitrogen. After 93 days of operation, the NRR was observed to be 2.33 kg/(m3⋅day) and high-throughput sequencing indicated that the relatively higher abundance (45.0%) of Candidatus Kuenenia stuttgartiensis was detected in the granular sludge of the bottom part of the reactor, which can produce more proteins and lipids, suggesting a good settleability. Overall, this study provides a high-efficient method to control PN and domesticate anammox for nitrogen removal from IORW.

Enhanced remediation of fracturing flowback fluids by the combined application of a bioflocculant/biosurfactant-producing Bacillus sp. SS15 and its metabolites.

Fracturing flowback fluids (FFFs), which is generated from the process of oil and gas exploitation, is one of the major environmental concerns. In this study, a bacterial strain, Bacillus sp. SS15, capable of producing both bioflocculant (BF) and biosurfactant (BS), was isolated from oil-contaminated mudflat sediment. The BS produced by SS15 was identified as lipopeptide, which could reduce the surface tension of water from 74.2 mN/m to 36.6 mN/m with a critical micelle concentration of 44.4 mg/L. It also exhibited strong tolerance against a wide range of pH (2-12), temperature (4-60 °C), and salinity (0-100 g/L). Meanwhile, the BF produced by SS15 exhibited high flocculating activity (84.9%) for kaolin suspension, and was confirmed to be thermostable, salt-tolerant, and alkaliphilic. The combined treatment of bioremediation (introducing SS15 and BS) followed by flocculation (introducing BF) greatly promoted the removal of chroma (85.7% reduction), suspended solids (94.4% reduction), chemical oxygen demand (84.9% reduction), n-alkanes (50.0% reduction), and polycyclic aromatic hydrocarbons (66.5% reduction), respectively. The genome analysis showed that strain SS15 possessed abundant genes related to the synthesis of carbohydrate, protein, and lipid, which might play an important role in BF and BS synthesis. The findings in this study demonstrated that Bacillus sp. SS15 has promising prospect in the remediation of FFFs.

Improved degradation of petroleum hydrocarbons by co-culture of fungi and biosurfactant-producing bacteria.

Microbial remediation has proven to be an effective technique for the cleanup of crude-oil contaminated sites. However, limited information exists on the dynamics involved in defined co-cultures of biosurfactant-producing bacteria and fungi in bioremediation processes. In this study, a fungal strain (Scedosporium sp. ZYY) capable of degrading petroleum hydrocarbons was isolated and co-cultured with biosurfactant-producing bacteria (Acinetobacter sp. Y2) to investigate their combined effect on crude-oil degradation. Results showed that the surface tension of the co-culture decreased from 63.12 to 47.58 mN m-1, indicating the secretion of biosurfactants in the culture. Meanwhile, the degradation rate of total petroleum hydrocarbon increased from 23.36% to 58.61% at the end of the 7-d incubation period. In addition, gas chromatography - mass spectrometry analysis showed a significant (P < 0.05) degradation from 3789.27 mg/L to 940.33 mg/L for n-alkanes and 1667.33 µg/L to 661.5 µg/L for polycyclic aromatic hydrocarbons. Moreover, RT-qPCR results revealed the high expression of alkB and CYP52 genes by Acinetobacter sp. Y2 and Scedosporium sp. ZYY respectively in the co-culture, which corelated positively (P < 0.01) with n-alkane removal. Finally, microbial growth assay which corresponded with Fluorescein diacetate hydrolysis activity, highlighted the synergistic behavior of both strains in tackling the crude oil. Findings in this study suggest that the combination of fungal strain and biosurfactant-producing bacteria effectively enhances the degradation of petroleum hydrocarbons, which could shed new light on the improvement of bioremediation strategies.

Electrostimulated bio-dechlorination of a PCB mixture (Aroclor 1260) in a marine-originated dechlorinating culture.

Aroclor 1260, a commercial polychlorinated biphenyl (PCB) mixture, is highly recalcitrant to biotransformation. A negatively polarized cathode (-0.35 V vs. standard hydrogen electrode) was applied for the first time to a marine-origin PCB dechlorinating culture that substantially increased the microbial dechlorination rate of Aroclor 1260 (from 8.6 to 11.6 µM Cl- d-1); meta-chlorine removal was stimulated and higher proportions of tetra-CBs (43.2-46.6%), the predominant dechlorination products, were observed compared to the open circuit conditions (23.7-25.1%). The dechlorination rate was further enhanced (14.1 µM Cl- d-1) by amendment with humin as a solid-phase redox mediator. After the suspension culture was renewed using an anaerobic medium, dechlorination activity was effectively maintained solely by cathodic biofilms, where cyclic voltammetry results indicated their redox activity. Electric potential had a significant effect on microbial community structure in the cathodic biofilm, where a greater abundance of Dehalococcoides (2.59-3.02%), as potential dechlorinators, was observed compared to that in the suspension culture (0.41-0.55%). Moreover, Dehalococcoides adhering to the cathode showed a higher chlorine removal rate than in the suspension culture. These findings provide insights into the dechlorination mechanism of cathodic biofilms involving Dehalococcoides for PCB mixtures and extend the application prospects of bioremediation to PCB contamination in the natural environment.

Histopathology and transcriptome reveals the tissue-specific hepatotoxicity and gills injury in mosquitofish (Gambusia affinis) induced by sublethal concentration of triclosan.

Triclosan (TCS), a ubiquitous antimicrobial agent, has been frequently detected in wild fish, leading to concerns regarding TCS safety in the aquatic environment. The present work aims to investigate the TCS-mediated effects on various tissues (the liver, gills, brain, and testes) of wild-sourced adult mosquitofish based on histological analysis and transcriptome. Severe morphological injuries were only found in the liver and gills. The histopathological alterations in the liver were characterized by cytoplasmic vacuolation and degeneration, eosinophilic cytoplasmic inclusions, and nuclear polymorphism. The gill lesions contained epithelial lifting, intraepithelial edema, fusion and shortening of the secondary lamellae. Consistently, the numbers of differently expressed genes (DEGs) identified by transcriptome were in the order of liver (1627) > gills (182) > brain (9) > testes (4). Trend-aligned histopathological and transcriptomic changes in the 4 tissues, suggesting the tissue-specific response manner of mosquitofish to TCS, and the liver and gills were the target organs. TCS interrupted many biological pathways associated with lipogenesis and lipid metabolism, transmembrane transporters, protein synthesis, and carbohydrate metabolism in the liver, and it induced nonspecific immune response in the gills. TCS-triggered hepatotoxicity and gills damnification may lead to inflammation, apoptosis, diseases, and even death in mosquitofish. TCS showed moderate acute toxicity and bioaccumulative property on mosquitofish, suggesting that prolonged or massive use of TCS may pose an ecological risk.

Concentration Addition, Independent Action, and Quantitative Structure-Activity Relationships for Chemical Mixture Toxicities of the Disinfection By products of Haloacetic Acids on the Green Alga Raphidocelis subcapitata.

The potential toxicity of haloacetic acids (HAAs), common disinfection by products (DBPs), has been widely studied; but their combined effects on freshwater green algae remain poorly understood. The present study was conducted to investigate the toxicological interactions of HAA mixtures in the green alga Raphidocelis subcapitata and predict the DBP mixture toxicities based on concentration addition, independent action, and quantitative structure-activity relationship (QSAR) models. The acute toxicities of 6 HAAs (iodoacetic acid [IAA], bromoacetic acid [BAA], chloroacetic acid [CAA], dichloroacetic acid [DCAA], trichloroacetic acid [TCAA], and tribromoacetic acid [TBAA]) and their 68 binary mixtures to the green algae were analyzed in 96-well microplates. Results reveal that the rank order of the toxicity of individual HAAs is CAA > IAA ≈ BAA > TCAA > DCAA > TBAA. With concentration addition as the reference additive model, the mixture effects are synergetic in 47.1% and antagonistic in 25%, whereas the additive effects are only observed in 27.9% of the experiments. The main components that induce synergism are DCAA, IAA, and BAA; and CAA is the main component that causes antagonism. Prediction by concentration addition and independent action indicates that the 2 models fail to accurately predict 72% mixture toxicity at an effective concentration level of 50%. Modeling the mixtures by QSAR was established by statistically analyzing descriptors for the determination of the relationship between their chemical structures and the negative logarithm of the 50% effective concentration. The additive mixture toxicities are accurately predicted by the QSAR model based on 2 parameters, the octanol-water partition coefficient and the acid dissociation constant (pKa ). The toxicities of synergetic mixtures can be interpreted with the total energy (ET ) and pKa of the mixtures. Dipole moment and ET are the quantum descriptors that influence the antagonistic mixture toxicity. Therefore, in silico modeling may be a useful tool in predicting disinfection by-product mixture toxicities. Environ Toxicol Chem 2021;40:1431-1442. © 2021 SETAC.

Toxic mechanism of three azole fungicides and their mixture to green alga Chlorella pyrenoidosa.

Currently, few studies have investigated the joint toxicity mechanism of azole fungicides at different exposure times and mixed at the relevant environmental concentrations. In this study, three common azole fungicides, namely, myclobutanil (MYC), propiconazole (PRO), and tebuconazole (TCZ), were used in studying the toxic mechanisms of a single substance and its ternary mixture exposed to ambient concentrations of Chlorella pyrenoidosa. Superoxide dismutase (SOD), catalase (CAT), chlorophyll a (Chla), and total protein (TP), were used as physiological indexes. Results showed that three azole fungicides and ternary mixture presented obvious time-dependent toxicities at high concentrations. MYC induced a hormetic effect on algal growth, whereas PRO and TCZ inhibit algal growth in the entire range of the tested concentrations. The toxicities of the three azole fungicides at 7 days followed the order PRO > TCZ > MYC. Three azole fungicides and their ternary mixture induced different levels of SOD and CAT activities in algae at high concentrations. The ternary mixture showed additive effects after 4 and 7 days exposure, but no effect was observed at actual environmental concentrations. The toxic mechanisms may be related to the continuous accumulation of reactive oxygen species, which not only affected protein structures and compositions but also damaged thylakoid membranes, hindered the synthesis of proteins and chlorophyll a, and eventually inhibited algal growth. These findings increase the understanding of the ecotoxicity of azole fungicides and use of azole fungicides in agricultural production.

Ecological and human health risk of sulfonamides in surface water and groundwater of Huixian karst wetland in Guilin, China.

Sulfonamide antibiotics are contaminants of emerging concern (CEC). These CECs raise considerable alarm because they are commonly present in water environments. Studies on the environmental existence of CECs in karst areas of Guilin (Southern China) have yet to be reported. Thus, this study aims to investigate the presence, temporal and spatial distributions of sulfonamides in surface water and groundwater of four major aquatic environments (i.e., aquafarm water, ditch water, wetland water, and groundwater) in the Huixian karst wetland system of Guilin. Furthermore, this study aims to determine the ecological and human health risks of individual sulfonamides and their mixtures. Ten sulfonamides (i.e., sulfadiazine, sulfapyridine, sulfamerazine, trimethoprim, sulfamethazine, sulfamethoxypyridazine, sulfachloropyridazine, sulfamethoxazole, sulfadimethoxine, and sulfaquinoxaline) were observed in the study area. The highest average concentrations of aquafarm water, ditch water, wetland water, and groundwater were those of sulfadiazine (48.24 µg/L), sulfamethoxypyridazine (1281.50 µg/L), sulfamethoxazole (51.14 µg/L), and sulfamethazine (20.06 µg/L), respectively. The potential ecological risks of the detected compounds were much higher in ditch water than in aquafarm water, wetland water, and groundwater. The most ecological risks were observed for sulfachloropyridazine with a risk quotient (RQ) reaching 335.5 to green algae and 152 to Daphnia magna in ditch water. Similarly, sulfachloropyridazine posed the highest ecological risks to green algae among the ten sulfonamides in aquafarm water (RQ = 3.39), wetland water (RQ = 2.98), and groundwater (RQ = 3.6). Human health risk for age groups<12 months was observed from sulfonamide in drinking groundwater. Ecological and human health risks caused by sulfonamide mixtures were larger than the individual risks. Overall, ecological and human health risks caused by sulfonamides were observed in the study area.

Predicting the cytotoxicity of disinfection by-products to Chinese hamster ovary by using linear quantitative structure-activity relationship models.

A suitable model to predict the toxicity of current and continuously emerging disinfection by-products (DBPs) is needed. This study aims to establish a reliable model for predicting the cytotoxicity of DBPs to Chinese hamster ovary (CHO) cells. We collected the CHO cytotoxicity data of 74 DBPs as the endpoint to build linear quantitative structure-activity relationship (QSAR) models. The linear models were developed by using multiple linear regression (MLR). The MLR models showed high performance in both internal (leave-one-out cross-validation, leave-many-out cross-validation, and bootstrapping) and external validation, indicating their satisfactory goodness of fit (R2 = 0.763-0.799), robustness (Q2LOO = 0.718-0.745), and predictive ability (CCC = 0.806-0.848). The generated QSAR models showed comparable quality on both the training and validation levels. Williams plot verified that the obtained models had wide application domains and covered the 74 structurally diverse DBPs. The molecular descriptors used in the models provided comparable information that influences the CHO cytotoxicity of DBPs. In conclusion, the linear QSAR models can be used to predict the CHO cytotoxicity of DBPs.