Effects of tire-road wear particles on the adsorption of tetracycline by aquatic sediments.

Tire-road wear particles (TRWPs) are formed by friction between the tire and the road. TRWPs are ubiquitous across the globe, especially in sediments. However, the possible effects of TRWPs on tetracycline (TC) in aquatic sediments are unknown. To investigate the potential role of TRWPs as carriers of co-pollutants, this study investigated the pore surface properties and TC adsorption behavior of TRWP-contaminated sediments and explored the TC behavior in water sediments, as well as the role of aging processes and TRWPs abundance. The results showed that the surface morphology of TRWP-contaminated sediments changed and the adsorption capacity of sediments to TC increased. The TC adsorption capacity of sediments contaminated by 2% TRWPs increased from 3.15 to 3.48 mg/g. Moreover, the surface physical and chemical properties of TRWPs after UV aging changed, which further increased the TC adsorption capacity. The TC adsorption capacity of the sediments contaminated by aged TRWPs increased from 3.48 to 3.65 mg/g. Changing the proportion of aged TRWPs, we found that the adsorption capacity of sediments contaminated by different proportions of TRWPs for TC was 2% > 1% > 0.5% > 4% > blank sediment. These results may contribute to predicting the potential environmental risks of TRWPs in aquatic sediments.

Fenton-like membrane reactor assembled by electron polarization and defect engineering modifying Co3O4 spinel for flow-through removal of organic contaminants.

The application of Fenton-like membrane reactors for water purification offers a promising solution to overcome technical challenges associated with catalyst recovery, reaction efficiency, and mass transfer typically encountered in heterogeneous batch reaction modes. This study presents a dual-modification strategy encompassing electron polarization and defect engineering to synthesize Al-doped and oxygen vacancies (OV)-enriched Co3O4 spinel catalysts (ACO-OV). This modification empowered ACO-OV with exceptional performance in activating peroxymonosulfate (PMS) for the removal of organic contaminants. Moreover, the ACO-OV@polyethersulfone (PES) membrane/PMS system achieved organic contaminant removal through filtration (with a reaction kinetic constant of 0.085 ms-1), demonstrating outstanding resistance to environmental interference and high operational stability. Mechanistic investigations revealed that the exceptional catalytic performance of this Fenton-like membrane reactor stemmed from the enrichment of reactants, exposure of reactive sites, and enhanced mass transfer within the confined space, leading to a higher availability of reactive species. Theoretical calculations were conducted to validate the beneficial intrinsic effects of electron polarization, defect engineering, and the confined space within the membrane reactor on PMS activation and organic contaminant removal. Notably, the ACO-OV@PES membrane/PMS system not only mineralized the targeted organic contaminants but also effectively mitigated their potential environmental risks. Overall, this work underscores the significant potential of the dual-modification strategy in designing spinel catalysts and Fenton-like membrane reactors for efficient organic contaminant removal.

Preparation of chitosan-iron oxide modified sludge-based biochar for effective removal of tetracycline from water: performance and mechanism.

The release of antibiotics has attracted wide attention due to their abuse and discharge. How to remove these emerging contaminants is an urgent need to be solved. In the present study, sludge-based biochar combining chitosan and iron oxide was prepared via municipal sewage sludge. The novel biochar modified with chitosan and iron oxide exhibited satisfying performance in eliminating antibiotics from water. The application of modified biochar combined with activated persulfate (PS) showed a remarkable removal efficiency of 96.98% for tetracycline (TC). Analysis of the surface characteristics of the modified biochar showed the presence of structural defects, dispersed iron oxides, abundant functional groups, a porous structure, and a relatively stable crystal structure. These characteristics attributed significant importance to facilitating the degradation of TC. A series of experimental conditions including preparation temperature (600-900 ℃), reaction temperature (15-45 ℃), contaminant concentration (30-180 mg/L), adsorbent usage (0.1-1 g/L), pH (2-10), and persulfate addition concentration (1-5 mmol) were conducted. The results revealed that the highest removal efficiency was achieved at 96.98% under the conditions of TC concentration at 30 mg/L, reaction temperature at 35 ℃, pH of 4, adsorbent addition amount of 0.6 g/L, and PS concentration of 2 mmol, respectively. Three degradation pathways and seven intermediate products of TC were proposed. Therefore, our study provides a promising approach for developing effective removal of antibiotic pollutants.

Acute toxicity of tire wear particles and leachate to Daphnia magna.

Tire wear particles (TWP) are a new pollutant widely present in the environment, and have been identified as microplastics (MPs), which are receiving increasing attention due to their toxic effects on aquatic organisms. In this study, D. magna was used as test organism, and the leachate from TWP was prepared by hot water extraction for 30 (30-E) and 120 min (120-E). The acute toxic effects of particles and leachate on D. magna were studied under different exposure concentrations. The results showed that zinc and pyrene were the highest detected contaminants in the leachate. The 48 h-LC50 values for particles and leachate were determined to be 56.99, 461.30 (30-E), and 153.00 mg/L (120-E), respectively. Following a 48 h exposure period, the immobilization of D. magna exposed to the particles and their leachate were increased with the concentration increase. The physical damage of the gut was found to be a possible mechanism for particle-induced biotoxicity. The compounds leached from TWP were responsible for the acute toxicity of leachate. Particles usually demonstrated a greater degree of toxicity in comparison to their leachate, especially at environmentally relevant concentrations. Exposure to particles and leachate resulted in the inhibition of swimming speed, swimming acceleration, filtration rate, and ingestion rate in D. magna. Furthermore, thoracic limb activity was observed to be inhibited. The heart rate of D. magna was significantly increased by the presence of particles at a concentration of 200 mg/L and leachate at concentrations of 400 and 800 mg/L (120-E). The observed alterations in behavior and physiological endpoints may be related to oxidative stress and neurotoxicity in the organism. Reduced superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) activities indicated that D. magna may suffer from excessive oxidative stress, whereas the increase of acetylcholinesterase (AChE) activity may serve as a biomarker of susceptibility to evaluate the environmental risks of TWP and corresponding leachates as potential aquatic pollutants.. Therefore, a more comprehensive risk assessment of TWP in the environment is necessary.

Photocatalytic O2 activation by metal-free carbon nitride nanotube for rapid reactive species generation and organic contaminants degradation.

Advanced oxidation processes (AOPs) using oxygen (O2) as an oxidant represent a low-cost and sustainable wastewater treatment process. Herein, a metal-free nanotubular carbon nitride photocatalyst (CN NT) was prepared to activate O2 to degrade organic contaminants. The nanotube structure allowed for sufficient O2 adsorption, while the optical and photoelectrochemical properties enabled photogenerated charge to be efficiently transferred to the adsorbed O2 to trigger the activation process. The developed CN NT/Vis-O2 system based on O2 aeration degraded various organic contaminants and mineralized 40.7% of chloroquine phosphate within 100 min. In addition, the toxicity and environmental risk of treated contaminants were reduced. Mechanistic studies suggested that the enhanced O2 adsorption capacity and fast charge transfer behavior on CN NT surface led to reactive·O2-, 1O2 and h+ generation, each of which played a distinct role in contaminants degradation. Importantly, the proposed process could overcome the interference from water matrices and outdoor sunlight, and the energy and chemical reagent savings reduced the operating cost to about 1.63 US$·m-3. Altogether, this work provides insights into the potential application of metal-free photocatalysts and green O2 activation for wastewater treatment.

Desorption behavior of antibiotics by microplastics (tire wear particles) in simulated gastrointestinal fluids.

Microplastics (MPs) are widely distributed throughout the environment. Upon ingesting MPs, the pollutants that they carry are then desorbed into organisms. This results in the accumulation of various chemicals within the organism. This study systematically examined the mechanism of antibiotic desorption using tire wear particles (TWP) as a carrier of antibiotics in simulated human gastrointestinal fluid and fish intestinal fluid. The findings of this study revealed the formation of cracks, pores, and depressions on the surface of photoaged TWP in an aquatic environment, as well as additional adsorption sites that are more favorable for the attachment of pollutants. Furthermore, the simulated human gastric fluid had a higher desorption rate than that of the fish intestinal fluid. The competition for TWP adsorption sites in the gastrointestinal fluid and the potential dissolution of antibiotics were the primary drivers of the increase in the desorption rate. The desorption rate in the simulated human gastrointestinal fluid was greater than that in the simulated fish intestinal fluid due to the composition of the gastrointestinal fluid. However, the carrying of pollutants by MPs poses a potential threat to human health. This study improves our understanding of TWP toxicity and has significant implications for the development of risk assessments.

Hydrothermal synthesis of sewage sludge biochar for activation of persulfate for antibiotic removal: Efficiency, stability and mechanism.

The use of biochar materials as catalysts to activate persulfate (PS) for the degradation of antibiotics has attracted much attention. In this study, a carbonaceous material (Cu/Zn-SBC) was prepared from sewage sludge by hydrothermal modification. The efficiency of PS activation by Cu/Zn-SBC was investigated using tetracycline (TC) as the model antibiotic. In the Cu/Zn-SBC + PS system, the TC removal rate reached 90.13% at 10 min and exceeded 99% within 4 h. This not only met the requirement of removing large amounts of pollutants in a short time but also achieved the complete removal of pollutants in the subsequent time. Additionally, the Cu/Zn-SBC + PS system was found to be dominated by radical and nonradical pathways. Cu, hydroxyl and carboxyl groups on the surface of Cu/Zn-SBC promoted the production of free radicals and non-free radicals. Under several changes in reaction conditions and water environment factors, the TC removal rate remained above 85% within 10 min. Furthermore, the removal rate of TC was still 85.79% when Cu/Zn-SBC combined with PS was reused twice and 77.14% when reused four times. This study provides an ideal solution for the treatment of sewage sludge, and offers a stable and efficient material for removing antibiotics from wastewater.

Investigation of the adsorption-desorption behavior of antibiotics by polybutylene succinate and polypropylene aged in different water conditions.

Microplastics (MPs) are widely present in aqueous environments and aged by natural components of complex water environments, such as salinity (SI) and dissolved organic matter (DOM). However, the effects of multicondition aging on the physicochemical properties and environmental behavior of MPs have not been completely investigated. In this study, the degradable MP polybutylene succinate (PBS) was used to investigate the environmental behavior of sulfamethoxazole (SMZ) and was compared with polypropylene (PP). The results showed that the single-factor conditions of DOM and SI, particularly DOM, promoted the aging process of MPs more significantly, especially for PBS. The degrees of MP aging under multiple conditions were lower than those under single-factor conditions. Compared with PP, PBS had greater specific surface area, crystallinity, and hydrophilicity and thus a stronger SMZ adsorption capacity. The adsorption behavior of MPs fitted well with the pseudo-second-order kinetic and Freundlich isotherm models, indicating multilayer adsorption. Compared with PP, PBS showed relatively a higher adsorption capacity, for example, for MPs aged under DOM conditions, the adsorption of SMZ by PBS was up to 5.74 mg/g, whereas that for PP was only 3.41 mg/g. The desorption experiments showed that the desorption amount of SMZ on MPs in the simulated intestinal fluid was greater than that in Milli-Q water. In addition, both the original PBS and the aged PBS had stronger desorption capacities than that of PP. The desorption quantity of PBS was 1.23-1.84 times greater than PP, whereas the desorption rates were not significantly different. This experiment provides a theoretical basis for assessing the ecological risks of degradable MPs in complex water conditions.

Insights into the characteristics, adsorption and desorption behaviors of microplastics aged with or without fulvic acid.

Many aging experiments on microplastics (MPs) have been carried out using UV radiation or strong oxidants. Little attention has been paid to the role of water environmental factors such as dissolved organic matter (DOM). In this study, the role of fulvic acid (FA), the main component of DOM, in the UV-aging process of MPs was explored. MPs aged under UV, and UV along with 0.5 mg/L and 2 mg/L FA, were selected as subjects. The results showed that (1) FA accelerated the aging process of polyethylene (PE). PE aged with FA had a larger specific area (SBET), with more holes and cracks on the surface. (2) FA enhanced the adsorption capacity of PE. The TC adsorption quantities of 0, 0.5, and 2 mg/L FA-aged PE were 1.100, 1.447, and 1.812 mg/L, respectively. (3) The quantity of TC desorbed by PE increased, whereas the desorption rate decreased as the FA concentration increased. The desorption rates of TC at 0, 0.5, and 2 mg/L FA-aged PE were 25.16%, 22.05%, and 19.52% in water, and 72.10%, 70.36%, and 59.51% in simulated intestinal fluid. This study explored the role of FA in the aging process of MPs. Moreover, research on the aging mechanism of MPs is enriched.

Excess sludge biochar facilitates persulfate activation for highly efficient tetracycline removal.

This study proposed a novel advanced oxidation system to treat metal and antibiotic pollution in water simultaneously. Meanwhile, the enhancement effect of absorbed metal pollution on the activation of persulfate in the system was also investigated. As the most widely used and polluting material, tetracycline (TC) and metal Fe were used as the pollutant models. In this study, a carbonaceous material (BC) was prepared from excess sludge and then combined with the persulfate system (Fe/BC/PS). It was found that the best biochar was obtained when the pyrolysis temperature reached 500 °C (BC500), with the specific surface area of 39.712 m2/g. Combining it with 300 mg/L PS, the removal rate of 120 mg/L TC reached 70.6%. Moreover, the sludge biochar itself possessed numerous reaction sites and good defective structure, which provided a perfect reaction site for the variable metals absorbed by BC. They accelerated electron conduction greatly, which led to the activation of PS very active and generating far more active radicals than normal. In addition, it also proposed the rational pathway and potential mechanism of TC degradation based on the degradation intermediates. This study has a high reference value for resource utilization of sewage sludge and antibiotics removal from water.

Optimization of PNP Degradation by UV-Activated Granular Activated Carbon Supported Nano-Zero-Valent-Iron-Cobalt Activated Persulfate by Response Surface Method.

Nitrophenols are toxic substances that present humans and animals with the risk of deformities, mutations, or cancer when ingested or inhaled. Traditional water treatment technologies have high costs and low p-nitrophenol (PNP) removal efficiency. Therefore, an ultraviolet (UV)-activated granular activated carbon supported nano-zero-valent-iron-cobalt (Co-nZVI/GAC) activated persulfate (PS) system was constructed to efficiently degrade PNP with Co-nZVI/GAC dosage, PS concentration, UV power, and pH as dependent variables and PNP removal rate as response values. A mathematical model between the factors and response values was developed using a central composite design (CCD) model. The model-fitting results showed that the PNP degradation rate was 96.7%, close to the predicted value of 98.05 when validation tests were performed under Co-nZVI/GAC injection conditions of 0.827 g/L, PS concentration of 3.811 mmol/L, UV power of 39.496 W, and pH of 2.838. This study demonstrates the feasibility of the response surface methodology for optimizing the UV-activated Co-nZVI/GAC-activated PS degradation of PNP.

Biochar produced from the co-pyrolysis of sewage sludge and waste tires for cadmium and tetracycline adsorption from water.

Application of sewage sludge biochar as an adsorbent for pollutant removal has obtained special attention due to their low cost and surface functionality. In this research, sludge-tire composite biochar (STB) was successfully prepared through co-pyrolysis at 300, 500 and 700 °C, respectively. Cadmium (Cd) and tetracycline (TC) were selected as the target pollutant. The results indicated that STB has the highest surface area (49.71 m2/g), more inorganic minerals (Kaolinite) as well as relatively stable physicochemical properties with 10% tire particles (TP) at 700 °C. The adsorption results indicated that the pseudo-second-order equation and Langmuir isotherm model could better describe the adsorption of Cd2+ and TC by STB. The maximum adsorption capacity of Cd2+ and TC was 50.25 mg/g and 90.09 mg/g, respectively. The main mechanism of the adsorption process of STB for Cd mainly involves anion binding adsorption and ion exchange. The main mechanism of the adsorption process of STB for TC mainly involves complexation and cation exchange. The present study could set a scientific foundation for further research on the recycle of sewage sludge and tires.

Adsorption and desorption behaviors of antibiotics by tire wear particles and polyethylene microplastics with or without aging processes.

Tire wear particles (TWP), as the significant proportion of microplastics (MPs), has adsorbed much attention due to its widespread presence in aquatic ecosystem. However, compared with traditional MPs, few studies have investigated the interaction between TWP and coexisting contaminants. The adsorption-desorption behavior of chlortetracycline (CTC) and amoxicillin (AMX) by original and aged TWP was studied, and polyethylene (PE) was studied for comparison. After aging, small holes and cracks were produced on the surfaces of the TWP and PE. Meanwhile, the specific surface areas (SBET) of TWP and PE increased, but the aged TWP had a larger SBET than the aged PE, which indicated that TWP was more likely to degrade than PE. The adsorption kinetics results showed that the adsorption of CTC and AMX by TWP and PE conformed to the pseudo-second-order model. The adsorption isotherm results showed that the Freundlich model could describe the adsorption isotherm data of TWP and PE. The adsorption capacity of antibiotics by TWP increased by 1.13-23.40 times, and by 1.08-14.24 times on PE, after aging. Desorption experiments showed that the desorption amount of antibiotics on TWP and PE in simulated gastric fluid was greater than that in ultrapure water. The desorption amount and rate of CTC and AMX from TWP were higher than those of PE, indicating that TWP might be more harmful to the aquatic environment and organisms. These findings indicated that, compared with PE, TWP might have stronger carrier effects on antibiotics, which might pose more serious potential risks to the aquatic environment and organisms, especially considering the effects of the aging process. This study would expand the research on environmental risk of MPs and contribute to providing new insights into the evaluation of tire material particles.

[Adsorption and Desorption Behaviors of Antibiotics on TWP and PVC Particles Before and After Aging].

In recent years, microplastics (MPs), a new type of pollutant, have been widely dispersed in aquatic ecosystems. Compared with typical MPs (PVC, PP, PE, and PS), tire wear particles (TWP) exhibit significant differences in composition, additives, and characteristics. In this study, the adsorption and desorption of organic pollutants were compared between the typical MPs and TWP. With TWP and polyvinyl chloride (PVC) particles as adsorbents, oxytetracycline (OTC) and sulfamethoxazole (SMZ) as adsorbates, the adsorption and desorption of organic pollutants by TWP and PVC particles before and after aging were studied. Correctly understanding the behavior of MPs in an aquatic environment is of great significance. The results indicated that during the UV aging process, both TWP and PVC exhibited cracks, pits, and bulges on the particle surface, increased specific surface areas, increased strength of oxygen-containing functional groups, and enhanced hydrophilicity. The adsorption modes of TWP and PVC before and after aging were in two stages:surface adsorption and liquid film diffusion. TWP has a better fit for the Freundlich model, belonging to multi-layer adsorption, while PVC has a better fit for the Langmuir model, belonging to monolayer adsorption. The carrier effect of TWP on antibiotics was better than that of PVC, with the adsorption capacity of OTC on virgin TWP and PVC reaching 5.14 mg·g-1 and 1.38 mg·g-1, respectively. Additionally, the adsorption capacity of OTC on the aged TWP and PVC reached 5.82 mg·g-1 and 2.13 mg·g-1, respectively, which was better than with the virgin samples. The desorption capacity of aged TWP and PVC for antibiotics was better than the virgin materials, while the desorption rate was lower. In the same desorption solution, the desorption effect of TWP on antibiotics before and after ageing was better than that of PVC. The desorption effect of TWP and PVC on antibiotics in a simulated intestinal fluid environment was significantly better than that in an ultra-pure water environment.

Investigation on the adsorption of antibiotics from water by metal loaded sewage sludge biochar.

Application of sewage sludge biochar as an adsorbent for antibiotics treatment has obtained special attention owning to its low cost and surface functionality. Three metal ions were selected to modify sewage sludge biochar through the pyrolysis with the metal loaded method. Fe loaded sewage sludge biochar (BC-Fe), Al loaded sewage sludge biochar (BC-Al) and Mn loaded sewage sludge biochar (BC-Mn) were characterized and used to explore the performance of adsorbing tetracycline (TC), sulfamethoxazole (SMZ) and amoxicillin (AMC). BC-Fe, BC-Al and BC-Mn possessed rougher surfaces, larger specific surface area and better pore structure. Intra-particle diffusion and Langmuir models were more suitable to describe the adsorption process. The maximum adsorption amount of TC, SMZ and AMC could reach 123.35, 99.01 and 109.89 mg/g by BC-Fe. Furthermore, the main mechanism of antibiotics adsorption by metal loaded sewage sludge biochars might be pores filling, Van der Waals forces and H-bonding. The study can not only solve the problems associated with the pollution of antibiotics from wastewater, but also reduced the treatment pressure of sewage sludge effectively.

Investigation on the adsorption and desorption behaviors of heavy metals by tire wear particles with or without UV ageing processes.

In recent years, tire wear particles (TWP), as the significant proportion of microplastics (MPs), has adsorbed much attention due to its widespread presence in aquatic ecosystem. Compared with typical MPs, TWP exists significant differences in composition, additives, characteristics and so on. With TWP and polypropylene (PP) as target MPs, Cd2+ and Pb2+ as target pollutants, the adsorption-desorption characteristics of heavy metal ions on original and aged MPs were studied. Compare with the PP, the SBET of TWP increased more significantly after the UV ageing process. Meanwhile, the zeta potential of TWP increased from -8.01 to -14.6 mV and PP from -5.36 to -9.52 mV, and the surface of the TWP were more negatively-charged. In addition, the hydrophilicity of MPs enhanced due to the increased oxygen-containing functional groups after ageing process. Compared with PP, the physicochemical properties of TWP changed more obviously during UV ageing processes. The adsorption results showed that the pseudo-second-order model could better describe the adsorption processes of Cd2+ and Pb2+ on MPs. Meanwhile, the orders of adsorption capacity of MPs for Cd2+ and Pb2+ were aged TWP > aged PP > original TWP > original PP. The phenomenon of adsorption confirmed that TWP had better vector effects for heavy metal ions than PP, and the ageing processes could enhance the adsorption capacity of MPs. Moreover, the desorption results demonstrated that, compared with PP, the TWP (with higher adsorption capacity) also had the better desorption capacity for heavy metal ions in simulated gastric fluid. Compared with PP, the TWP might cause a more serious hazard to aquatic environment and organisms. These investigations would contribute to assessing the potential environmental and biological risk of TWP, especially considering the effect of the ageing process.

Investigation on the adsorption and desorption behaviors of antibiotics by degradable MPs with or without UV ageing process.

To assess the potential vector effects of degradable MPs (microplastics) on the coexisting pollutant, the adsorption-desorption behaviors of tetracycline (TC) and ciprofloxacin (CIP) by the original and aged polylactic acid (PLA) was investigated. Compared with PVC, the physicochemical properties of PLA changed more observably during the UV ageing. The original smooth surface of PLA appeared holes and cracks, and the SBET of PLA increased a 2.66-fold after the aging experiments. During the ageing processes, the hydrophily of aged MPs was also enhanced due to the increase of oxygen-containing functional groups. And the zeta potential of PLA decreased from -7.79 to -13.51 mV and PVC from -4.96 to -8.34 mV, respectively. In adsorption experiment, both the original and aged PLA showed better vector effects for antibiotics than PVC. The ageing factor increased the adsorption capacity of antibiotics on PLA 1.18-2.19 times. The desorption experiments showed that the desorption amount of antibiotics on MPs in simulated intestinal fluid was greater than that in Milli-Q water. On this basis, the desorption capacity of antibiotics with PLA was better than that of PVC, which proved that the potential negative impact of PLA on the aquatic environment and organisms might be more serious.

Sorption and desorption behaviors of triphenyl phosphate (TPhP) and its degradation intermediates on aquatic sediments.

As triphenyl phosphate (TPhP) can biodegrade extensively in sediments, researches should further the understanding of the fate and transport of TPhP and its degradation intermediates in the environment. Therefore, the sorption/desorption behaviors of TPhP, diphenyl phosphate (DPhP) and phenyl phosphate (PhP) on sediments were investigated. The kinetic process was well-fitted by pseudo-second-order model, suggesting that chemisorption was involved. And the Langmuir model could describe the sorption isotherms of TPhP and DPhP well except for PhP. The redundancy analysis revealed that the sorption amount had a positive correlation with sediment organic matter, zeta potential and C/H of sediments. Besides the sorption/desorption behaviors were greatly influenced by the physicochemical properties of the sorbates. PhP with high molecular electrostatic potential (0.132 e0) was prone to protonation and formed hydrogen bonds, leading to higher sorption. Furthermore, hydrophobicity, π-π interactions, Lewis acid-base interaction and hydrogen bonding were involved in the sorption process and resulted in nonlinear sorption isotherms. TPhP, DPhP and PhP exhibited apparent desorption hysteresis on the sediments. Sediments with organic matter removed, which have complex pore distributions, exhibited more hysteresis. These results may contribute to the risk assessment and fate modeling of TPhP and its degradation products in sediments.

Toxicity of Three Crystalline TiO2 Nanoparticles in Activated Sludge: Bacterial Cell Death Modes Differentially Weaken Sludge Dewaterability.

The eco-toxicities of different crystalline phases of TiO2-NPs are controversial, and the effects and mechanisms on activated sludge are unclear. Therefore, we assessed the acute-toxicities (8-h exposure) of P25, anatase, and rutile TiO2-NPs in activated sludge using flow cytometry under simulated sunlight (hereafter-sun) and evaluated the relationship between sludge dewatering and bacterial cell death modes using Pearson's correlation coefficients ( r). Additionally, the response of the microbial community structure was examined by high throughput sequencing. Bacterial survival and death were observed by confocal laser scanning microscopy. Toxicity indicators (e.g., lactate dehydrogenase (LDH) and reactive oxygen species (ROS)) were determined. Overall, TiO2-NPs toxicity was concentration-dependent and crystalline-phase-dependent. The responses of bacterial communities to crystalline phases were more obvious than that of dosage. P25-sun and anatase-sun caused necrosis-like cell death via strong photo-oxidation confirmed by 131%/123% (1 mg/L) and 301%/254% (50 mg/L) LDH released by the control, while rutile-sun induced apoptosis-like death via intracellular ROS production increased to 165% (1 mg/L) and 420% (50 mg/L) of the control. P25 and anatase NPs had higher protein and polysaccharide affinities, while rutile NPs exhibited stronger attachment onto phospholipids. TiO2-NPs-sun reduced activated sludge dewaterability. Specific resistance to filtration (SRF) showed the strongest positive correlation with tightly bound extracellular polymeric substances (EPS) and total soluble microbial byproducts ( r = 0.974, p < 0.01) and was closely related to EPS content and composition, especially the increased bound water (BW) content and sludge protein concentrations. High Pearson correlation coefficients were observed between early apoptotic cells and BW content ( r = 0.952, p < 0.01) resulting from massive polysaccharides and between necrotic (including late apoptotic) cells and SRF ( r = 0.959, p < 0.01) resulting from high protein and EPS concentrations. Thus, in response to TiO2-NPs, bacterial cell death modes differentially weakened sludge dewatering.

Combined toxicity of organophosphate flame retardants and cadmium to Corbicula fluminea in aquatic sediments.

Organophosphate flame retardants (OPFRs), as alternatives to polybrominated biphenyl ethers (PBDEs), are frequently detected in various environmental matrices. Owing to urbanization and industrial pollution, co-contamination of OPFRs and heavy metals is ubiquitous in the environment. The toxicity of OPFRs in aqueous phase is a significant concern, but uncertainty still exists regarding the co-toxicity to benthic organisms of OPFRs and metals in sediments. Hence, we explored the physiological response of Corbicula fluminea to OPFRs and Cd in sediments. The results indicated that the antioxidant system in the clams was stimulated in the presence of OPFRs and Cd, and the oxidative stress increased with increasing concentrations of OPFRs. In contrast, the cytochrome P450 (CYP450) content and acetylcholinesterase (AChE) activity were reduced by exposure to both OPFRs and Cd. The cytochrome P450 4 family (CYP4) mRNA expression and OPFR toxicity were lower than those in previously reported experiments conducted in the water phase. Moreover, the expression levels of metallothionein (MT) and AChE mRNA decreased when OPFRs and Cd were present together. The highest integrated biomarker response (IBR) index (IBR = 15.41) was observed in the presence of 45 mg kg-1 Cd + 200 mg kg-1 OPFRs, rather than the 45 mg kg-1 Cd + 400 mg kg-1 OPFRs treatment (IBR = 9.48). In addition, CYP450 and AChE in the digestive glands of C. fluminea exhibited significant correlations with the concentration of the OPFR/Cd mixture (p < 0.01) and could be effective biomarkers for OPFR and Cd co-contamination. The results potentially contribute to more realistic predictions and evaluations of the environmental risks posed by OPFRs in aquatic sediments contaminated with heavy metals, particularly with respect to the risk to benthic organisms.