[Dynamic Changes of Dissolved Organic Matter Derived from Algal Decomposition and the Environmental Effects in Eutrophic Lakes].

The global occurrences of lake eutrophication have led to algal bloom and the subsequent algal decomposition, releasing high amounts of algae-derived dissolved organic matter (DOM) into the lake water. Algae-derived DOM could regulate the quantity and composition of DOM in lake water and further impact the biogeochemical cycles of multiple elements. In this study, the dynamic changes in the quantity and quality of DOM during algal decomposition under different eutrophic scenarios (e.g., from oligotrophication to severe eutrophication) were monitored, and the corresponding environmental effects (e.g., microbial responses and greenhouse gas emissions) caused by algal decomposition were further explored. The results showed that algal decomposition significantly increased the DOM levels, bioavailability, and intensities of fluorescent components in the water. The total DOM levels gradually decreased, whereas the average molecular weight increased along the decomposition process. Furthermore, unsaturated hydrocarbon and aliphatic compounds were preferentially utilized by microorganisms during algal decomposition, and some refractory molecules (e.g., lignin, condensed hydrocarbons, and tannin with high O/C values) were synchronously generated, as evidenced by the results from ultra-high-resolution mass spectrometry. The dominant bacterial species during algal decomposition shifted from Proteobacteria (46%) to Bacteroidetes (42%). In addition, algae addition resulted in 1.2-5 times the emissions of CO2 and CH4 from water, and the emission rates could be well predicted by the optical index of a254 in water. This study provides comprehensive perspectives for understanding the environmental behaviors of aquatic DOM and further paves the ways for the mitigation of lake eutrophication.

Spatiotemporal dynamics of dissolved organic matter and disinfection by-products formation potential of Shengzhong Lake in southwest China.

The quality and quantity of dissolved organic matter (DOM) in lakes as well as its environmental effects associated with the unintended disinfection by-products (DBPs) have received continuous attention. This work investigated the spatiotemporal dynamics of DOM in Shengzhong Lake in southwest China and the formed DBPs during the chlorine disinfection process. The results showed that lake water in summer had significantly higher dissolved oxygen and dissolved organic carbon than that in winter. In contrast, DOM in winter demonstrated an obviously higher aromaticity and molecular weight than that in summer. Four fluorescence components, i.e., terrestrial humic-like substances (C1), protein-like substances (C2), and microbial humic-like substances (C3 and C4), were identified, and their relative abundance followed in the order of C3 > C4 > C2 > C1 in winter and C4 > C3 > C1 > C2 in summer. The formation potential of trihalomethanes and haloacetic acids in winter was higher and lower than that in summer, which was mainly ascribed to the content of aromatic and hydrophobic substances. Compared to the significant seasonal dynamic, the spatial variation of DOM and the formed DBPs was not obvious. This work sheds light on the spatial-temporal distribution of DOM and the potentially formed DBPs in Shengzhong Lake, and will be helpful for understanding the biogeochemical cycle of carbon and assessing the drinking water safety.

Extraction of Common Small Microplastics and Nanoplastics Embedded in Environmental Solid Matrices by Tetramethylammonium Hydroxide Digestion and Dichloromethane Dissolution for Py-GC-MS Determination.

Determination of microplastics and nanoplastics (MNPs), especially small MPs and NPs (<150 µm), in solid environmental matrices is a challenging task due to the formation of stable aggregates between MNPs and natural colloids. Herein, a novel method for extracting small MPs and NPs embedded in soils/sediments/sludges has been developed by combining tetramethylammonium hydroxide (TMAH) digestion with dichloromethane (DCM) dissolution. The solid samples were digested with TMAH, and the collected precipitate was washed with anhydrous ethanol to eliminate the natural organic matter. Then, the MNPs in precipitate were extracted by dissolving in DCM under ultrasonic conditions. Under the optimized digestion and extraction conditions, the factors including sizes and concentrations of MNPs showed insignificant effects on the extraction process. The feasibility of this sample preparation method was verified by the satisfactory spiked recoveries (79.6-91.4%) of polystyrene, polyethylene, polypropylene, poly(methyl methacrylate), polyvinyl chloride, and polyethylene terephthalate MNPs in soil/sediment/sludge samples. The proposed sample preparation method was coupled with pyrolysis gas chromatography-mass spectrometry to determine trace small MPs and NPs with a relatively low detection limit of 2.3-29.2 µg/g. Notably, commonly used MNPs were successfully detected at levels of 4.6-51.4 µg/g in 6 soil/sediment/sludge samples. This proposed method is promising for evaluating small solid-embedded MNP pollution.

Molecular probing of dissolved organic matter and its transformation in a woolen textile wastewater treatment station.

Woolen textile industry produces enormous wastewater (WTIW) with high pollution loads, and needs to be treated by wastewater treatment stations (WWTS) before centralized treatment. However, WTIW effluent still contains many biorefractory and toxic substances; thus, comprehensive understandings of dissolved organic matter (DOM) of WTIW and its transformation are essential. In this study, total quantity indices, size exclusion chromatography, spectral methods, and Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) were used for comprehensively characterizing DOM and its transformation during full-scale treatments, including influent, regulation pool (RP), flotation pool (FP), up-flow anaerobic sludge bed (UA), anaerobic/oxic (AO) and effluent. DOM in influent featured a large molecular weight (5-17 kDa), toxicity (0.201 HgCl2 mg/L), and a protein content of 338 mg C/L. FP largely removed 5-17 kDa DOM with the formation of 0.45-5 kDa DOM. UA and AO removed 698 and 2042 chemicals, respectively, which were primarily saturated components (H/C > 1.5); however, both UA and AO contributed to the formation of 741 and 1378 stable chemicals, respectively. Good correlations were found among water quality indices and spectral/molecular indices. Our study reveals the molecular composition and transformation of WTIW DOM during treatments and encourages the optimization of the employed processes in WWTS.

Safety assessment of organic micropollutants in reclaimed water: Chemical analyses, ecological risk assessments, and in vivo endocrine-disrupting studies.

Reclaimed water from municipal wastewater has great potential in mitigating the water resource crisis, while the inevitable residue of organic micropollutants (OMPs) challenges the safety of reclaimed water reuse. Limited information was available regarding the overall adverse effects of mixed OMPs in reclaimed water, especially the endocrine-disrupting effects on living organisms. Herein, chemical monitoring in two municipal wastewater treatment plants showed that 31 of 32 candidate OMPs including polycyclic aromatic hydrocarbons (PAHs), phenols, pharmaceuticals and personal care products (PPCPs) were detected in reclaimed water, with a concentration ranging from ng/L to µg/L. Then, based on the risk quotient value, phenol, bisphenol A, tetracycline, and carbamazepine were ranked as high ecological risks. Most PAHs and PPCPs were quantified as medium and low risks, respectively. More importantly, using aquatic vertebrate zebrafish as an in vivo model, the endocrine-disrupting potentials of OMP mixtures were comprehensively characterized. We found that a realistic exposure to reclaimed water induced estrogen-like endocrine disruption and hyperthyroidism in zebrafish, abnormal expression of genes along the hypothalamus-pituitary-thyroid (-gonad) axes, reproductive impairment, and transgenerational toxicity. Based on the chemical analyses, risk quotient calculations, and biotoxicity characterization, this study contributed to understanding the ecological risks of reclaimed water and developing the control standards for OMPs. In addition, application of the zebrafish model in this study also highlighted the significance of in vivo biotoxicity test in water quality evaluation.

Machine learning-assisted data filtering and QSAR models for prediction of chemical acute toxicity on rat and mouse.

Machine learning (ML) methods provide a new opportunity to build quantitative structure-activity relationship (QSAR) models for predicting chemicals' toxicity based on large toxicity data sets, but they are limited in insufficient model robustness due to poor data set quality for chemicals with certain structures. To address this issue and improve model robustness, we built a large data set on rat oral acute toxicity for thousands of chemicals, then used ML to filter chemicals favorable for regression models (CFRM). In comparison to chemicals not favorable for regression models (CNRM), CFRM accounted for 67% of chemicals in the original data set, and had a higher structural similarity and a smaller toxicity distribution in 2-4 log10 (mg/kg). The performance of established regression models for CFRM was greatly improved, with root-mean-square deviations (RMSE) in the range of 0.45-0.48 log10 (mg/kg). Classification models were built for CNRM using all chemicals in the original data set, and the area under receiver operating characteristic (AUROC) reached 0.75-0.76. The proposed strategy was successfully applied to a mouse oral acute data set, yielding RMSE and AUROC in the range of 0.36-0.38 log10 (mg/kg) and 0.79, respectively.

Molecular insights into the dissolved organic matter of leather wastewater in leather industrial park wastewater treatment plant.

Leather wastewater (LW) effluent is characterized by complex organic matter, high salinity, and poor biodegradability. To meet the discharge standards, LW effluent is often mixed with municipal wastewater (MW) before being treated at a leather industrial park wastewater treatment plant (LIPWWTP). However, whether this method efficiently removes the dissolved organic matter (DOM) from LW effluent (LWDOM) remains debatable. In this study, the transformation of DOM during full-scale treatment was revealed using spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. LWDOM exhibited higher aromaticity and lower molecular weight than DOM in MW (MWDOM). The DOM properties in mixed wastewater (MixW) were similar to those in LWDOM and MWDOM. The MixW was treated using a flocculation/primary sedimentation tank (FL1/PST), anoxic/oxic (A/O) process, secondary sedimentation tank (SST), flocculation/sedimentation tank, denitrification filter (FL2/ST-DNF), and an ozonation contact reactor (O3). The FL1/PST unit preferentially removed the peptide-like compounds. The A/O-SST units had the highest removal efficiencies for dissolved organic carbon (DOC) (61.34 %) and soluble chemical oxygen demand (SCOD) (52.2 %). The FL2/ST-DNF treatment removed the lignin-like compounds. The final treatment showed poor DOM mineralization efficiency. The correlation between water quality indices, spectral indices, and molecular-level parameters indicated that lignin-like compounds were strongly correlated with spectral indices and CHOS compounds considerably contributed to the SCOD and DOC. Although the effluent SCOD met the discharge standard, some refractory DOM from LW remained in the effluent. This study illustrates the composition and transformation of DOM and provides theoretical guidance for improving the current treatment processes.

Comprehensive understanding of DOM reactivity in anaerobic fermentation of persulfate-pretreated sewage sludge via FT-ICR mass spectrometry and reactomics analysis.

Understanding the composition and reactivity of dissolved organic matter (DOM) at molecular level is vital for deciphering potential regulators or indicators relating to anaerobic process performance, though it was hardly achieved by traditional analyses. Here, the DOM composition, molecular reactivity and transformation in the enhanced sludge fermentation process were comprehensively elucidated using high-resolution mass spectrometry measurement, and data mining with machine learning and paired mass distance (PMD)-based reactomics. In the fermentation process for dewatered sludge, persulfate (PDS) pretreatment presented its highest performance in improving volatile fatty acids (VFAs) production with the increase from 2,711 mg/L to 3,869 mg/L, whereas its activation in the presence of Fe (as well as the hybrid of Fe and activated carbon) led to the decreased VFAs production performance. In addition to the conventional view of improved decomposition and solubilization of N-containing structures from sludge under the sole PDS pretreatment, the improved VFAs production was associated with the alternation of DOM molecular compositions such as humification generating molecules with high O/C, N/C, S/C and aromatic index (AImod). Machine learning was capable of predicting the DOM reactivity classes with 74-76 % accuracy and found that these molecular parameters in addition to nominal oxidation state of carbon (NOSC) were among the most important variables determining the generation or disappearance of bio-resistant molecules in the PDS pretreatment. The constructed PMD-based network suggested that highly connected molecular network with long path length and high diameter was in favor of VFAs production. Especially, -NH related transformation was found to be active under the enhanced fermentation process. Moreover, network topology analysis revealed that CHONS compounds (e.g., C13H27O8N1S1) can be the keystone molecules, suggesting that the presence of sulfur related molecules (e.g., cysteine-like compounds) should be paid more attention as potential regulators or indicators for controlling sludge fermentation performance. This study also proposed the non-targeted DOM molecular analysis and downstream data mining for extending our understanding of DOM transformation at molecular level.

Swelling-Induced Fragmentation and Polymer Leakage of Nanoplastics in Seawater.

Nanoplastics (NPs) have been successively detected in different environmental matrixes and have aroused great concern worldwide. However, the fate of NPs in real environments such as seawater remains unclear, impeding their environmental risk assessment. Herein, multiple techniques were employed to monitor the particle number concentration, size, and morphology evolution of polystyrene NPs in seawater under simulated sunlight over a time course of 29 days. Aggregation was found to be a continuous process that occurred constantly and was markedly promoted by light irradiation. Moreover, the occurrence of NP swelling, fragmentation, and polymer leaching was evidenced by both transmission electron microscopy and scanning electron microscopy techniques. The statistical results of different transformation types suggested that swelling induces fragmentation and polymer leakage and that light irradiation plays a positive but not decisive role in this transformation. The observation of fragmentation and polymer leakage of poly(methyl methacrylate) and poly(vinyl chloride) NPs suggests that these transformation processes are general for NPs of different polymer types. Facilitated by the increase of surface functional groups, the ions in seawater could penetrate into NPs and then stretch the polymer structure, leading to the swelling phenomenon and other transformations.

Fertilization regime shifts the molecular diversity and chlorine reactivity of soil dissolved organic matter from tropical croplands.

Soil-derived dissolved organic matter (SDOM) is an important site-specific disinfection byproduct (DBP) precursor in watersheds. However, it remains unclear how fertilization regime shifts the molecular diversity and chlorine reactivity of SDOM in cropland-impacted watersheds. Here, we analyzed the spectroscopic and molecular-level characteristics of the SDOM from croplands that had different fertilization regimes (i.e., non-fertilization, chemical fertilization, straw return, and chemical fertilization plus straw return) for 5 years and evaluated the chlorine reactivity of the SDOM by determining the 24-h chlorine consumption and specific DBP formation potential (SDBP-FP). The SDOM level decreased by chemical fertilization and was not significantly altered by straw return alone or combined with chemical fertilizer. However, all fertilization regimes elevated the molecular diversity of SDOM by increasing the abundance of protein-, lignin-, and tannin-like compounds. The chlorine reactivity of SDOM was reduced by chemical fertilization, but was significantly increased by straw return. Typically, straw return increased the formation potential of specific trihalomethane and chloral hydrate by 339% and 56% via increasing the aromatics in SDOM, whereas chemical fertilization could effectively decrease about 231% of the increased specific trihalomethane formation potential caused by straw return. This study highlights that fertilization regime can significantly shape the molecular diversity and chlorine reactivity of the SDOM in croplands and that partially replacing chemical fertilizer with crop straw is an advantageous practice for reducing DBP risks in drinking water in cropland-impacted watersheds.

Molecular-level investigation into UV-induced transformation of hydrophobic aquatic dissolved organic matter.

The ubiquitously present dissolved organic matter (DOM) greatly influence the efficiency of UV-based technologies due to its reactivity to UV irradiation. In this work, UV-induced changes within three hydrophobic DOM fractions isolated from different surface waters were investigated. Analysis on UV absorbance at 254 nm, electron donating capacity, fluorescence intensity and carbon content revealed small changes in DOM bulk properties associated with the UV-induced photochemical reactions. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was further used to explore the modification of the molecular distribution based on H/C and O/C ratios, m/z and DBE. The molecular-level investigation revealed that an average of 296 aromatic and lignin-like molecules were degraded, leading to the production of around 306 new molecules. The UV-reactive community were identified as CHO molecules with higher DBE (>10) and carbon number (>25) which could be readily transformed into smaller saturated molecules. Molecules containing nitrogen (N) or sulfur (S) atom, independent of aromaticity and molecular weight (m/z), were also highly UV susceptible and transformed into molecules with larger DBE and m/z. Possible reaction pathways responsible for the observations were discussed. The results indicated that UV-reactivity and subsequent transformation of DOM are remarkably correlated with its molecular composition and characteristics. Though the changes in bulk properties of DOM following UV irradiation were observed to be very small, the significant alteration in its molecular structures would have a profound impact on the UV-based treatment processes.

Heteroaggregation of different surface-modified polystyrene nanoparticles with model natural colloids.

This study investigated heteroaggregation of three surface-functionalized polystyrene nanoparticles (PSNPs), i.e. negatively charged unfunctionalized nanoparticles (Bare-PS) and carboxylated nanoparticles (COOH-PS), and positively charged amino-functionalized nanoparticles (NH2-PS), with two model natural colloids, positively charged hematite and negatively charged kaolin, respectively. Heteroaggregation was conducted at a constant natural colloid concentration and variable NP/colloid concentration ratios. Electrostatic interaction was the main mechanism driving the formation of heteroaggregates. In binary systems containing hematite and Bare-PS/COOH-PS, a charge neutralization - charge inverse mechanism was observed with the increase of PSNP concentration. At NP/hemetite concentration ratios much smaller or larger than the full charge neutralization point, the primary heteroaggregates were stable, while full charge neutralization induced the formation of large secondary heteroaggregates. Large aggregates were not observed in suspensions containing kaolin and NH2-PS, as highly positively charged NH2-PS reversed surface charges of kaolin at extremely low concentrations. Heteroaggregation between PSNPs and natural colloids with the same charge is unfavorable due to strong electrostatic repulsion. In the presence of electrolytes, homoaggregation and heteroaggregation both occurred, and homoaggregation of hematite played a key role when the concentration of PSNPs was low. The presence of Suwannee River natural organic matter (SRNOM) could modify surface charges of nanoparticles, and thus affect heteroaggregation behaviors of the binary suspension. When SRNOM and electrolytes were both present, whether SRNOM inducing or hindering the stability of the binary system was a combined effect of NP/colloid concentration ratios, SRNOM concentrations, electrolyte types and ionic strength. Mechanisms extensively reported in homoaggregation such as steric hindrance and cation bridging effects between SRNOM and Ca2+ also stand for heteroaggregation. These results highlight the critical role of surface modification on the environmental behaviors of NPs, and will underpin our understanding of the fate and transport of NPs in the aquatic environment.

Counting Nanoplastics in Environmental Waters by Single Particle Inductively Coupled Plasma Mass Spectroscopy after Cloud-Point Extraction and In Situ Labeling of Gold Nanoparticles.

The globally raising concern for nanoplastics (NPs) pollution calls for analytical methods for investigating their occurrence, fates, and effects. Counting NPs with sizes down to 50 nm in real environmental waters remains a great challenge. Herein, we developed a full method from sample pretreatment to quantitative detection for NPs in environmental waters. Various NPs of common plastic types and sizes (50-1200 nm) were successfully labeled by in situ growth of gold nanoparticles and counted by single particle inductively coupled plasma mass spectrometry. Sucrose density gradient centrifugation enables the isolation of gold-labeled NPs from homogeneously nucleated Au nanoparticles, enhancing the particle number detection limit to 4.6 × 108 NPs/L for 269 nm spherical polystyrene NPs. For real environmental water samples, the pretreatment of acid digestion with a mixture of 5 mM HNO3 and 40 mM HF eliminates the coexisting inorganic nanoparticles, while the following dual cloud-point extraction efficiently isolates NPs from various matrices and thus improves the Au-labeling efficiency. The high spiked recoveries (72.9%-92.8%) of NPs in different waters demonstrated the applicability of this method in different scenarios.

Reduction of Ionic Silver by Sulfur Dioxide as a Source of Silver Nanoparticles in the Environment.

The natural formation of silver nanoparticles (AgNPs) via biotic and abiotic pathways in water and soil media contributes to the biogeochemical cycle of silver metal in the environment. However, the formation of AgNPs in the atmosphere has not been reported. Here, we describe a previously unreported source of AgNPs via the reduction of Ag(I) by SO2 in the atmosphere, especially in moist environments, using multipronged advanced analytical and surface techniques. The rapid reduction of Ag(I) in the atmospheric aqueous phase was mainly caused by the sulfite ions formed from the dissolution of SO2 in water, which contributed to the formation of AgNPs and was consistent with the Finke-Watzky model with a major contribution of the reduction-nucleation process. Sunlight irradiation excited SO2 to form triplet SO2, which reacted with water to form H2SO3 and greatly enhanced Ag(I) reduction and AgNP formation. Different pH values affected the speciation of Ag(I) and S(IV), which were jointly involved in the reduction of Ag(I). The formation of AgNPs was also observed in the atmospheric gas phase via direct reduction of Ag(I) by SO2(gas), which occurred even in 50 ppbv SO2(gas). The natural occurrence of AgNPs in the atmosphere may also be involved in silver corrosion, AgNP transformation and regeneration, detoxification of gaseous pollutants, and the sulfur cycle in the environment.

Molecular characterization of transformation and halogenation of natural organic matter during the UV/chlorine AOP using FT-ICR mass spectrometry.

UV/chlorine process, as an emerging advanced oxidation process (AOP), was effective for removing micro-pollutants via various reactive radicals, but it also led to the changes of natural organic matter (NOM) and formation of disinfection byproducts (DBPs). By using negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), the transformation of Suwannee River NOM (SRNOM) and the formation of chlorinated DBPs (Cl-DBPs) in the UV/chlorine AOP and subsequent post-chlorination were tracked and compared with dark chlorination. In comparison to dark chlorination, the involvement of ClO•, Cl•, and HO• in the UV/chlorine AOP promoted the transformation of NOM by removing the compounds owning higher aromaticity (AImod) value and DBE (double-bond equivalence)/C ratio and causing the decrease in the proportion of aromatic compounds. Meanwhile, more compounds which contained only C, H, O, N atoms (CHON) were observed after the UV/chlorine AOP compared with dark chlorination via photolysis of organic chloramines or radical reactions. A total of 833 compounds contained C, H, O, Cl atoms (CHOCl) were observed after the UV/chlorine AOP, higher than 789 CHOCl compounds in dark chlorination, and one-chlorine-containing components were the dominant species. The different products from chlorine substitution reactions (SR) and addition reactions (AR) suggested that SR often occurred in the precursors owning higher H/C ratio and AR often occurred in the precursors owning higher aromaticity. Post-chlorination further caused the cleavages of NOM structures into small molecular weight compounds, removed CHON compounds and enhanced the formation of Cl-DBPs. The results provide information about NOM transformation and Cl-DBPs formation at molecular levels in the UV/chlorine AOP.

A feasible strategy to improve confident elemental composition determination of compounds in complex organic mixture such as natural organic matter by FTICR-MS without internal calibration.

Confident elemental composition determination of compounds in complex samples such as natural organic matter (NOM) by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is challenging due to the interference between multiple components in these samples during detection. Here the performance of Solarix 15T-FTICR-MS in terms of accurate relative natural isotope abundance (RIA) and mass measurements for elemental composition determination of compounds in complex samples such as NOM was systematically evaluated. The optimal sweep excitation power values ranging from 20% to 22% was found to significantly diminish the underestimation of RIA measurement for 13C1 peaks of NOM components by FTICR-MS. Random error was found to be one of the main sources for the RIA errors of 13C1 peaks with S/N ratios <25. The mean averaged RIA errors of less than 10% could be obtained by averaging the measured RIAs of each 13C1 peaks in five replicated runs. By adjusting the total ion abundance of NOM complex sample between 3.8-E7 and 1.4-E8 which was simultaneously similar to that of external calibrant during detection, mass errors of lower than 1 ppm for NOM components with m/z lower than 700 Da could be obtained without internal calibration. Meanwhile, a linear correlation between mass errors of ions in NOM complex sample and their m/z values could be obtained. The mass error deviation derived from the linearity was firstly used as new criterion to reduce the number of false formula candidates. A novel strategy of combination of high mass accuracy, high spectral accuracy, and mass error deviation for elemental composition determination of unknown compounds in complex sample such as NOM by FTICR-MS was proposed and applied for different complex samples. Compared to the traditional method, about one fold increasement in the number of the unique formula assignments for measured ions was obtained by using our strategy.

Analytical methods and environmental processes of nanoplastics.

The degradation of plastic debris may result in the generation of nanoplastics (NPs). Their high specific surface area for the sorption of organic pollutions and toxic heavy metals and possible transfer between organisms at different nutrient levels make the study of NPs an urgent priority. However, there is very limited understanding on the occurrence, distribution, abundant, and fate of NPs in the environment, partially due to the lack of suitable techniques for the separation and identification of NPs from complex environmental matrices. In this review, we first overviewed the state-of-the-art methods for the extraction, separation, identification and quantification of NPs in the environment. Some of them have been successfully applied for the field determination of NPs, while some are borrowed from the detection of microplastics or engineered nanomaterials. Then the possible fate and transport of NPs in the environment are thoroughly described. Although great efforts have been made during the recent years, large knowledge gaps still exist, such as the relatively high detection limit of existing method failing to detect ultralow masses of NPs in the environment, and spherical polystyrene NP models failing to represent the various compositions of NPs with different irregular shapes, which needs further investigation.

Toxicity of biosynthesized silver nanoparticles to aquatic organisms of different trophic levels.

Although biosynthesized nanoparticles are regarded as green products, research on their toxicity to aquatic food chains is scarce. Herein, biosynthesized silver nanoparticles (Alcea rosea-silver nanoparticles, AR-AgNPs) were produced by the reaction of Ag ions with leaf extract of herbal plant Alcea rosea. Then, the toxic effects of AR-AgNPs and their precursors such as Ag+ ions and coating agent (A. rosea leaf extract) on organisms of different trophic levels of a freshwater food chain were investigated. To the three studied aquatic organisms including phytoplankton (Chlorella vulgaris), zooplankton (Daphnia magna) and fish (Danio rerio), the coating agents of AR-AgNPs showed no toxic effects, and Ag+ ions were more toxic in comparison to AR-AgNPs. Further investigations revealed that the release of Ag+ ions from AR-AgNPs to the test media were not considerable due to the high stability of AR-AgNPs, thus the toxicity stemmed mainly from the particles of AR-AgNPs in all the three trophic levels. Based on values of 72-h EC50 for C. vulgaris, 48-h LC50 for D. magna and 96-h LC50 for D. rerio, the most sensitive organism to AR-AgNPs exposure was D. magna (the second trophic level).

Freezing-Induced Bromate Reduction by Dissolved Organic Matter and the Formation of Organobromine Compounds.

The freezing-induced acceleration of bromate reduction by humic substances (HS) contributes to HS bromination and the formation of organobromine compounds (OBCs). Herein, we report the enhanced reduction of bromate by dissolved organic matter and the formation of large amounts of OBCs in freezing solutions. After 48 h of freezing process, 78.1-100% of bromate was reduced by DOM at different initial concentrations of bromate and DOM in acidic solutions (pH 3 and 4). Bromide was one of the main reduction products, and it accounted for 30.9-47.8% of the total bromine content. Except for bromide, a large amount of OBCs formed by brominating DOM with reactive bromine species, like hypobromite, were detected. The conversion of bromate to OBCs, calculated as the total organobromine content to the initial bromate content, ranged from 28.2 to 52.5% and was mainly dependent on the bromate/DOM content. About 110-603 species of OBCs were detected by Fourier transform ion cyclotron resonance mass spectrometry, and they were primarily highly unsaturated and phenolic compounds. By analyzing the spectral variation before and after the freezing process, we found the disappearance of 900 compounds containing only C, H, and O with a low carbon oxidation state that was regarded as the main reductant of bromate. Our findings call for further investigation of the processes and the effects of bromate formation in aqueous environments.

Adsorption of extracellular polymeric substances from two microbes by TiO2 nanoparticles.

Extracellular polymeric substance (EPS) secreted by microbes can interact with nanoparticles (NPs) and thus influence environmental behavior and toxicity of NPs. The adsorption of EPSs from two species of microbes (Escherichia coli and Chlorella pyrenoidosa) by four types of titanium dioxide nanoparticles (nTiO2) (5, 10, and 40 nm anatase nTiO2 and 25 nm rutile nTiO2) were therefore specifically investigated. Results show that the adsorption kinetics and thermodynamics were dependent on sources and chemical properties of EPSs. EPS (20 mg C/L) from Escherichia coli mainly composed of protein (86%) with relatively higher molecular weight and aromaticity and more active functional groups (i.e., NH and -COOH) was effectively removed (>90%) by adsorption on nTiO2 (100 mg and more), while much less (<40%) EPS from Chlorella pyrenoidosa with a main component of polysaccharide (68%) was adsorptively removed. The Fourier transform ion cyclotron resonance mass spectrometry analysis revealed the selective adsorption of aromatic components of EPSs by nTiO2. The EPS adsorption capacity of nTiO2 linearly increased with the specific surface area of the NPs. The rutile nTiO2 with the smallest specific surface area had the highest EPS adsorption per unit surface area. These findings promote a deeper understanding of the interaction between EPS and NPs.