Partitioning of polybrominated diphenyl ethers to dissolved organic matter isolated from Arctic surface waters

Distribution characteristics of sulfonamide antibiotics between water and extracellular polymeric substances in municipal sludge

The interaction between extracellular polymeric substances (EPS) in municipal sludge and antibiotics in wastewater is critical in wastewater treatment, resource recovery, and sludge management. Therefore, it is increasingly urgent to investigate the distribution coefficient (Log K) of sulfonamide antibiotics (SAs) in EPS, particularly in sludge-derived dissolved organic carbon (DOC) and aqueous phase systems. Herein, through balance experiments, the concentrations of SAs were determined using alkaline extraction EPS (AEPS) and alginate-like extracellular polymer (ALE) systems, and the Log KDOC values were determined. The results showed that the Log KDOC of AEPS was higher than that of ALE, which exhibited a negative KDOC value, indicating an inhibitory effect on dissolution. For the three SAs studied, the Log KDOC values were in the following order: sulfamethoxazole > sulfapyridine > sulfadiazine. This order can be attributed to the differing physicochemical properties, such as polarity, of the SAs. Three-dimensional excitation-emission matrix fluorescence spectra and fitting results indicated a lack of aromatic proteins dominated by tryptophan and humus-like substances in ALE. Meanwhile, the hydrophobic interaction of aromatic proteins dominated by tryptophan was the main driving force in the binding process between AEPS and SAs.

Environmental implications of superoxide radicals: From natural processes to engineering applications

The roles of superoxide radical (O2•-) in the domains of physiological, physical, and material chemistry are becoming increasingly recognized. Although extensive efforts have been directed to understand O2•- functions in diverse aquatic systems, there is a lack of systematic and in-depth review for its kinetics and mechanisms in various environmental scenarios. This review aims to bridge this gap through discussion of O2•- generation pathways under both natural and controlled conditions. The merits and limitations of the generation and detection methods under various conditions are compared, with emphasis on different approaches for the determination of O2•--triggered reaction kinetics. We summarize the reaction rate constants of O2•- with organic contaminants covering a wide diversity of structures and reactivity. The comparison indicates that O2•- exhibits weak reactivity with most contaminants and lacks selectivity towards compounds with different functional groups, except with quinones which exhibit higher reactivity compared to non-quinones. Further, the reaction mechanisms, namely single electron transfer, nucleophilic substitution, hydrogen atom abstraction, and radical-adduct formation, are critically evaluated. Various environmental implications of O2•- are highlighted including maintenance of biogeochemical iron cycle, synthesis of nanoparticles for antibacterial purposes, desorption of contaminants from heterogeneous interfaces, and synergetic degradation of contaminants.

Hazard vs. exposure: Does it make a difference in identifying chemicals with persistence and mobility concerns?

Persistent and mobile (PM) chemicals are considered emerging threats to the environment and drinking water because they can be transported over long distances, penetrate natural and artificial barriers, and resist removal by traditional water treatment procedures. Current chemical regulatory frameworks raise concerns over PM chemicals due to their potential to cause high human exposure through drinking water contamination. However, the criteria used to screen and identify these chemicals often rely on hazard properties related to stability and sorption, such as biodegradation half-lives and organic-carbon-normalized sorption coefficients as respective measures of P and M. Here, we conduct a model-based assessment to examine the consistency between hazard-based and exposure-based approaches in assessing PM chemicals, by evaluating whether chemicals identified as highly P and M are consistently associated with high drinking water exposure potential (DWEP). We discover that chemicals with the top DWEPs tend to be PM chemicals, but the reverse is not always true, because DWEPs are also impacted by volatilization for air-distributed chemicals and advective particle-bound transport for particle-bound chemicals. Our findings suggest that the hazard metrics are better suited for de-prioritizing, as opposed to prioritizing, chemicals that are unlikely to result in significant human exposure through drinking water, as unfavorable values of hazard metrics are a necessary but not sufficient condition for a high DWEP. We also find that distinct mechanisms determine the DWEP in different sources of drinking water: Sorption and stability are more influential on the DWEP of chemicals in groundwater and surface water, respectively, whereas both sorption and stability equally impact water undergoing riverbank filtration. Future studies should focus on optimizing the identification of persistent and mobile chemicals to ensure that exposure potential is taken into consideration.

Chlorpyrifos fate in the Arctic: Importance of analyte structure in interactions with Arctic dissolved organic matter

The insecticide and current use pesticide chlorpyrifos (CLP) is transported via global distillation to the Arctic where it may pose a threat to this ecosystem. CLP is readily detected in Arctic environmental compartments, but current research has not studied its partitioning between water and dissolved organic matter (DOM) nor the role of photochemistry in CLP's fate in aquatic systems. Here, the partition coefficients of CLP were quantified with various types of DOM isolated from the Arctic and an International Humic Substances Society (IHSS) reference material Suwannee River natural organic matter (SRNOM). While CLP readily partitions to DOM, CLP exhibits a significantly higher binding constant with Arctic lacustrine DOM relative to fluvial DOM or SRNOM. The experimental partitioning coefficients (KDOC) were compared to a calculated value estimated using poly parameter linear free energy relationship (pp-LFER) and was found to be in good agreement with SRNOM, but none of the Arctic DOMs. We found that Arctic KDOC values decrease with increasing SUVA254, but no correlations were observed for the other DOM compositional parameters. DOM also mediates the photodegradation of CLP, with stark differences in photo-kinetics using Arctic DOM isolated over time and space. This work highlights the chemo-diversity of Arctic DOM relative to IHSS reference materials and highlights the need for in-depth characterization of DOM that transcends the current paradigm based upon terrestrial and microbial precursors.

Temperature Effects on Effluent Microgel Formation

Wastewater treatment plant effluent is considered an important hotspot of dissolved organic matter. The behavior and transformation of dissolved effluent organic matter (dEfOM) regulate particle sedimentation, pollutant fate, microbial attachment, and biofilm formation. However, studies have so far focused on the transformation of marine and riverine organic matter, and the current knowledge of dEfOM behavior is still limited. Fluctuations in water conditions, especially temperature, may directly alter the size, assembly speed, and structure of microgels, thereby potentially disturbing fate and the transportation of organic matter. In this study, we firstly investigated the effects of temperature on the behavior and capacity of dEfOM assembly into microgels and the possible mechanism. The microgel size and granularity of dEfOM were monitored by flow cytometry. Our results suggest that, with regard to microgels, a higher temperature leads to a higher assembly capacity but also a decrease in the size distribution. By contrast, assembly at 4 °C reduces the relative assembly capacity but increases the microgel size and granularity. The size distribution of the formed microgels at the various temperatures was ordered as follows: 4 °C > 20 °C > 35 °C. The size reduction in dEfOM assembly may be closely tied to the enhancement of hydrophobic interactions. The reduction in microgel granularity in warm conditions (35 °C) in terms of the effluent water may be caused by thermally induced condensation. Overall, the findings demonstrate the effects of temperature on dEfOM assembly and can facilitate further relevant studies on aquatic organic particle formation during current global warming scenarios.

Key factors controlling colloids-bulk soil distribution of polybrominated diphenyl ethers (PBDEs) at an e-waste recycling site: Implications for PBDE mobility in subsurface environment

Accumulation of polybrominated diphenyl ethers (PBDEs) in surface soils at elevated concentrations is common at e-waste recycling sites. Even though highly insoluble, migration of PBDEs into the vadose zone and groundwater is possible, due to their association with soil colloids. Here, we show that upon equilibration with artificial rainwater surface and subsurface soil samples collected at an e-waste recycling site release significant quantities of colloids, with the total concentrations of 14 PBDE congeners as high as 990 ng/g dw. The concentrations of different congeners vary markedly in the colloids, and that of BDE-209 is the highest in all the samples. Notably, even the colloids released from the soil collected at a depth of 95-105 cm contain high concentrations of PBDEs. Preferential binding of PBDEs to soil colloids is observed, with the colloids-soil distribution coefficients above 10 in certain cases. The extent of preferential binding displays no apparent correlation with the relative hydrophobicity of the PBDEs, nor can it be explained simply by considering the higher specific surface area, pore volume, and clay content of the soil colloids than the respective bulk soil. Principal component analysis shows that multiple soil properties are collectively responsible for the preferential distribution of PBDEs. Specifically, the differences in pore volume, soil organic carbon content, and pore size between colloids and soils are likely the major factors affecting the distribution of high-concentration PBDEs, whereas the differences in clay content, pore volume and specific surface area are the key factors affecting the distribution of low-concentration PBDEs. The findings clearly show that colloids are an important medium with which PBDEs are associated at contaminated sites, and underline the need of understanding colloid-facilitated transport of PBDEs at e-waste sites.

Interaction between polychlorinated biphenyls and dissolved organic matter of different molecular weights from natural and anthropic sources

Polychlorinated biphenyls (PCBs) are compounds of significant interest due to high toxicity, persistence, long-range atmospheric transport, and bioaccumulation. These compounds can interact with components present in the environment, including dissolved organic matter (DOM) in soils and waters, thereby modifying its availability and movement. In this study, DOM was fractionated by ultrafiltration and characterized according to its hydrophobicity and hydrophilicity, then the interaction of a series of PCBs and different DOM fractions was evaluated. The DOM was collected from the surface waters of three sectors located along a river in the southern part of America. These sectors are subject to different anthropic activities, thus the DOM of sector 1, with the least anthropic influence, was mainly hydrophobic and with a high content of aromatic structures. In contrast, the DOM collected from sectors 2 and 3, where anthropic activity is highest, was slightly hydrophobic and hydrophilic, respectively. The DOM of these two sectors was mainly composed of low molecular weight macromolecules. These results revealed that more hydrophobic PCBs (i.e., 101, 118, 138, and 180) have a greater affinity to DOM with a higher molecular weight (i.e., >1 kDa). In turn, PCBs with lesser chlorination and hydrophobicity presented a greater affinity to DOM with a lower molecular weight. In conclusion, our study shows that the high molecular weight DOM is responsible for mobilizing PCBs with a high degree of chlorination.

Groundwater antibiotic pollution and its relationship with dissolved organic matter: Identification and environmental implications

The occurrence of veterinary antibiotics and hydro-chemical parameters in eleven natural springs in a livestock production area is evaluated, jointly with the characterization of their DOM fingerprint by Orbitrap HRMS. Tetracycline and sulfonamide antibiotics were ubiquitous in all sites, and they were detected at low ng L^-1 concentrations, except for doxycycline, that was present at μg L^-1 in one location. DOM analysis revealed that most molecular formulas were CHO compounds (49 %-68 %), with a remarkable percentage containing nitrogen and sulphur (16 %-23 % and 11 %-24 %, respectively). Major DOM components were phenolic and highly unsaturated compounds (~90 %), typical for soil-derived organic matter, while approximately 11 % were unsaturated aliphatic, suggesting that springs may be susceptible to anthropogenic contamination sources. Comparing the DOM fingerprint among sites, the spring showing the most different profile was the one with surface water interaction and characterized by having lower CHO and higher CHOS formulas and aliphatic compounds. Correlations between antibiotics and DOM showed that tetracyclines positively correlate with unsaturated oxygen-rich substances, while sulfonamides relate with aliphatic and unsaturated oxygen-poor compounds. This indicates that the fate of different antibiotics will be controlled by the type of DOM present in groundwater.

Mechanistic insight into hydroxylation of 2,2',4,4'-tetrabromodiphenyl ether during biodegradation by typical aerobic bacteria: Experimental and computational studies

Polybrominated diphenyl ethers (PBDEs) are a group of persistent pollutants in the environment. Though aerobic biodegradation of PBDEs have been extensively studied, the involved hydroxylation mechanism decisive for whole biotransformation is not clear yet. During the effective biodegradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by B. xenovorans LB400, the depletion of endogenous ∙OH by scavenger could bring about the significant decrease of biodegradation efficiency whereas ·O₂^- was nearly not influential. Given the importance of ∙OH in hydroxylation, the reaction mechanisms along major pathways of electrophilic addition and hydrogen abstraction were theoretically examined by density functional theory (DFT). For the less demand of activation energy, the relative preference of electrophilic addition was shown at aromatic C3-site. When the secondary reaction was considered after addition at C4-site, the barrierless association of ∙OH at C3-site and deprotonation by H₂O was validated as the energetically-favorable pathway that may cause dihydroxylation of BDE-47 into 3,4-dihydroxyl-BDE-17. The electrophilic addition followed by seconary barrierless trans-association of ∙OH and then dehydration seemed favorable for monohydroxylation as regards energetic barrier merely up to 194.01 kJ mol^-1, while the hydrogen abstraction by ∙OH from C5-site was more privileged actually. The theoretical insights would help well understand the hydroxylation mechanism of PBDEs by aerobes.

Facile Surface Modification of Polyamide Membranes Using UV-Photooxidation Improves Permeability and Reduces Natural Organic Matter Fouling

A new optimized ultraviolet (UV) technique induced a photooxidation surface modification on thin-film composite (TFC) polyamide (PA) brackish water reverse osmosis (BWRO) membranes that improved membrane performance (i.e., permeability and organic fouling propensity). Commercial PA membranes were irradiated with UV-B light (285 nm), and the changes in the membrane performance were assessed through dead-end and cross-flow tests. UV-B irradiation at 12 J·cm^-2 enhanced the pure water permeability by 34% in the dead-end tests without decreasing the mono- or divalent ion rejections, as compared with the pristine PA membrane, and led to less fouling by natural organic matter in the cross-flow tests. Scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) confirmed that UV-B irradiation opened the pore structure and created carboxylic and amine groups on the PA surface, leading to increased membrane surface charge and hydrophilicity. Thus, an optimal UV-B dose appears to modify only a thin layer of the PA membrane surface, which favorably enhances the membrane performance. UV-B did not alter the structure, flux, or salt rejection for cellulose triacetate (CTA)-based membranes. While other membrane surface modifications include oxidants, strong acids, and bases, the UV-B facile treatment is chemical-free, thus reducing chemical wastes, and easy to apply in roll-to-roll fabrication processes of PA membranes. The results also showed that a low UV irradiation dose could be applied to PA or CTA membranes for disinfection or photocatalytic oxidation.

Stickiness of extracellular polymeric substances on different surfaces via magnetic tweezers

Organic particle dynamics in the surface ocean plays a critical part in the marine carbon cycle. Aggregation of marine organic particles drives their downward transport to support various marine organisms on their transit to the sediments. Extracellular polymeric substances (EPS) from various microbes are a major contributor to the oceanic organic particle pool. The stickiness of EPS is expected to play a determining role in the aggregation process of particles; however, stickiness parameters are usually indirectly estimated through data fitting without direct assessment. Here a magnetic tweezer method was developed to quantitatively assess the stickiness of three model EPS produced by: Amphora sp., (diatom), Emiliania huxleyi (coccolithophore), and Sagittula stellata (bacteria), under different in vitro environmental conditions (salinity or EDTA complexed cations) and surface matrices (EPS-EPS and bare glass). Our results showed the stickiness of three microbial EPS decreasing for S. stellata > E. huxleyi > Amphora sp., in line with their decreasing protein-to-carbohydrate (P/C) ratios (related to their relative hydrophobicity). The data not only emphasize the importance of hydrophobicity on EPS stickiness, but also demonstrates that salinity and the nature of the substrate surface can influence the stickiness. Furthermore, we investigated stickiness between various types of EPS, and the observed selective stickiness of EPS between species may shed light on the interactions among heterogeneous marine microorganisms. Overall, this newly developed system provides a platform to assess the EPS stickiness to advance our understanding of the aggregation and sedimentation process of organic particles that are critical for the fate of organic carbon as well as for biofilm formation and microbial colonization of surfaces in the ocean.

Current progress in degradation and removal methods of polybrominated diphenyl ethers from water and soil: A review

The widespread of polybrominated diphenyl ethers (PBDEs) in the environment has caused rising concerns, and it is an urgent endeavor to find a proper way for PBDEs remediation. Various techniques such as adsorption, hydrothermal and thermal treatment, photolysis, photocatalytic degradation, reductive debromination, advanced oxidation processes (AOPs) and biological degradation have been developed for PBDEs decontamination. A comprehensive review of different PBDEs remediation techniques is urgently needed. This work focused on the environmental source and occurrence of PBDEs, their removal and degradation methods from water and soil, and prospects for PBDEs remediation techniques. According to the up-to-date literature obtained from Web of Science, it could be concluded that (i) photocatalysis and photocatalytic degradation is the most widely reported method for PBDEs remediation, (ii) BDE-47 and BDE-209 are the most investigated PBDE congeners, (iii) considering the recalcitrance nature of PBDEs and more toxic intermediates could be generated because of incomplete degradation, the combination of different techniques is the most potential solution for PBDEs removal, (iv) further researches about the development of novel and effective PBDEs remediation techniques are still needed. This review provides the latest knowledge on PBDEs remediation techniques, as well as future research needs according to the up-to-date literature.

Simultaneous quantification of humic acid-water and silanized glass-water partition constants for PCBs, PCDDs and OCDF

Super-hydrophobic organic contaminants (SHOCs) such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and octachlorodibenzofuran (OCDF) can sorb to dissolved hydrophobic materials including humic acids (HAs), enhancing their apparent aqueous solubility and potentially resulting in increased groundwater contamination and offsite transport. To manage risks associated with transport of and contamination by SHOCs, modelling approaches incorporating partitioning data, i.e. dissolved organic carbon-water partition constants (K_DOC), are necessary. Measurement of K_DOC can however be compromised by SHOC sorption to glassware surfaces leading to an overestimation of experimental values resulting in larger K_DOC. A method for simultaneous derivation of K_DOC and glass-water partition constants (K_GW) is described. It involves a mass balance approach combined with HA as a co-solvent at various concentrations and accounts for SHOC losses to silanized glassware. Measured log K_DOC values ranged from 5.28 to 7.64 for tetra- to decachlorinated PCBs, 6.67 to 7.93 for tetra- to octachlorinated PCDDs and 8.20 for OCDF. These data were linear functions of log K_OW and consistent with relationships reported for more polar compounds. Log K_GW (mm³ mm^-2) values (1.62 to 4.06 for PCBs, 2.96 to 3.90 for PCDDs, 3.77 for OCDF) were one order of magnitude greater compared to literature PCB borosilicate glass-water partition constants. Techniques such as those presented in this work present simple, versatile means to provide prediction of the SHOC proportion remaining in aqueous solutions after loss to glassware that was inversely related to container surface area/volume ratio and log K_OW in our study.

The concentrations and characteristics of dissolved organic matter in high-latitude lakes determine its ambient reducing capacity

The reducing capacity (RC) of natural organic matter plays an important role in the carbon cycle and biogeochemical fates of environmental contaminants in the aquatic system. However, the electron donation potentials of dissolved organic matter (DOM) from high-latitude lakes are still uncertain. In this study, we collected DOM samples from high-latitude lakes across the Arctic and boreal regions in Sweden and Norway to investigate the effects of the DOM concentration and characteristics on its ambient reducing capacity (ARC). Mercury (Hg(II)) abiotic reduction in darkness was used to determine the ARC. The results showed that the DOM in Arctic lakes is less terrestrial-dominant than in reference sites (i.e., forest lakes). Between the two categories of Arctic lakes, tundra lakes are more terrestrial-influenced compared to mountain lakes. Additionally, terrestrial-originated DOM is a main controlling factor for enhancing the ambient reducing capacity, whereas the DOM concentration, i.e., dissolved organic carbon (DOC), resulted in variations in the Hg/DOC ratios that also cause the variations of the observed ARC values. Thus, comparisons of the ARC values can be conducted while oxidant/DOC ratios are kept the same and reported through the method using heavy metals as a chemical probe. After correction for Hg/DOC ratio interference, the ambient reducing capacity of DOM followed the order: boreal forest lakes > Arctic tundra lakes > Arctic mountain lakes. This study highlights that the DOM concentration should also be considered when estimating the ARC as compared to the previous that mainly focusing on the properties of DOM such as its origins. As climate change is projected to be severe in high latitudes, this study demonstrates a significant connection between aquatic DOM geochemical reactivity and terrestrial inputs, which is crucial for a better prediction of the role of DOM in high-latitude lakes in the context of climate change.

DOM as an indicator of occurrence and risks of antibiotics in a city-river-reservoir system with multiple pollution sources

Multiple sources contribute to the presence of antibiotic residues in water environments, and the environmental risks caused by antibiotics were paid more and more attention. This work aims to establish a relationship between optical properties of dissolved organic matter (DOM) and sources and risks of antibiotics. Occurrence of antibiotics and DOM in a city-river-reservoir freshwater system containing distinct antibiotic sources was investigated during three seasons using LC-MS and fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC), respectively. The results showed that antibiotics and DOM in the water had trends of increasing levels from the upstream to the midstream in the system. Five classes of antibiotics had statistically significant correlations with the humic-like component (C3) in the water (Pearson, p < 0.05). Especially, norfloxacin (NFX), which was dominant in the aquaculture source, significantly increased the fluorescence of C3 according to the fluorescence titration (R² = 0.86, p < 0.01). Furthermore, fluorescence signature in the aquaculture pond posed broad humic acid-like peaks with relatively higher abundances compared to other areas. These results suggested that C3 could be recognized as an indicator of NFX from aquaculture sources. Meanwhile, C3 can largely account for ecological risks of tetracyclines according to the results of redundancy analysis. This work highlights the roles of EEM-PARAFAC on tracing the source of antibiotics and the correlations between environmental risks of antibiotics and DOM in the aquatic environment.

Solubility, uptake, and translocation of BDE 47 as affected by DOM extracted from agricultural wastes

Dissolved organic matter (DOM) extracted from wheat straw (SDOM) and cow manure (MDOM) were used to investigate their effects on the solubilization, uptake, and translocation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). Partition coefficients (K_DOC) of BDE 47 between water and the two types of DOM were measured by the solubility enhancement method. The uptake and translocation of BDE 47 by wheat plants were explored by hydroponic exposure experiments. In the range of 0 to 100 mg/L of DOM, the solubility of BDE 47 increased with increasing concentrations of DOM. The log [K_DOC] values of BDE 47 in SDOM and MDOM solutions were 5.77 and 5.31, respectively. The log [K_DOC] values of BDE 47 in SDOM solutions were higher than those in MDOM solutions, which might be ascribed to the higher content of aliphatic carbon and lower molecular weight of SDOM. The addition of DOM (50 mg/L) significantly increased the accumulation of BDE 47 in the shoots of wheat plants. Wheat straw DOM had greater effect than MDOM in enhancing the accumulation of BDE 47. This study demonstrated the potential risk of BDE 47 to plants resulting from DOM-facilitated transport or the changes in metabolic properties.

Anaerobic degradation of deca-brominated diphenyl ether contaminated in products: Effect of temperature on degradation characteristics

In this study, a 200-day deca-brominated diphenyl ether (deca-BDE) degradation activity experiment was carried out, using consumer-use curtain material as the substrate. During the degradation process, polybrominated diphenyl ether (PBDE) products with fewer bromine atoms were gradually generated by the debromination of deca-BDE. The influences of temperature, initial substrate dosing mass, and pH were also investigated. Interestingly, thermophilic conditions proved more beneficial for deca-BDE degradation than mesophilic conditions. The results also demonstrate that the debromination rate increased with the initial deca-BDE dosing mass, and that pH 7 was the most suitable for the reaction.

Photosensitized diastereoisomer-specific degradation of hexabromocyclododecane (HBCD) in the presence of humic acid in aquatic systems

Humic acids (HA) are the most important photosensitizers in the ocean and generate highly reactive oxygen species (ROS), known as photochemically produce reactive intermediates (PPRI), which degrade organic pollutants. Thus, to reveal the fate of organic pollutants in an aqueous environment, it is important to understand the natural photodegradation phenomenon caused by HA. Three ROS generated from HA, ¹O₂, O₂-, and OH, were measured using different probe compounds and instrumental techniques. In this study, HBCD (hexabromocyclododecane), a newly listed one of persistent organic pollutants (POPs) under the Stockholm Convention, was studied to understand the phototransformation mechanism, which has not been sufficiently investigated in terms of its environmental fate and transport, despite the distinctive features of its diastereoisomers. The results showed that the diastereoisomer-specific distributions of α-, β-, and γ-HBCD were related to the acceleration and retardation of photodegradation in the presence of AHA (Aldrich Humic Acid) under simulated solar light, and only α-HBCD was rapidly photodegraded as the amount of AHA increased relative to the absence of AHA. This study provides the first characterization of the behavior of photosensitized HBCD degradation in aquatic systems.

Distribution characteristics of poly-brominated diphenyl ethers between water and dissolved organic carbon from anaerobic digestate: Effects of digestion conditions

It is becoming increasingly urgent to investigate the partition coefficients (expressed as log K_DOC values) of polybrominated diphenyl ethers (PBDEs) in dissolved organic carbon (DOC) present in wastewater. In the current study, after 72 h of equilibration, the concentrations of four common PBDEs were measured in the presence of four DOC solutions from two laboratories and two full-scale anaerobic digestion plants. Sixteen log K_DOCs were determined by calculation and unit conversion. The results for the laboratory samples, such as log K_DOCs for 2,2',4,4',5,5'-hexabromodiphenyl ether being 6.38 and 5.46 at different reaction temperatures during the cultivate procedure, suggest that a thermophilic environment promotes the solubility of PBDEs to a greater extent than mesophilic conditions. DOC composition directly influences the solubility of PBDEs, even at the same cultivating temperature: the highest log K_DOCs for 2,2',4,4',5,6'-hexabromodiphenyl ether were 6.71 and 6.33 in different full-scale plant digestates. A linear regression with an R² of 0.9863 was used to construct a model describing the potential relationship between log K_DOC and the composition of DOC, which includes proteins, polysaccharides and lipids, and which takes into account the positions of bromine atoms, for use in predicting the log K_DOC values of PBDEs in different water systems.

Molecular characteristics, proton dissociation properties, and metal binding properties of soil organic matter: A theoretical study

Soil organic matter (SOM) is a key soil sorbent with a large number of reactive binding sites that may complex with metals, controlling their fate, transport, and bioavailability in soil. However, due to the complex and heterogeneous nature of SOM, it is not easy to probe its physical and chemical properties at the molecular level. In this study, an a priori method was developed to predict the molecular properties of SOM, which incorporated computational molecular modeling, SPARC Performs Automated Reasoning in Chemistry's (SPARC's) chemical reactivity models, and linear free energy relationships (LFERs). Specifically, the method uses SOM models simulated by molecular dynamics modeling based on the experimental elemental composition and functional group information of SOM. For the molecular characteristics, the molecular H/C and O/C ratios, molecular weight, aromatic index, and double bond equivalence of the SOM molecules were calculated. For the proton binding constants, the SPARC was used to calculate the microscopic pK_a values of every binding sites of individual molecules of the SOM model. Based on the pK_a values, the metal binding constants for individual monodentate binding sites were calculated using the Irving-Rossotti LFERs for different heavy metals. The results agreed reasonably with the default values used in the Windermere Humic Aqueous Model (WHAM) (VI) for the investigated metals. The theoretical SOM models, to some extent, represented the average properties of the investigated SOM. Overall, this study gives new quantitative and molecular insight into the structure and chemical properties of SOM. Detailed deprotonation and metal-SOM complexation information was gained for individual SOM binding sites. Such feasible and straightforward predictive scheme is useful to assess the risk of heavy metals in various aquatic and terrestrial environment involving heterogeneous natural organic matter.

Environmental and Agricultural Relevance of Humic Fractions Extracted by Alkali from Soils and Natural Waters

To study the structure and function of soil organic matter, soil scientists have performed alkali extractions for soil humic acid (HA) and fulvic acid (FA) fractions for more than 200 years. Over the last few decades aquatic scientists have used similar fractions of dissolved organic matter, extracted by resin adsorption followed by alkali desorption. Critics have claimed that alkali-extractable fractions are laboratory artifacts, hence unsuitable for studying natural organic matter structure and function in field conditions. In response, this review first addresses specific conceptual concerns about humic fractions. Then we discuss several case studies in which HA and FA were extracted from soils, waters, and organic materials to address meaningful problems across diverse research settings. Specifically, one case study demonstrated the importance of humic substances for understanding transport and bioavailability of persistent organic pollutants. An understanding of metal binding sites in FA and HA proved essential to accurately model metal ion behavior in soil and water. In landscape-based studies, pesticides were preferentially bound to HA, reducing their mobility. Compost maturity and acceptability of other organic waste for land application were well evaluated by properties of HA extracted from these materials. A young humic fraction helped understand N cycling in paddy rice ( L.) soils, leading to improved rice management. The HA and FA fractions accurately represent natural organic matter across multiple environments, source materials, and research objectives. Studying them can help resolve important scientific and practical issues.

A flow-through aqueous standard generation system for thin film microextraction investigations of UV filters and biocides partitioning to different environmental compartments

In this paper problems associated with preparation of aqueous standard of highly hydrophobic compounds such as partial precipitation, being lost on the surfaces, low solubility in water and limited sample volume for accurate determination of their distribution coefficients are addressed. The following work presents two approaches that utilize blade thin film microextraction (TFME) to investigate partitioning of UV filters and biocides to humic acid (dissolved organic carbon) and sediment. A steady-state concentration of target analytes in water was generated using a flow-through aqueous standard generation (ASG) system. Dialysis membranes, a polytetrafluoroethylene permeation tube, and a frit porous (0.5 μm) coated by epoxy glue were basic elements used for preparation of the ASG system. In the currently presented study, negligible depletion TFME using hydrophilic-lipophilic balance (HLB) and octadecyl silica-based (C18) sorbents was employed towards the attainment of free concentration values of target analytes in the studied matrices. Thin film geometry provided a large volume of extraction phase, which improved the sensitivity of the method towards highly matrix-bound analytes. Extractions were performed in the equilibrium regime so as to prevent matrix effects and with aims to reach maximum method sensitivity for all analytes under study. Partitioning of analytes on dissolved organic carbon (DOC) was investigated in ASG to facilitate large sample volume conditions. Binding percentages and DOC distribution coefficients (Log K_DOC) ranged from 20 to 98% and 3.71-6.72, respectively. Furthermore, sediment-water partition coefficients (K_d), organic-carbon normalized partition coefficients (Log K_OC), and DOC distribution coefficients (Log K_DOC) were investigated in slurry sediment, and ranged from 33 to 2860, 3.31-5.24 and 4.52-5.75 Lkg^-1, respectively. The obtained results demonstrated that investigations utilizing ASG and TFME can yield reliable binding information for compounds with high log K_OW values. This information is useful for study of fate, transport, and ecotoxicological effects of UV filters and biocides in aquatic environment.

Using Polyethylene Passive Samplers To Study the Partitioning and Fluxes of Polybrominated Diphenyl Ethers in an Urban River

In the aquatic environment, the behavior of hydrophobic organic contaminants (HOCs), such as polybrominated diphenyl ethers (PBDEs), depends on the congeners' physicochemical properties, environmental conditions and the presence of competing natural sorbents, including particulate and dissolved organic carbon (DOC) and black carbon (BC). Although BC is known as an important sedimentary sorbent for HOCs, its affinity for PBDEs has been poorly constrained. To better understand the biogeochemical controls on PBDEs, 12 PBDE congeners were measured in air, water, sediment and porewater of the lower Passaic River. BDE-47 and BDE-99 dominated in all media. In sediments and water, the dual OC + BC approach better predicted PBDE partitioning compared to the simple OC isotherm. Field-derived K_BC values for PBDEs were inversely correlated with aqueous solubility [log K_{BC sediments(water)} = -log C_w^sat * 0.95 (1.2) + 0.36 (-0.69)]; they reflected near background to highly contaminated regions across the Passaic River. In the water column, PBDEs appeared at equilibrium partitioning between particles and colloids: OC + BC were responsible for the sorption of 65% of PBDEs, followed by colloids (30%); only 5% of PDBEs were truly dissolved. Calculated sediment-water diffusive fluxes greatly overwhelmed the atmospheric depositional flux to the river.

Role of microgel formation in scavenging of chromophoric dissolved organic matter and heavy metals in a river-sea system

We use riverine and marine dissolved organic carbon (DOC) polymers to examine their aggregation behavior, and to evaluate the roles of microgel formation in scavenging of chromophoric dissolved organic matter (CDOM) and heavy metals in a river-sea system. Our results indicate that riverine and marine microgels did not exhibit very much difference in size and self-assembly curve; however, the assembly effectiveness ([microgel]/DOC) of marine samples was much higher than riverine. Instead of concentration of DOC, other factors such as types and sources of DOC polymers may control the microgel abundance in aquatic environments. After filtering water samples (microgels removed), the CDOM and selected metals (Cu, Ni, Mn) in the filtrate were quantified. CDOM and metals were concurrently removed to an extent via DOC polymer re-aggregation, which also suggested that the microgels had sequestering capability in CDOM and metals. This finding provides an alternative route for CDOM and heavy metals removal from the water column. As such the process of re-aggregation into microgels should then be considered besides traditional phase partitioning in the assessment of the ecological risk and fate of hazardous materials.

Mitigating 17α-ethynylestradiol water contamination through binding and photosensitization by dissolved humic substances

Photodegradation is an important abiotic pathway transforming organic pollutants in natural waters. Humic substances (HS), including humic and fulvic acids, are capable of accelerating the photodegradation of steroid estrogens. However, how the photodegradtion of the emerging pollutants influenced by HS is not clear. Thus, we studied the roles and mechanisms of HS in inducing the photodegradation of 17α-ethynylestradiol (EE2). HS generally induces EE2 photodegradation through binding and reactive species generation. Apart from hydroxyl radical (HO), the excited triplets of humic substances (³HS*) are other key reactive species degrading EE2 by abstracting electrons. HO and ³HS* were responsible for about 60% of the overall EE2 photodegradation at 250μmol HS L^-1. Most of EE2 molecules bound to the HS via H-bonding, π-π and hydrophobic interactions. The binding role of HS in promoting EE2 photodegradation was rationalized by 17β-estradiol competitive binding with EE2 to the humic and fulvic acids. Furthermore, HS-promoted photodegradation can alter EE2 toxicity to wheat, rice and Ormosia plants. This study extends our knowledge on the photochemical behaviors and ecological risks of steroid estrogens in natural waters.

Characterization of PBDEs and novel brominated flame retardants in seawater near a coastal mariculture area of the Bohai Sea, China

The concentrations and distributions of PBDEs and novel brominated flame retardants (NBFRs) in dissolved phase of surface seawater near a coastal mariculture area of the Bohai Sea were investigated. The total concentrations of PBDE and NBFRs were in the range of 15.4-65.5 and 2.12-13.6ng/L, respectively. The highest concentration was discovered in the water near an anchorage ground, whereas concentrations in water samples from offshore cage-culture area were not elevated. Relatively high concentrations of BDE28, 99, and 100 were discovered in the medium range of distance from shore, where is the path of tidal or coastal current. This suggested that inputs from ships or through tidal current rather than mariculture activities may be the main sources of BFRs in this area. BDE209, BDE47, hexabromobenzene (HBB), and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB) were the most abundant BFR congeners. Relatively high proportions of these BFRs may originate from discharge of wastewater nearby or degradation from higher brominated PBDEs. No correlations were found between BFR concentrations and water dissolved organic carbon, suggesting that concentrations and distributions of BFRs in this area were source-dependent. The relatively high concentrations in this study emphasized the importance of monitoring and managing BFR contaminations in mariculture areas of China.

Tolerance of cyanobacteria to the toxicity of BDE-47 and their removal ability

Polybrominated diphenyl ethers are ubiquitous and toxic contaminants in aquatic environments. The effect of polybrominated diphenyl ether BDE-47 on five species of cyanobacteria, along with their removal ability was investigated. Four species, namely Synechocystis sp., Oscillatoria planctonica, Microcystis flos-aquae and Nostoc sp., were exposed to BDE-47 at concentrations ranging from 0.05 to 1.0 mg L^-1 for 14 days, while the exposure time for Pseudanabaena sp. was 30 days. The first four species were very tolerant to BDE-47 while growth and photosynthesis of Pseudanabaena were significantly inhibited by BDE-47 at concentrations over 0.1 mg L^-1. However, this species could recover from the toxicity of high concentrations of BDE-47 after 30 days of exposure, indicating the development of some "resistance" after pre-exposure to 1.0 mg L^-1 BDE-47. The "resistant" cells had a higher growth rate, photosynthesis and glutathione S-transferase activity than normal Pseudanabaena cells. The sensitivity of Pseudanabaena to BDE-47 toxicity was affected by its initial filament density, with cultures having a low filament density (2.3 × 10⁶ filaments mL^-1) being up to 14-15 times more sensitive than cultures with a high filament density (13 × 10⁶ filaments mL^-1). All cyanobacteria could remove 70-82% of BDE-47 in their media, with more than 60% of BDE-47 accumulated in cells. This is the first study showing the high tolerance of different cyanobacteria species to BDE-47 toxicity and their removal ability. The study also revealed that the sensitive Pseudanabaena could acquire a "resistance" to BDE-47, which was transferred to the next generation.

Sea-air exchange of bromoanisoles and methoxylated bromodiphenyl ethers in the Northern Baltic

Halogenated natural products in biota of the Baltic Sea include bromoanisoles (BAs) and methoxylated bromodiphenyl ethers (MeO-BDEs). We identified biogenic 6-MeO-BDE47 and 2'-MeO-BDE68 in Baltic water and air for the first time using gas chromatography - high resolution mass spectrometry. Partial pressures in air were related to temperature by: log p/Pa=m/T(K)+b. We determined Henry's law constants (HLCs) of 2,4-dibromoanisole (2,4-DiBA) and 2,4,6-tribromoanisole (2,4,6-TriBA) from 5 to 30°C and revised our assessment of gas exchange in the northern Baltic. The new water/air fugacity ratios (FRs) were lower, but still indicated net volatilization in May-June for 2,4-DiBA and May - September for 2,4,6-TriBA. The net flux (negative) of BAs from Bothnian Bay (38,000km²) between May - September was revised from -1319 to -532kg. FRs of MeO-BDEs were >1, suggesting volatilization, although this is tentative due to uncertainties in their HLCs and binding to dissolved organic carbon.

Impacts of loach bioturbation on the selective bioaccumulation of HBCDD diastereoisomers and enantiomers by mirror carp in a microcosm

To assess the impacts of bioturbation at the water-sediment interface on the bioaccumulation of hexabromocyclododecane diastereoisomers (HBCDDs) by pelagic organisms and the bioisomerization and enantioselectivity therein, we built microcosms containing water, mirror carp (Cyprinus carpio), and sediment. The microcosms were sorted into two groups, with or without loach (Misgurnus anguillicaudatus) living at the water-sediment interface. A 50-d accumulation test was conducted by spiking the microcosms with the three main HBCDD diastereoisomers (α-, β-, and γ-HBCDDs) separately. The HBCDDs were mainly associated with the sediment. The dissolved organic matter and suspended particulate matter content increased due to loach bioturbation, which promoted the release of sediment-associated HBCDDs and led to enhanced HBCDD bioaccumulation in the carp. Isomerization from β- and γ-HBCDD to α-HBCDD occurred in the carp, and the amounts of isomerization did not increase proportionally with increasing bioaccumulation. Moreover, the enantioselectivity of the HBCDD diastereoisomers showed species-specific differences between mirror carp and loach, and no significant change in the enantioselectivity in the carp was observed in the presence of loach.

Modification of PBDEs (BDE-15, BDE-47, BDE-85 and BDE-126) biological toxicity, bio-concentration, persistence and atmospheric long-range transport potential based on the pharmacophore modeling assistant with the full factor experimental design

In this study, the properties of AhR binding affinity, bio-concentration factor, half-life and vapor pressure were selected as the typical indicators of biological toxicity, bio-concentration, persistence and atmospheric long-range transport potential for polybrominated diphenyl ethers (PBDEs), respectively. A three-dimensional pharmacophore modeling assistant with a full factor experimental design for each property was used to reveal the significant pharmacophore features and the substituent effects to obtain reasonable modified schemes for the selected target PBDEs. Finally, the performances of the persistent organic pollutant (POP) properties, the synthesis feasibility and the fire resistance of the modified compounds were evaluated. The most influential pharmacophore feature for all POP properties was the hydrophobic group, especially the vinyl and propyl groups. Modified compounds with two additional hydrophobic groups exhibited a better regulatory performance. The average reduction in the proportions of the four POP properties for the modified compounds (except for 3-phenyl-BDE-15) was 70.60%, 52.44%, 47.04% and 70.88%. In addition, the energy and the C-Br bond dissociation enthalpy of the four typical PBDEs were higher than those of the modified compounds (except for 3-phenyl-BDE-15), indicating the synthesis feasibility and the lower energy barrier of the modified compounds to release Br free radicals to provide fire resistance.

Characterization of Dissolved Organic Matter in River Water by Conventional Methods and Direct Sample Analysis-Time of Flight-Mass Spectrometry

The dissolved organic matter in surface waters is composed of fractions of different molecular weight and polarity, characteristics that determine their capacity for complexing different types of pollutants and their environmental impact. In this study, the dissolved organic matter in the surface water of the Bio-Bio River (Central Region of Chile) was characterized chemically and spectroscopically after fractionating by molecular weight and polarity. The technique of direct sample analysis-time of flight-mass spectrometry (DSA-TOF-MS) was used to obtain more information on the composition of dissolved organic matter. It is concluded that dissolved organic matter found in the water of the river from the site of minor human impact (Rucalhue) has a predominantly natural origin, with a high content of aromatic carbon, in contrast to dissolved organic matter found in the waters of the sites that have higher human impact (Laja and Concepción), characterized by a greater molecular size and higher organic carbon content. These results are consistent with those obtained from DSA-TOF-MS, where higher correlation was observed between the mass spectrum of the standard commercial humic acid and dissolved organic matter found in the sectors of Laja and Concepción, unlike the spectrum mass of lignin which is more like dissolved organic matter found in the sector Rucalhue.

Influences of binding to dissolved organic matter on hydrophobic organic compounds in a multi-contaminant system: Coefficients, mechanisms and ecological risks

The complexation flocculation (CF) method was successfully employed to identify binding coefficients (Kdoc) of specific organic contaminants to dissolved organic matter (DOM, often indicated by dissolved organic carbon, DOC) in a multi-contaminant hydrophobic organic contaminant (HOC) system. Kdoc values were obtained for most of the evaluated 33 HOCs, indicating the feasibility and applicability of the CF method in a multi-contaminant system. Significant positive correlations were observed between binding coefficients and octanol-water partition coefficients (Kow) for organic halogen compounds, such as polybrominated diphenyl ethers (PBDEs) (R(2) = 0.95, p < 0.05) and organic chlorine pesticides (OCPs) (methoxychlor excluded, R(2) = 0.82, p < 0.05). The positive correlations identified between the lgKdoc and lgBCF (bioconcentration factor) for PBDEs and OCPs, as well as the negative correlation observed for polycyclic aromatic hydrocarbons (PAHs), indicated that different binding or partition mechanisms between PAHs and organic halogen compounds exist. These differences further result in discriminative competition partitions of HOCs between DOM and organisms. Assuming that only freely dissolved HOCs are bioconcentrative, the results of DOM-influenced bioconcentration factor (BCFDOM) and DOM-influenced lowest observed effect level (LOELDOM) indicate that the ecological risk of HOCs is decreased by DOM.

Effect of Pb2+, Cd2+, Cu2+ and dissolved organic carbon (DOC) on the distribution and partition of decabromodiphenyl ether (BDE-209) in a water–sediment system

The combined pollution of polybrominated diphenyl ethers (PBDEs) and heavy metals in electronic waste dismantling areas has received increasing concern in recent years.