Effects of natural dissolved organic matter on the complexation and biodegradation of 17α-ethinylestradiol in freshwater lakes

Depth-dependent variations of physicochemical properties of sedimentary dissolved organic matter and the influence on the elimination of typical pharmaceuticals

Sedimentary dissolved organic matter (DOM) could exert a significant influence on the transformation of trace organic contaminants. However, the variations of sedimentary DOM properties with depth and their impact on trace organic contaminants biodegradation remain unclear. In this study, the qualitative changes in DOM properties with depth were assessed using spectral techniques. Specifically, within the sediment range of 0-30 cm, humic acid and fulvic acid fractions exhibited higher degrees of humification and aromatization at 10-20 cm, while hydrophilic fractions showed higher degrees of humification and aromatization at 20-30 cm. Furthermore, electrochemical methods were employed to quantitatively assess the electron transfer capacity of sedimentary DOM at different depths, which displayed consistent variation trend with humification and aromatization degree. The high degree of humification and aromatization, along with strong electron-accepting capability of DOM, significantly enhanced the biodegradation rates of tetracycline and ritonavir. To gain deeper insights into the influence of molecular composition of DOM on its properties, two-dimensional gas chromatography-quadrupole mass spectrometry analysis revealed that quinones and phenolic hydroxyl compounds govern the redox reactivity of DOM. Simulated experiment of DOM-mediated biodegradation of typical pharmaceuticals confirmed the role of quinones and phenolic hydroxyl groups in the redox reactivity of DOM.

Influence of dissolved organic carbon on multimedia distribution and toxicity of fipronil and its transformation products in lotic waterways

Environmental fate and ecological impacts of fipronil and its transformation products (FIPs) in aquatic environment have caused worldwide attention, however, the influence of dissolved organic carbon (DOC) on multimedia distribution, bioavailability, and toxicity of FIPs in field waterways was largely unknown. Here, we collected 11 companion water and sediment samples along a lotic stream in Guangzhou, South China. FIPs were ubiquitous with total water concentrations ranging from 1.22 to 43.2 ng/L (14.8 ± 12.9 ng/L) and fipronil sulfone was predominant in both water and sediment. More than 70% of FIPs in aqueous phase were bound to DOC and the K_DOC values of FIPs were approximately 1-2 orders of magnitude higher than K_d-s/K_OC, emphasizing the significance of DOC in phase partitioning and transport of FIPs in aquatic environment. Water and sediment samples were more toxic to Chironomus dilutus than Hyallela azteca, and FIPs (especially fipronil sulfone) pronouncedly contributed toxicity to C. dilutus. Toxic units (TU) based on freely dissolved concentrations in water determined by solid phase microextraction significantly improved toxicity estimation of FIPs to the invertebrates compared to TUs based on aqueous concentrations. The present study highlights the significance of DOC association on fate and ecological risk of hydrophobic insecticides in lotic ecosystem.

Algal organic matter and dissolved Mn cooperatively accelerate 17α-ethinylestradiol photodegradation: Role of photogenerated reactive Mn(III)

Algal extracellular organic matter (EOM), a major fraction of the dissolved organic matter found in eutrophic plateau lakes, can act as a photosensitizer to drive the abiotic oxidation of Mn(II). This process has the potential to generate reactive Mn(III) and influence the fate of organic pollutants. In this study, the photodegradation of 17α-ethinylestradiol (EE2) in the presence of Mn(II) and EOM was investigated with emphasis on the photogeneration mechanism of Mn(III). The results indicated that Mn(II) can accelerate EE2 photodegradation in EOM solution owing to the photogeneration of reactive Mn(III), and the enhancement was greater at higher Mn(II) concentrations. The generation of reactive Mn(III) was mainly attributable to the action of superoxide radical generated by photosensitization of EOM. In addition, the photodegradation of EE2 was slower at higher pH, possibly because of the deactivation of Mn(III) under alkaline conditions. Single-electron transfer was an indispensable process in the photodegradation. The differences in fluorophore content, pH, and NO₃^- concentrations are all important determinants for EE2 photodegradation in natural waters. The information obtained in this research would contribute to the understanding of reactions between Mn(II) and EOM, and provide new insights into the behaviors of reactive Mn(III) in eutrophic water irradiated by sunlight.

Linking pharmaceutical residues to dissolved organic matter and aquatic bacterial communities in a highly urbanized bay

Pharmaceuticals are causing environmental concerns associated with their widespread distribution in aquatic ecosystems. The environmental fate and behavior of pharmaceutical residues are related to dissolved organic matter and bacterial communities, both of which are strongly influenced by human activities. However, the relationships among pharmaceutical pollution, dissolved organic matter pool, and bacterial community structure under the pressure of human activities are still unclear, especially in highly urbanized bay areas. In this study, we investigated the occurrence and distribution of 35 pharmaceuticals in a typical urbanized bay (Hangzhou Bay) in Eastern China, and analyzed their relationships with dissolved organic matter and aquatic bacterial community structure. The target pharmaceuticals were ubiquitously detected in surface water samples, with their concentrations ranging from undetectable to 263 ng/L. The detected pharmaceuticals were mostly sulfonamides, macrolides, antidepressants, and metabolites of stimulants. Significant positive correlations were observed between the concentrations of pharmaceuticals and the intensity of human activities. Strong correlations also emerged between the concentration of antidepressants and the speed of urban expansion, as well as between the concentration of cardiovascular drugs and the population density or nightlight index. Three fluorescent components (protein-like C1, terrestrial humic-like C2, protein tryptophan-like C3) were significantly positively correlated with the total concentration of pharmaceuticals. Pharmaceutical pollution reshaped aquatic bacterial communities, based on the close correlation observed between pharmaceutical concentration and bacterial community structure. The results elucidate the potential dynamics of dissolved organic matter pool and aquatic bacterial communities in response to pharmaceutical pollution in urbanized bay ecosystems.

Embryo developmental toxicity in marine medaka (Oryzias melastigma) due to parental and embryonic 17α-ethinylestradiol exposure

The synthetic estrogen 17α-ethinylestradiol (EE2) is a common component of hormone therapy and oral contraceptives and has been widely used for nearly 60 years. Numerous studies have shown that exposure to EE2 can affect embryonic development in a number of fish species. The effects of parental and embryonic EE2 exposure on embryo developmental toxicity and the underlying molecular mechanisms, however, have rarely been examined. In this study, embryos collected from parental EE2-exposed adult fish were examined to assess EE2-induecd toxicity during embryo development. The rate of embryo development including heart rate, hatching rate, and larval locomotion were measured to assess embryo developmental toxicity. The embryonic transcriptome was used to delineate the related developmental toxicity pathways. Our results suggest that parental and embryonic EE2 exposure resulted in growth retardation including a reduction in embryo heart rate, a delay in the appearance eye pigmentation, decreased hatching rate and impaired larval locomotion. In addition, gene ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and Ingenuity Pathway Analysis (IPA) of transcriptome revealed that these impairments are controlled by estrogen receptor and related to eye structure, neuronal and synaptic structure, and behaviour. The key factors identified, including PRKAA2, APOB, EPHB2, OXTR, NR2E3, and POU4F2, could serve as biomarkers for assessing EE2-induced embryo developmental toxicity. For the first time, our results show that eye pigmentation is a potentially sensitive marker of EE2-induced embryo developmental toxicity.

Effects of dissolved organic matter derived from chicken manure on the biotransformation of roxarsone in soil

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX), widely used as a livestock feed additive, is excreted untransformed in large concentrations. Accumulation of this manure in the open environment increases dissolved organic matter (DOM) and ROX in soil within the aeration zone. And microbial action plays a dominant role in the transformation of ROX. However, the specific effect of DOM on the biotransformation of ROX is not known. In this paper, we investigated the transformation rate, metabolite content, and microbial community response of ROX in soils with different DOM concentrations (71.61, 100, 200, 500, and 800 mg L-1). The transformation of ROX was consistent with first-order transformation kinetics. DOM promoted the transformation of ROX, and with high DOM (DOM ≥200 mg L-1), ROX was transformed almost completely within two days. In this case, DOM provided nutrients to microorganisms and promoted their growth, accelerating the transformation of ROX. Also, the solubility of ROX was enhanced by DOM to increase its bioavailability. The microbial diversity was negatively correlated with DOM concentration and ROX transformation time; during the transformation of ROX, Bacillus, Arthrobacter, Enterococcus, Acinetobacter, and Pseudomonas became dominant in the soil with anomalously high levels of DOM. This study demonstrates the transformation process of ROX under actual environmental conditions where organic matter coexists with ROX, and this understanding is important for the prevention and control of arsenic pollution in soil within the aeration zone with anomalously high levels of DOM.

(Anti)estrogenic activity impacted by complex environmental matrices: A DOM and multiphase distribution approach

The presence of estrogenic endocrine disruptors in aquatic environments has been a concern and bioassays are recommended tools for their monitoring. However, the physicochemical properties of contaminants and the environmental matrix features may influence the resultant response. This study aimed to assess this influence on the Yeast Estrogen Screen (YES) assay. Mixtures of 17β-estradiol (E2) and humic acid (HA) were evaluated through the Schild approach aiming to investigate the interactions between estrogens and dissolved organic matter (DOM). Moreover, environmental samples from municipal landfill leachate and wastewater treatment plant (WWTP) influents and effluents were screened for (anti)estrogenic activity at both dissolved and particulate phases. Finally, results were statistically confronted with physicochemical parameters through principal component analysis (PCA). The HA test concentrations strongly reduced the E2 response, even at low levels. Humic substances may not only reduce estrogen bioavailability, but also interfere with the assay mechanism through enzymatic inhibition thus masking the sample estrogenic potential. Landfill leachate had total E2-Eq in the range 1282-2591 ng L^-1, while WWTP influent and effluent were in the range 12.1-41.4 and <DL-2.3 ng L^-1, so estrogenicity was reduced 92% in average. Particulate phase was responsible for 33-100% of measured E2-Eq between matrices, though cytotoxicity occurred in some extracts. Antiestrogenic activity was observed in both phases and might also have masked the estrogenicity of samples. PCA did not resulted in positive correlations supporting a multiphase distribution pattern of estrogenic compounds. Nevertheless, the solids and organic matter characteristics supported the data interpretation. In conclusion, the in vitro YES assay is subjected to factors intrinsic to the environmental sample that can influence on the measured estrogenic response. Therefore, results interpretation should be performed together with organic matter characterization parameters, cytotoxicity and antiestrogenic activity evaluation.

Continuous 17α-ethinylestradiol exposure impairs the sperm quality of marine medaka (Oryzias melastigma)

17α-ethinylestradiol (EE2) is an anthropogenic estrogen that is widely used for hormone therapy and oral contraceptives. It was reported that EE2 exposure induced reproductive impairments through processes affecting reproduction behavior and inducing ovotestis. However, the effects of continuous EE2 exposure on the reproductive performance remain largely unknown. In this study, adult marine medaka fish (Oryzias melastigma) were exposed to EE2 (85 ng/L) for one (F₀) and two (F₁) generations. Our results indicate that continuous EE2 exposure reduced fecundity and sperm motility. The testicular transcriptome, followed by bioinformatic analysis revealed the dysregulation of pathways related to steroidogenesis, sperm motility, and reproductive system development. Collectively, our findings indicate that continuous EE2 exposure directly affected sperm quality via the alteration of steroidogenesis and dysregulation of reproductive system development. The identified key factors including DNM1, PINK1, PDE7B, and SLC12A7 can serve as biomarkers to assess EE2-reduced sperm motility.

Silica-catalyzed ozonation of 17α -ethinyl-estradiol in aqueous media-to better understand the role of silica in soils

A promising route for thorough removal of 17α-ethinyl estradiol (EE2) from aqueous media was achieved through ozonation using mesoporous silicas such SBA-15, SBA-16, MCM-41 and MCM-48 as catalysts. Comparison with aluminosilicates along with Zeta potential and particle size measurements allowed demonstrating that EE2 interaction with silanols and hydrophobic -Si-O-Si- groups are essential requirements for the catalytic activity. Acid-base interactions, if any, should have minor contribution. EE2 hydroxylation appears to be an early step in the ozonation on all catalysts, but MCM-41 showed increased activity in phenolic ring cleavage. Confrontation of HPLC-UV and UV-Vis and HPLC-UV measurements revealed highest catalytic activity for MCM-41 and to a lesser extend of MCM-48 due to their higher specific surface area and weaker acid character. These results provide valuable findings for judiciously tailoring optimum [EE2-Silica:Water] interactions for thorough oxidative degradation of endocrine disrupting compounds (EDC).

Insight into the effect of wastewater-derived dissolved organic matter composition on norgestrel degradation in activated sludge: Coupled bacterial community and molecular characteristics

Dissolved organic matter (DOM) mediates the microbial transformation of micropollutants, including norgestrel (NGT) in natural waters. However, little is known of the effect of complex and variable wastewater-derived DOM composition on NGT degradation during wastewater treatment. In this study, the relationship between the compositions of initial DOM and NGT removal efficiencies of 17 wastewater treatment plants (WWTPs) in spring and summer were analyzed. The different molecular composition of DOM was selected in the lab to further explore its effect on NGT degradation by activated sludge. Results indicated that the DOM composition was a substantial driver of NGT removal in WWTPs. The discrepancies in the initial DOM composition contributed to the differences in the kinetics of NGT degradation by activated sludge. The larger rapid decay phase rates of NGT are usually accompanied by a large proportion of labile substances in DOM. High-throughput sequencing and ultrahigh-resolution mass spectrometry were used to further analyze the evolution of bacterial communities and DOM molecular composition were combined with network analysis to reveal the intrinsic relationship that how DOM composition affected NGT degradation by regulating core microbes. Eighty-nine core OTUs were significantly associated with NGT degradation, and 73 occurred in the rapid decay phase, implying that NGT degradation was mainly regulated by the initial composition of DOM. Nine major transformation products were identified in different groups with widely varying concentrations or relative abundances of these transformation products. This work provides valuable insights into the effects of wastewater-derived DOM composition on NGT degradation by activated sludge and innovatively explores the influence mechanisms from the bacterial community and molecular characterization perspectives.

Multi-spectroscopic investigation of the molecular weight distribution and copper binding ability of dissolved organic matter in Dongping Lake, China

The properties and metal-binding abilities of dissolved organic matter (DOM) rely on its molecular weight (MW) structure. In this study, the spatial differences of DOM in compositions, MW structures, and binding mechanisms with copper (Cu²⁺) in Dongping Lake were investigated by applying excitation-emission matrix combining parallel factor analysis (EEM-PARAFAC), synchronous fluorescence (SF) spectra, two-dimensional correlation spectra (2D-COS), and Fourier transform infrared (FTIR) spectra. The EDOM for the entrance of the Dawen River and PDOM for the macrophyte-dominated region were divided from DOM of Dongping Lake based on hierarchical clustering analysis (HCA) and principal component analysis (PCA) and were size-fractioned into MW < 500 kDa and <100 kDa fractions. According to EEM-PARAFAC, Dongping Lake was dominated by tryptophan-like substances with MW < 500 kDa. The concentration of PDOM was higher than that of EDOM (p < 0.05). 2D-COS showed that protein-like components preceded humic-like components binding to Cu²⁺ regardless of sample type (215 nm > 285 nm > 310-360 nm). The Cu²⁺ binding capacity of DOM exhibited specific differences in space, components, and molecular weights. The humic-like component 1 (C1) and tryptophan-like component 4 (C4) of PDOM showed stronger binding abilities than those of EDOM. Endogenous tryptophan-like component 4 (C4) had a higher binding affinity for Cu²⁺ than humic-like components (logK_a: C4 > C1 > C2) in PDOM irrespective of MW. Humic-like components with MW < 500 kDa displayed higher binding potentials for Cu²⁺. FTIR spectra showed that the main participants of DOM-Cu complexation included aromatic hydrocarbons, aliphatic groups, amide Ⅰ bands, and carboxyl functional groups. This study provides spatial-scale insights into the molecular weight structure of DOM in influencing the behavior, fate, and bioavailability of heavy metals in lakes.

Responses of steroid estrogen biodegradation to cyanobacterial organic matter biodegradability in the water column of a eutrophic lake

The co-occurrence of cyanobacterial harmful algal blooms and contaminants is an increasing environmental concern in freshwater worldwide. Our field investigations coupled with laboratory incubations demonstrated that the microbial degradation potential of 17β-estradiol (E2) with estrone as the intermediate was primarily driven by increased dissolved organic matter (DOM) in the water column of a cyanobacterial bloom. To explain the intrinsic contribution of cyanobacterial-derived DOM (C-DOM) to estrogen biodegradation, a combination of methods including bioassay, ultrahigh-resolution mass spectrometry, and microbial ecology were applied. The results showed that preferential assimilation of highly biodegradable structures, including protein-, carbohydrate-, and unsaturated hydrocarbon-like molecules sustained bacterial growth, selected for more diverse microbes, and resulted in greater estrogen biodegradation compared to less biodegradable molecules (lignin- and tannin-like molecules). The biodegradability of C-DOM decreased from 78% to 1%, whereas the E2 biodegradation rate decreased dramatically at first, then increased with the accumulation of recalcitrant, bio-produced lipid-like molecules in C-DOM. This change was linked to alternative substrate-induced selection of the bacterial community under highly refractory conditions, as suggested by the greater biomass-normalized E2 biodegradation rate after a 24-h lag phase. In addition to the increased frequency of potential degraders, such as Sphingobacterium, the network analysis revealed that C-DOM molecules distributed in high H/C (protein- and lipid-like molecules) were the main drivers structuring the bacterial community, inducing strong deterministic selection of the community assemblage and upregulating the metabolic capacity for contaminants. These findings provide strong evidence that estrogen biodegradation in eutrophic water may be facilitated by cyanobacterial blooms and provide a theoretical basis for ecological remediation of estrogen pollution.

Effect of colloidal fluorescence properties on the complexation of chloramphenicol and carbamazepine to the natural aquatic colloids

The complexation mechanism between pharmaceuticals and natural colloids is still uncertain due to the complexity, heterogeneity, and polydispersity of colloids. Therefore, this study investigated the effect of fluorescence properties on the complexation of chloramphenicol (CAP) and carbamazepine (CBZ) to the colloids from Poyang Lake Basin based on the multiple spectroscopic techniques and methods. Three-dimensional excitation-emission matrix fluorescence spectroscopy-parallel factor analysis results illustrated that two humic-like components and two protein-like components of colloids from the rivers and lakes were identified, with the much higher fluorescence intensity of the protein-like substance observed in lake samples. The protein-like substance decreased dramatically with the addition of CAP and CBZ, suggesting its higher binding capacity towards these drugs, especially for CBZ. In addition, the fluorescence quenching titration was proceeded to explore the binding mechanism between the colloids and the pharmaceuticals. Results of synchronous fluorescence spectra and two-dimensional correlation spectroscopy demonstrated that the fluorescence quenching effect occurred preferentially between the protein-like substances and the pharmaceuticals, with the stronger complexation for CBZ. Ryan-Weber model fitting results showed that the stability constant ranged from 4.02 to 5.04 with the higher binding capacity observed for the tryptophan-like substance. Combined, the fluorescence components in aquatic colloids could be significantly impacted the complexation of the pharmaceuticals. This study provides deep insights into the fate and pollution protection of pharmaceuticals.

Critical assessment of an equilibrium-based method to study the binding of waterborne organic contaminants to natural dissolved organic matter (DOM)

Dissolved organic matter (DOM) can play a major role in determining availability of pollutants to aquatic biota. Equilibrium dialysis is the most commonly used method to assess the interaction between DOM and organic contaminants. However, results obtained through this method can be affected by confounding factors linked to the diffusion of DOM through the membrane or the interaction of DOM and/or the compounds with the membrane itself. In this study, we propose an improved experimental approach, where highly hydrophilic cellulose-ester membranes with small molecular cut-off (100-500 Da) were used to overcome some of these hindrances. The performance of the method to determine the binding of a commonly used moderately hydrophobic herbicide (Isoproturon - ISU) with natural DOM was critically evaluated through a set of quality assurance criteria, across a range of DOM concentrations and pH conditions. DOM trans-membrane diffusion was prevented by the smaller pore size of the dialysis membrane. Good measurement reproducibility, mass balance closure, and successful trans-membrane equilibrium of ISU were obtained. ISU showed relatively low affinity with DOM (log K_DOC 1-2 L g^-1), which was significantly influenced by varying pH and DOM concentration. An alternative membrane may be needed for higher pH conditions as the greater adsorption effect blurred the observation of trans-membrane equilibrium and confounding mass balance closure. The paper makes recommendations on how to avoid measurement artefacts, while considering criteria for the expected mass distribution of compounds at equilibrium and for sorption onto the membrane and surfaces of the experimental units.

Characterization and biogeochemical implications of dissolved organic matter in aquatic environments

Dissolved organic matter (DOM) is viewed as one of the most chemically active organic substances on earth. It plays vital roles in the fate, bioavailability and toxicity of aquatic exogenous chemical species (e.g., heavy metals, organic pollutants, and nanomaterials). The characteristics of DOM such low concentrations, salt interference and complexity in aquatic environments and limitations of pretreatment for sample preparation and application of characterization techniques severely limit understanding of its nature and environmental roles. This review provides a characterization continuum of aquatic DOM, and demonstrate its biogeochemical implications, enabling in-depth insight into its nature and environmental roles. A synthesis of the effective DOM pretreatment strategies, comprising extraction and fractionation methods, and characterization techniques is presented. Additionally, the biogeochemical dynamics of aquatic DOM and its environmental implications are discussed. The findings indicate the collection of representative DOM samples from water as the first and critical step for characterizing its properties, dynamics, and environmental implications. However, various pretreatment procedures may alter DOM composition and structure, producing highly variable recoveries and even influencing its subsequent characterization. Therefore, complimentary use of various characterization techniques is highly recommended to obtain as much information on DOM as possible, as each characterization technique exhibits various advantages and limitations. Moreover, DOM could markedly change the physical and chemical properties of exogenous chemical species, influencing their transformation and mobility, and finally altering their potential bioavailability and toxicity. Several research gaps to be addressed include the impact of pretreatment on the composition and structure of aquatic DOM, molecular-level structural elucidation for DOM, and assessment of the effects of DOM dynamics on the fate, bioavailability and toxicity of exogenous chemical species.

Degradation of dissolved organic matter in effluent of municipal wastewater plant by a combined tidal and subsurface flow constructed wetland

Dissolved organic matter (DOM) is an important constituent of wastewater treatment plant (WWTP) effluent. A novel combined tidal and subsurface flow constructed wetland (TF-SSF-CW) of 90 L was constructed for a ten-month trial of advanced treatment of the WWTP effluent. Excitation emission matrix (EEM) fluorescence spectroscopy, parallel factor (PARAFAC) analysis and a two end-member mixing model were employed to characterize the composition and removal process of the effluent DOM (EfOM) from the WWTP. The results showed that the TF-SSF-CW performed an efficient EfOM removal with dissolved organic carbon (DOC) removal rate of 88% and dissolved organic nitrogen (DON) removal rate of 91%. Further analysis demonstrated that the EfOM consisted mainly of two protein moieties and two humic-like groups; protein moieties (76%) constituted the main content of EfOM in raw water and humic-like groups (57%) became the dominating contributor after treatment. The EfOM from the WWTP was mainly of aquatic bacterial origin and evolved to a higher proportion of terrigenous origin with higher humification in the TF-SSF-CW effluent. A common controlling treatment-related factor for determining the concentrations of the same kind of substances (protein groups or humic-like groups) was revealed to exist, and the ratio of removal rates between the same substances in treatment was calculated. Our study demonstrates that the TF-SSF-CW can be a novel and effective treatment method for the EfOM from WWTPs, and is helpful for understanding of the character of EfOM in wetland treatment.

Sorption Constant of Bisphenol A and Octylphenol Onto Size-Fractioned Dissolved Organic Matter Using a Fluorescence Method

Dissolved organic matter (DOM) is a complex and heterogeneous mixture ubiquitously present in aquatic systems. DOM affects octylphenol (OP) and bisphenol A (BPA) distribution, transport, bioavailability, and toxicity. This study investigated OP and BPA sorption constants, log K_COC, with three size-fractioned DOM. The molecular weights of the sized fractions were low molecular weight DOM (LDOM, <1 kDa), middle molecular weight DOM (MDOM, 1–10 kDa), and high molecular weight DOM (HDOM, 10 kDa–0.45 μm). The log K_COC ranged from 5.34 to 6.14 L/kg-C for OP and from 5.59 to 6.04 L/kg-C for BPA. The OP and BPA log K_COC values were insignificantly different (p = 0.37) and had a strong positive correlation (r = 0.85, p < 0.001). The OP and BPA LDOM log K_COC was significantly higher than the HDOM and MDOM log K_COC (p = 0.012 for BPA, p = 0.023 for OP). The average specific ultraviolet absorption (SUVA₂₅₄) values were 32.0 ± 5.4, 13.8 ± 1.0, and 17.9 ± 2.8 L/mg-C/m for LDOM, MDOM, and HDOM, respectively. The log K_COC values for both OP and BPA had a moderately positive correlation with the SUVA₂₅₄ values (r = 0.79–0.84, p < 0.002), which suggested the aromatic group content in the DOM had a positive impact on sorption behavior.

Contrasting the Optical Characterization of Dissolved Organic Matter in Water and Sediment from a Nascent River-Type Lake (Chongqing, China)

Carbon cycling in rivers is altered by the creation of impoundments through dam construction. This paper seeks to identify the source and composition of dissolved organic matter (DOM) in both water and sediment in Lake Longjing by contrasting the optical characterization of DOM. By comparing the dissolved organic carbon (DOC) concentrations, we show that the sediment (53.7 ± 16.6 mg/L) acts as a DOC source to the overlying water (23.1 ± 1.4 mg/L). The estimated DOC flux in the original reservoir region (88.3 mg m−2 d−1) is higher than that in the newly submerged region (26 mg m−2 d−1), whereas the latter has larger contribution to the DOC annual load because of its larger sediment area. Spectroscopic analysis suggested that pore waters had higher aromaticity and lower proportion of fresh DOM than those in surface waters and benthic overlying waters. Through Parallel Factor Analysis, four fluorescent components were identified, i.e., two terrestrial humic-like components, one protein-like, and one microbial humic-like. Spearman correlation and Non-Metric-Multidimensional Scaling (NMDS) analysis manifested that fluorescent DOM in surface sediments is mainly contributed by autochthonous source, the others by allochthonous source. Due to the high sensitivity of the fluorescent intensity of the protein-like component, it is a useful indicator to reveal the changes of source of DOM.

Priming effect of autochthonous organic matter on enhanced degradation of 17α-ethynylestradiol in water-sediment system of one eutrophic lake

Climate change and increasing eutrophication are expected to increase the release of autochthonous organic matter (OM) to sediments, where most contaminants are transformed or mineralized in freshwater lakes. This study sought to evaluate how cyanobacteria- and macrophyte-derived OM (COM and MOM) affected the microbial attenuation of 17α-ethinylestradiol (EE2) in the sediment from eutrophic Lake Taihu in China. In two months of water-sediment microcosm experiments, the input of COM and MOM both promoted EE2 degradation more strongly than humic acids, and the degradation efficiency was significantly and positively correlated with the cometabolism of increasing organic carbon in sediments (P < 0.001). The enhanced degradation was explained by responses of indigenous bacterial community to OM amendment as a priming effect. The immediate breakdown of biodegradable components such as proteinaceous substances in COM and MOM remarkably augmented the metabolic activity of bacteria in terms of the stimulated activity of extracellular enzymes including fluorescein diacetate and dehydrogenase, as well as the elevated production of proteins and polysaccharides in extracellular polymeric substances. In the meantime, the bacterial community composition was reshaped toward a more eutrophic state, leading to the clear upregulation of metabolic function genes of organic carbon and xenobiotics. Correlation-based network analysis further determined the strong facilitative coordination between the community members and the compositional variability of OM in the cometabolism. These results suggest that cyanobacterial blooms-dominated zones are potential hotspot areas for steroid estrogen attenuation, a finding of significance for the control and management of complex pollution in freshwater lakes.

Biodegradation of bisphenol compounds in the surface water of Taihu Lake and the effect of humic acids

Bisphenol analogues (BPs) pollution in the aquatic environment is increasingly a worldwide concern. There is an urgent need to understand the fate of BPs in the aquatic environment. In this study, we studied the biodegradation of eight BPs in Taihu Lake and discussed the effect of humic acid (HA), which was extracted from Taihu Lake sediment, on the disappearance of BPs. Under aerobic conditions, bisphenol AF (BPAF) and bisphenol S (BPS) were recalcitrant to biodegradation in the lake water. The half-lives for bisphenol F (BPF), bisphenol A (BPA), bisphenol B (BPB), bisphenol E (BPE), bisphenol Z (BPZ), and bisphenol M (BPM) ranged from 34 to 75 days in the Taihu Lake water collected in October 2018 and 12-72 days in that collected in May 2019. The biodegradation of BPs in summer was significantly higher than that in autumn. The presence of HA promoted the disappearance of BPs from Taihu Lake water by adsorbing and binding BPs. The disappearance rate of BPs accelerated with increasing concentrations of HA. However, the presence of HA decreased the biodegradation of BPs. When the concentration of HA was 10 mg/L, the single-adsorption capacities for BPS, BPA, BPB, BPM and BPAF were 3.18-10.33 mg/g in the Taihu Lake water with little desorption. BP adsorption and desorption in the BP mixtures were different from that in the single BPs. Competitive desorption occurred among the mixtures. The results of this study are the first to indicate the biodegradation of eight BPs in natural lake water and the possible effect of HA on the fate of BPs in the environment.

Experimental and modeling study of proton and copper binding properties onto fulvic acid fractions using spectroscopic techniques combined with two-dimensional correlation analysis

Fulvic acid (FA) significantly influences the bioavailability and fate of heavy metals in environments, while its acid-base characters and metal binding processes are still unclear. Here, spectroscopic techniques combined with multiple models (e.g., NICA-Donnan model) and two-dimensional correlation spectroscopy (2D COS) were applied to explore the proton and copper binding properties of FA sub-fractions (FA₃-FA₁₃). The charge densities, average contents of carboxylic and phenolic groups, average dissociation constants pKa₁ and pKa₂ of sub-fractions ranged 0-16 meq∙g∙C^-1, 5.03-9.58 meq∙g∙C^-1, 2.52-4.67 meq∙g∙C^-1, 4.15-4.33 and 8.52-9.72, respectively. FA sub-fractions had a relatively narrow distribution of carboxyl group and a broad distribution of phenolic group. FA sub-fractions also exhibited roughly two phenolic hydroxyl groups per every 1-3 phenyl rings. Differential absorbance spectra (DAS) derived Gaussian bands were associated to the inter-chromophore interactions, the changes of molecular conformations and functional groups with copper addition. Differential spectra slopes (DSlope_{275-295&325-375}) were more significant with higher copper concentration and copper amounts bonded to carboxylic groups. UV-Vis and fluorescence spectra with 2D heterospectral COS revealed the copper binding heterogeneities and sequential orders of chromophores and fluorophores, quantitatively confirming by the order of conditional stability constants (log K_Cu: 4.64-5.56). Salicylic-/polyhydroxyphenolic, hydroxyl and amino groups were strongly associated to the basic units for fluorophores. Sequential changes followed the order of humic-like→fulvic-like materials for FA₃/FA₅, humic-like→fulvic-like→tryptophan-like materials for FA₇, and humic-like→tryptophan-like→fulvic-like→tyrosine-like materials for FA₉/FA₁₃. Spectroscopic techniques combined with various models (especially for 2D COS) are beneficial to elucidate the binding heterogeneity and sensitivity for metal-organic matters at the functional group level.

Effects of dissolved organic carbon on desorption of aged phenanthrene from contaminated soils: A mechanistic study

Dissolved organic carbon (DOC) has a major influence upon sorption/desorption and transport of hydrophobic organic contaminants (HOCs) in soil environments. However, the molecular mechanisms of DOC sorption and its effects on aged HOC desorption in contaminated soils still remain largely unclear. Here, effects of three different DOC (one from commercial peat and two from biochars produced at 300 °C and 500 °C pyrolysis temperatures, respectively) and oxalate (as a reference) on abiotic desorption behavior of aged phenanthrene from three agricultural soils were investigated. Results showed that desorption of aged phenanthrene from soils was predominantly dependent on soil organic carbon content. The presence of DOC and oxalate resulted in higher desorption of phenanthrene compared to water alone, and the effects were positively related to soil organic carbon content and DOC/oxalate concentration. The facilitating effects of DOC were further increased during the second consecutive desorption, whereas oxalate had no such effect. Ultra-high-resolution Fourier transform-ion cyclotron resonance-mass spectrometry confirmed the molecular fractionation of DOC at the soil-water interface during DOC sorption. Specifically, the DOC molecules with O-rich moieties were preferentially adsorbed, whereas the molecules with phenolic and aromatic structures were selectively retained in the soil solutions through competitive displacement and co-sorption reactions during sorption. The enriched phenyl structures in the retained DOC facilitated its association with phenanthrene in the solutions and thus the release of phenanthrene from the soils. In contrast, oxalate replaced some organic carbon from the soils and thus released the associated phenanthrene into the solutions. Our findings highlight the importance of the molecular composition and structure of DOC for the desorption of phenanthrene in soil-water environments, which may help improve our understanding of the release and transport of organic compounds in the environments.

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.