Behavior of selected organophosphate flame retardants (OPFRs) and their influence on rhizospheric microorganisms after short-term exposure in integrated vertical-flow constructed wetlands (IVCWs)

High-throughput zebrafish screening reveals cardiotoxic effects of organophosphate flame retardants

The toxicity of organophosphorus flame retardants (OPFRs) remains poorly understood, despite their widespread environmental presence and potential risks to human and ecological health. This study aimed to characterize the cardiovascular developmental toxicity of OPFRs using a high-throughput zebrafish screening model. Over thirty representative OPFRs, classified into three major groups-alkyl, aryl, and halogenated-were evaluated. Our results demonstrated that aryl-substituted OPFRs, such as triphenyl phosphate (TPHP) and tris(3,5-dimethylphenyl) phosphate (TXP), exhibit significantly more potent cardiotoxic effects compared to alkyl- and halogenated-substituted OPFRs. Specifically, heart rate of zebrafish increased by 8.3% and 11.9%, and cardiac output increased by 30.8% and 39.9% for TPHP and TXP, respectively, at a concentration of 160 μg/L. Additionally, exposure to aryl-substituted compounds like TPHP resulted in notable developmental abnormalities, including pericardial edema and skeletal bending. Molecular descriptor analysis further identified a series of essential structural features, including estrogen receptor agonist activity and bioconversion rates, which are closely linked to the observed cardiotoxicity, thus providing a mechanistic explanation for these effects. These findings offer valuable insights into the molecular mechanisms underlying OPFRs toxicity, which could inform the development of safer flame retardant alternatives. Moreover, addressing the research gaps in translating zebrafish findings to other species and real-world ecological scenarios should be further concerned.

Tricresylphosphate isomers: A review of toxicity pathways

Synthetiс organophosphates are a large group of chemicals, annually produced by an industry with their further application as oil additives, flame retardants, plasticizers, warfare agents and insecticides for domestic use and in the control of vector-borne diseases. Consequently, organophosphates are often detected in the environment and human samples, which can have adverse effects on ecosystems and human health. This review aimed to summarize recent findings about different aspects of tricresyl phosphate mixture and separate isomers toxicity, including their impact on nervous, endocrine, and reproductive systems studied in animal models or in vitro. We also discuss the underlying molecular and cellular mechanisms involved in these processes, which comprise inhibition of neuropathy target esterase (NTE), overactivation of neuregulin1/ErbB and MAPK signaling pathways, impairment of glutamate signaling as well as interaction with nuclear hormone. Finally, we outline potential therapeutic targets and promising agents as important directions for future research.

Mechanistic insights into tris(2-chloroisopropyl) phosphate biomineralization coupled with lead (II) biostabilization driven by denitrifying bacteria

The ubiquity and persistence of organophosphate esters (OPEs) and heavy metal (HMs) pose global environmental risks. This study explored tris(2-chloroisopropyl)phosphate (TCPP) biomineralization coupled to lead (Pb2+) biostabilization driven by denitrifying bacteria (DNB). The domesticated DNB achieved synergistic bioremoval of TCPP and Pb2+ in the batch bioreactor (efficiency: 98 %).TCPP mineralized into PO43- and Cl-, and Pb2+ precipitated with PO43-. The TCPP-degrading/Pb2+-resistant DNB: Achromobacter, Pseudomonas, Citrobacter, and Stenotrophomonas, dominated the bacterial community, and synergized TCPP biomineralization and Pb2+ biostabilization. Metagenomics and metaproteomics revealed TCPP underwent dechlorination, hydrolysis, the TCA cycle-based dissimilation, and assimilation; Pb2+ was detoxified via bioprecipitation, bacterial membrane biosorption, EPS biocomplexation, and efflux out of cells. TCPP, as an initial donor, along with NO3-, as the terminal acceptor, formed a respiratory redox as the primary energy metabolism. Both TCPP and Pb2+ can stimulate phosphatase expression, which established the mutual enhancements between their bioconversions by catalyzing TCPP dephosphorylation and facilitating Pb2+ bioprecipitation. TCPP may alleviate the Pb2+-induced oxidative stress by aiding protein phosphorylation. 80 % of Pb2+ converted into crystalized pyromorphite. These results provide the mechanistic foundations and help develop greener strategies for synergistic bioremediation of OPEs and HMs.

Microbial community diversity of an integrated constructed wetland used for treatment of sewage

The microbial community diversity in Constructed Wetland System (CWS) plays a key role in the removal of pollutants from waste water. An integrated functional CWS developed at Neela Hauz Biodiversity Park, Delhi was selected to assess the diversity in composition and structure of microbial community diversity of sludge and sediment of CWS, based on metagenomic approach using 16S rRNA genes. The sediment showed higher diversity than sludge and both formed distinct clusters. The taxonomic structure of the microbial community of CWS is represented by 6,731 OTUs distributed among 2 kingdoms, 103 phyla, 227 classes, 337 orders, 320 families, 295 identified genera, and 84 identified species. The relative abundance of top 5 dominant phyla of sludge and sediment varied from 3.77% (Acidobacteria) to 35.33% (Proteobacteria) and 4.07% (Firmicutes) to 28.20% (Proteobacteria), respectively. The range of variation in relative abundance of top 5 dominant genera of sludge and sediment was 2.58% (Hyphomicrobium) to 6.61% (Planctomyces) and 2.47% (Clostridium) to 4.22% (Syntrophobacter), respectively. The rich microbial diversity of CWS makes it perform better in pollutants removal (59.91-95.76%) than other CWs. Based on the abundance values of taxa, the taxa are grouped under four frequency distribution classes-abundant (>20), common (10-19), rare (5-9), and very rare (1-4). The unique structure of microbial communities of integrated CWS is that the number of abundant taxa decreases in descending order of taxonomic hierarchy, while the number of rare and very rare taxa increases. For example, the number of abundant phyla was 14 and 21 in sludge and sediment, respectively and both communities have only 3 abundant genera each. This is in contrast to 4 and 17 very rare phyla in sludge and sediment, respectively and both the communities have 114 and 91 very rare genera, respectively. The outcomes of the study is that the integrated CWS has much higher microbial community diversity than the diversity reported for other CWs, and the rich diversity can be used for optimizing the performance efficiency of CWS in the removal of pollutants from waste water. Such structural diversity might be an adaptation to heterogeneous environment of CWS.

Emerging organic contaminants in the soil-plant-receptor continuum: transport, fate, health risks, and removal mechanisms

There is a lack of comprehensive reviews tracking emerging organic contaminants (EOCs) within the soil-plant continuum using the source-pathway-receptor-impact-mitigation (SPRIM) framework. Therefore, this review examines existing literature to gain insights into the occurrence, behaviour, fate, health hazards, and strategies for mitigating EOCs within the soil-plant system. EOCs identified in the soil-plant system encompass endocrine-disrupting chemicals, surfactants, pharmaceuticals, personal care products, plasticizers, gasoline additives, flame retardants, and per- and poly-fluoroalkyl substances (PFAS). Sources of EOCs in the soil-plant system include the land application of biosolids, wastewater, and solid wastes rich in EOCs. However, less-studied sources encompass plastics and atmospheric deposition. EOCs are transported from their sources to the soil-plant system and other receptors through human activities, wind-driven processes, and hydrological pathways. The behaviour, persistence, and fate of EOCs within the soil-plant system are discussed, including sorption, degradation, phase partitioning, (bio)transformation, biouptake, translocation, and bioaccumulation in plants. Factors governing the behaviour, persistence, and fate of EOCs in the soil-plant system include pH, redox potential, texture, temperature, and soil organic matter content. The review also discusses the environmental receptors of EOCs, including their exchange with other environmental compartments (aquatic and atmospheric), and interactions with soil organisms. The ecological health risks, human exposure via inhalation of particulate matter and consumption of contaminated food, and hazards associated with various EOCs in the soil-plant system are discussed. Various mitigation measures including removal technologies of EOCs in the soil are discussed. Finally, future research directions are presented.

Development and trends of constructed wetland substrates over the past 30 years: a literature visualization analysis based on CiteSpace

Constructed wetland substrates (CWSs) have received considerable attention owing to their importance in adsorbing and degrading pollutants, providing growth attachment points for microorganisms, and supporting wetland plants. There are differences in the configurations and functions of constructed wetlands (CWs) for treating different water bodies and sewage, resulting in a wide variety of substrates. Research on the application and mechanism of CWSs is not sufficiently systematic. Therefore, the current research advancements and hotspots must be identified. Hence, we used CiteSpace to analyze 1955 English publications from the core collection database of the Web of Science to assess the current state of the CWS research field. Based on the cooperative network analysis, the roles of various countries, institutions, and authors in research on CWSs were reviewed. Keyword co-occurrence and cluster analyses were used to discuss the transformation of CWSs from removing traditional pollutants to emerging pollutants and the transition from incorporating natural substrates to artificial substrates. Finally, we underscored the need for more emphasis to be placed on the collocation and application of the CWSs at different latitudes. Furthermore, the substrate micro-interface process and its effects on the interaction patterns of pollutants and microorganisms should be thoroughly investigated to provide theoretical guidance for the development of wetland applications and mechanisms.

Synthesis of EDTA-cysteine-β-cyclodextrin for the removal of organophosphate flame retardants (OPFR) from sediments and soil samples from the Buffalo River Estuary, Eastern Cape of South Africa

Due to the growing water and environmental pollution worldwide, it is important to develop new effective materials for the remediation of sediments, soil and water contaminated with organic pollutants including flame retardants. In this study, a new soluble and hydrophilic polymer material containing ethylenediaminetetraacetic acid (EDTA), cysteine and beta cyclodextrin (β-CD) depicted as EDTA-Cysteine-β-Cyclodextrin was prepared for the removal of organophosphate flame retardants (OPFRs) from simulated sediment and soil samples and those collected from the Buffalo River Estuary in East London, Eastern Cape Province of South Africa. The β-CD was modified using cysteine and EDTA. The EDTA-Cysteine-β-Cyclodextrin was characterized by Fourier transform infrared (FTIR), scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDX). The results show that a non-porous spherical and bubble shaped material was synthesized. For the adsorption study, different contaminants' concentrations, solution pH, adsorbent dose and contact time were varied to ascertain the optimum conditions for the removal of OPFRs from soil and sediment. The removal of OPFRs was highly dependent on pH, adsorbent dose, concentration and contact time of the adsorption process. The optimum pH, contact time, OPFRs concentration and adsorbent dose were 3, 120 min, 60 mM and 5 mL, respectively with average adsorption percentage of 97.13 ± 14.04 %. The results proved that this newly developed polymer can decontaminate sediments and soil. The EDTA-Cysteine-β-Cyclodextrin gave promising possibilities for practical application for the remediation of OPFRs from sediment and soil samples through adsorption process.

Uptake mechanism, translocation, and transformation of organophosphate esters in water hyacinth (Eichhornia crassipes): A hydroponic study

Owing to their dominant wastewater origin, bioavailability, and toxicity, the occurrence and behavior of organophosphate esters (OPEs) in aquatic systems have attracted considerable attention over the past two decades. Aquatic plants can accumulate and metabolize OPEs in water, thereby playing an important role in their behavior and fate in waterbodies. However, their uptake, translocation and transformation mechanisms in plants remain incompletely characterized. We investigated the accumulation and transformation of OPEs in water hyacinth (Eichhornia crassipes) through a series of hydroponic experiments using three representative OPEs, tris(2-chloroethyl) phosphate (TCEP), tris(2-butoxyethyl) phosphate (TBEP), and triphenyl phosphate (TPP). These OPEs can not only be adsorbed onto and enter plant roots via passive diffusion pathways, which are facilitated by anion channels and/or aquaporins, but also can return to the solution when concentration gradients exist. After entry, hydrophilic TCEP showed a dominant distribution in the cell sap, strong acropetal transportability, and rapid translocation rate, whereas hydrophobic TPP was mostly retained in the root cell wall and therefore demonstrated weak acropetal transportability; TBEP with moderate hydrophilicity remained in the middle. All these OPEs can be transformed into diesters, which presented higher proportions in the cell sap and therefore have stronger acropetal transferability than their parent OPEs. TCEP exhibits the lowest biodegradability, followed by TPP and TBEP. These OPEs exerted apparent effects on plant growth, photosynthesis, and the diversity and composition of the rhizosphere microbial community.

Aerobic Microbial Transformation of Fluorinated Liquid Crystal Monomer: New Pathways and Mechanism

Fluorinated liquid crystal monomers (FLCMs) have been suggested as emerging contaminants, raising global concern due to their frequent occurrence, potential toxic effects, and endurance capacity in the environment. However, the environmental fate of the FLCMs remains unknown. To fill this knowledge gap, we investigated the aerobic microbial transformation mechanisms of an important FLCM, 4-[difluoro(3,4,5-trifluorophenoxy)methyl]-3, 5-difluoro-4'-propylbiphenyl (DTMDPB), using an enrichment culture termed as BG1. Our findings revealed that 67.5 ± 2.1% of the initially added DTMDPB was transformed in 10 days under optimal conditions. A total of 14 microbial transformation products obtained due to a series of reactions (e.g., reductive defluorination, ether bond cleavage, demethylation, oxidative hydroxylation and aromatic ring opening, sulfonation, glucuronidation, O-methylation, and thiolation) were identified. Consortium BG1 harbored essential genes that could transform DTMDPB, such as dehalogenation-related genes [e.g., glutathione S-transferase gene (GST), 2-haloacid dehalogenase gene (2-HAD), nrdB, nuoC, and nuoD]; hydroxylating-related genes hcaC, ubiH, and COQ7; aromatic ring opening-related genes ligB and catE; and methyltransferase genes ubiE and ubiG. Two DTMDPB-degrading strains were isolated, which are affiliated with the genus Sphingopyxis and Agromyces. This study provides a novel insight into the microbial transformation of FLCMs. The findings of this study have important implications for the development of bioremediation strategies aimed at addressing sites contaminated with FLCMs.

An overview of current knowledge on organophosphate di-esters in environment: Analytical methods, sources, occurrence, and behavior

Organophosphate di-esters (di-OPEs) are highly related to tri-OPEs. The presence of di-OPEs in the environment has gained global concerns, as some di-OPEs are more toxic than their respective tri-OPE compounds. In this study, current knowledge on the analytical methods, sources, environmental occurrence, and behavior of di-OPEs were symmetrically reviewed by compiling data published till March 2023. The determination of di-OPEs in environmental samples was exclusively achieved with liquid chromatography mass spectrometry operated in negative mode. There are several sources of di-OPEs, including industrial production, biotic and abiotic degradation from tri-OPEs under environmental conditions. A total of 14 di-OPE compounds were determined in various environments, including dust, sediment, sludge, water, and atmosphere. The widespread occurrence of di-OPEs suggested that human and ecology are generally exposed to di-OPEs. Among all environmental matrixes, more data were recorded for dust, with the highest concentration of di-OPEs up to 32,300 ng g-1. Sorption behavior, phase distribution, gas-particle partitioning behavior was investigated for certain di-OPEs. Suggestions on future studies in the perspective of human exposure to and environmental behavior of di-OPEs were proposed.

Metagenomic insights into the mechanisms of triphenyl phosphate degradation by bioaugmentation with Sphingopyxis sp. GY

Biodegradation of triphenyl phosphate (TPHP) by Sphingopyxis sp. GY was investigated, and results demonstrated that TPHP could be completely degraded in 36 h with intracellular enzymes playing a leading role. This study, for the first time, systematically explores the effects of the typical brominated flame retardants, organophosphorus flame retardants, and heavy metals on TPHP degradation. Our findings reveal that TCPs, BDE-47, HBCD, Cd and Cu exhibit inhibitory effects on TPHP degradation. The hydrolysis-, hydroxylated-, monoglucosylated-, methylated products and glutathione (GSH) conjugated derivative were identified and new degradation pathway of TPHP mediated by microorganism was proposed. Moreover, toxicity evaluation experiments indicate a significant reduction in toxicity following treatment with Sphingopyxis sp. GY. To evaluate its potential for environmental remediation, we conducted bioaugmentation experiments using Sphingopyxis sp. GY in a TPHP contaminated water-sediment system, which resulted in excellent remediation efficacy. Twelve intermediate products were detected in the water-sediment system, including the observation of the glutathione (GSH) conjugated derivative, monoglucosylated product, (OH)2-DPHP and CH3-O-DPHP for the first time in microorganism-mediated TPHP transformation. We further identify the active microbial members involved in TPHP degradation within the water-sediment system using metagenomic analysis. Notably, most of these members were found to possess genes related to TPHP degradation. These findings highlight the significant reduction of TPHP achieved through beneficial interactions and cooperation established between the introduced Sphingopyxis sp. GY and the indigenous microbial populations stimulated by the introduced bacteria. Thus, our study provides valuable insights into the mechanisms, co-existed pollutants, transformation pathways, and remediation potential associated with TPHP biodegradation, paving the way for future research and applications in environmental remediation strategies.

Exploring the resilience of constructed wetlands to harmful algal blooms disturbances: A study on microbial response mechanisms

Constructed wetlands (CWs) have emerged as a promising environmentally sustainable technique for wastewater treatment. However, the susceptibility of CWs to disturbances caused by harmful algal blooms (HABs) raises concerns. This study aimed to investigate the impact of HABs on the pollutants' removal performance of CWs and the response of rhizosphere microbial community. Results revealed that CWs possessed an adaptive capacity that enabled them to recover caused by HABs. The rhizosphere was found to stimulate the occurrence of Acinetobacter, which played a critical role to help resist HABs disturbance. This study also observed an increased dissimilatory nitrate reduction metabolic pathway which promoted denitrification and enhanced the nitrogen removal efficiency of CWs. Additionally, the structural equation model further suggested that dissolved oxygen exerted a significant influence on the microbial activities and then affected the pollutants removal performance. Overall, our findings shed light on the mechanism for CW stability maintenance during HABs disturbance.

Uptake, accumulation, and translocation of organophosphate esters and brominated flame retardants in water hyacinth (Eichhornia crassipes): A field study

Mechanisms underlying the plant uptake, accumulation, and translocation of organophosphate esters (OPEs) and brominated flame retardants (BFRs) in field environments remain ambiguous. To better understand these processes, we selected a typically polluted river with steady flow and rampant water hyacinth (Eichhornia crassipes) and investigated 25 OPEs and 23 BFRs in 24 sets of matched water-plant samples. Both OPEs and BFRs showed high or ultra-high levels in field water hyacinths, statistically positive water-plant/root concentration correlations, and dominant distributions in the roots. Passive root uptake was the dominant route for OPEs and BFRs to enter the water hyacinth. Both OPEs and BFRs in water hyacinth exhibited acropetal translocation from the root and possible basipetal translocation from the leaf. The accumulation and translocation of OPEs in water hyacinth were significantly affected by their substituents and structures, including the chlorination degree, alkyl chain length, side chain, and methylation degree of aryl-substituted OPEs. The translocation of BFRs in water hyacinth also showed close association with their bromination degree, but their accumulation in roots showed anomaly, indicating possible transformations. Overall, the enrichment and behavior of OPEs and BFRs in water hyacinth seemed to be mainly controlled by physicochemical parameters. OPE/BFR concentrations in total suspended particulate (TSP), TSP-associated organic carbon content, TSP concentration, and plant biomass all showed significant effects on their root accumulation and translocations in water hyacinth. This study provides rare field evidences and novel insights into the basipetal translocation of OPEs and BFRs in plants.

Analysis and subcellular distribution of organophosphate esters (OPEs) in rice tissues

Recent studies have identified the ability of plants to uptake and translocate organophosphate esters (OPEs) within cells. In response to the increasing interest in OPEs and their occurrence in paddy fields and rice, the current study aimed to present an effective and sensitive GC-MS based methodology for quantitative determination of 11 OPEs with octanol-water coefficients ranging from 1.6 to 10. Rice was sonicated with hexane and dichloromethane, and fractionated on two columns: one consisting of neutral alumina, and neutral silica, and the other consisting of graphitized carbon black. Method precision was validated using spiked rice (n = 30) and procedural blanks (n = 9). The mean recovery of matrix spikes for all target OPEs were within 78-110% with relative standard deviation lower than 25%, with a few exceptions. This method was applied to process the wild rice (O. sativa) in which tri-n-propyl phosphate was the dominant targeted OPE. The recoveries of surrogate standards were 81 ± 17% for d₁₂- tris(2-chloroethyl) phosphate and 95 ± 8.8% for ¹³C₁₂- triphenyl phosphate. The developed method was further used to examine the recoveries of target OPEs in the subcellular structure of rice tissues, including cell wall, cell organelles, cell water-soluble fractions, and cell residue. Recoveries of most target OPEs were in the range of 50-150%; however, ion enhancement was observed for four OPEs in root and shoot tissues. Hydrophobic OPEs accumulated in the cell wall, cell residue, and cell organelles while chlorinated OPEs mainly distributed in the cell water-soluble fraction. These results provide new insight for the ecological risk assessment of OPEs in an important food staple.

Enhancement of micropollutant biotransformation by adding manganese sand in constructed wetlands

Recent investigations have shown that the addition of manganese (Mn) sand to constructed wetlands (i.e., Mn-amended CWs) can improve the performance of organic micropollutants (MPs) removal. In addition to the direct oxidation and adsorption of Mn oxides, the indirect role of Mn oxides in MP biotransformation is crucial to the removal of MPs but has seldom been referred to. Herein, we constructed lab-scale CWs with or without the addition of natural Mn sand (∼35% Mn oxides) to decipher the influence of Mn oxides on the biotransformation of the six selected MPs which commonly existed in the wastewater. The experimental results showed that the addition of Mn sand to CWs can improve the removal of MPs (8.48% atrazine, 13.16% atenolol, and 6.27% sulfamethoxazole [pairwise Wilcoxon test p < 0.05]). Combining the detection of transformation products and metagenomic sequencing, we found that the enhanced removal of atrazine in the Mn-amended CWs was mainly due to the bioaugmented hydroxylation process. The enrichment of biotransformation-related genes and associated microbes of atenolol and sulfamethoxazole in Mn-amended CWs indicated that the addition of Mn sand to CWs can strengthen the biotransformation of MPs. Furthermore, we found that these MP-biodegrading microbes were widely present in the full-scale CWs. Overall, our research provides fundamental information and insights for further application of Mn-amended CWs in MP removal.

Organophosphate Esters (OPEs) Flame Retardants in Water: A Review of Photocatalysis, Adsorption, and Biological Degradation

As a substitute for banned brominated flame retardants (BFRs), the use of organophosphate esters (OPEs) increased year by year with the increase in industrial production and living demand. It was inevitable that OPEs would be discharged into wastewater in excess, which posed a great threat to the health of human beings and aquatic organisms. In the past few decades, people used various methods to remove refractory OPEs. This paper reviewed the photocatalysis method, the adsorption method with wide applicability, and the biological method mainly relying on enzymolysis and hydrolysis to degrade OPEs in water. All three of these methods had the advantages of high removal efficiency and environmental protection for various organic pollutants. The degradation efficiency of OPEs, degradation mechanisms, and conversion products of OPEs by three methods were discussed and summarized. Finally, the development prospects and challenges of OPEs’ degradation technology were discussed.

Translocation and metabolism of tricresyl phosphate in rice and microbiome system: Isomer-specific processes and overlooked metabolites

Tricresyl phosphate (TCP) is extensively used organophosphorus flame retardants and plasticizers that posed risks to organisms and human beings. In this study, the translocation and biotransformation behavior of isomers tri-p-cresyl phosphate (TpCP), tri-m-cresyl phosphate (TmCP), and tri-o-cresyl phosphate (ToCP) in rice and rhizosphere microbiome was explored by hydroponic exposure. TpCP and TmCP were found more liable to be translocated acropetally, compared with ToCP, although they have same molecular weight and similar K_ow. Rhizosphere microbiome named microbial consortium GY could reduce the uptake of TpCP, TmCP, and ToCP in rice tissues, and promote rice growth. New metabolites were successfully identified in rice and microbiome, including hydrolysis, hydroxylated, methylated, demethylated, methoxylated, and glucuronide- products. The methylation, demethylation, methoxylation, and glycosylation pathways of TCP isomers were observed for the first time in organisms. What is more important is that the demethylation of TCPs could be an important and overlooked source of triphenyl phosphate (TPHP), which broke the traditional understanding of the only manmade source of toxic TPHP in the environment. Active members of the microbial consortium GY during degradation were revealed and metagenomic analysis indicated that most of active populations contained TCP-degrading genes. It is noteworthy that the strains and function genes in microbial consortium GY that responsible for TCP isomers' transformation were different. These results can improve our understanding of the translocation and transformation of organic pollutant isomers in plants and rhizosphere microbiome.

Use of constructed wetlands to prevent overloading of wastewater treatment plants

The fluctuation in the number of people in tourist areas affects the wastewater quality and quantity. Constructed wetlands (CWs) aim to simulate physical, chemical, and biological processes occurring in natural environments for wastewater treatment and are considered a sustainable system. The current study aimed at evaluating the effectiveness of in-vessel CWs for supporting the wastewaters treatment plants in periods of overloading. Such approach can be quickly implementable, economic, and the CWs can be fast regenerated in the framework of sustainable good practices. Three pilot scale CWs were prepared in as many containers layering 10 cm of gravel, 60 cm of sand and 10 cm of gravel, and placing pieces of giant reed rhizomes in the upper layers. The bottom of each CW had a tap, and CWs were irrigated with a real municipal sewage three times a week. Before each new irrigation, the tap was opened, and the effluent collected for determining gross parameters, elemental composition, and contaminants of emerging concern (CECs). CWs significantly reduced almost all gross parameters considered and half the CECs, except for a couple of metabolites of corresponding parental compounds. With regards to the potentially toxic elements, all reduced their concentration from the influents to the effluents. The results of this study were promising and highlighted good efficiency of constructed wetlands as pre-treatment of real municipal sewage to reduce the overloading of the wastewater treatment plant.

Advances in microbial electrochemistry-enhanced constructed wetlands

Constructed wetland (CW) is an effective ecological technology to treat water pollution and has the significant advantages of high impact resistance, simple construction process, and low maintenance cost. However, under extreme conditions such as low temperature, high salt concentration, and multiple types of pollutants, some bottlenecks exist, including the difficulty in improving operating efficiency and the low pollutant removal rate. Microbial electrochemical technology is an emerging clean energy technology and has the similar structure and pollutant removal mechanism to CW. Microbial electrochemistry combined with CW can improve the overall removal effect of pollutants in wetlands. This review summarizes characterization methods of microbial electrochemistry-enhanced constructed wetland systems, construction methods of different composite systems, mechanisms of single and composite systems, and removal effects of composite systems on different pollutants in water bodies. Based on the shortcomings of existing studies, the potential breakthroughs in microbial electrochemistry-enhanced constructed wetlands are proposed for developing the optimization solution of constructed wetlands.

Occurrence, seasonal variation, potential sources, and risks of organophosphate esters in a cold rural area in Northeast China

Organophosphate esters (OPEs) in the environment have been the focus of increasing attention due to their ubiquity and potential toxicity. However, there is little information on the occurrence and characteristics of OPEs in rural areas, especially those with cold year-round temperatures and frozen soil in winter. In this study, environmental samples were collected, in summer and winter, from villages and towns in Northeast China differing in the types and intensities of their anthropogenic activities. The samples were analyzed for 12 OPEs. The results showed the widespread presence of alkyl-OPEs, Cl-OPEs, and aryl-OPEs in the water, soil, snow, and ice of the study sites. In summer, tris(1-chloro-2-propyl) phosphate (TCPP) and tris(2-chloroethyl) phosphate (TCEP) were the primary compounds in water and soil, respectively. The ∑₁₂OPE concentration in three villages varied from 46.26 to 257.37 ng/L in water, and from 6.62 to 19.46 ng/g in soils. The ∑₁₂OPE concentrations in water were lower in winter than summer, but conversely, ∑₁₂OPE concentrations in frozen soils in winter were higher than those in soils in summer. In winter, there was a shift in the predominant OPEs in water and frozen soils, with dominance of TCEP and complex compounds, respectively. Obvious seasonal characteristics of the potential sources and ecological risks of OPEs in these areas were also determined, with more complex sources of OPEs seen in summer than winter. In summer, only 2-ethylhexyl diphenyl phosphate (EHDPP) in water posed a potential risk, while in summer and, especially, in winter, EHDPP and tris(2-ethylhexyl) phosphate posed potential risks in soils. The high ∑₁₂OPE concentration in snow (56.77 ng/L) implied that wet deposition can amplify OPEs in other environmental compartments. This is the first systematic report on OPEs in a cold rural area. Our findings highlight the need for seasonal monitoring of OPEs in similar areas.

Suspect and nontarget screening of known and unknown organophosphate esters (OPEs) in soil samples

Ninety-five soil samples (n = 95) were analyzed using an integrated suspect and non-target organophosphate ester (OPE) screening strategy. This suspect and non-target screening strategy allowed us to fully or tentatively identify 26 OPEs or OPE-like substances. Among these 26 newly identified contaminants, bisphenol A bis(diphenylphosphate) (BPABDP) exhibited the highest detection frequency of 83.2 %, with a concentration range of ND - 385 ng/g dry weight (dw). We also observed that BPABDP was significantly correlated with all other OPEs (p < 0.001 in all pairs), suggesting that BPABDP is widely used as a plasticizer and flame retardant in various commercial products. Another interesting finding was the discovery of four novel OPE structures with tentatively proposed chemical structures. Among these four non-target OPEs, (tert-butyl) phenyl bis(2,4-di-tert-butylphenyl) phosphate (TBPBDTBPP) shared a backbone structure very similar to that of the well-known OPE, tris(2,4-di-tert-butylphenyl) phosphate (TDTBPP). Detection frequency of this newly discovered OPE was high, up to 69.5 %, and it was significantly correlated with isodecyl diphenyl phosphate (IDDP), BPABDP, diphenyl 2-isopropylphenyl phosphate (2IPPDPP), and tricresyl phosphate (TCrP, p < 0.05 in all pairs), respectively. This study reported the most comprehensive suite of OPEs in soil samples, and 16 out of them were recognized in soil for the first time.

Biodegradation of tricresyl phosphates isomers by a novel microbial consortium and the toxicity evaluation of its major products

A novel microbial consortium ZY1 capable of degrading tricresyl phosphates (TCPs) was isolated, it could quickly degrade 100% of 1 mg/L tri-o-cresyl phosphate (ToCP), tri-p-cresyl phosphate (TpCP) and tri-m-cresyl phosphate (TmCP) within 36, 24 and 12 h separately and intracellular enzymes occupied the dominated role in TCPs biodegradation. Additionally, triphenyl phosphate (TPHP), 2-ethylhexyl diphenyl phosphate (EHDPP), bisphenol-A bis (diphenyl phosphate) (BDP), tris (2-chloroethyl) phosphate (TCEP) and tris (1-chloro-2-propyl) phosphate (TCPP) could also be degraded by ZY1 and the aryl-phosphates was easier to be degraded. The TCPs reduction observed in freshwater and seawater indicated that high salinity might weak the degradability of ZY1. The detected degradation products suggested that TCPs was mainly metabolized though the hydrolysis and hydroxylation. Sequencing analysis presented that the degradation of TCPs relied on the cooperation between sphingobacterium, variovorax and flavobacterium. The cytochrome P450/NADPH-cytochrome P450 reductase and phosphatase were speculated might involve in TCPs degradation. Finally, toxicity evaluation study found that the toxicity of the diesters products was lower than their parent compound based on the generation of the intracellular reactive oxygen (ROS) and the apoptosis rate of A549 cell. Taken together, this research provided a new insight for the bioremediation of TCPs in actual environment.

A Review on Microorganisms in Constructed Wetlands for Typical Pollutant Removal: Species, Function, and Diversity

Constructed wetlands (CWs) have been proven as a reliable alternative to traditional wastewater treatment technologies. Microorganisms in CWs, as an important component, play a key role in processes such as pollutant degradation and nutrient transformation. Therefore, an in-depth analysis of the community structure and diversity of microorganisms, especially for functional microorganisms, in CWs is important to understand its performance patterns and explore optimized strategies. With advances in molecular biotechnology, it is now possible to analyze and study microbial communities and species composition in complex environments. This review performed bibliometric analysis of microbial studies in CWs to evaluate research trends and identify the most studied pollutants. On this basis, the main functional microorganisms of CWs involved in the removal of these pollutants are summarized, and the effects of these pollutants on microbial diversity are investigated. The result showed that the main phylum involved in functional microorganisms in CWs include Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. These functional microorganisms can remove pollutants from CWs by catalyzing chemical reactions, biodegradation, biosorption, and supporting plant growth, etc. Regarding microbial alpha diversity, heavy metals and high concentrations of nitrogen and phosphorus significantly reduce microbial richness and diversity, whereas antibiotics can cause large fluctuations in alpha diversity. Overall, this review can provide new ideas and directions for the research of microorganisms in CWs.

Effects of temperature and relative humidity on soil-air partition coefficients of organophosphate flame retardants and polybrominated diphenyl ethers

The soil-air partition coefficients (K_SA) of polybrominated diphenyl ethers (PBDEs) and organophosphate flame retardants (OPFRs) is important for determining their fate in soil and air media. However, K_SA values of OPFRs and PBDEs are not available from the current literature, and the effects of environmental factors such as temperature and relative humidity (RH) on K_SA values are not clear. In this study, a solid-phase fugacity meter was used to measure the K_SA values of PBDEs and OPFRs at different temperatures (25, 30, 35, 40, and 45 °C) and relative humidity (RH) conditions (<3 and 100% RH), the relationships between K_SA and octanol-air partition coefficients (K_OA) for OPFRs and PBDEs were analyzed. The results showed that an increase in temperature and RH resulted in a decrease of all K_SA values for PBDEs and OPFRs. Furthermore, the effects of RH on the soil-air partitioning behavior of PBDEs were larger than that of OPFRs. In addition, a significant correlation (p < 0.0001) was observed between log K_SA and log K_OA. The experimental K_SA values of OPFRs and PBDEs were quite different from the predicted K_SA, when calculated with their K_OA values. Overall, this study provides a better understanding for predicting the behavior and fate of OPFRs and PBDEs in soil-air systems.

Effects of sulfamethoxazole on nitrogen removal and molecular ecological network in integrated vertical-flow constructed wetland

Response of nitrogen removal efficiency and microbial interactions to organic pollution has been a major issue in wastewater treatment system. However, the nitrogen removal efficiency and interactions among microbial community under antibiotics press is still unclear. Thus, the effect of sulfamethoxazole (SMX) on nitrogen removal and microbial responses of IVCWs was investigated through recorded the nitrogen removal efficiency before and after adding SMX and random matrix theory (RMT)-based network analysis. Results showed that better NH₄⁺-N removal (>90%) after a long period of operation were achieved in IVCWs, but NO₃^--N was accumulated. However, nitrate removal rates were significantly increased after long-term exposure (60 d) to 100 μgL^-1 SMX (from 27.35% to 35.57%) with relatively high SMX removal (53.50%). Surprisingly, the ammonia nitrogen removal rate (90.07-92.70%) were not significantly affected by SMX in IVCWs. Moreover, the bacterial richness was decreased and the bacterial community structures were altered by the presence of SMX, especially those of nitrogen-transforming microorganisms. Molecular ecological network analysis suggested that SMX had positive influences on denitrifying bacteria interactions but reduced the network complexity and microbial interactions on whole molecular network, and among-module connections were weakened obviously at SMX.

Newly discovered bis-(2-ethylhexyl)-phenyl phosphate (BEHPP) was a ubiquitous contaminant in surface soils from a typical region, South China

The organophosphate ester (OPE), bis-(2-ethylhexyl)-phenyl phosphate (BEHPP), was recently identified as an abundant contaminant in indoor dust samples; however, its pollution status in other matrices remains unknown. Here, n = 95 surface soil samples were collected from a prefecture-level city (hereafter referred to as D city) in South China during 2019, and further analyzed to accurately determine the concentrations of BEHPP and eight other OPEs, including tris(2-chloroethyl) phosphate (TCEP), tris(1,3-dichloro-isopropyl) phosphate (TDCIPP), triphenyl phosphate (TPHP), tris(2-butoxyethyl) phosphatetris (TBOEP), 2-ethylhexyl diphenyl phosphate (EHDPP), tris(2-ethylhexyl) phosphate (TEHP), 4-biphenylol diphenyl phosphate (BPDPP), and tris(2-biphenyl) phosphate (TBPHP). BEHPP was detected in all six functional areas (agricultural, scenic, commercial, industrial, and residential areas) of this region, and exhibited a high detection frequency of 67.4%, with a median concentration of 0.455 ng/g dry weight (DW range: nd-7.05 ng/g dw), regardless of the functional area. Samples from commercial, industrial, and residential areas contained significantly greater BEHPP concentrations than those from agricultural and scenic areas. Furthermore, strong and statistically significant correlations were observed between BEHPP and other OPE congeners, particularly for TEHP (r = 0.764, p < 0.001), TBOEP (r = 0.687, p < 0.001), and TPHP (r = 0.709, p < 0.001), indicating that BEHPP may have similar commercial applications and sources to these compounds in surface soil. Collectively, this study provides the first evidence of the presence of BEHPP in soil samples, and indicates that this emerging contaminant is widely distributed across all five functional areas of a typical region (South China).

Insights into the Occurrence, Fate, and Impacts of Halogenated Flame Retardants in Municipal Wastewater Treatment Plants

Halogenated flame retardants (HFRs) have been extensively used in various consumer products and many are classified as persistent organic pollutants due to their resistance to degradation, bioaccumulation potential and toxicity. HFRs have been widely detected in the municipal wastewater and wastewater treatment solids in wastewater treatment plants (WWTPs), the discharge and agricultural application of which represent a primary source of environmental HFRs contamination. This review seeks to provide a current overview on the occurrence, fate, and impacts of HFRs in WWTPs around the globe. We first summarize studies recording the occurrence of representative HFRs in wastewater and wastewater treatment solids, revealing temporal and geographical trends in HFRs distribution. Then, the efficiency and mechanism of HFRs removal by biosorption, which is known to be the primary process for HFRs removal from wastewater, during biological wastewater treatment processes, are discussed. Transformation of HFRs via abiotic and biotic processes in laboratory tests and full-scale WWTPs is reviewed with particular emphasis on the transformation pathways and functional microorganisms responsible for HFRs biotransformation. Finally, the potential impacts of HFRs on reactor performance (i.e., nitrogen removal and methanogenesis) and microbiome in bioreactors are discussed. This review aims to advance our understanding of the fate and impacts of HFRs in WWTPs and shed light on important questions warranting further investigation.

Genomic studies on natural and engineered aquatic denitrifying eco-systems: A research update

Excess nitrogenous compounds in municipal or industrial wastewaters can stimulate growth of denitrifying bacteria, in return, to convert potentially hazardous nitrate to inorganic nitrogen gas. To explore the community structure, distributions and succession of functional strains, and their interactions with other microbial communities, contemporary studies were performed based on detailed genomic analysis. This mini-review updated contemporary genomic studies on denitrifying genes in natural and engineered aquatic systems, with the constructed wetlands being the demonstrative system for the latter. Prospects for the employment of genomic studies on denitrifying systems for process design, optimization and development of novel denitrifying processes were discussed.

Effects of matrix modification and bacteria amendment on the treatment efficiency of municipal tailwater pollutants by modified vertical flow constructed wetland

Although vertical flow constructed wetland (VFCW) has great potentials for degradation of water contaminants, traditional VFCW has limited removal efficiencies for pollutants. This study constructed three sets of modified VFCW systems, including VFCW-A with matrix-modification using mixture of biochar and activated carbon, VFCW-B with microbial amendment using denitrifying bacteria, and VFCW-C with combined treatments of both. Their removal efficiencies for various pollutants in synthetic municipal tailwater were investigated. Results showed that the removal efficiencies for NH₄-N, NO₃-N, total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) by VFCW-C were higher than VFCW-B throughout the experimental period, indicating that matrix-modification could improve the VFCW performance. The higher removal efficiencies for TN, TP, and COD by VFCW-C than VFCW-A also suggested the effectiveness of microbial amendment in VFCW. However, the improved removal for NO₃-N by VFCW-C over VFCW-A became less obvious at later operation stage due to insufficient carbon source. All three VFCWs achieved their best removal efficiency when carbon source was supplemented at CH₃COO^-/TN ratio of 0.5. Our study suggested that the combined treatment of matrix-modification using biochar/activated carbon mixture and microbial amendment using denitrifying bacteria could effectively enhance the treatment efficiency of VFCW systems for tailwater pollutants from sewage plant.

A pilot study of organophosphate esters in surface soils collected from Jinan City, China: implications for risk assessments

Data monitoring is a prerequisite for the occurrence of organophosphate esters (OPEs) in the soil environment in light of their potential toxicity, bioaccumulation, and environmental persistence. In this study, we determined the concentrations and profiles of OPEs in surface soils collected from Jinan City, East China. The soil concentrations of ΣOPE (sum of all OPEs) were in the range of 2.55-581 ng/g dry weight (dw), with an average value of 106 ng/g dw. Industrial soils (mean: 433 ng/g dw) had significantly higher levels of ΣOPE compared with those in urban (42.1 ng/g dw) and farmland soils (7.89 ng/g dw) (p < 0.01), suggesting that industrial activity is an important source of OPEs to ambient soil environment. Tris(1-chloro-2-propyl) phosphate (TCIPP), triphenyl phosphate (TPHP), and tris(2-butoxyethyl) phosphate (TBOEP) were the most abundant OPEs in industrial soils, contributing 30%, 25%, and 20% of ΣOPE, respectively. Principal component analysis revealed that TCIPP, TPHP, and TBOEP in soils derived from respective industrial activities. As compared with other cities within China, the surface soil of Jinan City was mildly contaminated by OPEs, and its human exposure and eco-toxicological risks were found to be negligible. Our study provides current contamination status of OPEs in soils across the multiple functional regions of Jinan, which could be used to support the authorities to make relevant regulations.

Removal of tri-(2-chloroisopropyl) phosphate (TCPP) by three types of constructed wetlands

In this study, three types of constructed wetlands (CWs) (biofilm-attachment-surface-CWs, packed bed-CWs and traditional-CWs) were assembled to comparatively evaluate their ability and mechanism to remove tri-(2-chloroisopropyl) phosphate (TCPP) under continuous flow operation. The removal rate (26%-28%) of TCPP in two types of CWs containing plants was twice as much as that in plant-free CWs in 6-month experiments, and TCPP showed a terminal accumulation phenomenon in Cyperus alternifolius with the order of accumulation of leaf>stem>root. The mass balance indicated that the contributions of filler and hydrophyte absorption to TCPP removal were less than 1%, but the transpiration of hydrophytes may make an important contribution (approximately 10%) to TCPP removal. Species in the genera Massilia, Denitratisoma and SM1A02 may be responsible for TCPP biodegradation. In addition, the effect of TCPP on the metabolic pathways and energy generation in the roots of C. alternifolius suggested that TCPP may be transported and utilized through cellular metabolism.