Meta-omics elucidates key degraders in a bacterial tris(2-butoxyethyl) phosphate (TBOEP)-degrading enrichment culture

Key genes and microbial ecological clusters involved in organophosphate ester degradation in agricultural fields of a typical watershed in southwest China

Organophosphate esters (OPEs) are widely used as flame retardants and plasticizers, and they have raised global concern due to their persistence, bioaccumulation, and potential toxicity. However, OPE contamination characteristics and microbial degradation mechanisms in agricultural soils remain poorly understood. This study investigated agricultural soils from the riparian zone of the Anning River Basin in southwest China. The concentrations of 12 OPEs were determined using gas chromatography-tandem mass spectrometry. The results revealed that the total OPE concentration was moderate, with triethyl phosphate being the most abundant compound. Metagenomic techniques and Bayesian linear regression analysis were employed in combination with the Kyoto Encyclopedia of Genes and Genomes database to identify potential degradation pathways for triethyl phosphate and tris (2-chloroethyl) phosphate. The phoA, phoB, phoD, and glpQ genes, which encode phosphatases, catalyze ester bond cleavage, thereby facilitating the degradation of OPEs. Further microbial interaction network analysis identified core OPE-degrading microorganisms, including Pimelobacter simplex, Nocardioides sp. JS614, Nocardioides daphniae, and Methylocystis heyeri. Additionally, neutral community models indicated that environmental selection drives microbial community structure. In conclusion, this study provides an in-depth understanding of OPE contamination and its microbial degradation mechanisms in agricultural soils, offering theoretical insights for pollution management and remediation strategies.

Gestation Exposure to Organophosphate Esters: Structure-Dependent Transplacental Transfer Patterns, Mechanisms, and Toxicity

Organophosphate esters (OPEs), characterized by diverse chemical substituents, exhibit varying environmental exposure and toxicity profiles. Therefore, OPEs may have potential for placental transfer and could impact neonatal development. However, the structural-specific transplacental mechanisms and toxicity effects of the OPEs remain poorly understood. Herein, we develop an integrated evaluation system with human biomonitoring, uterine perfusion in pregnant rats, and placental cells. OPEs were frequently observed in maternal and cord whole blood, urine, and amniotic fluid samples (n = 41 sample sets) with median concentrations of 9.47, 9.31, 9.90, and 5.98 ng/mL, respectively. Rat uterine perfusion experiment suggested that chlor-OPEs exhibited relatively higher transplacental efficiency compared to alkyl- and aryl-OPEs. Passive diffusion dominated by lipophilicity (log Kow) and transporters dominated active transport may be involved in the transplacental transportation mechanisms. The results from exposure experiments to placenta BeWo cells indicated that organophosphate triesters (tri-OPEs) (IC50 values of 145 to 1464 μM) exhibited higher toxicity to the corresponding organophosphate diesters (di-OPEs) (IC50 values of 752 to 1794 μM). In addition, chlor-OPEs represented significantly greater cytotoxic potential to placenta cells in comparison to alkyl and aryl-OPEs. More attention should be paid for chlor-OPEs as its higher transplacental and toxicity potential compared to alkyl- and aryl-OPEs.

Degradation mechanisms of isodecyl diphenyl phosphate (IDDP) and bis-(2-ethylhexyl)-phenyl phosphate (BEHPP) using a novel microbially-enriched culture

Organophosphate esters (OPEs) pose significant environmental concerns due to their widespread presence, potential toxicity, and persistence. This study investigated the degradation of the isodecyl diphenyl phosphate (IDDP) and bis-(2-ethylhexyl)-phenyl phosphate (BEHPP) using a novel enrichment culture, which could degrade 85.4 % and 78.2 % of 1 mg/L IDDP and BEHPP after 192 h and 172 h, respectively, under extremely low bacterial dosage (the initial OD600 nm= 0.0075, biomass was approximately 1 mg/L). The identification of intermediate products suggested that the degradation reactions likely included hydrolysis, hydroxylation, methylation, carboxylation, and glycosylation. Metagenomic analysis highlighted the crucial role of enzymes in degrading IDDP and BEHPP, including phosphatase, phosphodiesterase, cytochrome P450, and hydroxylase. Pure strains Burkholderia cepacia ZY1, Sphingopyxis terrae ZY2, and Amycolatopsis ZY3 were isolated, and their efficient individual degradation abilities were confirmed. These efficiencies were lower compared to the enrichment culture, emphasizing the importance of microbial interactions for effective degradation. The pathways identified for these strains illustrated their involvement in different degradation steps, reinforcing the synergy between different degraders. Molecular dynamics simulations provided insights into the interactions between alkaline phosphatase (ALP), cytochrome P450 (CYP450), and hydroxylase with OPEs. These enzymes demonstrated a strong binding capacity with both BEHPP and IDDP, exhibiting distinct binding site preferences that may contribute to varied metabolic pathways. These findings comprehensively reveal the transformation mechanisms of OPEs.

Target and Nontarget Analysis of Organophosphorus Flame Retardants and Plasticizers in a River Impacted by Industrial Activity in Eastern China

Industrial activities are a major source of organophosphorus flame retardants (OPFRs) and plasticizers in aquatic environments. This study investigated the distribution of 40 OPFRs in a river impacted by major industrial manufacturing plants in Eastern China by target analysis. Nontarget analysis using high-resolution mass spectrometry was further employed to identify novel organophosphorus compounds (NOPs). Thirty-four OPFRs were detected in river water samples, with total concentrations of 62.9-1.06 × 103 ng/L (median: 455 ng/L). Triphenylphosphine oxide and diphenyl phosphoric acid were ubiquitously detected up to 620 and 127 ng/L, respectively. Among 26 identified NOPs, 17 were reported for the first time in the environment, including 14 novel organophosphate esters (especially 4 heterocycles and 3 oligomers), 2 organophosphites, and an organophosphonate. Bis(2,4-di-tert-butylphenyl) hydrogen phosphate and 2,2-dimethylpropoxy(propyl)phosphinic acid with high predicted persistence or toxicity were widely detected, with semiquantified concentrations up to 990 and 1.0 × 103 ng/L, respectively. Structurally similar organophosphorus heterocycles exhibited consistent variation trends, suggesting a common emission source. Estimated annual river discharges to the sea were 20.6-37.0 kg/yr for OPFRs and 30.8-161 kg/yr for NOPs. These findings indicate that industrial activities contribute OPFRs and NOPs to the river catchment and its estuary, posing ecological risks to both terrestrial and marine environments.

Degradation of organophosphate flame retardants by white-rot fungi: Degradation pathways and associated toxicity

The environmental persistence of organophosphate flame retardants (OPFRs) in water is becoming and environmental concern. White Rot Fungi (WRF) have proven its capability to degrade certain OPFRs such as tributyl phosphate (TBP), tris(2-butoxyethyl) phosphate (TBEP), tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloroisopropyl) phosphate (TCPP). Despite this capability, there is limited knowledge about the specific pathways involved in the degradation. In this study, three different WRF were paired with individual OPFRs, and potential transformation products (TPs) were identified by UHPLC-HRMS. Some compounds structures were further validated by NMR. From these data degradation pathways were proposed. TBP was degraded by successive hydroxylation and hydrolysis reactions, with a novel dehydrogenation step suggested. Both TCEP and TCPP underwent oxidative dechlorination, with TCEP experiencing subsequent hydrolysis. Uncommon reductive dehalogenation was also observed. TCPP further underwent hydroxylation and environmentally relevant methylation. TBEP generated numerous TPs, mainly by successive dealkylations, along with hydroxylation. Notably, demethylation in TBEP degradation was proposed for the first time. Additional secondary products were formed through hydroxylation and oxidation of the initial metabolites. Finally, in vivo and in silico toxicity assessments were conducted, identifying certain TPs as potentially toxic.

Metabolism of isodecyl diphenyl phosphate in rice and microbiome system: Differential metabolic pathways and underlying mechanisms

Isodecyl diphenyl phosphate (IDDP) is among the emerging aromatic organophosphate esters (aryl-OPEs) that pose risks to both human beings and other organisms. This study aims to investigate the translocation and biotransformation behavior of IDDP in rice and the rhizosphere microbiome through hydroponic exposure (the duration of hydroponic exposure was 10 days). The rhizosphere microbiome 9-FY was found to efficiently eliminate IDDP, thereby reducing its uptake in rice tissues and mitigating the negative impact of IDDP on rice growth. Furthermore, this study proposed the first-ever transformation pathways of IDDP, identifying hydrolysis, hydroxylation, methylation, methoxylation, carboxylation, and glucuronidation products. Notably, the methylation and glycosylation pathways were exclusively observed in rice, indicating that the transformation of IDDP in rice may be more complex than in microbiome 9-FY. Additionally, the presence of the product COOH-IDDP in rice suggested that there might be an exchange of degradation products between rice and rhizobacteria, implying their potential interaction. This finding highlights the significance of rhizobacteria's role which cannot be overlooked in the accumulation and transformation of organic pollutants in grain crops. The study revealed active members in 9-FY during IDDP degradation, and metagenomic analysis indicated that most of the active populations contained IDDP-degrading genes. Moreover, transcriptome sequencing showed that cytochrome P450, acid phosphatase, glucosyltransferase, and methyltransferases genes in rice were up-regulated, which was further confirmed by RT-qPCR. This provides insight into the intermediate products identified in rice, such as hydrolysis, hydroxylated, glycosylated, and methylated products. These results significantly contribute to our understanding of the translocation and transformation of organophosphate esters (OPEs) in plants and the rhizosphere microbiome, and reveal the fate of OPEs in rice and microbiome system to ensure the paddy yield and rice safety.

Spatiotemporal distribution and transport flux of organophosphate esters in the sediment of the Yangtze River

The Yangtze River Basin is an important area for organophosphate esters (OPEs) consumption and emission. Studies proved high OPE detection in Yangtze River water, but there is limited information about the spatiotemporal distribution and transport flux of OPEs in sediment. The present study investigated 16 OPEs in sediment from upstream to mid-downstream of the Yangtze River. The mean concentration of OPEs was 84.30 ng/g, and alkyl-OPEs was the primary component. Great specific surface area and high content of organic carbon significantly increased OPE concentration in Three Gorges Reservoir (TGR) by physical adsorption and chemical bonds (p < 0.05), making TGR the most contaminated area in mainstream. No significant differences in OPE constituents were found in seasonal distribution. Four potential sources of OPEs were identified by principal component analysis and self-organizing maps, and traffic emissions were the dominant source for OPEs. The hazard quotient model results indicated that aryl-OPEs showed moderate risks in the mainstream of Yangtze River, alkyl-OPEs and Cl-OPEs showed low risks. TGR was a significant sink of OPEs in Yangtze River and buried 7.41 tons of OPEs in 2020, a total of 14.87 tons of OPE were transported into the sea by sediment.

OPFR removal by white rot fungi: screening of removers and approach to the removal mechanism

The persistent presence of organophosphate flame retardants (OPFRs) in wastewater (WW) effluents raises significant environmental and health concerns, highlighting the limitations of conventional treatments for their remotion. Fungi, especially white rot fungi (WRF), offer a promising alternative for OPFR removal. This study sought to identify fungal candidates (from a selection of four WRF and two Ascomycota fungi) capable of effectively removing five frequently detected OPFRs in WW: tributyl phosphate (TnBP), tributoxy ethyl phosphate (TBEP), trichloroethyl phosphate (TCEP), trichloro propyl phosphate (TCPP) and triethyl phosphate (TEP). The objective was to develop a co-culture approach for WW treatment, while also addressing the utilization of less assimilable carbon sources present in WW. Research was conducted on carbon source uptake and OPFR removal by all fungal candidates, while the top degraders were analyzed for biomass sorption contribution. Additionally, the enzymatic systems involved in OPFR degradation were identified, along with toxicity of samples after fungal contact. Acetate (1.4 g·L-1), simulating less assimilable organic matter in the carbon source uptake study, was eliminated by all tested fungi in 4 days. However, during the initial screening where the removal of four OPFRs (excluding TCPP) was tested, WRF outperformed Ascomycota fungi. Ganoderma lucidum and Trametes versicolor removed over 90% of TnBP and TBEP within 4 days, with Pleorotus ostreatus and Pycnoporus sanguineus also displaying effective removal. TCEP removal was challenging, with only G. lucidum achieving partial removal (47%). A subsequent screening with selected WRF and the addition of TCPP revealed TCPP's greater susceptibility to degradation compared to TCEP, with T. versicolor exhibiting the highest removal efficiency (77%). This observation, plus the poor degradation of TEP by all fungal candidates suggests that polarity of an OPFR inversely correlates with its susceptibility to fungal degradation. Sorption studies confirmed the ability of top-performing fungi of each selected OPFR to predominantly degrade them. Enzymatic system tests identified the CYP450 intracellular system responsible for OPFR degradation, so reactions of hydroxylation, dealkylation and dehalogenation are possibly involved in the degradation pathway. Finally, toxicity tests revealed transformation products obtained by fungal degradation to be more toxic than the parent compounds, emphasizing the need to identify them and their toxicity contributions. Overall, this study provides valuable insights into OPFR degradation by WRF, with implications for future WW treatment using mixed consortia, emphasizing the importance of reducing generated toxicity.

Co-occurrence of organophosphate diesters and organophosphate triesters in daily household products: Potential emission and possible human health risk

Eight paired organophosphate diesters (Di-OPs) and organophosphate triesters (Tri-OPs) were investigated in wipes from analytical instruments and 47 material samples related to household products, including textiles, electrical/electronic devices, building/ decoration materials and children's products. The total concentrations of Di-OPs ranged in 3577-95551 ng/m2 in the wipes and limit of detection-23002 ng/g in the materials. The Tri-OPs concentrations varied significantly in the ranges of 107218-1756892 ng/m2 and 2.13-503149 ng/g, respectively. Four industrial Di-OPs were detected in > 65% of the studied samples suggesting their direct application in the studied materials. Furthermore, we demonstrated for the first time that four non-industrial Di-OPs, e.g., bis(2-chloroethyl) phosphate, bis(1-chloro-2-propyl) phosphate, bis(1,3-dichloro-2-propyl) phosphate, and bis(butoxyethyl) phosphate, identified as degradation products of their respective Tri-OPs were also detected in these studied samples, which might act as important emission sources of Di-OPs in indoor environments. We estimated the burden of Di-OPs and Tri-OPs in a typical residential house and instrumental room, which both exhibited important contributions from furniture, building and decoration materials, and electrical/electronic devices. Limit health risk was posed to local people via air inhalation.

Insights into electrochemical oxidation of tris(2-butoxyethyl) phosphate (TBOEP) in aquatic media: Degradation performance, mechanisms and toxicity changes of intermediate products

Tris (2-butoxyethyl) phosphate (TBOEP) has gained significant attention due to its widespread presence and potential toxicity in the environment. In this study, the degradation of TBOEP in aquatic media was investigated using electrochemical oxidation technology. The anode Ti/SnO2-Sb/La-PbO2 demonstrated effective degradation performance, with a reaction constant (k) of 0.6927 min-1 and energy consumption of 1.24 kW h/m3 at 10 mA/cm2. CV tests, EPR tests, and quenching experiments confirmed that indirect degradation is the main degradation mechanism and ·OH radicals were the predominant reactive species, accounting for up to 93.8%. The presence of various factors, including Cl-, NO3-, HCO3- and humic acid (HA), inhibited the degradation of TBOEP, with the inhibitory effect dependent on the concentrations. A total of 13 intermediates were identified using UPLC-Orbitrap-MS/MS, and subsequent reactions led to their further degradation. Two main degradation pathways involving bond breaking, hydroxylation, and oxidation were proposed. Both Flow cytometry and the ECOSAR predictive model indicated that the intermediates exhibited lower toxic than the parent compound, resulting in a high detoxification rate of 95.9% for TBOEP. Although the impact of TBOEP on the phylum-level microbial community composition was found to be insignificant, substantial alterations in bacterial abundance were noted when examining the genus level. The dominant genus Methylotenera, representing 17.4% in the control group, decreased to 6.9% in the presence of TBOEP and slightly increased to 8.7% in the 4-min exposure group of degradation products. Electrochemical oxidation demonstrated its effectiveness for the degradation and detoxification of TBOEP in aqueous solutions, while it is essential to consider the potential impact of degradation products on sediment microbial communities.