Discovery of Three Organothiophosphate Esters in River Water Using High-Resolution Mass Spectrometry

Emerging and legacy organophosphate flame retardants in the tropical estuarine food web: Do they exhibit similar bioaccumulation patterns, trophic partitioning and dietary exposure?

Emerging organophosphate flame retardants (E-OPFRs) are a new class of pollutants that have attracted increasing attention, but their bioaccumulation patterns and trophodynamic behaviors in aquatic food webs still need to be validated by comparison with legacy OPFRs (L-OPFRs). In this study, we simultaneously investigated the bioaccumulation, trophic transfer, and dietary exposure of 8 E-OPFRs and 10 L-OPFRs in a tropical estuarine food web from Hainan Island, China. Notably, the Σ10L-OPFRs concentration (16.1-1.18 × 105 lipid weight (lw)) was significantly greater than that of Σ8E-OPFRs (nondetectable (nd) - 2.82 × 103 ng/g lw) among the investigated organisms, and they both exhibited similar trends: fish Collapse

Key Words

• Bioaccumulation
• Biotransformation
• Legacy and emerging organophosphate flame retardants
• Organism partitioning
• Trophic transfer

Collapse

MESH Headings Collapse

Grants Collapse

Affiliation(s)

Qianyi Huang Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China University of Chinese Academy of Sciences, Beijing 100049, China
Rui Hou Guangdong Provincial Key Laboratory of Water Quality Improvement and Ecological Restoration for Watersheds, School of Ecology, Environment and Resources, Guangdong University of Technology, Guangzhou 510006, China
Yuchen Wang College of Life Sciences and Engineering, Jinan University, Guangzhou 510632, China
Lang Lin South China Sea Bureau of Ministry of Natural Resources, Guangzhou 510310, China
Hengxiang Li Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
Shan Liu Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
Xiangrong Xu Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Coral Reef Research Center of China, School of Marine Sciences, Guangxi University, Nanning 530004, China
Kefu Yu Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Coral Reef Research Center of China, School of Marine Sciences, Guangxi University, Nanning 530004, China Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
Xiaoping Huang Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China

Collapse

Maternal Exposure to Environmentally Relevant Concentrations of Tris(2,4-di-tert-butylphenyl) Phosphate-Induced Developmental Toxicity in Zebrafish Offspring via Disrupting foxO1/ripor2 Signaling

Abnormal development and mortality in early life stages pose significant threats to the growth and continuation of fish populations. Tris(2,4-di-tert-butylphenyl) phosphate (TDtBPP) is a novel organophosphate ester contaminant detected in natural waters. However, the potential effects of maternal exposure to TDtBPP on the early development of offspring embryos in fish remain unknown. Here, 30-day-old zebrafish were exposed to TDtBPP at 0, 50, 500, or 5000 ng/L for 180 days, and the exposed females were spawned with unexposed males. TDtBPP accumulation was detected in offspring embryos, accompanied by an increased malformation rate and mortality. The developmental abnormality of offspring embryos was identified to originate from the gastrula stage. Furthermore, based on transcriptome analysis, the down-regulation of RHO family interacting cell polarization regulator 2 gene (ripor2) was considered as a key toxic event, and this was confirmed in the subsequent knockdown experiment. Moreover, molecular docking studies and forkhead box O1 (foxO1) transcription factor inhibitor (AS1842856) exposure experiments demonstrated that the blockade of foxO1 transcriptional regulation was responsible for the decreased expression of ripor2. The results of this study demonstrated that the occurrence of developmental malformation and mortality in zebrafish offspring embryos following maternal TDtBPP exposure were triggered by the blockade of foxO1 transcriptional regulation and the consequent down-regulation of ripor2.

Novel Organophosphate Ester Tris(2,4-di-tert-butylphenyl)phosphate Alters Lipid Metabolism: Insights from Lipidomic Analysis and mRNA Expression

Tris(2,4-di-tert-butylphenyl)phosphate (TDTBPP), a novel organophosphate ester (OPE), has been extensively detected in various environmental and biological samples; however, its potential biological effects remain unexplored. In this study, we investigated biotransformation characteristics, alteration of lipid metabolism, and mRNA expression in primary mouse hepatocytes (PMHs) following exposure to TDTBPP. After 36-h exposure in PMHs, TDTBPP exhibited a high stability potential with no statistically significant degradation trend. Subsequently, we analyzed the disruption of lipid homeostasis in PMHs following exposure to 0-4.5 μM TDTBPP. Lipidomic analysis indicated that TDTBPP disrupted lipid homeostasis in PMHs, and several lipid classes were dysregulated, in particular, glycerolipids and glycerophospholipids. Additionally, three lipids were proposed as potential lipid biomarkers of TDTBPP exposure, including triglycerides (TGs) and phosphatidylcholines (PCs). These observations were further supported by transcriptional changes, with significant alteration observed in genes associated with lipid uptake, de novo lipogenesis, β-oxidation of fatty acids, glycerolipid metabolism, and lipid export. Overall, these findings highlight the detrimental effects of TDTBPP on lipid homeostasis, providing important insights for health risk assessments of this abundant OPE in the environment.

Identification and Prioritization of Emerging Organophosphorus Compounds Beyond Organophosphate Esters in Chinese Estuarine Waters

Organophosphorus compounds (OPCs) pose potential hazards to human health and aquatic ecosystems. However, limited knowledge of emerging OPCs beyond organophosphate esters (OPEs) hinders a thorough understanding of the environmental occurrence and exposure risks. Through target, suspect, and nontarget screening analysis, 64 OPCs were successfully identified in Chinese estuarine waters, including 24 known OPEs and 40 emerging analogues (i.e., quaternary phosphonium, phosphine oxide, organophosphonate, and organothiophosphate esters). Domestic wastewater and agricultural and industrial discharges were factors influencing the OPC distribution patterns. In particular, quaternary phosphoniums and phosphine oxides accounted for over 50% of the total OPC loading in the Yellow and Jia Rivers, which were likely polluted by phosphorus-related industries. Risk quotient (RQ) calculations showed that tetrabutylphosphonium contributed the most to algae toxicity due to the biocidal effects of onium salts, while chloroalkyl OPEs dominated the ecological risks for daphnia and fish. The multicriteria decision analysis approach was further introduced for relative chemical ranking by considering the variations in hazard criteria of environmental occurrence, fate, and toxicity of the OPCs. The results indicate that aryl phosphoniums and aryl phosphine oxides have a hazard priority similar to that of the OPEs and, therefore, require more attention.

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.

A Novel Organophosphate Ester, Tris(2,4-ditert-butylphenyl) Phosphate, Induced Reproductive Toxicity in Male Zebrafish at Environmentally Relevant Concentrations

As a novel organophosphate ester (NOPE), tris(2,4-ditert-butylphenyl) phosphate (TDtBPP) has attracted significant attention due to its unexpectedly high detection in natural environments. However, the ecological toxic effects of environmentally relevant concentrations of TDtBPP in organisms remain entirely unknown. In this study, 1 month old zebrafish were exposed to 0, 50, 500, or 5000 ng/L TDtBPP for 150 days, and the reproductive toxicity in male fish was evaluated. Results demonstrated that TDtBPP exposure significantly inhibited the maturation of spermatozoa and thus decreased spermatogenesis. Furthermore, abnormal sperm morphology and decreased sperm motility were also observed. The decrease in sperm quantity and quality eventually resulted in the declining fecundity. Moreover, TDtBPP exposure downregulated the expression of hsd3b1 in vivo and in vitro and subsequently inhibited the synthesis of androgens in zebrafish testes and Leydig cells. This inhibition of androgen synthesis appeared to be responsible for the observed reproductive toxicity in male fish. Molecular docking and dual-luciferase reporter gene experiments elucidated that TDtBPP inhibited the promotion of vitamin D on hsd3b1 transcription by the vitamin D receptor and thus downregulated the expression of hsd3b1. Our findings provide first time evidence that TDtBPP poses a risk to male fish reproduction at environmentally relevant levels.

First Evidence of Novel Organothiophosphate Esters as Prevalent New Pollutants in Dust from Automotive Repair Shops Discovered by High-Resolution Mass Spectrometry

The occurrence of organophosphorus compounds has garnered global concern due to their widespread production and potential environmental risks. Limited structural information has hindered a comprehensive understanding of their composition. By characteristic fragmentation-based nontarget analysis, the occurrence and composition of organothiophosphate esters (OTPEs), which are antiwear additives in lubricant oils that have received little attention previously, were investigated in dust from automotive repair shops and surrounding buildings. Fourteen OTPEs were tentatively identified, including four triarylphosphorothionates, six O,O-dialkyl phosphorothioates, and four O-alkyl O-alkyl sulfone phosphorothioates, among which four OTPEs were further confirmed by authentic standards or an industrial product. Triphenyl phosphorothioate (TPhPt) and tris(2,4-di-tert-butylphenyl) phosphorothioate (AO168=S) were prevalently detected in automotive repair shops with median concentrations of 230 and 246 ng/g, respectively, closely comparable to triphenyl phosphate (TPhP, median concentration: 302 ng/g). O,O-Dihexyl phosphorothioate (DHPt), O,O-dioctyl phosphorothioate (DOPt), O-hexyl O-hexyl sulfone phosphorothioate (DHSPt), and O-octyl O-octyl sulfone phosphorothioate (DOSPt) were the abundant analogues in automotive repair shops with semiquantitative median concentrations in the range of 119-1.05 × 103 ng/g. Hierarchical cluster analysis showed that OTPEs exhibited similar distribution patterns across automotive repair shops, indicating that these chemicals had similar sources. Moreover, the concentrations of OTPEs were usually higher in automotive repair shops than that in surrounding buildings, suggesting a motor vehicle related emission source. To our knowledge, 12 out of the 14 detected OPTEs were reported in the environment for the first time. The discovery of these OTPEs expanded the scope of known organophosphorus pollutants, highlighting the potential contaminants of OTPEs from lubricant oils for automotive and industrial applications.

Contamination Status of Novel Organophosphate Esters Derived from Organophosphite Antioxidants in Soil and the Effects on Soil Bacterial Communities

The contamination status of novel organophosphate esters (NOPEs) and their precursors organophosphite antioxidants (OPAs) and hydroxylated/diester transformation products (OH-OPEs/di-OPEs) in soils across a large-scale area in China were investigated. The total concentrations of the three test NOPEs in soil were 82.4-716 ng g-1, which were considerably higher than those of traditional OPEs (4.50-430 ng g-1), OPAs (n.d.-30.8 ng g-1), OH-OPEs (n.d.-0.49 ng g-1), and di-OPEs (0.57-21.1 ng g-1). One NOPE compound, i.e., tris(2,4-di-tert-butylphenyl) phosphate (AO168 = O) contributed over 65% of the concentrations of the studied OPE-associated contaminants. A 30-day soil incubation experiment was performed to confirm the influence of AO168 = O on soil bacterial communities. Specific genera belonging to Proteobacteria, such as Lysobacter and Ensifer, were enriched in AO168 = O-contaminated soils. Moreover, the ecological function of methylotrophy was observed to be significantly enhanced (t-test, p < 0.01) in soil treated with AO168 = O, while nitrogen fixation was significantly inhibited (t-test, p < 0.01). These findings comprehensively revealed the contamination status of OPE-associated contaminants in the soil environment and provided the first evidence of the effects of NOPEs on soil microbial communities.

Acute exposure to tris(2,4-di-tert-butylphenyl)phosphate elicits cardiotoxicity in zebrafish (Danio rerio) larvae via inducing ferroptosis

Tris(2,4-di-tert-butylphenyl)phosphate (AO168 =O), a novel organophosphate ester, is prevalent and abundant in the environment, posing great exposure risks to ecological and public health. Nevertheless, the toxicological effects of AO168 =O remain entirely unknown to date. The results in this study indicated that acute exposure to AO168 =O at 10 and 100 μg/L for 5 days obviously impaired cardiac morphology and function of zebrafish larvae, as proofed by decreased heartbeat, stroke volume, and cardiac output and the occurrence of pericardial edema and ventricular hypertrophy. Transcriptomics, polymerase chain reaction, and molecular docking revealed that the strong interaction of AO168 =O and transferrin receptor 1 activated the transportation of ferric iron into intracellular environment. The release of free ferrous ion to cytoplasmic iron pool also contributed to the iron overload in heart region, thus inducing ferroptosis in larvae via generation of excessive reactive oxygen species, glutathione peroxidase 4 inhibition, glutathione depletion and lipid peroxidation. Ferroptosis inhibitor (Fer-1) co-exposure effectively relieved the cardiac dysfunctions of zebrafish, verifying the dominant role of ferroptosis in the cardiotoxicity caused by AO168 =O. This research firstly reported the adverse impact and associated mechanisms of AO168 =O in cardiomyogenesis of vertebrates, underlining the urgency of concerning the health risks of AO168 =O.

Discovering Novel Organophosphorus Compounds in Wastewater Treatment Plant Effluents through Suspect Screening and Nontarget Analysis

Limited knowledge on the structure of emerging organophosphorus compounds (OPCs) hampers our comprehensive understanding of their environmental occurrence and potential risks. Through suspect and nontarget screening, combining data-dependent acquisition, data-independent acquisition, and parallel reaction monitoring modes, we identified 60 OPCs (17 traditional and 43 emerging compounds) in effluents of 14 wastewater treatment plants (WWTPs) in Beijing and Qinghai, China. These OPCs comprise 26 organophosphate triesters, 17 organophosphate diesters, 6 organophosphonates, 7 organothiophosphate esters, and 4 other OPCs. Notably, 14 suspect OPCs were newly identified in WWTP effluents, and 16 nontarget OPCs were newly discovered in environmental matrices. Specifically, the cyclic phosphonate, (5-ethyl-2-methyl-1,3,2-dioxaphosphorinan-5-yl)methyl dimethyl phosphonate P-oxide (PMMMPn), consistently appeared in all WWTP effluents, with semiquantitative concentrations ranging from 44.4 to 282 ng/L. Its analogue, di-PMMMPn, presented in 93% of wastewater samples. Compositional differences between the WWTP effluents of two cities were mainly attributed to emerging OPCs. Hazard and ecological risk assessment underscored the substantial contribution of chlorinated organophosphate esters and organothiophosphate esters to overall risks of OPCs in WWTP effluents. This study provides the most comprehensive OPC profiles in WWTP effluents to date, highlighting the need for further research on their occurrence, fate, and risks, particularly for chlorinated OPCs.

Unravelling bioaccumulation, depletion and metabolism of organophosphate triesters in laying hens: Insight of in vivo biotransformation assisted by diester metabolites

Organophosphate triesters (tri-OPEs) threaten human health through dietary exposure, but little is known about their feed-to-food transfer and in vivo behavior in farm animals. Herein 135 laying hens were fed with contaminated feed (control group, low-level group and high-level group) to elucidate the bioaccumulation, distribution, and metabolism of the six most commonly reported tri-OPEs. The storage (breast muscle), metabolism and mobilization (liver and blood) and non-invasive (feather) tissues were collected. The exposure-increase (D1∼14) and depuration-decrease (D15∼42) trends indicated that feed exposure caused tri-OPE accumulation in animal tissues. Tissue-specific and moiety-specific behavior was observed for tri-OPEs. The highest transfer factor (TF) and transfer rate (TR) were observed in liver (TF: 14.8%∼82.3%; TR: 4.40%∼24.5%), followed by feather, breast muscle, and blood. Tris(2-chloroisopropyl) phosphate (TCIPP) had the longest half-life in feather (72.2 days), while triphenyl phosphate (TPhP) showed the shortest half-life in liver (0.41 days). Tri-OPEs' major metabolites (organophosphate diesters, di-OPEs) were simultaneously studied, which exhibited dose-dependent and time-dependent variations following administration. In breast muscle, the inclusion of di-OPEs resulted in TF increases of 735%, 1108%, 798%, and 286% than considering TCIPP, tributyl phosphate, tris(2-butoxyethyl) phosphate and tris(2-ethylhexyl) phosphate alone. Feather was more of a proxy of birds' long-term exposure to tri-OPEs, while short-term exposure was better reflected by di-OPEs. Both experimental and in silico modeling methods validated aryl-functional group facilitated the initial accumulation and metabolism of TPhP in the avian liver compared to other moiety-substituted tri-OPEs.

Bringing the emerging organophosphate flame retardants (eOPFRs) into view: A hidden ecological and human health threat

The production and usage of organophosphate flame retardants (OPFRs) in textiles, plastics, and electronics have surged, with phosphorus-based flame retardants constituting over 30 % of the global consumption of flame retardants. Meanwhile, concerns regarding the potential hazards of OPFRs to ecosystems and human health including disruptions in the endocrine system, inhibition of reproduction, and manifestation of developmental defects have intensified. However, our comprehensive data analysis has unveiled a pronounced and critical knowledge gap, as at present, a majority of studies emphasize the attributes of traditional OPFRs, such as triphenyl phosphate (TPHP), while emerging OPFRs (eOPFRs) remain undeservedly overlooked. We elaborated on the current advancements and challenges regarding eOPFRs research and demonstrated that eOPFRs exhibit considerable diversity in terms of their chemical structures, substantial residue levels, broad sources of occurrence, and limited understanding of their potent (eco)toxicological implications. In light of these attributes, it becomes evident that the environmental and health risks of eOPFRs can be comparable to, if not surpass, those attributed to traditional OPFRs. This compelling observation underscores an imperative need for heightened research focus and extensive research efforts dedicated to the study of eOPFRs, rather than still focusing on the realm of their traditional counterparts. Despite the challenges ahead, the emphasized environmental surveillance and toxicological assessment are imperative to prevent the potential evolution of these compounds into a significant ecological and human health threat.

Discovery and occurrence of organophosphorothioate esters in food contact plastics and foodstuffs from South China: Dietary intake assessment

A recent study revealed the presence of non-pesticide organothiophosphate esters (OTPEs) - precursors to organophosphate esters (OPEs) contaminants - in river water. Since OPEs have demonstrated adverse reproductive outcomes in humans, this accentuates the urgency to explore the prevalence of non-pesticide OTPEs in other potential human exposure matrices. In this study, a nontarget screening method based on high-resolution mass spectrometry was used to identify OTPEs in food contact plastic (FCP) samples collected from South China. O,O,O-triphenyl phosphorothioate (TPhPt) and O,O,O-tris(2,4-di-tert-butylphenyl) phosphorothioate (AO168 = S) were unequivocally identified (Level 1), while O,O-di(di-butylphenyl) O-methyl phosphorothioate (BDBPMPt) was tentatively identified (Level 2b, indicating probable structure based on diagnostic evidence). Among n = 70 FCP samples, AO168 = S emerged with the highest detection frequency and median concentration of 74 % and 111 ng/g, respectively. Significant Pearson correlations were observed in log-transformed peak areas of AO168 = S and TPhPt in FCPs with their respective oxons, respectively. Occurrences of AO168 = S and TPhPt were further investigated in n = 100 foodstuff samples using a market basket method. AO168 = S and TPhPt exhibited detection frequencies of 43 % and 44 % in all food items with mean concentrations of 2.17 ng/g wet weight (ww) (range: <0.53-67.8 ng/g ww) and 0.112 ng/g ww (range: <0.006-2.39 ng/g ww), respectively. The highest mean concentrations for AO168 = S and TPhPt were found in vegetables (4.62 ng/g ww) and oil (3.00 ng/g ww), respectively. The median estimated daily intakes (EDIs) of AO168 = S and TPhPt via diet were calculated as 10.4 and 1.51 ng/kg body weight/day, respectively. For AO168 = S, only meat and vegetables contributed to the median EDI, whereas for TPhPt, oil was identified as the principal contributor to the median EDI. This study for the first time evaluated human exposure to OTPEs via diet, providing new insights to overall human exposure to OPEs.

Unregistered Hexaphenoxycyclotriphosphazene and Its Metabolite Antagonize Retinoic Acid and Retinoic X Receptors and Cause Early Developmental Damage

Hexaphenoxycyclotriphosphazene (HPCTP), an unregistered chemical, has been used as a substitute for triphenyl phosphate in flame retardants and plasticizers. Here, we identified its metabolite, pentaphenoxycyclotriphosphazene (PPCTP) in the liver of Japanese medaka exposed to HPCTP. When sexually mature female medaka were exposed to HPCTP at 37.0, 90.4, and 465.4 ng/L for 35 days, the HPCTP concentration (642.1-2531.9 ng/g lipid weight [lw]) in the embryos considerably exceeded that (34.7-298.1 ng/g lw) in the maternal muscle, indicating remarkable maternal transfer. During 0-9 days postfertilization, the HPCTP concentration in the embryos decreased continuously, while the PPCTP concentration increased. HPCTP and PPCTP antagonized the retinoic X receptor with 50% inhibitory concentrations (IC50) of 34.8 and 21.2 μM, respectively, and PPCTP also antagonized the retinoic acid receptor with IC50 of 2.79 μM. Such antagonistic activities may contribute to eye deformity (4.7% at 465.4 ng/L), body malformation (2.1% at 90.4 ng/L and 6.8% at 465.4 ng/L), and early developmental mortality (11.6-21.7% in all exposure groups) of the embryos. HPCTP was detected in a main tributary of the Yangtze River Basin. Thus, HPCTP poses a risk to wild fish populations, given the developmental toxicities associated with this chemical and its metabolite.