Accumulation and distribution of organophosphate flame retardants (PFRs) and their di-alkyl phosphates (DAPs) metabolites in different freshwater fish from locations around Beijing, China

Phosphorus Deficiency Promoted Hydrolysis of Organophosphate Esters in Plants: Mechanisms and Transformation Pathways

The biotransformation of organophosphate esters (OPEs) in white lupin (Lupinus albus) and wheat (Triticum aestivum L.) was investigated in hydroponic experiments with different phosphorus (P)-containing conditions. The hydrolysis rates of OPEs followed the order of triphenyl phosphate (TPHP) > tri-n-butyl phosphate (TnBP) > tris(1,3-dichloro-2-propyl) phosphate (TDCPP). Hydrolysis of OPEs was accelerated at P-deficient conditions, and faster hydrolysis took place in white lupin than in wheat. Coincidingly, the production of acid phosphatase (ACP) in both plants was promoted, and much higher intracellular and extracellular ACPs were observed in white lupin under P-deficient conditions. In vitro experiments revealed that ACP was a key enzyme to hydrolyze OPEs. The hydrolysis rates of OPEs were significantly correlated with the Hirshfeld charges, calculated by density functional theory, of the oxygen atom in the single P-O bond. Using ultra-high-performance liquid chromatography coupled with Orbitrap Fusion mass spectrometer, 30 metabolites were successfully identified. Some of these metabolites, such as sulfate-conjugated products, hydration of cysteine-conjugated products of TPHP, and reductively dechlorinated metabolites of TDCPP, were observed for the first time in plants. It is noteworthy that OPEs may transform into many hydroxylated metabolites, and special attention should be paid to their potential environmental effects.

Lifetime bioaccumulation, gender difference, tissue distribution, and parental transfer of organophosphorus plastic additives in freshwater fish

Plastic pollution has been a growing global issue. Various plastic additives may enter the environment with plastic debris, which could also become contaminants. Lifetime bioaccumulation, gender difference, tissue distribution, and parental transfer potential of commonly applied organophosphorus plastic additives (OPPAs) were investigated in wildlife fish of the Pearl River system, China. The OPPAs were widely detected in 7 consumable fish species. Tris (2-chloropropyl) phosphate was the predominant compound, with a median concentration of 18.8 ng/g lipid weight. The total OPPA concentrations (ΣOPPAs) were higher in the livers and swimming bladders, suggesting important roles of lipophilicity on the OPPAs accumulation in the fish. Besides, the livers were more abundant in the non-chlorinated OPPAs relative to the other tissues, indicating potentially stronger metabolism of the chlorinated OPPAs in the livers. Redbelly tilapia contained obviously lower ΣOPPAs than the other species. On the other hand, proportions of the chlorinated OPPAs were obviously lower in barbel chub and Guangdong black bream. For an individual species, higher ΣOPPAs were usually detected in the female than in the male fish. Furthermore, the females contained higher proportions of the non-chlorinated OPPAs. These results suggested potentially more accumulation of the OPPAs, particularly the non-chlorinated OPPAs in the female than in the male fish. Body weight dependence of the OPPAs accumulation showed varied patterns depending on species, tissue, and compound. Species-specific characteristics affected by both ecology and organisms' physiology should be considered in combination in assessing bioaccumulation of the OPPAs. The OPPAs were slightly bioaccumulative with LogBAFs of 1.2-3.3. The OPPAs did not show obvious inclination to be partitioned to biota from sediment. Omnipresence of the OPPAs in both egg/ovary and testis of the fish suggested potential transgenerational transfer of these chemicals, which can be a serious ecological issue and warrants further research.

Organophosphorus flame retardants (OPFRs) in the seawater and sediments of the Qinzhou Bay, Northern Beibu Gulf: Occurrence, distribution, and ecological risks

The occurrence, distributions, and ecological risks of 11 organophosphate flame retardants (OPFRs) were investigated in the seawater and sediment samples from the Qinzhou Bay. The Σ₁₁OPFRs in the surface seawater and sediments ranged from 150 to 885 ng/L and from <the limit of quantification (LOQ) to 32.2 ng/g dw, respectively, with high levels of OPFRs in the industrialized and port areas. Tris (2-chloro-propyl) phosphate (TCIPP), tris (2-chloroethyl) phosphate (TCEP), and tri-n-butyl phosphate (TNBP) were the dominant OPFRs in the surface seawater and sediments. The Σ₁₁OPFRs concentrations in the sediment core ranged 1.2-18.6 ng/g dw and the vertical trends showed a recent increase of OPFRs emissions, especially for TNBP and triphenyl phosphate (TPHP). Risk assessment revealed that individual OPFR could pose low to medium ecological risks, but the risk from the mixture of OPFRs on aquatic organisms requires more attention.

Tris(1,3-dichloro-2-propyl)phosphate Reduces Growth Hormone Expression via Binding to Growth Hormone Releasing Hormone Receptors and Inhibits the Growth of Crucian Carp

Tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) has commonly been used as an additive flame retardant and frequently detected in the aquatic environment and in biological samples worldwide. Recently, it was found that exposure to TDCIPP inhibited the growth of zebrafish, but the relevant molecular mechanisms remained unclear. In this study, 5 day-old crucian carp (Carassius auratus) larvae were treated with 0.5, 5, or 50 μg/L TDCIPP for 90 days; the effect on growth was evaluated; and related molecular mechanisms were explored. Results demonstrated that 5 or 50 μg/L TDCIPP treatment significantly inhibited the growth of crucian carp and downregulated the expression of growth hormones (ghs), growth hormone receptor (ghr), and insulin-like growth factor 1 (igf1). Molecular docking, dual-luciferase reporter gene assay, and in vitro experiments demonstrated that TDCIPP could bind to the growth hormone releasing hormone receptor protein of crucian carp and disturb the stimulation of growth hormone releasing hormone to the expression of ghs, resulting in the decrease of the mRNA level of gh1 and gh2 in pituitary cells. Our findings provide new perceptions into the molecular mechanisms of developmental toxicity of TDCIPP in fish.

Tissue-Specific Distribution of Legacy and Emerging Organophosphorus Flame Retardants and Plasticizers in Frogs

Five types of tissues, including the liver, kidney, intestine, lung, and heart, were collected from black-spotted frogs and bullfrogs to study the tissue-specific accumulation of organophosphorus flame retardants (PFRs) and plasticizers. Thirteen PFRs and nine plasticizers were detected, with average total concentrations of 1.4–13 ng/g ww and 858–5503 ng/g ww in black-spotted frogs, 3.6–46 ng/g ww and 355–3504 ng/g ww in bullfrogs. Significant differences in pollutant concentrations among different tissues in the two frog species were found, indicating the specific selectivity distribution of PFRs and plasticizers. Overall, liver tissues exhibited significantly higher pollutant concentrations. The pollutant concentration ratios of other tissue to the sum of liver tissue and other tissues (OLR, C_other/(C_other + C_liver)) corresponding to male frogs were significantly greater than those of females, suggesting that male frogs could have higher metabolic potentials for PFRs and plasticizers. No obvious correlations between OLR and log K_OW were found, indicating that the other factors (e.g., bioaccumulation pathway and metabolism) besides lipophicity could influence the deposition of PFRs and plasticizers in frog livers. Different parental transfer patterns for PFRs and plasticizers were observed in frogs when using different tissues as parental tissues. Moreover, the liver tissues had similar parental transfer mechanism with muscle tissues.

Occurrence, distribution, and potential exposure risk of organophosphate flame retardants in house dust in South Korea

Concentrations of organophosphate flame retardants (OPFRs), which are used in various plastic products, were analyzed in house dust samples collected from three Korean cities (Suwon, n = 23; Jeonju, n = 20; Kunsan, n = 42). OPFRs, including tris (2-chloroethyl) phosphate (TCEP), tris (2-chloroisopropyl) phosphate (TCPP), and tris (1,3-dichloro-2-propyl) phosphate (TDCPP), were detected in 95%-100% of the samples analyzed, suggesting the widespread use of these compounds in Korea. The levels of TCEP, TCPP, and TDCPP in Suwon, Jeonju, and Kunsan ranged from the limit of quantitation to 46,000, 28,000, and 2400 ng/g, respectively. The concentrations of all OPFRs were significantly higher in house dust samples from Suwon than from Jeonju and Kunsan; this is likely due to the increased use of these compounds in Suwon, which may be associated with the number, volume, and variety of household products in homes. In Korean homes, the estimated daily intake (EDI) of OPFRs through house dust ingestion was lower than the guideline values; however, the EDI of OPFRs for toddlers was 30-fold greater than for adults, suggesting a limited risk to human health. This is the first comprehensive study of the occurrence and distribution of OPFRs in house dust in Korea.

Occurrence and trophic transfer of synthetic musks in the freshwater food web of a large subtropical lake

Synthetic musks (SMs) have drawn worldwide attention, as they are persistent, bioaccumulative, and toxic to many organisms. There is not enough information on the bioaccumulation and trophodynamic behavior of SMs in freshwater food webs to reliably understand the associated ecological risks. In this study, the concentrations of six SM congeners in fifteen aquatic species from Lake Chaohu, China, was investigated. The total concentrations of the six SMs ranged from 0.29 to 59.7 ng/g dry weight (median, 4.41) in fish muscle tissue and in the whole body tissues of small fish species and shrimps. Galaxolide (HHCB) and tonalide (AHTN) were the predominant congeners, accounting for 65.0% and 28.5% of the total SM concentration, respectively. On the whole, the total concentrations of SMs in livers and gills were 0.18-32.8 and 0.84-254 times higher than those in muscle tissues in fish species, respectively. In the food web of Lake Chaohu, cashmeran (DPMI) and HHCB showed a trend towards trophic magnification, and AHTN tended to show trophic dilution, but these trends were not statistically significant. This suggested that the trophic transfer of these chemicals through the food web was strongly influenced by many factors, including tissue-specific distribution within individuals at higher trophic levels. More investigation into the trophic transfer of SMs in aquatic ecosystems and the factors influencing uptake is needed.

In vitro metabolic kinetics of cresyl diphenyl phosphate (CDP) in liver microsomes of crucian carp (Carassius carassius)

Cresyl diphenyl phosphate (CDP), as a kind of aryl substituted organophosphate esters (OPEs), is commonly used as emerging flame retardants and plasticizers detected in environmental media. Due to the accumulation of CDP in organisms, it is very important to discover the toxicological mechanism and metabolic process of CDP. Hence, liver microsomes of crucian carps (Carassius carassius) were prepared for in vitro metabolism kinetics assay to estimate metabolism rates of CDP. After 140 min incubation, the depletion of CDP accounted for 58.1%-77.1% (expect 0.5 and 2 μM) of the administrated concentrations. The depletion rates were best fitted to the Michaelis-Menten model (R² = 0.995), where maximum velocity (V_max) and Michaelis-Menten constant (K_m) were 12,700 ± 2120 pmol min^-1·mg^-1 protein and 1030 ± 212 μM, respectively. Moreover, the in vitro hepatic clearance (C_Lint) of CDP was 12.3 μL min^-1·mg^-1 protein. Log K_ow and bioconcentration factor (BCF) of aryl-OPEs were both higher than those of alkyl- and chlorinated-OPEs, indicating that CDP may easily accumulate in aquatic organisms. The results made clear that the metabolism rate of CDP was greater than those of other OPEs detected in liver microsomes in previous research. This paper was first of its kind to comprehensively investigate the in vitro metabolic kinetics of CDP in fish liver microsomes. The present study might provide useful information to understand the environmental fate and metabolic processes of these kinds of substances, and also provide a theoretical basis for the ecological risk assessment of emerging contaminants.

Aerobic degradation of nonhalogenated organophosphate flame esters (OPEs) by enriched cultures from sludge: Kinetics, pathways, bacterial community evolution, and toxicity evaluation

The degradation by bacteria has been considered the main process for eliminating nonhalogenated organophosphate esters (OPEs) from wastewater treatment plants (WWTPs), but limited research has reported the biodegradation processes and clarified the microbial-mediated mechanisms for nonhalogenated OPE degradation in WWTPs. The aim of this study was to monitor the biodegradation of the most common nonhalogenated OPEs, namely, tris(2-butoxyethyl) phosphate (TBOEP), tris (n-butyl) phosphate (TNBP) and trisphenyl phosphate (TPHP), under aerobic conditions by sludge cultures from a conventional sewage plant. The microbial cultures were enriched separately with each OPE from activated sludge cultures, and the presence of glucose significantly enhanced degradation of the OPEs during the enrichment. The removal ratios for the three OPEs reached 29.3-89.9% after 5 cycles (25 days) of cultivation, and the first-order degradation kinetics followed the order of TPHP > TBOEP > TNBP, with their half-lives ranging between 12.8 and 99.0 h. Pathways of hydrolysis, hydroxylation, methoxylation, and substitution were confirmed for the aerobic biodegradation of these nonhalogenated OPEs, but only di-alkyl phosphates (DAPs) largely accumulated in culture medium as the most predominant transformation products. Phylotypes in Klebsiella were significantly more abundant during OPE biodegradation than in the initial sludge, which indicated that these microorganisms are associated with the biodegradation of nonhalogenated OPEs in sludge culture. Biodegradation of all investigated nonhalogenated OPEs was associated with a significant reduction in the residual toxicity to Vibrio fischeri, indicating a rather positive ecotoxicological outcome of the aerobic biotransformation processes achieved by the enriched sludge culture.

Be Aware of Organophosphate Diesters as Direct Sources in Addition to Organophosphate Ester Metabolites in Food Supplies

The substantial application of organophosphate triesters (tri-OPEs) may lead to a concentration escalation of their major metabolites, organophosphate diesters (di-OPEs) in animal-derived and plant-derived animal protein supplement feeds (APFs). APFs are major food for raised animals and may bring OPEs into the food supply. In the present study, the concentrations of Σ₈di-OPEs in animal-derived and plant-derived APFs were in the range of 1.98-182 ng/g dw (average: 39.2 ng/g dw). Meat meal had the highest average concentrations of di-OPEs (52.1 ng/g dw), followed by blood meal (49.9 ng/g), feather meal (23.3 ng/g dw), and plant-derived feeds (18.3 ng/g dw). The concentrations of di-OPEs were at the same order of magnitude as those of tri-OPEs in APFs. Bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) was the major contributor in blood meal, feather meal, and plant-derived APFs, while dimethyl phosphate dominated in meat meal. The ratios of di-OPEs/tri-OPEs (R_di/tri) displayed large variability, ranging from 0 for the bis(2-chloroethyl) phosphate-tris(2-chloroethyl) phosphate pair to 175 for the BDCIPP-tris(1,3-dichloroisopropyl) phosphate pair, which indicated that the metabolism capacities and environmental sources for di-OPEs are diverse in APFs. Different R_di/tri between APFs and similar food matrices implied that di-OPEs may have different environmental sources. The similar R_di/tri values for some of the di-/tri-OPE pairs among APFs and dust samples indicated that dust may be a direct exogenous source of OPE exposure in some APF matrices. Future studies should simultaneously focus on tri- and di-OPEs, together of which may reflect the actual exposure to OPEs through the food supply.

Tissue distribution and bioaccumulation of organophosphate esters in wild marine fish from Laizhou Bay, North China: Implications of human exposure via fish consumption

Despite organophosphate esters (OPEs) are ubiquitous in the environment, limited information is available about their tissue-specific accumulation potential in marine fish and exposure risks. Ten fish species from the coastal area of Laizhou Bay, North China, were sampled and analyzed to investigate tissue levels, bioaccumulation, and human exposure risks of 20 OPEs. Seventeen OPEs were detected in fish tissues with total concentration ranging from 6.6-107 ng/g dry weight. The average log bioaccumulation factor (BAF) values of OPEs ranged from 2.8 to 4.4 in livers, 2.3-3.8 in muscles, 2.5-3.9 in gills, and 2.8-4.4 in kidneys. The log BAF values of OPEs significantly increased with increasing their log K_OW values (r = 0.55-0.63, p < 0.001). The estimated daily intake of OPEs ranged from 1.7-12.0 and 3.1-22.1 ng/kg bw/d for rural and urban residents, respectively. The hazard quotients of OPEs were in the range of 4 × 10 ^-5 to 6.7 × 10 ^-4 and 7 × 10 ^-5 to 1.2 × 10 ^-3 for rural and urban residents, respectively. Results showed that the human health risks of OPEs associated with fish consumption is at low level.

Transcriptomics and metabolomics reveal Ca2+ overload and osmotic imbalance-induced neurotoxicity in earthworms (Eisenia fetida) under tri-n-butyl phosphate exposure

Tri-n-butyl phosphate (TNBP) is mass-produced and widely utilized in many products, which has increasingly drawn concern about its potential environmental risks. However, little is known about the toxic mechanism on soil-dwelling organisms caused by TNBP. In this study, earthworms (Eisenia fetida) were exposed to environmentally relevant or higher concentrations of TNBP (0, 0.1, 1, and 10 mg/kg) in artificial soil for 14 days. Our results showed that TNBP accumulated in earthworm nervous tissue (cerebral ganglions). In addition, the content of glutamate in cerebral ganglions decreased compared to the control (p < 0.05). The concentration of Ca²⁺ in earthworm cerebral ganglions increased. However, both Na⁺/K⁺-ATPase and Ca²⁺-ATPase activities were significantly reduced compared to the control (p < 0.05), which led to neurotoxicity in earthworm nervous tissue. Furthermore, the transcriptome and metabolomics revealed the toxic mechanism in earthworm nervous tissue caused by TNBP. Results indicated that the main neurotoxicity mechanisms induced by TNBP were an osmotic imbalance and Ca²⁺ overload in cerebral ganglions. Our findings fill a gap in the literature on neurotoxicity mechanisms of earthworm response to TNBP exposure and contribute to a better understanding of the adverse effects of TNBP on soil-dwelling organisms in terrestrial ecological systems.

Occurrence, analysis and risk assessment of organophosphate esters (OPEs) in biota: A review

Due to their widespread use, organophosphate esters (OPEs) are commonly detected in various environmental matrices and have been identified as emerging contaminants. In this review article, the occurrence and analytical techniques of OPEs in the biotic environment have been compiled and reviewed. Data from studies published the last decade all over the world covering a variety of species in trophic chain have been synthesized and evaluated. OPEs are among the most frequent detected flame retardants and high concentrations are detected in biota to date. Knowledge gaps and recommendations for future research are discussed emphasizing on further monitoring, advanced analytical methodologies, and risk assessment studies to completely understand the science of OPEs in biota.

Legacy and emerging organophosphorus flame retardants and plasticizers in frogs: Sex difference and parental transfer

Black-spotted frogs and bullfrogs from an e-waste polluted area were collected and examined for legacy and emerging organophosphorus flame retardants (PFRs) and plasticizers. Total concentrations of PFRs and plasticizers were 0.62-15 ng/g wet weight (ww) and 316-4904 ng/g ww in muscles, 2.2-59 ng/g ww and 127-5757 ng/g ww in eggs and gonads, and 1.2-15 ng/g ww and 51-1510 ng/g ww in oviducts, respectively. For muscle tissues, concentrations of ∑PFRs, triethyl phosphate, tris-(2-chloroethyl) phosphate, and tris-(chloro-2-propyl) phosphate were significantly higher in the males than females (p < 0.05). However, for reproductive tissues, eggs exhibited higher levels of those contaminants than gonads (p < 0.05). No significant sex difference in levels of plasticizers was observed in muscles. In contrast, levels for (2-ethylhexyl) phthalate, di-n-butyl phthalate, and di-iso-butyl phthalate in gonads were significantly higher than those in eggs (p < 0.05). Significantly negative linear correlations between maternal transfer ratios and log K_OW were found in female frogs. Paternal transfer potentials were first significantly and positively correlated to log K_OW (<6) and then decreased afterward in the males. These results indicated that parental transfer was answer for the sex-specific accumulation of PFRs and plasticizers in frogs.

In vitro methods for predicting the bioconcentration of xenobiotics in aquatic organisms

The accumulation of anthropogenic chemical substances in aquatic organisms is an immensely important issue from the point of view of environmental protection. In the context of the increasing number and variety of compounds that may potentially enter the environment, there is a need for efficient and reliable solutions to assess the risks. However, the classic approach of testing with fish or other animals is not sufficient. Due to very high costs, significant time and labour intensity, as well as ethical concerns, in vivo methods need to be replaced by new laboratory-based tools. So far, many models have been developed to estimate the bioconcentration potential of chemicals. However, most of them are not sufficiently reliable and their predictions are based on limited input data, often obtained with doubtful quality. The octanol-water partition coefficient is still often used as the main laboratory tool for estimating bioconcentration. However, according to current knowledge, this method can lead to very unreliable results, both for neutral species and, above all, for ionic compounds. It is therefore essential to start using new, more advanced and credible solutions on a large scale. Over the last years, many in vitro methods have been newly developed or improved, allowing for a much more adequate estimation of the bioconcentration potential. Therefore, the aim of this work was to review the most recent laboratory methods for assessing the bioconcentration potential and to evaluate their applicability in further research.

Beyond Traditional Organophosphate Triesters: Prevalence of Emerging Organophosphate Triesters and Organophosphate Diesters in Indoor Dust from a Mega E-waste Recycling Industrial Park in South China

Numerous studies have reported the environmental contamination with traditional organophosphate triesters (tri-OPEs), but there is very little information on emerging tri-OPEs and organophosphate diesters (di-OPEs), especially in e-waste recycling areas. In this study, we conducted a comprehensive survey to monitor a broad suite of 11 traditional tri-OPEs, 12 emerging OPEs, and 10 di-OPEs in indoor dust collected from the workshops of (n = 42) and residential homes adjacent to (n = 24) a mega e-waste recycling industrial park in South China. In addition to traditional tri-OPEs, all of the emerging OPEs and di-OPEs were frequently detected in the dust samples. Total concentrations of emerging tri-OPEs and di-OPEs were in the range of 1210-62 900 and 2010-55 600 ng/g in the workshop dust and 435-23 700 and 186-4350 ng/g in the local home dust, respectively, which were comparable to those of traditional tri-OPEs (1160-61 500 and 370-13 900 ng/g, respectively). Most OPEs exhibited significantly higher concentrations in workshop dust versus local home dust (p < 0.05), indicating that e-waste dismantling activities contributed to the high residues of OPEs in indoor dust. Correlation analysis revealed that tri-OPEs have some common emission sources, i.e., e-waste and household products, while di-OPEs could originate from different sources, e.g., tri-OPE degradation, direct commercial application, and impurities in tri-OPE formulas. For both occupational workers and local adults, the median estimated daily intake values of emerging tri-OPEs (7.5 and 1.7 ng/kg bw/day, respectively) and di-OPEs (3.9 and 0.2 ng/kg bw/day, respectively) were comparable to that of traditional tri-OPEs (4.3 and 1.0 ng/kg bw/day, respectively), which suggests the important contribution of the emerging tri-OPEs and di-OPEs to the overall risks of human external exposure to OPE chemicals.

Organophosphate Diesters (Di-OPEs) Play a Critical Role in Understanding Global Organophosphate Esters (OPEs) in Fishmeal

Organophosphate triesters (tri-OPEs) have recently been widely identified in aquatic ecosystems, but information on their organophosphate diester (di-OPE) metabolites is sparsely available. Herein, uniform fishmeal products were collected across the globe (the U.S., China, Europe, South America, and Southeast Asia). Sixteen representative tri-OPEs and eight di-OPEs were investigated to reveal whether industrial production, metabolism, environmental persistence, or physicochemical properties are the key factors influencing their environmental burden and distribution. Tri-OPEs and di-OPEs were 100% detected in fishmeal, with bis(2-chloroethyl) hydrogen phosphate (BCEP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) at discernible levels in marine fauna for the first time. Average concentration of di-OPEs (49.6 ± 27.5 ng/g dw) was of the same order of magnitude as that of tri-OPEs (59.3 ± 92.2 ng/g dw). Geographical-specific distributions of tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP), triphenyl phosphate (TPhP), tris(2-butoxyethyl) phosphate (TBOEP), and 2-ethylhexyl diphenyl phosphate (EHDPP) were statistically significant (p < 0.05). Mean concentration ratios ranged from 0.087 for the BCEP-TCEP pair to 507 for the dimethyl phosphate (DMP)-trimethyl phosphate (TMP) pair. Only the TPhP-diphenyl phosphate (DPhP) pair presented a strong positive linear correlation (r = 0.731; p < 0.01), and DPhP was proved a degradation origin. Commercial sources had a significant overall impact on distribution patterns of the DMP-TMP and the dibutyl phosphate (DnBP) - tri-n-butyl phosphate (TnBP) pairs, whereas biotic transformation and abiotic stability profoundly influenced the bis(2-ethylhexyl) phosphate (BEHP)-tris(2-ethylhexyl) phosphate (TEHP), the bis(1-chloro-2-propyl) phosphate (BCIPP)-TCIPP, and the BCEP-TCEP pairs. Di-OPEs are critical to understand environmental behavior of tri-OPEs in marine fauna.

Biochemical responses of a freshwater fish Cirrhinus mrigala exposed to tris(2-chloroethyl) phosphate (TCEP)

Freshwater fish Cirrhinus mrigala were exposed to tris(2-chloroethyl) phosphate (TCEP) with three different concentrations (0.04, 0.2, and 1 mg/L) for a period of 21 days. During the study period, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels were significantly (p < 0.05) inhibited. The superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and lipid peroxidation (LPO) levels were increased significantly (p < 0.05) in gills, liver, and kidney tissues, whereas glutathione (GSH) and glutathione peroxidase (GPx) (except liver tissue) activities were inhibited when compared to the control group. Likewise, exposure to TCEP significantly (p < 0.05) altered the biochemical (glucose and protein) and electrolyte (sodium, potassium, and chloride) levels of fish. Light microscopic studies exhibited series of histopathological anomalies in the gills, liver, and kidney tissues. The present study reveals that TCEP at tested concentrations causes adverse effects on fish and the studied biomarkers could be used for monitoring the ecotoxicity of organophosphate esters (OPEs).

Three organophosphate flame retardants (OPFRs) reduce sperm quality in Chinese rare minnows (Gobiocypris rarus)

Organophosphate flame retardants (OPFRs) are widespread in the aquatic environment, but the effects of these chemicals on reproductive toxicity are far from clear. In this study, sperm quality in adult male Chinese rare minnows after exposure to tris-(2-butoxyethyl) phosphate (TBOEP), tris-(1,3-dichloro-2-propyl) phosphate (TDCIPP), and triphenyl phosphate (TPHP) was investigated. No obvious change in sperm concentration and vitality was observed after treatments, whereas significant changes in sperm velocity and morphology were found following all treatments (P < 0.05). Moreover, OPFR exposure significantly increased the apoptosis ratios in testis cells. Analysis of the transcriptomic data revealed that Na⁺/K⁺ ATPase (NKA) related genes were significantly downregulated, and the NKA enzyme activities after all treatments were significantly inhibited (P < 0.05). However, no obvious change in hormone levels in the groups exposed to TBOEP and TDCIPP was observed. These findings indicate that the OPFR-induced reduction of sperm quality might be due to the effects of OPFRs on NKA enzyme instead of changes in hormone levels.

Organophosphate esters and their specific metabolites in chicken eggs from across Australia: Occurrence, profile, and distribution between yolk and albumin fractions

A substantial increase in the usage of organophosphate esters (OPEs) as flame retardants and plasticizers in rubbers, textiles, upholstered furniture, lacquers, plastics, building materials and electronic equipment has resulted in their increasing concentrations in the environment over time. However, little is known about the concentrations and fate of OPEs and their metabolites (mOPEs) in biota, including chicken eggs. The aim of this study was to understand the spatial variation in the concentrations in chicken eggs and the partitioning between yolk and albumin. In total, 153 chicken eggs were purchased across Australia and analysed for 9 OPEs and 11 mOPE. Most of the compounds were found to be deposited in egg yolk, where diphenyl phosphate (DPHP, 3.8 ng/g wet weight, median) and tris(2-chloroisopropyl) phosphate (TCIPP, 1.8 ng/g wet weight, median) were predominant mOPE and OPE, respectively. Moreover, no spatial differences in concentrations of OPEs and mOPEs in eggs purchased from different locations were found in this study. Although comparable levels of ∑OPEs were detected in egg yolk and albumin, much higher concentrations of ∑mOPEs were found in yolk than albumin. Meanwhile, a negative correlation (R² = 0.964, p = 0.018) was found between the molecular mass of analytes and partitioning coefficient of C_yolk/C_yolk+albumin (defined as chemical concentration in egg yolk divided by the sum of chemical concentrations in both yolk and albumin). These results indicate that n-octanol/water partition coefficients (log K_OW) may not be a crucial factor in the distribution of OPEs and mOPEs between egg yolk and albumin, which is important in understanding distribution of emerging organic contaminants in biota.

The interactions of diet-induced obesity and organophosphate flame retardant exposure on energy homeostasis in adult male and female mice

Previously, sex-dependent alterations in energy homeostasis were reported in adult mice fed a standard chow attributed to exposure to a mixture of organophosphate flame retardants (OPFRs) via estrogen receptors (ERα). In this study, adult male and female mice (C57BL/6J; Taconic) were treated with the same mixture of OPFRs (1 mg/kg each of tricresyl phosphate (TCP), triphenyl phosphate (TPP), and tris(1-3-dichloro-2propyl)phosphate (TDCPP)) for 7 weeks on a low-fat diet (LFD, 10% kcal fat) or a high fat (HFD, 45% kcal fat) in a diet-induced obesity model. Consistent with our previous observations, OPFRs altered weight gain in males, differentially with diet, while females remained unaffected. OPFR treatment also revealed sex-dependent perturbations in metabolic activity. During the night (approximately 0100-0400 hr), males exhibited elevated activity and oxygen consumption, while in females these parameters were decreased, irrespective of diet. OPFR disrupted feeding behavior and abolished diurnal water intake patterns in females while increasing nighttime fluid consumption in males. Despite no marked effect of OPFRs on glucose or insulin tolerance, OPFR treatment altered circulating insulin and leptin in females and ghrelin in males. Data indicate that adult OPFR exposure might influence, and perhaps exacerbate, the effects of diet-induced obesity in adult mice by altering activity, ingestive behavior, and metabolism.

Tissue-specific bioaccumulation, metabolism and excretion of tris (2-ethylhexyl) phosphate (TEHP) in rare minnow (Gobiocyprisrarus)

Tris (2-ethylhexyl) phosphate (TEHP) is one of the most commonly used organophosphorus flame retardant (OPFR) analogues and is commonly detected in surface water and sediments. Limited information is available about the metabolic pathway or metabolite formation related to TEHP in fish. In this study, rare minnows (Gobiocyprisrarus) were exposed to TEHP in static water for 30 d to investigate the bioaccumulation and metabolite distribution in the fish muscle, liver, kidney, gill, GI-tract, ovary and testis. Based on the estimated k_up,_parent and k_d,parent values, the bioconcentration factors (BCF_parent) of TEHP in fish tissues were calculated in the order of kidney > ovary ≈ liver ≈ testis > gill ≈ GI-tract > muscle; this finding was consistent with the results of our previous study on other alkyl-substituted OPFRs. In addition, this study identified the metabolic profiles of TEHP in the liver. TEHP was oxidatively metabolized by the fish to a dealkylated metabolite (di 2-ethylhexyl phosphate; DEHP) and hydroxylated TEHP (OH-TEHP). OH-TEHP further underwent extensive phase II metabolism to yield glucuronic acid conjugates. DEHP was mainly distributed in rare minnow in the following order: liver > GI-tract > kidney ≫ other tissues. However, the metabolite showed lower accumulation potential in fish tissues than TEHP, with metabolite parent concentration factors (MPCFs) for DEHP of less than 0.1 in all the investigated tissues. The BCF_parent values of TEHP in various fish tissues were only 9.0 × 10^-3-7.2 × 10^-4 times its estimated tissue-water partition coefficient (K_tissue-water) values based on tissue lipid, protein and water contents, which indicated the significance of biotransformation in reducing the bioaccumulation potential of TEHP in fish. The toxicokinetic data in the present study help in understanding the tissue-specific bioaccumulation and metabolism pathways of TEHP in fish and highlight the importance of toxicology research on TEHP metabolites in aquatic organisms.

In vitro oxidative stress, mitochondrial impairment and G1 phase cell cycle arrest induced by alkyl-phosphorus-containing flame retardants

Phosphorus-containing flame retardants (PFRs) have been frequently detected in various environmental samples at relatively high concentrations and are considered emerging environmental pollutants. However, their biological effects and the underlying mechanism remain unclear, especially alkyl-PFRs. In this study, a battery of in vitro bioassays was conducted to analyze the cytotoxicity, oxidative stress, mitochondrial impairment, DNA damage and the involved molecular mechanisms of several selected alkyl-PFRs. Results showed that alkyl-PFRs induced structural related toxicity, where alkyl-PFRs with higher logKow values induced higher cytotoxicity. Long-chain alkyl-PFRs caused mitochondrial and DNA damage, resulting from intracellular reactive oxygen species (ROS) and mitochondrial superoxide overproduction; while short-chain alkyl-PFRs displayed adverse outcomes by significantly impairing mitochondria without obvious ROS generation. In addition, alkyl-PFRs caused DNA damage-induced cell cycle arrest, as determined by flow cytometry, and transcriptionally upregulated key transcription factors in p53/p21-mediated cell cycle pathways. Moreover, compared to the control condition, triisobutyl phosphate and trimethyl phosphate exposure increased the sub-G1 apoptotic peak and upregulated the p53/bax apoptosis pathway, indicating potential cell apoptosis at the cellular and molecular levels. These results provide insight into PFR toxicity and the involved mode of action and indicate the mitochondria is an important target for some alkyl-PFRs.

Occurrence and ecological implications of organophosphate triesters and diester degradation products in wastewater, river water, and tap water

The occurrence and composition profiles of 13 triester organophosphate flame retardants and their three diester metabolites in river water, wastewater, and tap water in China were studied. Most target organophosphate esters (OPEs) were found in water samples, with average concentrations of 787 ng/L for triethyl phosphate (TEP) and 0.1 ng/L for tripropyl phosphate (TPP) in wastewater, 1.48 × 10³ ng/L for TEP and 0.12 ng/L for tripentyl phosphate (TPeP) in river water, and 15.5 ng/L for tris(2-chloroethyl) phosphate (TCEP) and 0.08 ng/L for tritolyl phosphate (TMPP) in tap water. TEP was the most abundant compound among the detected OPEs in all water types. The exposure of zebrafish embryos showed negligible effects of TEP, triphenyl phosphate (TPHP), and diphenyl phosphate (DPHP), while mixed solutions that mimic river water and wastewater composition disturbed the development of embryos and led to the altered transcription of genes relating to the hypothalamic-pituitary-thyroid (HPT) axis. In addition, the binding affinity between OPEs and a thyroid hormone receptor (TRβ) protein was further investigated by molecular docking modeling, which helped to estimate the effects of OPEs on TRβ. This research provides experimental and theoretical evidence for the ecotoxicological effects of OPEs in aquatic environments.

Legacy and emerging semi-volatile organic compounds in sentinel fish from an arctic formerly used defense site in Alaska

The Arctic is subject to long-range atmospheric deposition of globally-distilled semi-volatile organic compounds (SVOCs) that bioaccumulate and biomagnify in lipid-rich food webs. In addition, locally contaminated sites may also contribute SVOCs to the arctic environment. Specifically, Alaska has hundreds of formerly used defense (FUD) sites, many of which are co-located with Alaska Native villages in remote parts of the state. The purpose of this study was to investigate the extent of SVOC contamination on Alaska's St. Lawrence Island through the analysis of sentinel fish, the ninespine stickleback (Pungitius pungitius), collected from Troutman Lake located within the watershed of an FUD site and adjacent to the Yupik community of Gambell. We measured the concentrations of legacy and emerging SVOCs in 303 fish samples (81 composites), including polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), organophosphate esters (OPEs) and their diester metabolites, and per- and poly-fluoroalkyl substances (PFAS). PBDEs and PCBs were the most abundant SVOC groups found in stickleback with ΣPBDE and ΣPCB median concentrations of 25.8 and 10.9 ng/g ww, respectively, followed by PFAS (median ΣPFAS 7.22 ng/g ww). ΣOPE and ΣOPE metabolite concentrations were lower with median concentrations of 4.97 and 1.18 ng/g ww, respectively. Chemical patterns and distributions based on correlations and comparison with SVOC concentrations in stickleback from other parts of the island suggest strong local sources of PCBs, PBDEs, and PFAS on St. Lawrence Island.

Occurrence, biomagnification and maternal transfer of legacy and emerging organophosphorus flame retardants and plasticizers in water snake from an e-waste site

Water snake and small common carp samples collected from a Chinese pond polluted with electronic waste (e-waste) were analyzed for organophosphorus flame retardants (PFRs), PFR metabolites, and plasticizers to investigate their occurrence, biomagnification, and maternal transfer in ovoviviparous species. Mean concentrations of total PFRs, PFR metabolites, and plasticizers were 2.2-16, 1.3-2.8 and 151-1320 ng/g wet weight (ww), respectively in analyzed organisms. Metabolites of PFRs were found in the same order of magnitude as or even higher than their parent compounds, indicating the importance of monitoring metabolites to evaluate the internal exposure of PFRs in organisms. Biomagnification factors (BMFs) were below 1 for all targeted chemicals and negatively correlated with metabolite/parent ratios (MPRs), suggesting a biodilution driven by metabolism. The lipid normalized concentrations were lower in eggs than in muscle for most of targeted chemicals. The maternal transfer potential was significantly and positively correlated with log K_OW (p < 0.05) when log K_OW was below 6.

Organophosphate flame retardants in heron eggs from upper Yangtze River basin, southwest China

The egg samples of four heron species, including black-crowned night heron (Nycticorax nycticorax), little egret (Egretta garzetta), Chinese pond heron (Ardeola bacchus) and cattle egret (Bubulcus ibis), were collected from the upper Yangtze River (Changjiang) Basin, Southwest China in early summer of 2017. Nine out of ten target organophosphate flame retardants (PFRs) were detected in these heron egg samples. The sum of concentrations of the PFRs quantified (∑PFRs) ranged from 63 to 590 pmol g^-1 ww (18-185 ng g^-1 ww) with a median value of 139 pmol g^-1 ww (48 ng g^-1 ww) among all samples. The median ∑PFRs in eggs of night herons (160 pmol g^-1 ww) was higher than Chinese pond herons (median 121 pmol g^-1 ww) and little egrets (median 109 pmol g^-1 ww). In heron eggs, ∑PFRs were mainly contributed by tri-n-butyl phosphate (TNBP), tris (isobutyl) phosphate (TIBP), tris (1-chloro-2-propyl) phosphate (TCIPP) and tri-2-methylphenyl phosphate (TMPP). Alkyl-PFRs accounted for approximately 28%-85% (median 57%) of the nine PFRs quantified while the rest is contributed by aryl-PFRs and chlorinated PFRs. Lower levels of PFRs in little egret eggs were found upstream than downstream of the Yangtze. In addition, the daily intakes of PFRs through ingestion of heron eggs were estimated at lower levels.

Organophosphorus flame retardants in a typical freshwater food web: Bioaccumulation factors, tissue distribution, and trophic transfer

Water, sediment, and wild aquatic species were collected from an electronic waste (e-waste) polluted pond in South China. This study aimed to investigate the bioaccumulation, tissue distribution, and trophic transfer of organophosphorus flame retardants (PFRs) in these aquatic organisms. The concentrations of PFRs detected in the analyzed organisms were between 1.7 and 47 ng/g wet weight (ww). Oriental river prawn and snakehead exhibited the highest and lowest levels, respectively. Tri-n-butyl phosphate (TnBP), tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCPP) and triphenyl phosphate (TPhP) were dominant contaminants, accounting for approximately 86% of the total sum. The mean values of bioaccumulation factors (BCFs) and logarithmic biota-sediment accumulation factors (log BSAFs) for individual PFRs varied from 6.6 to 1109 and from -2.0 to 0.41, respectively. Both log BCFs and log BSAFs of PFRs were significantly and positively correlated with their octanol-water partitioning coefficient (log K_OW). The concentrations of PFRs in tissues of large mud carp and snakehead were significantly and positively correlated with the lipid content (each p < 0.05) and the liver, kidney, and gill exhibited high PFR levels. When the concentration was expressed on a lipid basis, liver exhibited the lowest level, indicating the probable effects of metabolism. Significantly positive correlation was also found between lipid content and total PFR concentration in muscle of all aquatic organisms, given the strong correlation between lipid content and the concentration of TnBP. Trophic magnification factors (TMF) of TnBP and TPhP were lower than 1 (0.57 and 0.62), indicating that these PFRs undergo trophic dilution in this aquatic food web.

Distribution of flame retardants in smartphones and identification of current-use organic chemicals including three novel aryl organophosphate esters

Smartphones have become an integral tool of society; in the year 2017, approximately 30% of the global population used smartphones. After their life cycle of use, most smartphones are not recycled and are instead discarded as e-waste, which increases the probability that chemicals they contain will eventually be released into the natural environment. In this study, the concentration and distribution of 52 major flame retardant (FR) chemicals were measured in eight components of seven models of largely produced smartphones. The results demonstrated that organophosphate esters (OPEs) were the principal FRs in these smartphone devices, while a suite of halogenated flame retardants (HFRs), including 25 polybrominated diphenyl ethers (PBDEs), were not detected. Triphenyl phosphate (TPHP) was the primary FR in the smartphones, followed by tris(2-butoxyethyl) phosphate (TBOEP), 2-ethylhexyl diphenyl phosphate (EHDPP), triethyl phosphate (TEP), tris(2-chloroethyl) phosphate (TCEP), and tris(2-chloroisopropyl) phosphate (TCIPP), respectively. The average smartphone contained 3.37 × 10⁷ ng TPHP/unit, which was concentrated in the phone screen. We estimated the annual amount of ΣOPEs and TPHP in smartphones used globally to be 53.5 and 51.8 tons, respectively. Extracts of phone screens were further analyzed by use of an untargeted screening strategy, and other 10 organic chemicals were identified. Interestingly, 3 out of them shared similar backbone structure of TPHP, and these 3 chemicals were tri(2,4-di-t-butylphenyl) phosphate (TDTBPP; CAS No. 95906-11-9), 2-biphenylol diphenyl phosphate (BPDPP; 132-29-6), and tris (2-biphenyl) phosphate (TBPHP; 132-28-5). Collectively, this study provided the first information on distribution of major FRs in different components of smartphones, and also identified other 10 current-use organic chemicals including three novel aryl OPEs which should be considered in further environmental studies including in toxicological and monitoring programs.

Bioaccumulation and Trophic Transfer of Emerging Organophosphate Flame Retardants in the Marine Food Webs of Laizhou Bay, North China

Despite the increase in production, usage, and discharge of organophosphate flame retardants (OPFRs), little information is available about their bioaccumulation and trophic transfer in the marine food web. In this study, seawater, sediment, and marine species (10 fish and 9 invertebrate species) collected from Laizhou Bay, North China, were analyzed to investigate the levels, bioaccumulation, and biomagnification of OPFRs in a marine food web. Of 20 OPFRs screened for, 17 were quantifiable in seawater, sediment, and organisms. The ∑OPFRs concentrations ranged from 0.2 to 28.4 ng/L in seawater, 0.1-96.9 ng/g dry weight in sediment, and 21.1-3510 ng/g lipid weight in organisms. Benthic fish accumulated more OPFRs than pelagic fish and invertebrates. A linear and significant increase of bioaccumulation factors with increasing lipophilicity of OPFRs was observed (R² = 0.63, p < 0.05), and the biota-sediment accumulation factors increased with hydrophobicity up to log K_OW = 4.59 and then decreased with increase in log K_OW. Trophic magnification factors of OPFRs ranged from 1.06 to 2.52, indicating biomagnification potential of OPFRs in a marine food web. This study provides important insight into the biomagnification potential of OPFRs and suggests further investigation on this group of chemicals.

Enhanced degradation of triphenyl phosphate (TPHP) in bioelectrochemical systems: Kinetics, pathway and degradation mechanisms

Triphenyl phosphate (TPHP) is one of the major organophosphate esters (OPEs) with increasing consumption. Considering its largely distribution and high toxicity in aquatic environment, it is important to explore an efficient treatment for TPHP. This study aimed to investigate the accelerated degradation of TPHP in a three-electrode single chamber bioelectrochemical system (BES). Significant increase of degradation efficiency of TPHP in the BES was observed compared with open circuit and abiotic controls. The one-order degradation rates of TPHP (1.5 mg L^-1) were increased with elevating sodium acetate concentrations and showed the highest value (0.054 ± 0.010 h^-1) in 1.0 g L^-1 of sodium acetate. This result indicated bacterial metabolism of TPHP was enhanced by the application of micro-electrical field and addition acetate as co-substrates. TPHP could be degraded into diphenyl phosphate (DPHP), hydroxyl triphenyl phosphate (OH-TPHP) and three byproducts. DPHP was the most accumulated degradation product in BES, which accounted more than 35.5% of the initial TPHP. The composition of bacterial community in BES electrode was affected by the acclimation by TPHP, with the most dominant bacteria of Azospirillum, Petrimonas, Pseudomonas and Geobacter at the genera level. Moreover, it was found that the acute toxic effect of TPHP to Vibrio fischeri was largely removed after the treatment, which revealed that BES is a promising technology to remove TPHP threaten in aquatic environment.

Biomonitoring of organophosphate triesters and diesters in human blood in Jiangsu Province, eastern China: Occurrences, associations, and suspect screening of novel metabolites

Since organophosphate (OP) triesters are ubiquitous in environmental matrices, there is an increasing concern regarding human exposure to OP triesters or their metabolites. In this study, we measured levels of 16 OP triesters and 4 OP diesters in n = 99 human blood samples of non-occupationally exposed adults (aged 18-87) from Jiangsu Province, eastern China. Based on the measured concentrations, statistical difference and correlativity were calculated to characterize the population diversity and potential sources of OP triester and diester. Di (2-ethylhexyl) phosphate (DEHP) and 2-ethylhexyl diphenyl phosphate (EHDPP) were found in many participants' blood, with median concentrations of 1.2 (range: n.d. - 44.7, detection frequency: 99%) and 0.85 (n.d. - 28.8, 68%) ng mL^-1, respectively. Blood samples of older participants contained significantly lower concentrations of OP diesters or triesters than their younger counterparts (p < 0.01). Regional- and age-specific differences in the blood concentrations of OP triesters and diesters were attributed to disparities in environmental exposure intensity. EHDPP and tris (phenyl) phosphate (TPHP), the predominant OP triesters, exhibited significant positive correlation (p < 0.01, r = 0.84) suggestive of analogous transport behavior from similar exposure sources to humans. The increased correlations between diphenyl phosphate (DPHP) and TPHP as well as with EHDPP as observed from the multivariate regression suggests that DPHP could be derived from the metabolism of both TPHP (the crucial precursor) and EHDPP. When the blood samples were subsequently screened using high-resolution spectrometry, we detected five novel OP metabolites: glucuronide conjugates of hydroxylated DEHP (OH-DEHP glucuronide conjugate), 2-ethylhexyl monophenyl phosphate (EHMPP), hydroxylated EHMPP (OH-EHMPP), dihydroxylated bis(2-butoxyethyl) phosphate (di-OH-BBOEP), and dihydroxylated tris(butyl) phosphate (di-OH-TNBP). Overall, this study provides novel information regarding the occurrence of OP triesters and diesters, and further suggested several novel OP metabolites in human blood.

Organophosphate flame retardants (OPFRs) induce genotoxicity in vivo: A survey on apoptosis, DNA methylation, DNA oxidative damage, liver metabolites, and transcriptomics

BACKGROUND

As potential substitutes for polybrominated diphenyl ethers (PBDEs), organophosphate flame retardants (OPFRs) have been frequently detected in the environment. However, the genotoxicity induced by these OPFRs has rarely been described, and the results reported in previous studies are conflicting and inconsistent.

OBJECTIVES

The present study aimed to determine how OPFRs induced genetic toxicity in vivo.

METHODS

Using Chinese rare minnow as a model, the toxicity of three OPFRs was screened with RNA-seq. To verify the OPFR-induced genotoxicity, alkaline comet assay, cell apoptosis analysis, HPLC-based DNA methylation assay, 8-OHdG assay, bioconcentration and biotransformation investigation were performed.

RESULTS

According to transcriptomic data, TDCIPP exposure substantially altered the pathways related to DNA damage, including the cell cycle, DNA replication, Fanconi anemia pathway, p53 signaling pathway, and various DNA repair pathways. Although TBOEP and TPHP did not affect DNA damage, TDCIPP induced DNA damage in a dose-dependent manner. TDCIPP also induced apoptosis, altered the activities of caspase-3 and -9, and increased the 8-OHdG levels, while a significant difference in the levels of DNA methylation induced by OPFRs was not observed.

CONCLUSIONS

Based on these results, TDCIPP induced DNA oxidative damage, eventually leading to genotoxicity in vivo.

A Review of a Class of Emerging Contaminants: The Classification, Distribution, Intensity of Consumption, Synthesis Routes, Environmental Effects and Expectation of Pollution Abatement to Organophosphate Flame Retardants (OPFRs)

Organophosphate flame retardants (OPFRs) have been detected in various environmental matrices and have been identified as emerging contaminants (EC). Given the adverse influence of OPFRs, many researchers have focused on the absorption, bioaccumulation, metabolism, and internal exposure processes of OPFRs in animals and humans. This paper first reviews the evolution of various types of flame retardants (FRs) and the environmental pollution of OPFRs, the different absorption pathways of OPFRs by animals and humans (such as inhalation, ingestion, skin absorption and absorption), and then summarizes the environmental impacts of OPFRs, including their biological toxicity, bioaccumulation, persistence, migration, endocrine disruption and carcinogenicity. Based on limited available data and results, this study also summarizes the bioaccumulation and biomagnification potential of OPFRs in different types of biological and food nets. In addition, a new governance idea for the replacement of existing OPFRs from the source is proposed, seeking environmentally friendly alternatives to OPFRs in order to provide new ideas and theoretical guidance for the removal of OPFRs.

Toxicokinetic patterns, metabolites formation and distribution in various tissues of the Chinese rare minnow (Gobiocypris rarus) exposed to tri(2‑butoxyethyl) phosphate (TBOEP) and tri-n-butyl phosphate (TNBP)

Alkylated organophosphate esters (alkyl-OPEs) are widely used and extensively detected in aquatic organisms. This work investigated the tissue-specific toxicokinetics of two common alkyl-OPEs, tri(2‑butoxyethyl) phosphate (TBOEP) and tri‑n‑butyl phosphate (TNBP) in Chinese rare minnow (Gobiocypris rarus) through a 50 day uptake and depuration experiment. The tissue-specific bioconcentration factor (BCF) values for the two alkyl-OPEs ranged from 1 to 30 L/kg wet weight (ww), with the kidney and ovary as the tissues with the highest accumulation. The tissue BCFs only exhibited a significant correlation with lipid contents only in storage tissues (i.e., muscle, brain, ovary and testis), indicating that lipids might not be the major contributor to tissue distribution of TBOEP and TNBP. However, the contribution of blood perfusion and active transport to tissue-specific OPE accumulation needs to be further investigated. Lower accumulation of metabolites than parent chemicals was observed, with metabolite parent concentration factors (MPCFs) <1. Di-alkyl phosphate (DAP), bis(2‑butoxyethyl) phosphate (BBOEP) and di(n-butyl) phosphate (DNBP) were the most abundantly formed metabolites of TBOEP and TNBP in various tissues, followed by the monohydroxylated OPEs (OH-OPEs). However, bis(2‑butoxyethyl) hydroxyethyl phosphate (BBOEHEP), was detected at much lower levels in the tissues. All the investigated metabolites showed high production rates (k_{prod,metabolites}) in the fish liver, followed by the GI tract and the kidney, indicating the importance of the hepatobiliary and urinary systems in eliminating the metabolites. Our study suggested that metabolism plays an important role in eliminating these two alkyl-OPEs in rare minnow and results in different tissue distribution mechanisms for metabolites and their compounds.

Bioconcentration and biotransformation of organophosphorus flame retardants (PFRs) in common carp (Cyprinus carpio)

Understanding the bioaccumulation and biotransformation of xenobiotic compounds is critical for evaluating their fate and potential toxicity in vivo. In the present study, the tissue specific accumulation and depuration of seven organophosphorus flame retardants (PFRs) in common carp (Cyprinus carpio) were investigated after exposing the fish to an environmental relevant level of PFRs. The log K_ow of PFRs was significantly negatively correlated to the percentages of individual PFRs to the total PFRs in serum (p < 0.04), whereas significantly positive correlations were observed in all other tissues (p < 0.02). Significant correlations (p < 0.01) between the log K_ow of PFRs and their log bioconcentration factor (BCF_ww) were also found in all investigated tissues except for serum. This suggests that the hydrophobicity of PFRs played a significant role in the distribution and body compartment accumulation of PFRs in common carp. The bioaccumulation potential of PFRs in serum was different from the other tissues, probably due to its specific properties. Dialkyl and/or diaryl phosphate esters (DAP) and hydroxylated PFRs (HO-PFRs) were quantified as the major metabolites. Their levels in liver and intestine were significantly higher than in other tissues. Biotransformation processes also played a crucial role in the accumulation of PFRs in fish. Our results provide critical information for further understanding the bioconcentration, tissue distribution and metabolism of PFRs in fish.

Organophosphorus flame retardants in fish from Rivers in the Pearl River Delta, South China

Twelve organophosphorus flame retardants (PFRs) were detected in the muscle of 3 species of fish, mud carp (Cirrhinus molitorella), tilapia (Tilapia nilotica), and plecostomus (Hypostomus plecostomus), from rivers in the Pearl River Delta (PRD) region. The total concentrations of PFRs in the mud carp, tilapia, and plecostomus ranged from 2.3 to 16, 3.4 to 16, and 3.5 to 30 ng/g wet weight (ww), respectively. Generally, tris(2-ethylhexyl) phosphate (TEHP), tris (2-chloro-isopropyl) phosphate (TCPP), tris (2-chloroethyl) phosphate (TCEP), and tri-n-butyl phosphate (TnBP) were the dominant compounds of the PFRs, collectively accounting for up to 90% of the total PFR levels. Concentrations of PFRs were significantly higher in the plecostomus than in the mud carp and tilapia (p < 0.05), which could be explained by differences in habitat and feeding habits of the fish species. High concentrations of PFRs were found mainly in the Guangzhou section of the Pearl River (site P1, P2, and P3) and site B3, which was similar to our previous study of PFRs in sediment from the Pearl River Delta, indicating a relatively high level of PFRs pollution in these regions. The estimated daily intake (EDI) of total PFRs from consumption of fish was 17 ng/kg bw/day to 98 ng/kg bw/day for adults and children, which was three to four orders of magnitude lower than reference dose values.

Bioavailability and biomagnification of organophosphate esters in the food web of Taihu Lake, China: Impacts of chemical properties and metabolism

The bioavailability and biomagnification of organophosphate esters (OPEs) were investigated in a food web in the Zhushan Bay of Taihu Lake, China. The organisms included mainly three biological groups: plankton, invertebrates, and fish, which displayed distinctly different compositional profiles of OPEs. In general, the log BAFs (bioaccumulation factor) of OPEs displayed a significant correlation with their log K_ow (octanol-water partitioning coefficient), suggesting that the bioaccumulation was mainly controlled by the hydrophobicity. The log BAFs of the more hydrophobic OPEs in benthic invertebrates were higher than in fish, suggesting that ingesting sediment constituted additional exposure route for benthic invertebrates. The log BSAFs (biota-sediment accumulation factor) in the benthic invertebrates increased with log K_ow in the range of 1.44-5.73 and decreased afterwards. The depressed bioavailability of the highly hydrophobic OPEs was attributed to their strong adsorption to the sediment. The biomagnification potency of OPEs was affected by hydrophobicity of the compounds and biotransformation properties in the organisms at different trophic levels. 2-Ethylhexyl diphenyl phosphate biomagnified in the fish food web of Taihu Lake with a TMF (trophic magnification factor) of 3.61, which was due to the combined results of its relatively high hydrophobicity (log K_ow of 5.73) and decreased metabolism potential in the high-trophic-level fish. The constant metabolism diminished the biomagnification potency of hydrophobic compounds triphenyl phosphate and tricresyl phosphate in this food web.

A nationwide survey of 31 organophosphate esters in sewage sludge from the United States

Organophosphate esters (OPEs) are used as flame retardants and plasticizers in a wide range of consumer products. Nevertheless, studies on the occurrence and inventory of OPEs in sewage sludge are limited. In this study, 20 OP triesters and 11 diesters were measured in 75 archived sewage sludge samples collected from 67 wastewater treatment plants (WWTPs) across the United States (US). The median concentrations of ∑20OP-triesters and ∑11OP-diesters in sludge were 1290 and 78.4 ng/g dry weight (dw), respectively. Sludge samples originating from the Western and Northeastern US contained higher concentrations of OP triesters than did those from the Midwestern and Southern US. Sludge samples from WWTPs with larger treatment capacity (>38 million liters per day) contained higher concentrations of OP diesters (p < 0.05). OP diesters in sludge originated from two sources, triester degradation and direct inputs. Land application of sludge to US soils was estimated to result in annual mass inputs of 12,400-14,900 kg/year of OP triesters and 663-796 kg/year of OP diesters. A hazard assessment was performed for 14 OPEs found in sludge, which suggested a low level of risk at the current land application practices of sludge.

Global microRNA and isomiR expression associated with liver metabolism is induced by organophosphorus flame retardant exposure in male Chinese rare minnow (Gobiocypris rarus)

To reveal the adverse effects of organophosphorus flame retardants (OPFRs) on aquatic organisms at the epigenetic level, male Chinese rare minnows were exposed to 0.24 mg/L tris(2‑butoxyethyl) phosphate (TBOEP), 0.04 mg/L tris(1,3‑dichloro‑2‑propyl) phosphate (TDCIPP), or 0.012 mg/L triphenyl phosphate (TPHP) for 14 days. The effects of sub-acute OPFR exposure on liver miRNA and the 3' isomiR expression profiles of Chinese rare minnows were investigated. Through small RNA sequencing and bioinformatics analysis, a total of 32, 84, and 19 differentially expressed miRNAs were detected for TBOEP, TDCIPP, and TPHP exposure, respectively (p < 0.05). Target prediction of the differentially expressed miRNAs and pathway enrichment analysis indicated that predicted altered mRNAs for all three OPFRs were associated with metabolic pathways, whereas base excision repair was only predicted to be perturbed by the TPHP treatment. In addition, 3' isomiR-Us were unexpectedly abundant in all groups (e.g., miR-143), and TDCIPP strongly increased the ratio of 3' isomiR-U expression. Finally, histological examination and metabolic enzyme activity analyses werein agreement with the predicted metabolic pathways. As such, our study indicates that the investigation of epigenetics changes in miRNA gene transcription is a considerable method for the assessment of aquatic toxicity.

Measurement and prediction of bioconcentration factors of organophosphate flame retardants in common carp (Cyprinus carpio)

The increase in the production and usage plus the toxicity nature of organophosphate flame retardants (OPFRs) has become a concern. However, limited information is available about the bioaccumulation potential of OPFRs in fish. In this study, we determined the 96 h LC₅₀ s_, and evaluated the bioaccumulation potential of six most frequently reported OPFRs in gill, kidney, liver, and muscle tissues of common carp (Cyprinus carpio) for 48 d, and a quantitative structure-activity relationship (QSAR) model was developed to predict bioconcentration factors (BCFs) for the remaining 16 OPFRs. The BCFs and half-lives (t_1/2) in the tissues ranged from 6.54 (Tris (2-chloroisopropyl) phosphate, (TCPP)) to 528.15 (Tris (2-ethylhexyl) phosphate (TEHP)), and 2.25-5.78 days, respectively. The tissue-specific concentration and BCFs values followed the order of liver > kidney ≥ intestine >> muscle. The proposed QSAR model with a high cross-validated value (Q²_(cum)) of 0.930 and a correlation coefficient of 0.94 was obtained and was able to predict log BCF from parameters related to molar volume and isotropic average static field polarizability. The results show that the model has a high level of accuracy, making the proposed approach a suitable method for predicting the log BCF.

Concentrations of Organophosphate Esters and Their Specific Metabolites in Food in Southeast Queensland, Australia: Is Dietary Exposure an Important Pathway of Organophosphate Esters and Their Metabolites?

There were several studies that measured organophosphate esters (OPEs) in foods to assess the dietary intake of OPEs but none has measured OPE metabolites (mOPEs) in the same samples. In this study, we measured the concentrations of OPEs and mOPEs in 87 food samples and in five tap water samples collected in Queensland, Australia belonging to eight food groups. Tris(2-chloroisopropyl) phosphate (TCIPP) (detection frequency (DF), 77%) and tributyl phosphate (TBP) (DF, 71%), were the most frequently detected OPEs, while dibutyl phosphate (DBP) (DF, 84%) and diphenyl phosphate (DPhP) (DF, 86%) were the most frequently detected mOPEs. Vegetables had the highest concentrations of both ∑₉OPEs and ∑₁₁mOPEs, with the mean concentrations of 2.6 and 17 ng/g wet weight. Compared with dust ingestion and inhalation, dietary intake was the most important exposure pathway for tris(2-chloroethyl) phosphate (TCEP) (4.1 ng/kg bw/day), TCIPP (25 ng/kg bw/day), and TBP (6.7 ng/kg bw/day), accounting for >75% of total intake. Furthermore, we found that the intakes of some mOPEs, that is, bis(1,3-dichloroisopropyl) phosphate (BDCIPP) and DPhP from diet were typically higher than that of their parent OPEs. Such high levels of mOPE intakes could interfere with the utilization of mOPEs as biomarkers for assessing OPE exposure and warrant further investigation.

Trophic transfer of organophosphorus flame retardants in a lake food web

Despite increasing use of organophosphorus flame retardants (OPFRs), their food web transfer behavior is not well known. In this study, concentrations of fourteen OPFRs were measured in 17 species from Taihu Lake, China, and their trophodynamics were assessed. Of the 14 OPFRs, nine were detected in at least 70% of the food web samples, including tris(ethyl) phosphate (TEP), tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP), tris(isobutyl) phosphate (TIBP), tris(1,3-dichloroisopropyl) phosphate (TDCIPP), tris(n-butyl) phosphate (TNBP), tris(phenyl) phosphate (TPHP), tris(methylphenyl) phosphate (TMPP), and 2-ethylhexyl diphenyl phosphate (EHDPP). The total OPFR concentrations were 100 ± 23 ng/g ww in plankton, 17 ± 11 ng/g ww in invertebrates, and 9.8 ± 6.2 ng/g ww in fish. TIBP (93 ± 16 ng/g ww) was the dominant OPFR in plankton, whereas TCEP (2.4 ± 3.9 ng/g ww) and TPHP (3.3 ± 16 ng/g ww) were dominant in fish. While negative relationships between concentration and aquatic species trophic level were observed for all nine OPFRs, only those for TCIPP (p = 0.022), TDCIPP (p = 0.029), and TMPP (p = 0.021) were statistically significant, with trophic magnification factors (TMFs) of 0.55, 0.39, and 0.42, respectively. This study provides fundamental information for assessing ecological risks of OPFRs.

Triphenyl Phosphate (TPHP)-Induced Neurotoxicity in Adult Male Chinese Rare Minnows ( Gobiocypris rarus)

The neurotoxicity of triphenyl phosphate (TPHP) in exposed humans and laboratory animals is under debate. The rapid crossing of the blood-brain barrier (BBB) and high distribution of TPHP in fish brains have raised widespread concerns about potential neurotoxicity. Adult male Chinese rare minnows ( Gobiocypris rarus) were used as a model and exposed to 0, 20, or 100 μg/L TPHP for 28 days. We evaluated the BBB permeability, neuroinflammatory response, cell proliferation and apoptosis, synaptic plasticity and synapse loss in fish brains via the learning/memory performance of fish following 28 days of TPHP exposure. TPHP significantly increased the BBB permeability, activated the neuroinflammatory response, and decreased the tight junction-related mRNA levels of claudin-5α and occludin in the fish brain. In addition, cell proliferation was inhibited by treatment with 100 μg/L TPHP, but no significant apoptosis was observed in the brain. Fish exposed to 100 μg/L TPHP exhibited significantly decreased dendritic arborization in pyramidal neurons in the cerebellum (Ce), and the maze test indicated impaired learning/memory performance. Taken together, these findings provide scientific evidence that TPHP is neurotoxic to fish and further suggest that TPHP may not be a safe alternative for aquatic organisms.

Partition and source identification of organophosphate esters in the water and sediment of Taihu Lake, China

Taihu Lake is the third largest freshwater lake in China, and has been heavily polluted by surrounding industrial activities. This study aimed to investigate the sources of organophosphate esters (OPEs) in Taihu Lake, and their partitioning behaviors between sediment and water. The total concentrations of the eleven target OPEs (∑OPEs) in the water and sediment of Taihu Lake were 166-1530 ng/L and 2.82-47.5 ng/g dw, respectively. The ∑OPEs in both water and sediment generally decreased from northwest to southeast. Extremely high level of ∑OPEs (1410-15,300 ng/L) was found in the flow-in rivers passing through the OPE manufacturing regions in Yixing. In both water and sediment, tris(2-chloroisopropyl) phosphate and tris(chloroethyl) phosphate were the predominant OPEs. The sediment-water partitioning coefficients, log K_oc, of OPEs were calculated based on paired sediment and water samples, and they displayed strong correlation with their log K_ow (octanol-water), suggesting that their partition was dominated by hydrophobic interaction. Principle component analysis indicated that OPE manufacturing in Yixing was an important point source of OPEs, especially of TCIPP in Taihu Lake. Many OPE-related industries, such as electronic, textile, machine and plastic industries around Taihu Lake also made contributions to OPEs in the Lake.

Occurrences, sources, and transport of hydrophobic organic contaminants in the waters of Fildes Peninsula, Antarctica

As a pristine continent, Antarctica provides a good opportunity to study the spatial transport and temporal accumulation of environmental contaminants and the impacts of anthropogenic activities, both of which have given rise to ongoing public concern. In this research, an approach of coupling aquatic time-integrated passive sampling with chemical analysis and bioassays was used to assess pollution by hydrophobic organic contaminants in Antarctic waters. Passive samplers were deployed in waters of Fildes Peninsula, Antarctica, and their extracts were used for chemical analyses of sixty-six hydrophobic organic contaminants belonging to five groups [organophosphorus flame retardants (PFRs), phthalic acid esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and polychlorinated biphenyls (PCBs)] and in vitro bioassays for endocrine disruption and genotoxicity. In total, twenty pollutants (six PFRs, one PAE, two PAHs, six OCPs, and five PCBs) were quantified, and six PFRs had concentrations that ranged from ND (not detected) to 44.37 ng L^-1 in Antarctic waters. The concentrations detected in the waters were generally low and insufficient to have significant in vitro endocrine disruption potential or genotoxicity. The source and transport pathways of PFRs and PAE in Fildes Peninsula were studied, and multiple local sources (wastewater, air traffic, research stations, and animal feces) for different PFRs were proposed. A spatial and temporal analysis showed slight changes in the exposure of OCPs and PCBs in Antarctic waters. Furthermore, a comparison among a variety of Antarctic water sampling cases revealed that passive sampling can be a tool for aquatic time-integrated investigations in polar regions.

The neuropeptides of Asian freshwater clam (Corbicula fluminea) as new molecular biomarker basing on the responses of organophosphate chemicals exposure

In the present study, to discover new biomarker of Asian freshwater clam (Corbicula fluminea) to assess impact of environmental pollutions, cholecystokinin (CCK), conopressin, and Neuropeptide FF (FFamide) in C. fluminea were selected as potent biomarkers. Therefore, their full-length cDNAs were cloned and characterized to investigate the molecular characteristics and expression patterns of neuropeptides in C. fluminea. According to the sequence analysis, CCK, conopressin, and FFamide encoded proteins of 173, 152, and 90 amino acids, respectively. Moreover, the multiple sequence alignment revealed that the bioactive regions of these neuropeptides were well conserved among different invertebrates. In addition, under basal conditions, CCK, conopressin and FFamide mRNA were mainly expressed in the visceral mass, whereas the FFamide mRNA was rarely detected in the foot and mantle. Exposure to 20 and 200 μg/L Tris (2-butoxyethyl) phosphate (TBOEP) and tri-butyl-phosphate (TBP) exposure significantly up-regulated the expression of the CCK and FFamide mRNAs in the visceral mass (p < 0.05), whereas no significant changes in conopressin mRNA levels were observed in response to any treatment. Therefore, CCK and FFamide of C. fluminea neuropeptides are feasible new biomarkers for screening and assessing responses to organophosphate chemicals.

Tissue-specific distribution and bioaccumulation potential of organophosphate flame retardants in crucian carp

The concentrations, distributions, and bioaccumulation of nine organophosphate flame retardants (OPFRs) were investigated in both abiotic and biotic media, comprising river water, sediment, and crucian carp. The highest concentrations were observed in liver (6.22-18.1 ng/g ww), and the levels in muscle (4.23-7.75 ng/g ww) and gonad (3.08-7.70 ng/g ww) were similar. In whole blood, tris(2-butoxyethyl) phosphate (TBOEP; 31.1-256 ng/mL) accounted for 90% of the total OPFR concentration. Distributions of OPFRs differed between biotic and abiotic media, as tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), and TBOEP were dominant in abiotic media, whereas triethyl phosphate (TEP), tri-n-butyl phosphate (TNBP), TCEP, and TBOEP dominated in crucian carp. The TNBP had remarkable accumulation potential among nine OPFRs, which the TNBP concentrations in muscle increased with increased total length and body weight. The higher perfusion rate of TNBP to female eggs were observed rather than to male gonads as the concentrations were higher in males than in females, while the opposite results were observed in gonad. Moreover, the concentration of TNBP in female muscle began to decrease near maximum growth as a sexually dimorphic difference in crucian carp. This is the first study to simultaneously investigate the fate of OPFRs in biotic and abiotic media and to show sex differences.

Characterized in Vitro Metabolism Kinetics of Alkyl Organophosphate Esters in Fish Liver and Intestinal Microsomes

Tris(2-butoxyethyl) phosphate (TBOEP) and tris( n-butyl) phosphate (TNBP) are the most commonly used alkyl organophosphate esters (alkyl-OPEs), and they increasingly accumulate in organisms and create potential health hazards. This study examined the metabolism of TNBP and TBOEP in Carassius carassius liver and intestinal microsomes and the production of their corresponding monohydroxylated and dealkylated metabolites. After 140 min of incubation with fish liver microsomes, the rapid depletion of TNBP and TBOEP were both best fitted to the Michaelis-Menten model (at administrated concentrations ranging from 0.5 to 200 μM), with a CL_int (intrinsic clearance) of 3.1 and 3.9 μL·min^-1·mg^-1 protein, respectively. But no significant ( P > 0.05) biotransformation was observed for these compounds in intestinal microsomes at any administrated concentrations. In fish liver microsomes assay, bis(2-butoxyethyl) hydroxyethyl phosphate (BBOEHEP) and bis(2-butoxyethyl) 3-hydroxyl-2-butoxyethyl phosphate (3-OH-TBOEP) were the most abundant metabolites of TBOEP, and dibutyl-3-hydroxybutyl phosphate (3-OH-TNBP) was the predominant metabolite of TNBP. Similarly, the apparent V_max values (maximum metabolic rate) of BBOEHEP and 3-OH-TNBP were also respectively highest among those of other metabolites. Further inhibition studies were conducted to identify the specific cytochrome P450 (CYP450) isozymes involved in the metabolism of TNBP and TBOEP in liver microsomes. It was confirmed that CYP3A4 and CYP1A were the significant CYP450 isoforms catalyzing the metabolism of TNBP and TBOEP in fish liver microsomes. Overall, this study emphasized the importance of hydroxylated metabolites as biomarkers for alkyl-OPEs exposure, and further research is needed to validate the in vivo formation and toxicological implications of these metabolites.