Metabolism of tri-n-butyl phosphate in earthworm Perionyx excavatus

Maternal exposure to organophosphate flame retardants and neonatal anthropometric measures

BACKGROUND

Organophosphate flame retardants (OPFRs) are widely used as flame retardants and plasticizers. Laboratory evidence has suggested that maternal OPFR exposure may adversely affect fetal growth, but the epidemiological data are limited.

OBJECTIVES

To investigate the association of maternal OPFR exposure with neonatal anthropometric measures.

METHODS

This study included 354 mother-newborn pairs from the Laizhou Wan Birth Cohort (LWBC), China. Ten OPFR metabolites were measured in maternal urine samples collected before delivery. Neonatal anthropometric data was collected from medical records and standardized into z-scores using the WHO standards (2007), including the weight-for-age (WAZ), length-for-age (LAZ), body mass index-for-age (BMIZ), weight-for-length (WLZ), and head circumference-for-age z-score (HCZ). Multiple linear regression and weighted quantile sum (WQS) regression were used to estimate the associations of individual OPFR metabolites and their mixtures with neonatal anthropometrics, respectively. Stratified analysis by sex was performed.

RESULTS

The detection rates of BCEP, DPHP, BCIPP, BDCIPP, BBOEP, DnBP and DiBP were above 60%, with median concentrations ranging from 0.14 to 3.60 μg/g creatinine. Most OPFR metabolites (i.e., BCIPP, BDCIPP, DiBP, DnBP, or BBOEP) were associated with decreased offspring WAZ and HCZ. When using WQS analysis, the OPFR metabolite mixture was inversely associated with the WAZ, BMIZ and HCZ, whereas DnBP had the highest weights. After stratified by gender, the negative associations were more pronounced among males.

CONCLUSIONS

Maternal OPFR exposure was negatively associated with offspring WAZ, BMIZ, and HCZ, and males seemed to be more vulnerable to the developmental toxicity of certain OPFRs.

A critical review on sources and environmental behavior of organophosphorus flame retardants in the soil: Current knowledge and future perspectives

Organophosphorus flame retardants (OPFRs) have been widely used in industrial and commercial applications. Unfortunately, the chemical constituents of OPFRs, organophosphate esters (OPEs), which have been proven to be carcinogenic and biotoxic, can release into the environment and pose potential risks to human health. This paper reviews the research progress of OPEs in the soil through bibliometric analysis and comprehensively elaborates on their pollution status, potential sources, and environmental behaviors. The OPE pollution is widely distributed in the soil at concentrations ranging from several to tens of thousands of ng/g dw. Some novel OPEs, newly discovered OPEs in the environment in recent years, are also detected. OPE concentrations vary substantially among landuses, and waste processing areas are important point sources of OPE pollution in the soil. Emission source intensity, physicochemical properties of compounds, and soil properties play important roles in the transfer process of OPEs in the soil. Biodegradation, especially microbial degradation, has potential application prospects in the remediation of OPE-contaminated soil. Brevibacillus brevis, Sphingomonas, Sphingopyxis, Rhodococcus, and other microorganisms can degrade some OPEs. This review helps clarify the pollution status of OPEs in the soil and highlights perspectives for future research.

Safe and sustainable by design: A computer-based approach to redesign chemicals for reduced environmental hazards

Persistency of chemicals in the environment is seen a pressing issue as it results in accumulation of chemicals over time. Persistent chemicals can be an asset in a well-functioning circular economy where products are more durable and can be reused or recycled. This objective can however not always be fulfilled as release of chemicals from products into the environment can be inherently coupled to their use. In these situations, chemicals should be designed for degradation. In this study, a systematic and computer-aided workflow was developed to facilitate the chemical redesign for reduced persistency. The approach includes elements of Essential Use, Alternatives Assessment and Green and Circular Chemistry and ties into goals recently formulated in the context of the EU Green Deal. The organophosphate chemical triisobutylphosphate (TiBP) was used as a case study for exploration of the approach, as its emission to the environment was expected to be inevitable when used as a flame retardant. Over 6.3 million alternative structures were created in silico and filtered based on QSAR outputs to remove potentially non-readily biodegradable structures. With a multi-criteria analysis based on predicted properties and synthesizability a top 500 of most desirable structures was identified. The target structure (di-n-butyl (2-hydroxyethyl) phosphate) was manually selected and synthesized. The approach can be expanded and further verified to reach its full potential in the mitigation of chemical pollution and to help enable a safe circular economy.

Biological responses of Eisenia fetida towards the exposure and metabolism of tris (2-butoxyethyl) phosphate

The toxicity of various organophosphorus flame retardants (OPFRs) is of increasing concern. However, there is still a lack of research on the toxicity of OPFRs to terrestrial invertebrates and its metabolism in vivo. Herein, earthworms (Eisenia fetida) were exposed to soil spiked with 0, 0.05, 0.5, and 5 mg/kg tris(2-butoxyethyl) phosphate (TBOEP, a typical alkyl OPFRs) for 28 d to study the biological responses to the exposure and metabolism of TBOEP. TBOEP exposure inhibited the activity of acetyl-cholinesterase (64.4-68.6% of that in the control group), increased the energy consumption level, and affected calcium-dependent pathways of E. fetida, which caused a 3.6-12.4% reduction in the weight gain rate (developmental toxicity), a 10.6-69.4% reduction in the number of juveniles (reproduction toxicity), and neurotoxicity to E. fetida. The 5 mg/kg TBOEP exposure caused a significant accumulation of malondialdehyde (1.68 times higher than that in the control group) in E. fetida, which indicated that the balance of oxidation and anti-oxidation of E. fetida was broken. Meanwhile, E. fetida maintained the absorption and metabolic abilities to TBOEP under the environmental condition. The removal rate of soil TBOEP was increased by 25.1-35.5% by the presence of E. fetida. Importantly, TBOEP could accumulate in E. fetida (0.09-76.0 μg/kg) and the activation of cytochrome P450 and glutathione detoxification pathway promoted the metabolism of TBOEP in E. fetida. These findings link the biological responses and metabolic behavior of earthworms under pollution stress and provide fundamental data for the environmental risk assessment and pollution removal of OPFRs in soil.

In vitro Phase I metabolism of newly identified plasticizers using human liver microsomes combined with high resolution mass spectrometry and based on non-targeted and suspect screening workflows

Three plasticizers, namely bis (3,5,5-trimethylhexyl) phosphate (TMHPh), di(propylene glycol) dibenzoate (DiPGDB), and tri-n-butyl trimellitate (TBTM), were recently identified and reported in high concentrations in indoor dust from Belgian homes. In this study, their behavior within the human body was investigated by generating Phase I biotransformation products for the first time. Human liver microsomes (HLMs) were used following an in vitro assay and liquid chromatography time of flight mass spectrometry (LC-QTOF-MS) was employed for the analysis. Biotransformation products were identified for TMHPh as products of hydroxylation reactions that took place in one or two positions in the structure of the substrate. For DiPGDB, biotransformation products were formed after hydrolysis of carboxylic esters and oxidative-O-dealkylation. For TBTM, biotransformation products were formed through hydrolysis of the different carboxylic esters of the molecule, in agreement with studies on structurally similar compounds. The generated results can contribute to biomonitoring studies creating new knowledge on human exposure to emerging compounds and on the metabolism of xenobiotics.

A review on organophosphate flame retardants in the environment: Occurrence, accumulation, metabolism and toxicity

Organophosphate flame retardants (OPFRs), as a substitute for brominated flame retardants (BFRs), are widely used in industrial production and life. The presence of OPFRs in the environment has an adverse effect on the ecological environment system. This review provides comprehensive data for the occurrence of OPFRs and their diester metabolites (OP diesters) in wastewater treatment plants, surface water, drinking water, sediment, soil, air and dust in the environment. In particular, the accumulation and metabolism of OPFRs in organisms and the types of metabolites and metabolic pathways are discussed for animals and plants. In addition, the toxicity of OP triesters and OP diesters in organisms is discussed. Although research on OPFRs has gradually increased in recent years, there are still many gaps to be filled, especially for metabolic and toxicity mechanisms that need in-depth study. This review also highlights the shortcomings of current research and provides suggestions for a basis for future research on OPFRs.

Organophosphate (OP) diesters and a review of sources, chemical properties, environmental occurrence, adverse effects, and future directions

Over the course of the continual phase-outs of toxic halogenated flame retardants (HFRs), there has been an increasing demand for organophosphate esters (OPEs) in global FR markets. OPE-FRs have largely been identified as OP triesters, which have a basic chemical structure of O = P(OR)₃. In addition to OP triesters, OPEs can refer to another class of related substances, namely, OP diesters that have a typical chemical structure of O = P(OR)₂(OH)). OP diesters are known as biotic or abiotic degradation products of OP triesters. In recent years, environmental scientists have proven that OP diesters widely exist in a variety of environmental matrices and biotic samples around the world, implying the potential risks from OP diester exposure to biota and humans in the environment. Here, we have reviewed the scientific literature for studies involving OP diesters and up to the end of 2020. The aim of the present review is to assess the present understanding of the physicochemical properties, sources (industrial production and degradation), environmental occurrence of OP diesters, and adverse effects to exposed organisms. Based on the literature in the Web of Science core collection, we found that at least 23 OP diesters have been reported as contaminants in various environments or as degradation products of OP triesters. The physicochemical properties of OP diesters vary depending on their specific chemical structures. OP diesters containing halogen atoms and aryl groups seem to be more persistent (with greater estimated half-life (t_1/2) values) in environmental matrices. There were multiple sources of OP diesters, including industrial production and biotic or abiotic degradation from OP triesters. Specifically, we found that ten OP diesters are produced somewhere in the world, and the total annual output was estimated to be 17,050 metric tons (this number is underestimated due to the limitation of the available information). In addition, the wide application of OP triesters worldwide makes the degradation of OP triesters another critical source of OP diesters to the environment and to organisms. Current monitoring studies have demonstrated that some OP diesters were detectable in the human body (via both blood and urine samples), indoor dust, wastewater, or sewage sludge worldwide. The highest concentrations of diphenyl phosphate (DPHP) in human urine have been reported as high as 727 ng/mL (children (aged 0-5 years) urine samples from Australia). In addition, adverse effects following direct or indirect exposure to 11 OP diesters in organisms (including animals, bacteria, and algae) have been reported, and the recorded adverse outcomes following exposure to OP diesters included developmental toxicity, alteration of gene expression, and disturbance of nuclear receptor activity. Biomonitoring studies regarding human samples have frequently reported statistically significant associations between the concentrations of OP diesters and markers of human health (mainly related to reproductive toxicity). Finally, on the basis of current knowledge on OP diesters, we propose prospects for related research directions in future studies.

Human internal exposure to organophosphate esters: A short review of urinary monitoring on the basis of biological metabolism research

As alternatives to traditional brominated flame retardants, organophosphate flame retardants (OPFRs), especially for organophosphate esters (OPEs) -- the most widely used and investigated OPFRs, have raised people's concern on their environmental and health-related risks over the years. Considering their extensive environmental occurrence and potential adverse effects, precise estimation on the human body burden of OPEs will be conducive to the restrictions on the usage of these compounds scientifically. Biomonitoring research can provide precise information on human exposure to OPEs as it reveals the degree of external exposure from all exposure routes. Knowledge on biotransformation and metabolism of OPEs in the biosystems is of great significance for our understanding of the internal exposure to these compounds. In this study, the biological metabolic processes of nine OPEs prevalent in the environment, involving tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tripropyl phosphate (TPrP), tri-n-butyl phosphate (TnBP), tris(2-butoxyethyl) phosphate (TBOEP), triphenyl phosphate (TPhP), 2-ethylhexyl diphenyl phosphate (EHDPP), and tricresyl phosphate (TCrP), are comprehensively reviewed. Specifically, the metabolic pathway, kinetics and mechanism of OPEs are depicted in detail. Under this context, the advances and limitations on biomonitoring of OPE metabolites in human urine are summarized. The requirements of specificity, quantitative stability, high detection frequency/concentration are needed for OPE metabolites to be considered and validated as biomarkers. Thus far, deeper elucidations on the metabolic processes and identification of biomarkers of OPEs are urgently required, given that some OPEs have no suitable biomarkers in human biomonitoring. For better assessment of the body burden of OPEs in humans, reliable and effective methodologies for urine sampling and estimation on internal exposure to OPEs need to be further developed in the future.

Ecological and toxicological assessments of anthropogenic contaminants based on environmental metabolomics

There has long been a great concern with growing anthropogenic contaminants and their ecological and toxicological effects on living organisms and the surrounding environment for decades. Metabolomics, a functional readout of cellular activity, can capture organismal responses to various contaminant-related stressors, acquiring direct signatures to illustrate the environmental behaviours of anthropogenic contaminants better. This review entails the application of metabolomics to profile metabolic responses of environmental organisms, e.g. animals (rodents, fish, crustacean and earthworms) and microorganisms (bacteria, yeast and microalgae) to different anthropogenic contaminants, including heavy metals, nanomaterials, pesticides, pharmaceutical and personal products, persistent organic pollutants, and assesses their ecotoxicological impacts with regard to literature published in the recent five years. Contaminant-induced metabolism alteration and up/down-regulation of metabolic pathways are revealed in typical organisms. The obtained insights of variations in global metabolism provide a distinct understanding of how anthropogenic contaminants exert influences on specific metabolic pathways on living organisms. Thus with a novel ecotechnique of environmental metabolomics, risk assessments of anthropogenic contaminants are profoundly demonstrated.

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.

Tri-n-butyl phosphate induced earthworm intestinal damage by influencing nutrient absorption and energy homeostasis of intestinal epithelial cells

Tri-n-butyl phosphate (TnBP) is a typical alkyl organophosphate ester that has been used for decades in various products. However, toxicity on terrestrial organisms induced by TnBP has been rarely reported though soil is a predominant sink for hydrophobic organic compounds. The objective of this study was to investigate the TnBP-induced intestinal toxicity mechanism on earthworm Eisenia fetida as well as the potential role of gut bacteria on host's health. TnBP was found to have high bioconcentrations in earthworm intestinal tract. Digestive tract degradation and digestive enzyme activities disruption associated with nutrients absorption were noticed. Using multi-omics approaches, detailed intestinal toxic mechanism of earthworms under TnBP exposure was provided. Tight junctions between small intestinal epithelial cells and osmotic equilibrium were destroyed under 10 mg/kg TnBP, leading to nutrient absorption disturbance. To satisfy the excessive energy requirements induced by TnBP, amino acids gluconeogenesis and protein degradation were detected. Moreover, TnBP significantly decreased the diversity of gut microbiota and changed their structure and function involved in hosts' health and nutrients supply. Overall, this study provides insight into the molecular mechanism of intestinal toxicity by which earthworms respond to TnBP exposure and offer important information for risk assessment of organophosphate esters on soil ecosystems.

Ultrasensitive detection of amoxicillin by TiO2-g-C3N4@AuNPs impedimetric aptasensor: Fabrication, optimization, and mechanism

The trace amount of antibiotics in water can be enriched in the human body through the food chain, leading to extremely harmful effects on people's health. Therefore, it is urgent to develop new methods to detect trace pollutants in various aquatic phase. An analytical method utilizing the synergistic effect between the sensing strategy and catalytic material with high electron transfer capacity can be used to detect trace antibiotics. In this paper, an ultrasensitive impedimetric aptasensor was fabricated by the synergy between functionalized materials (TiO₂-g-C₃N₄) and gold nanoparticles (Au NPs). Due to the formation of the 'Au-S' bond between the thiol-aptamer and Au NPs, amoxicillin and the aptamer can be specifically recognized on the modified glassy carbon electrode (GCE), and the impedance signal increased rapidly. Meanwhile, the Box-Behnken Design (BBD) strategy was used to reduce the random error of the experiment, so that the prepared aptasensor has the highest sensitivity to the detection of amoxicillin. Under optimized conditions, the sensor successfully achieved the detection of amoxicillin in the ultra-low detection range (0.5-3 nM) and reached the ultra-low detection limit (0.2 nM). The detection strategy has good selectivity, reproducibility, and stability, and thus has good potential to detect amoxicillin in actual wastewater.

Joint toxic effects of cadmium and four pesticides on the earthworm (Eisenia fetida)

The contaminants, instead of single contaminants, are usually found as chemical mixtures in terrestrial environment. However, little information is now available about the joint effects of heavy metals and farm chemicals on the soil organism. Our current study aimed to assess the combined toxicity of cadmium (Cd) and four pesticides (atrazine, chlorpyrifos, lambda-cyhalothrin and abamectin) to the earthworm (Eisenia fetida) with binary, ternary, quaternary and quinquenary mixtures. Two distinct kinds of bioassay systems were applied in this study, including contact filter paper test and artificial soil test. Synergistic effects were observed from two quaternary mixtures (Cd-Atrazine-Chlorpyrifos-Lambda-cyhalothrin and Cd-Chlorpyrifos-Lambda-cyhalothrin-Abamectin) and one quinquenary mixture (Cd-Atrazine-Chlorpyrifos-Lambda-cyhalothrin-Abamectin) in both bioassay systems. Besides, two binary mixtures (Cd-Atrazine and Cd-Lambda-cyhalothrin) and three ternary mixtures (Cd-Atrazine-Chlorpyrifos, Cd-Atrazine-Lambda-cyhalothrin and Cd-Chlorpyrifos-Lambda-cyhalothrin) also exhibited synergistic effects on E. fetida by the soil toxicity test. It is more practical to evaluate the contaminant toxicities to earthworm by soil toxicity test. Therefore, the effects of chemical mixtures on soil invertebrates might be underestimated by data obtained from single toxicant. Our findings would offer a better understanding of the complex effects of chemical mixtures on non-target living creatures, and these findings provided valuable insights into the interplay of different chemicals in natural environment.

ROS changes are responsible for tributyl phosphate (TBP)-induced toxicity in the alga Phaeodactylum tricornutum

As a newly emerging environmental contaminant, tributyl phosphate (TBP) is an additive flame retardant of high production volume that is frequently detected in biota and the environment. Despite evidence that TBP is a potential threat to marine organisms, ecotoxicology data for TBP in marine organisms at low trophic levels are scarce. In this study, the acute toxicological effect of TBP on the marine phytoplankton Phaeodactylum tricornutum was thoroughly investigated, and the possible mechanism was explored. The results showed that TBP at concentrations ≥0.2 mg L^-1 significantly inhibited P. tricornutum growth in a clear dose-response manner, with 72-h EC₁₀, EC₂₀, EC₅₀ and EC₉₀ values of 0.067, 0.101, 0.219 and 0.716 mg L^-1, respectively. Algal cells treated with TBP exhibited distorted shapes, ruptured cell membranes and damaged organelles, especially mitochondria. Additionally, apoptosis was triggered, followed by a decrease in mitochondrial membrane potential, indicating that cellular damage occurred during exposure. Although the activities of two antioxidant enzymes, superoxide peroxidase and catalase, were upregulated by TBP at 1.2 mg L^-1, excess reactive oxygen species (ROS) and malondialdehyde still accumulated in algal cells after exposure, suggesting that the cells experienced oxidative stress. Moreover, both growth inhibition and apoptosis were positively correlated with ROS levels and were ameliorated by pretreatment with the ROS scavenger N-acetyl-l-cysteine. Taken together, the results indicate that TBP exposure leads to growth inhibition and cellular damage in P. tricornutum, and a ROS-mediated pathway might contribute to these observed toxicological effects.

Untargeted metabolomics reveals transformation pathways and metabolic response of the earthworm Perionyx excavatus after exposure to triphenyl phosphate

Triphenyl phosphate (TPHP) is one of the most highly utilized organophosphorus flame retardants, and has been frequently detected in various environmental matrices, including soil. So far, limited information is known regarding the potential toxicity of TPHP to the earthworm-soil ecosystem. We investigated the metabolism of TPHP and the perturbation of the endogenous metabolome in the earthworm, Perionyx excavatus, using gas chromatography mass spectrometry (GC-MS) and liquid chromatography quadrupole time-of-flight (LC-QTOF)-based untargeted metabolomics approach after acute exposure to TPHP for one and two days through a filter paper contact test, as well as after chronic exposure for 28 days in a soil microcosm experiment. TPHP showed low bioaccumulation potential in the earthworm-soil ecosystem at concentrations of 10 mg/kg and 50 mg/kg. Identified phase I metabolites include diphenyl phosphate, mono-hydroxylated and di-hydroxylated TPHP. Two groups of phase II metabolites, thiol conjugates (including mercaptolactic acid, cysteine, cysteinylglycine, and mercaptoethanol conjugates) and glucoside conjugates (including glucoside, glucoside-phosphate, and C₁₄H₁₉O₁₀P conjugates), were putatively identified. Only acute TPHP exposure caused significant perturbations of the endogenous metabolome in earthworms, featuring fluctuations in amino acids, glucose, inosine and phospholipids. These results reveal novel phase II metabolism and toxicity of TPHP in P. excavatus.