Tricresyl Phosphates Research Articles

The mechanism of interaction between tri-para-cresyl phosphate and human serum protein: A multispectroscopic and in-silico study

Organophosphate flame retardants (OPFRs) pose the significant risks to the environment and human health and have become a serious public health issue. Tricresyl phosphates (TCPs), a group of aryl OPFRs, exhibit neurotoxicity and endocrine disrupting toxicity. However, the binding mechanisms between TCPs and human serum albumin (HSA) remain unknown. In this study, through fluorescence and ultraviolet–visible (UV–vis) absorption spectroscopy, molecular docking and molecular dynamics (MD), tri-para-cresyl phosphate (TpCP) was selected to explore potential interactions between HSA and TCPs. The results of the fluorescence spectroscopy demonstrated that a decrease in the fluorescence intensity of HSA and a blue shift were observed with the increasing concentrations of TpCP. The binding constant (Ka) was 2.575 × 104 L/mol, 4.701 × 104 L/mol, 5.684 × 104 L/mol and 9.482 × 104 L/mol at 293 K, 298 K, 303 K, and 310 K, respectively. The fluorescence process between HSA and TpCP involved a mix of static and dynamic quenching mechanism. The gibbs free energy (ΔG0) of HSA-TpCP system was −24.452 kJ/mol, −25.907 kJ/mol, -27.363 kJ/mol, and - 29.401 kJ/mol at 293 K, 298 K, 303 K, and 310 K, respectively, suggesting that the HSA-TpCP reaction was spontaneous. The enthalpy change (ΔH0) and thermodynamic entropy change (ΔS0) of the HSA-TpCP system were 60.83 kJ/mol and 291.08 J/(mol·>k), respectively, indicating that hydrophobic force was the major driving force in the HSA-TpCP complex. Furthermore, multispectral analysis also revealed that TpCP could alter the microenvironment of tryptophan residue and the secondary structure of HSA and bind with the active site I of HSA. Molecular docking and MD simulations confirmed that TpCP could spontaneously form a stable complex with HSA, which was consistent with the fluorescence experimental results. This study provides novel insights into the mechanisms of underlying the transportation and distribution of OPFRs in humans.

Differentiating Toxic and Nontoxic Tricresyl Phosphate Isomers Using Ion–Molecule Reactions with Oxygen

Ortho-substituted isomers of tricresyl phosphates (TCPs) and their toxic metabolites (e.g., CBDP: cresyl saligenin phosphate) can cause neurotoxic effects in humans. When TCP is introduced to an atmospheric pressure chemical ionization source using gas chromatography, radical cations M•+ are formed by charge exchange. The mass spectrum of an ortho-substituted isomer displays two intense peaks that are absent in the spectra of non-ortho-substituted isomers, leading us to propose structure-diagnostic ion-molecule reactions between ions M•+ and oxygen species present in the source. However, the mechanisms of these reactions have not yet been established. In this study, we propose a mechanism and provide support through computational and experimental analyses using density functional theory and cyclic ion mobility-mass spectrometry. The mechanism consists of a multistep reaction starting with the rearrangement of the molecular ion into a distonic isomer followed by an oxidation step and then decomposition into [CBDP-H]+. This proposal is consistent with the results obtained from a series of isotopically labeled analogues. Cyclic ion mobility experiments with a tri-o-cresyl phosphate standard reveal the presence of at least two hydrogen shift isomers of the product ion [CBDP-H]+ that are connected by a low-lying barrier. The selectivity of the ion-molecule reactions toward ortho-substituted cresyl TCP isomers provides us with an identification tool that can select potentially neurotoxic triaryl phosphate esters present in complex mixtures that are produced in large volume by industry.

Determination and environmental risk assessment of organophosphorus flame retardants in sediments of the South China Sea.

As ubiquitous contaminants in the environment, organophosphorus flame retardants (OPFRs) would eventually settle in marine sediment. In this study, concentrations, spatial distributions, and ecological risks of seven OPFRs in sediment samples of the South China Sea (SCS) were investigated for the first time. Total concentration of all OPFRs ranged from 2.5 to 32.3ng/g dry weight (dw), in which the abundance of tri-cresyl phosphates (TCPs) was the highest. OPFRs in the SCS were at a medium level compared with those from other parts of the world. The nearshore ocean current, ship transportation, and riverine inputs might influence the spatial distributions of OPFRs. The total inventory of six OPFRs in sediment was estimated to be 202.8 tons (16.7×104 km2). The hazard quotient (HQ) of OPFRs ranged from 0 to 3.2E-02, indicating the ignorable ecological risk of OPFRs in sediments of the SCS. This study provides insight into the occurrence of current-use OPFRs in the SCS which deserved long-term concern in the future due to their continuous terrigenous inputs.

Legacy and emerging flame retardants in indoor and outdoor dust from Indo-Gangetic Region (Patna) of India: implication for source apportionment and health risk exposure.

The fate of legacy and emerging flame retardants are poorly reported in developing countries, including India. Also, the positive matrix factorization (PMF) application-based source apportionment of these pollutants is less comprehensive. This study analyzed the contamination level and sources of 25 flame retardants in dust from India's central Indo-Gangetic Plain (Patna city) using the PCA and PMF model. Dust samples were collected from various functional areas of indoor (n = 22) and outdoor (n = 16) environments. The sum of four groups of FRs in indoor dust (median 8080ng/g) was 3-4 times greater than the outdoor dust (median 2410ng/g). The novel-brominated flame retardants (NBFRs) and organophosphate esters (OPFRs) were more dominant than polybrominated diphenyl ethers (PBDEs), indicating the influence of worldwide elimination of PBDEs. The median concentration of ∑NBFRs in indoor and outdoor dust was 1210ng/g and 6820ng/g, while the median concentration of ∑OPFRs was measured to be 383ng/g and 1210ng/g, respectively. Likewise, ∑9PBDEs in indoor and outdoor dust ranged from 2-1040ng/g (median 38.8ng/g) to 0.62-249ng/g (median 10.7ng/g), respectively. Decabromodiphenylethane (DBDPE) was identified as the most abundant NBFR in dust, comprising 99.9% of ∑6NBFR, while tri-cresyl phosphates (TMPPs) showed the highest concentration among OPFR and accounted for 75% ∑8OPFRs. The PMF analysis indicated that a significant fraction of FRs in the dust (80%) could derive from plastics, textiles, polyurethane foam, anti-foam agents, PVC, paint, and coatings. In comparison, debromination of higher PBDE congeners contributed 20% in the dust environment. FR's estimated daily exposure risk in dust showed dermal absorption as the main route of FR's intake to adult and children populations. Children were more vulnerable to the risk of FRs than the adult population. The estimated daily exposure risk for selected FRs in this study was 4-6 orders of magnitude lesser than the respective reference dose (RfD), proposing negligible health risk.

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

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

Biodegradation of Tricresyl Phosphates Isomers by a Novel Microbial Consortium and the Toxicity Evaluation of its Major Products

Biodegradation of Tricresyl Phosphates Isomers by a Novel Microbial Consortium and the Toxicity Evaluation of its Major Products

Tricresyl phosphate isomers exert estrogenic effects via G protein-coupled estrogen receptor-mediated pathways

Tricresyl phosphates (TCPs), as representative aromatic organophosphate flame retardants (OPFRs), have received much attention due to their potential neurotoxicity and endocrine-disrupting effects. However, the role of estrogen receptor α (ERα) and G protein-coupled estrogen receptor (GPER) in their estrogen disrupting effects remains poorly understood. Therefore, in this study, three TCP isomers, tri-o-cresyl phosphate (ToCP), tri-m-cresyl phosphate (TmCP) and tri-p-cresyl phosphate (TpCP), were examined for their activities on ERα by using two-hybrid yeast assay, and action on GPER by using Boyden chamber assay, cAMP production assay, calcium mobilization assay and molecular docking analysis. The results showed that three TCP isomers were found to act as ERα antagonists. Conversely, they had agonistic activity on GPER to promote GPER-mediated cell migration of MCF7 cells and SKBR3 cells. Both ToCP and TpCP activated GPER-mediated cAMP production and calcium mobilization, whereas TmCP had different mode of action, it only triggered GPER-mediated calcium mobilization, as evidenced by using the specific GPER inhibitor (G15) and GPER overexpressing experiments. Molecular docking further revealed that the way of interaction of TmCP and TpCP with GPER was different from that of ToCP with GPER, and higher activity of ToCP in activating GPER-mediated pathways might be associated with the alkyl substitution at the ortho position of the aromatic ring. Our results, for the first time, found a new target, GPER, for TCPs exerting their estrogen-disrupting effects, and demonstrated complex estrogen-disrupting effects of three TCP isomers involved their opposite activities toward ERα and GPER.

Biodegradation of tricresyl phosphate isomers by Brevibacillus brevis: Degradation pathway and metabolic mechanism

Tricresyl phosphates (TCPs), a typical sort of organophosphate flame retardants, has received extensive concerns due to its potential adverse effects. However, limited information is available on the efficient and safe removal methods of TCPs. In this regard, TCPs were tentatively biodegraded with Brevibacillus brevis. A probable degradation pathway was further proposed with the cellular reactions discussed in detail. Experiments showed that B. brevis at 2 g L−1 could degrade 1 mg L−1 tri-m-cresyl phosphate, tri-p-cresyl phosphate, and tri-o-cresyl phosphate by 82.91%, 93.91%, and 53.92%, respectively, within five days. In the process of biodegradation, B. brevis metabolism caused the release of Na+ and Cl− as well as the absorption of some nutrient ions including K+, PO43−, Mg2+, and SO42−; the presence of oxalic acid, citric acid, acetic acid, and malonic acid was also detected. Similar metabolic pathways were found among different TCPs isomers, but tri-o-cresyl phosphate induced more reactive oxygen species than the other two did. This work develops novel insights into the potential mechanisms of TCPs biodegradation by microorganisms.

Cabin air quality – Quantitative comparison of volatile air contaminants at different flight phases during 177 commercial flights

Quantitative assessment of human exposure to semi-volatile organic compounds (SVOC), such as tricresyl phosphates (TCP) that may originate from engine oil contamination of the cabin air, during air travel is challenging due to the technical complexity of the air supply in commercial jet aircraft. Normal flight operations involve reduced air exchange before and during takeoff, which results in increased concentrations of potential cabin air pollutants. During cruise, normal ventilation rates (>20 h− 1) are reestablished and thus lower pollutant concentrations are also reestablished. This relationship between changes in ventilation rate and associated changes in pollutant concentrations during the departure phase is first described in the present study, although this effect was found by previous studies that investigated distinct flight phases.The perception of so-called "smell events" in cabin air does not necessarily indicate the presence of harmful contaminants and TCP-containing oil mist must be clearly distinguished thereof. Thus, aldehydes, VOCs, and organophosphates such as TCP were investigated. In this paper, the occurrence of TCP contamination in a bleed air free Boeing 787 (B787) aircraft is reported for the first time. The results presented here show that there are TCP sources other than bleed air from leaky engines. Furthermore, exceptional release behavior of TCP suggests that a more detailed classification for engine oil-triggered cabin air contamination (CAC) events is necessary. This study evaluated measurement data from 177 flights that were either commissioned by the EASA or conducted as part of studies with the support of Lufthansa, Condor, and British Airways.

Electrochemical Detection of Tricresyl Phosphates in Gas

Tricresyl phosphate (TCP) is a class of neurotoxic organophosphate cholinesterase inhibitors, exposure to which may induce nausea, vomiting, diarrhea and abdominal pain. Despite of its acute toxicity, TCP is widely used in industrial applications, including flame retardants, and plasticizers. Many military and commercial aircrafts have employed hydraulic fluids containing TCP organophosphates additive since the 1970s. Potentially TCP could be released into the cabin air environment during oil leakage on aircraft hydraulic systems. Exposure to passengers and crew occurs mainly through ingestion, inhalation of aerosols, and dermal sorption. In this study, an automatic electrochemical detection system was developed to measure the TCP in gas. TCP was absorbed and hydrolyzed by an alkaline alumina column, to obtain hydrolysates that are electrochemically active, i.e. cresol, and then washed out by buffer for direct electrochemical detection. After each detection, NaOH solution was used to regenerate the column. The effects of different experiment conditions were investigated such as elution time, alumina type, the composition of regeneration solution, flow rate, temperature, etc. Through the optimization, an automatic TCP detection device was obtained with features of high sensitivity, regeneration capability and portability, which could be utilized in site test of cabin.

Assessment of neurotoxic effects of tri-cresyl phosphates (TCPs) and cresyl saligenin phosphate (CBDP) using a combination of in vitro techniques

Environmental exposures to tri-cresyl phosphates (TCPs) and the possible formation of toxic metabolites (e.g. cresyl saligenin phosphate; CBDP) may cause a variety of neurotoxic effects in humans. As reported for other organophosphorus compounds (OPs), the inhibition of acetylcholine esterase (AChE) has also been proposed as the underlying mechanism for TCP neurotoxicity. The ortho-isomer, ToCP and its metabolite CBDP are also known to affect neuropathy target esterase (NTE) leading to organophosphate-induced delayed neuropathy (OPIDN). Recently, in vitro testing has led to the identification of other molecular targets and alternative mechanisms of ToCP toxicity. The metabolite CBDP and other isomers, as well as commercial mixtures have not been tested for such additional modes of actions. Accordingly, the present study investigates alterations of neurobiological correlates of central nervous processes using different in vitro techniques. The three symmetric TCP isomers – ToCP, TpCP, and TmCP – that contain a methyl group at the ortho-, para-, or meta-position of the aromatic ring system, respectively, together with a commercial TCP mixture, and CBDP were all tested using concentrations not exceeding their cytotoxic concentrations. Isolated cortical neurons were kept in culture for 6days followed by 24h incubation with different concentrations of the test compounds. Thus, all endpoints were assessed after 7days in vitro (DIV 7), at which time cell viability, neurite microstructure, and the function of glutamate receptors and voltage-gated calcium cannels (VGCC) were measured. While the cytotoxic potential of the TCP isomers and their mixture were comparable (IC50≥80μM), CBDP was more cytotoxic (IC50: 15μM) to primary cortical neurons. In contrast, CBDP (up to 10μM) did not compromise the microstructure of neurites. Ten μM of ToCP significantly reduced the size and complexity of neurite networks, but neither TmCP and TpCP nor the mixture affected this second endpoint of neurotoxicity assessment. TCPs and their mixture significantly reduced the Ca2+ influx in response to glutamate and KCl stimulation in concentrations of 10μM. Only ToCP showed a specific effect on glutamate receptors with 100nM reducing the evoked Ca2+ influx. The effects of CBDP on the provoked Ca2+ influx were much weaker than those observed for TCPs. These results confirmed that ToCP has a unique mode of action on glutamate receptors that are not observed with the metabolite CBDP and the other symmetric TCP isomers. In addition, the TmCP isomer seems to have the lowest potency with respect to inducing neurotoxic effects. CBDP did not affect the neurospecific endpoints investigated in this study. Therefore, the specific affinity of CBDP for NTE and the reported general cytotoxicity might be the most relevant modes of action of this toxic metabolite in the context of ToCP-induced neurotoxicity, including OPIDN.

In vitro neurotoxic hazard characterization of different tricresyl phosphate (TCP) isomers and mixtures

Exposure to tricresyl phosphates (TCPs), via for example contaminated cabin air, has been associated with health effects including the so-called aerotoxic syndrome. While TCP neurotoxicity is mainly attributed to ortho-isomers like tri-ortho-cresyl phosphate (ToCP), recent exposure and risk assessments indicate that ToCP levels in cabin air are very low. However, the neurotoxic potential of non-ortho TCP isomers and TCP mixtures is largely unknown. We therefore measured effects of exposure (up to 48h) to different TCP isomers, mixtures and the metabolite of ToCP (CBDP: cresyl saligenin phosphate) on cell viability and mitochondrial activity, spontaneous neuronal electrical activity, and neurite outgrowth in primary rat cortical neurons.The results demonstrate that exposure to TCPs (24–48h, up to 10μM) increases mitochondrial activity, without affecting cell viability. Effects of acute TCP exposure (30min) on neuronal electrical activity are limited. However, electrical activity is markedly decreased for the majority of TCPs (10μM) following 48h exposure. Additional preliminary data indicate that exposure to TCPs (48h, 10μM) did not affect the number of neurites per cell or average neurite length, except for TmCP and the analytical TCP mixture (Sigma) that induced a reduction of average neurite length.The combined neurotoxicity data demonstrate that the different TCPs, including ToCP, are roughly equipotent and a clear structure-activity relation is not apparent for the studied endpoints. The no-observed-effect-concentrations (1μM) are well above current exposure levels indicating limited neurotoxic health risk, although exposures may have been higher in the past. Moreover, prolonged and/or repeated exposure to TCPs may exacerbate the observed neurotoxic effects, which argues for additional research.

Pollutant exposures and health symptoms in aircrew and office workers: Is there a link?

Sensory effects in eyes and airways are common symptoms reported by aircraft crew and office workers. Neurological symptoms, such as headache, have also been reported. To assess the commonality and differences in exposures and health symptoms, a literature search of aircraft cabin and office air concentrations of non-reactive volatile organic compounds (VOCs) and ozone-initiated terpene reaction products were compiled and assessed. Data for tricresyl phosphates, in particular tri-ortho-cresyl phosphate (ToCP), were also compiled, as well as information on other risk factors such as low relative humidity.A conservative health risk assessment for eye, airway and neurological effects was undertaken based on a “worst-case scenario” which assumed a simultaneous constant exposure for 8h to identified maximum concentrations in aircraft and offices. This used guidelines and reference values for sensory irritation for eyes and upper airways and airflow limitation; a tolerable daily intake value was used for ToCP. The assessment involved the use of hazard quotients or indexes, defined as the summed ratio(s) (%) of compound concentration(s) divided by their guideline value(s).The concentration data suggest that, under the assumption of a conservative “worst-case scenario”, aircraft air and office concentrations of the compounds in question are not likely to be associated with sensory symptoms in eyes and airways. This is supported by the fact that maximum concentrations are, in general, associated with infrequent incidents and brief exposures. Sensory symptoms, in particular in eyes, appear to be exacerbated by environmental and occupational conditions that differ in aircraft and offices, e.g., ozone incidents, low relative humidity, low cabin pressure, and visual display unit work. The data do not support airflow limitation effects. For ToCP, in view of the conservative approach adopted here and the rareness of reported incidents, the health risk of exposure to this compound in aircraft is considered negligible.

Commentary on: de Ree H, et al. “Health risk assessment of exposure to tricresyl phosphates (TCPs) in aircraft: A commentary” [Neurotoxicology (2014), http://dx.doi.org/10.1016/j.neuro.2014.08.011

Environmental toxicants such as bisphenol-A (BPA) and polychlorinated biphenyls (PCBs) are prevalent in our water supply, soil, and many food products and can profoundly affect the central nervous system. Both BPA and PCBs can disrupt endocrine signaling, which is important for auditory development and function, but the effect of these toxicants on the auditory periphery is not understood. In this study we investigated the effect of PCB-95 and BPA on lateral line development, function, and regeneration in larval zebrafish. The lateral line is a system of mechanosensory hair cells on the exterior of the fish that are homologous to the hair cells located in the mammalian inner ear. We found that PCB-95 had no effect on lateral line development or hair cell survival. BPA also did not affect lateral line development, but instead had a significant effect on both hair cell survival and regeneration. BPA-induced hair cell loss is both dose- and time-dependent, with concentrations of 1 μM or higher killing lateral line hair cells during a 24 h exposure period. Pharmacologic manipulation experiments suggest that BPA kills hair cells via activation of oxidative stress pathways, similar to prior reports of BPA toxicity in other tissues. We also observed that hair cells killed with neomycin, a known ototoxin, failed to regenerate normally when BPA was present, suggesting that BPA in aquatic environments could impede innate regenerative responses in fishes. Collectively, these data demonstrate that BPA can have detrimental effects on sensory systems, both in aquatic life and perhaps in terrestrial organisms, including humans.

Impairment of glutamate signaling in mouse central nervous system neurons in vitro by tri-ortho-cresyl phosphate at noncytotoxic concentrations.

Occupational and environmental exposure to tri-cresyl phosphates (TCPs) may cause various types of neurotoxicity. Among the TCP isomers, tri-ortho-cresyl phosphate is a well-studied organophosphate (OP) known to cause OP-induced delayed neuropathy (OPIDN). Clinically, OPIDN is characterized by limb paralysis caused by the inhibition of neuropathy target esterase. Like other OPs, TOCP may also trigger acute toxicity by yet unknown mechanisms. Neurotoxic effects of TCPs, including TOCP, on central nervous system functions have not been studied in depth, and such non-OPIDN mechanisms might be related to the aerotoxic syndrome. To identify alternative mechanisms of TOCP neurotoxicity, we conducted an in vitro study using primary cortical neurons isolated from mouse embryos (E 16.5). After 24 h or 6 days in vitro (DIV), cell cultures were treated with different TOCP concentrations for 24 h. On DIV 2 and 7, we investigated three different endpoints--general cytotoxicity, neurite outgrowth, and glutamatergic signaling. At both time points, the EC50 for TOCP-induced cell death was 90 μM, however, neurite outgrowth was already significantly affected at TOCP concentrations of 10 μM. The number of cells responding to glutamate, as well as the corresponding mean response amplitudes were reduced with TOCP concentrations as low as 100 nM. For the first time, functional neurotoxicity is observed with very low TOCP concentrations, and in the absence of structural damages. Our proposed mechanism is that TOCP exposure may lead to cognitive deficits relevant in aerotoxic syndrome by inhibiting the signaling of glutamate, the most abundant excitatory neurotransmitter in the brain.

Health risk assessment of exposure to TriCresyl Phosphates (TCPs) in aircraft: A commentary

Possible exposure to TriCresyl Phosphates (TCPs) has led to concerns among airline crew members. One isomer, Tri-ortho-Cresyl Phosphate (ToCP) is known to be neurotoxic and exposure to ToCP via contaminated cabin air has been suggested to be associated with the alleged Aerotoxic syndrome. The symptoms associated with Aerotoxic syndrome are diverse, including headaches, loss of balance, numbness and neurobehavioral abnormalities such as emotional instability, depression and cognitive dysfunction. Other ortho-isomers are toxic as well, but the non-ortho isomers are regarded as less toxic.In a collaborative effort to increase insight into the possible association between exposure to TCPs via contaminated cabin air and Aerotoxic syndrome, we performed an exposure- and toxicological risk assessment. Measurements in KLM 737 aircraft have demonstrated the presence of non-ortho isomers in low concentrations, though ToCP and other ortho-isomers could not be detected. Based on this exposure assessment, we established a toxicological risk model that also takes into account human differences in bioactivation and detoxification to derive a hazard quotient. From this model it appears unlikely that the health effects and alleged Aerotoxic syndrome are due to exposure to ToCP. Alternative explanations for the reported symptoms are discussed, but evaluation of the current findings in light of the criteria for occupational disease leads to the conclusion that the Aerotoxic Syndrome cannot be regarded as such. Additional research is thus required to unravel the underlying causes for the reported health complaints.

Haloalkylphosphorus hydrolases purified from Sphingomonas sp. strain TDK1 and Sphingobium sp. strain TCM1.

Phosphotriesterases catalyze the first step of organophosphorus triester degradation. The bacterial phosphotriesterases purified and characterized to date hydrolyze mainly aryl dialkyl phosphates, such as parathion, paraoxon, and chlorpyrifos. In this study, we purified and cloned two novel phosphotriesterases from Sphingomonas sp. strain TDK1 and Sphingobium sp. strain TCM1 that hydrolyze tri(haloalkyl)phosphates, and we named these enzymes haloalkylphosphorus hydrolases (TDK-HAD and TCM-HAD, respectively). Both HADs are monomeric proteins with molecular masses of 59.6 (TDK-HAD) and 58.4 kDa (TCM-HAD). The enzyme activities were affected by the addition of divalent cations, and inductively coupled plasma mass spectrometry analysis suggested that zinc is a native cofactor for HADs. These enzymes hydrolyzed not only chlorinated organophosphates but also a brominated organophosphate [tris(2,3-dibromopropyl) phosphate], as well as triaryl phosphates (tricresyl and triphenyl phosphates). Paraoxon-methyl and paraoxon were efficiently degraded by TCM-HAD, whereas TDK-HAD showed weak activity toward these substrates. Dichlorvos was degraded only by TCM-HAD. The enzymes displayed weak or no activity against trialkyl phosphates and organophosphorothioates. The TCM-HAD and TDK-HAD genes were cloned and found to encode proteins of 583 and 574 amino acid residues, respectively. The primary structures of TCM-HAD and TDK-HAD were very similar, and the enzymes also shared sequence similarity with fenitrothion hydrolase (FedA) of Burkholderia sp. strain NF100 and organophosphorus hydrolase (OphB) of Burkholderia sp. strain JBA3. However, the substrate specificities and quaternary structures of the HADs were largely different from those of FedA and OphB. These results show that HADs from sphingomonads are novel members of the bacterial phosphotriesterase family.

Aircraft Recirculation Filter for Air-Quality and Incident Assessment

The current research examines the possibility of using recirculation filters from aircraft to document the nature of air-quality incidents on aircraft. These filters are highly effective at collecting solid and liquid particulates. Identification of engine oil contaminants arriving through the bleed air system on the filter was chosen as the initial focus. A two-step study was undertaken. First, a compressor/bleed air simulator was developed to simulate an engine oil leak, and samples were analyzed with gas chromatograph-mass spectrometry. These samples provided a concrete link between tricresyl phosphates and a homologous series of synthetic pentaerythritol esters from oil and contaminants found on the sample paper. The second step was to test 184 used aircraft filters with the same gas chromatograph-mass spectrometry system; of that total, 107 were standard filters, and 77 were nonstandard. Four of the standard filters had both markers for oil, with the homologous series synthetic pentaerythritol esters being the less common marker. It was also found that 90% of the filters had some detectable level of tricresyl phosphates. Of the 77 nonstandard filters, 30 had both markers for oil, a significantly higher percent than the standard filters.

On the proportion of ortho isomers in the tricresyl phosphates contained in jet oil

On the proportion of ortho isomers in the tricresyl phosphates contained in jet oil

Occupational exposure of air crews to tricresyl phosphate isomers and organophosphate flame retardants after fume events

Aircraft cabin air can possibly be contaminated by tricresyl phosphates (TCP) from jet engine oils during fume events. o-TCP, a known neurotoxin, has been addressed to be an agent that might cause the symptoms reported by cabin crews after fume events. A total of 332 urine samples of pilots and cabin crew members in common passenger airplanes, who reported fume/odour during their last flight, were analysed for three isomers of tricresyl phosphate metabolites as well as dialkyl and diaryl phosphate metabolites of four flame retardants. None of the samples contained o-TCP metabolites above the limit of detection (LOD 0.5 μg/l). Only one sample contained metabolites of m- and p-tricresyl phosphates with levels near the LOD. Median metabolite levels of tributyl phosphate (TBP), tris-(2-chloroethyl) phosphate (TCEP) and triphenyl phosphate (TPP) (DBP 0.28 μg/l; BCEP 0.33 μg/l; DPP 1.1 μg/l) were found to be significantly higher than in unexposed persons from the general population. Median tris-(2-chloropropyl) phosphate (TCPP) metabolite levels were significantly not higher in air crews than in controls. Health complaints reported by air crews can hardly be addressed to o-TCP exposure in cabin air. Elevated metabolite levels for TBP, TCEP and TPP in air crews might occur due to traces of hydraulic fluid in cabin air (TBP, TPP) or due to release of commonly used flame retardants from the highly flame protected environment in the airplane. A slight occupational exposure of air crews to organophosphates was shown.