Polychlorinated Diphenyl Ethers Congeners Research Articles

Persistent Halogenated Organic Pollutants in Deep-Water-Deposited Particulates from South China Sea.

POP data are limited in the marine environment; thus, this study aimed to investigate background persistent organic pollutant (POP) levels in oceanic deep-water-deposited particulates in the South China Sea (SCS). Six POPs, including polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (DL-PCBs), polybrominated diphenyl ethers (PBDEs), polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs), polychlorinated diphenyl ethers (PCDEs), and polybrominated biphenyls (PBBs), were investigated in eight pooled samples from the SCS from 20 September 2013 to 23 March 2014 and 15 April 2014 to 24 October 2014 at depths of 2000 m and 3500 m. PBDEs were the most predominant compounds, with the highest mean Σ14PBDE of 125 ± 114 ng/g dry weight (d.w.), followed by Σ17PCDD/F, Σ12PBDD/F, and Σ12DL-PCB (275 ± 1930, 253 ± 216, and 116 ± 166 pg/g d.w., respectively). Most PBDD/F, PBB, and PCDE congeners were below the detection limits. PCDDs had the highest toxic equivalency (TEQ), followed by PBDDs and DL-PCBs. Among the six POPs, PBDEs were the major components of the marine-deposited particles, regarding both concentrations and mass fluxes. Compared to 3500 m, PBDE levels were higher at a depth of 2000 m. PBDE mass fluxes were 20.9 and 14.2 ng/m2/day or 68.2 and 75.9 ng/m2/year at deep-water 2000 and 3500 m, respectively. This study first investigated POP levels in oceanic deep-water-deposited particles from existing global data.

Bioaccumulation, Trophic Transfer, and Biotransformation of Polychlorinated Diphenyl Ethers in a Simulated Aquatic Food Chain.

Polychlorinated diphenyl ethers (PCDEs) are detected in aquatic environments and demonstrate adverse effects in aquatic organisms. However, data regarding the environmental behavior of PCDEs in aquatic ecosystems are lacking. In the present study, a simulated aquatic food chain (Scenedesmus obliquus-Daphnia magna-Danio rerio) was constructed in a lab setting, and the bioaccumulation, trophic transfer, and biotransformation of 12 PCDE congeners were quantitatively investigated for the first time. The log-transformed bioaccumulation factors (BCFs) of PCDEs in S. obliquus, D. magna, and D. rerio were in the range of 2.94-3.77, 3.29-4.03, and 2.42-2.89 L/kg w.w., respectively, indicating the species-specific bioaccumulation of PCDE congeners. The BCF values increased significantly with the increasing number of substituted Cl atoms, with the exception of CDE 209. The number of Cl atoms at the para and meta positions were found to be the major positive contributing factors for BCFs in the case of the same number of substituted Cl. The lipid-normalized biomagnification factors (BMFs) of S. obliquus to D. magna, D. magna to D. rerio, and the whole food chain for the 12 PCDE congeners ranged at 1.08-2.27, 0.81-1.64, and 0.88-3.64, respectively, suggesting that some congeners had BMFs comparable to PBDEs and PCBs. Dechlorination was the only metabolic pathway observed for S. obliquus and D. magna. For D. rerio, dechlorination, methoxylation, and hydroxylation metabolic pathways were observed. 1H nuclear magnetic resonance (NMR) experiments and theoretical calculations confirmed that methoxylation and hydroxylation occurred at the ortho position of the benzene rings. In addition, reliable quantitative structure-property relationship (QSPR) models were constructed to qualitatively describe the relationships between molecular structure descriptors and BCFs for PCDEs. These findings provide insights into the movement and transformation of PCDEs in aquatic ecosystems.

Polychlorinated Diphenyl Ethers in the Environment: A Review and Future Perspectives.

Polychlorinated diphenyl ethers (PCDEs) are a class of synthetic halogenated aromatic compounds, which have gradually attracted widespread attention due to potential environmental risks to humans and ecosystems. This paper presents a literature review of research on PCDEs using PubMed, Web of Science and Google Scholar as search engines/databases with no constraints on publishing year or number. A total of 98 publications on the sources, environmental levels, environmental behavior and fate, synthesis and analysis and toxicology of PCDEs were retrieved. Existing studies have shown that PCDEs widely exist in the environment with the ability of long-range transport, bioaccumulation and biomagnification, which are almost comparable to polychlorinated biphenyls. They can elicit adverse effects including hepatic oxidative stress, immunosuppression, endocrine disorders, growth retardation, malformations, reduced fertility and increased mortality in organisms, among which some seem to be related to the activation of the aryl hydrocarbon receptor. PCDEs can be metabolized into other organic pollutants, such as hydroxylated and methoxylated PCDEs and even polychlorinated dibenzo-p-dioxins and furans through biotransformation, photolysis and pyrolysis reactions in the environment. Compared with reviews on PCDEs published previously, some new information and findings are summarized in this review, such as new sources, current environmental exposure levels, main metabolism pathways in aquatic organisms, acute toxicity data for more species and relationships between structural parameters and toxicity and bioaccumulation potentials of PCDE congeners. Finally, current research deficiencies and future research perspectives are proposed to facilitate the assessment of health and ecological risks of PCDEs.

Acute toxicity of polychlorinated diphenyl ethers (PCDEs) in three model aquatic organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio) of different trophic levels

The frequent detection of polychlorinated diphenyl ethers (PCDEs) in aquatic systems has aroused widespread concerns, however, their potential hazard to aquatic ecosystems has been poorly understood. Here the acute toxicity of 12 PCDE congeners was evaluated in three model aquatic organisms representing different trophic levels following OECD test guidelines, including green algae (Scenedesmus obliquus), water flea (Daphnia magna), and zebrafish (Danio rerio). Dose-dependent increases in growth inhibition and mortality were observed for all tested PCDE congeners. Most of the PCDE congeners, in particular 3,3′,4,4′-tetra-CDE, were highly toxic to the three aquatic organisms with EC50 or LC50 values below 1 mg L-1. Their toxicities were generally comparable with those of certain polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). Moreover, D. magna was the most sensitive species among the three aquatic organisms. In addition, the EC50 or LC50 values had an extremely significant correlation with the n-octanol-water partition coefficient (logKow) of the PCDE congeners. The established quantitative structure-property relationship (QSPR) models indicated that the molecular polarizability (α) could significantly influence the acute toxicity of PCDEs on Daphnia magna and Danio rerio, and the energy of the lowest unoccupied molecular orbital (ELUMO) is the key factor of the acute toxicity of PCDEs in Scenedesmus obliquus. In addition, even at environmental levels, 3,3′,4,4′-tetra-CDE could induced seveve oxidative damages in the three aquactic species. These findings would contribute to the understanding of adverse effects of PCDEs in aquatic organisms.

Mechanisms of transformation of polychlorinated diphenyl ethers into polychlorinated dibenzo-p-dioxins and dibenzofurans

This study presents a detailed mechanistic account of the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) from polychlorinated diphenyl ethers (PCDEs). It applies the recently developed meta hybrid M06-2X functional and deploys the 2,2′-dichlorodiphenylether (2,2′-DCDE) molecule as a representative model compound for all PCDEs congeners. We find that, exceedingly high activation enthalpies prevent the direct formation of PCDFs from PCDEs via unimolecular elimination of HCl or Cl2. Rather, loss of an ortho H/Cl atom initiates the transformation of PCDEs into PCDD/Fs. Subsequent formation of PCDFs takes place through ring-closure reactions with modest activation enthalpies, whereas the addition of a ground state oxygen molecule at an apparent ortho radical site of a PCDE congener commences a complex, yet very exothermic, mechanism leading to the formation of PCDDs. Splitting the ether linkage through H/Cl addition at the pivot carbon constitutes a major source for the formation of chlorophenoxy radicals and chlorobenzene molecules. Our kinetic and mechanistic analyses demonstrate that, the degree and pattern of chlorination of PCDEs display a negligible effect on the formation pathways of PCDD/Fs from PCDEs.

QSPR/QSAR models for prediction of the physico-chemical properties and biological activity of polychlorinated diphenyl ethers (PCDEs)

Polychlorinated diphenyl ethers (PCDEs) are a group of important persistent organic pollutants. In the present study, geometrical optimization and electrostatic potential calculations have been performed for all 209 PCDE congeners at the HF/6-31G * level of theory. A number of statistically-based parameters have been obtained. Linear relationships between gas-chromatographic relative retention time ( RRT), n-octanol/water partition coefficient (log K OW), 298 K supercooled liquid vapour pressures (log p L), aqueous solubilities (log S w,L) and the immunotoxicity values (log ED 50) of PCDEs and the structural descriptors have been established by multiple linear regression method. The result shows that the quantities derived from electrostatic potential V s,min , ∑ V s + , V s,av - , Π , σ tot 2 , σ + 2 , ν , and N v + , together with the number of the chlorine atoms on the two phenyl rings ( N Cl ) can be well used to express the quantitative structure–property (activity) relationships of PCDEs. Good predictive capabilities have also been demonstrated by leave-group(1/5)-out cross-validation and external test set. Based on these equations, the predicted values have been presented for those PCDE congeners whose experimentally determined physico-chemical properties are unavailable.

Quantitative structure–property relationships for predicting subcooled liquid vapor pressure ( PL) of 209 polychlorinated diphenyl ethers (PCDEs) by DFT and the position of Cl substitution (PCS) methods

Optimization of the molecular geometry of 209 polychlorinated diphenyl ethers (PCDEs) and diphenyl ether (DE) were carried out at the B3LYP/6-31G* level with Gaussian 98 program. Based on the theoretical linear solvation energy relationship (TLSER) model, the obtained structural parameters were taken as theoretical descriptors to establish the first novel QSPR model (I) for predicting subcooled liquid vapor pressure ( P L) of PCDEs. The model (I) achieved in this work contains three variables: most negative atomic partial charge in molecule ( q − ), dipole moment of the molecules ( μ) and mean molecular polarizability ( α), of which r 2=0.988, SD=0.134. Meanwhile, it was found that there was significant correlation between the Cl substitution positions and some structural parameters. Consequently, the numbers of Cl substitution positions were also taken as theoretical descriptors to establish the second novel QSPR model (II) for predicting P L of all PCDE congeners, of which r 2=0.991, SD=0.112. In addition, the t-values of two models are both large and the variation inflation factors (VIF) of variables herein are all less than 5.0, suggesting significant statistics of the P L predicting models. And the results of cross-validation test also showed that the second model exhibited optimum stability and better predictive power. Moreover, results of prediction were further compared with data from similar studies by semi-empirical PM3 method, molecular connectivity indices (MCIs) method and molecular descriptors method.

Human exposure to polychlorinated diphenyl ethers through the diet in Catalonia, Spain.

Although polychlorinated diphenyl ethers (PCDEs) are recognized environmental pollutants, information concerning human exposure to these organic substances is very scarce. For the present study the concentrations of PCDEs in a number of foodstuffs acquired in Catalonia, Spain, were determined. The dietary intake of PCDEs was estimated for various age groups of the general population living in this Spanish region. With the exception of fish and shellfish, PCDE concentrations were under the limit of detection in the 10 remaining food groups analyzed. For an adult (20-65 years old) male of 70 kg average body weight, the estimated total dietary intake of PCDEs was 41 ng/day. It was assumed that if a PCDE congener was below the detection limit, the concentration was equal to half of the limit of detection. The highest exposure to PCDEs through the diet corresponded to the group aged 51-65 years, whereas the lowest intake corresponded to the youngest group (4-9 years). With the exception of the group aged >65 years, PCDE intake was always higher in males than in females. The results of this study should be of interest for future assessments of time trends in human exposure to PCDEs through the diet.

QSPR models for physicochemical properties of polychlorinated diphenyl ethers

Partial least squares regression together with 17 theoretical molecular structural descriptors was successfully used to develop QSPR models on sub-cooled liquid vapor pressures ( P L), n-octanol/water partition coefficients ( K OW) and sub-cooled liquid water solubilities ( S W,L) of polychlorinated diphenyl ethers (PCDEs). Only a few theoretical molecular descriptors were included in the QSPR models, including average molecular polarizability, molecular weight, total energy and standard heat of formation, which implies that intermolecular dispersive forces play an important role in governing the magnitude of P L and K OW. The models were tested as acceptable for prediction of P L and K OW by validation set. The consistency between observed and predicted values for P L is the best, followed by K OW and S W,L. The Q 2 cum values of the PLS models obtained are higher than 0.95, indicating high robustness of the models. Since P L, K OW and S W,L values for many PCDE congeners are not available, the developed models can be used for estimation.

Prediction of vapour pressures for halogenated diphenyl ether congeners from molecular descriptors.

Polychlorinated diphenyl ethers (PCDE) and polybrominated diphenyl ethers (PBDE) have both been identified as environmental contaminants. The physical properties are important in determining the distribution and fate of organic contaminants in the environment. The purpose of the present investigation was to characterise halogenated diphenyl ethers using computationally derived descriptors, and to develop calibration models for the vapour pressure from published experimental data. Experimental data for vapour pressures were obtained from the literature. The chemical structure of each PCDE and PBDE congener was optimised prior to descriptor generation. The data analysis was performed using principal component analysis (PCA) and partial least squares regression (PLSR). The calibration models were validated with external test sets. All congeners of PCDEs and PBDEs were characterised by 795 molecular descriptors and two principal components could account for about two thirds of the variance within each group. Bilinear calibration models were developed that could explain 99.4% of the variance in the external validation test sets. Vapour pressures were subsequently predicted for all congeners that were adequately described by these calibration models. The type and number of halogen atoms in the molecule were the main factors influencing the vapour pressures of halogen substituted diphenyl ethers, but the variations in substitution pattern was also shown to be a significant factor. The molecular descriptor patterns of halogenated aromatic compounds such as diphenyl ethers can be described and interpreted using principal component analysis (PCA). The major sources of variation in the descriptor spaces for PCDEs and PBDEs are the same as those contributing to the differences in vapour pressure, similar to what has previously been reported for the PCBs. The bilinear calibration models for vapour pressure presented here, has a standard error of prediction that is lower than what is reported as the experimental uncertainty or observed as deviations between experimental investigations. The estimated prediction errors are expected to be within the reported boundaries when the models are applied to new objects within the same molecular descriptor space, and model predictions can hence extend the current database of experimental values. The results from this investigation and others show that the establishment of quantitative structure-property relationships (QSPR) is a viable approach to estimate physical properties for halogenated diphenyl ethers. It is easy to foresee an increased need for using QSPR estimation methods in the future, for evaluation of the environmental fate for organic pollutants. Despite method developments and automation, it is unlikely that laboratory determinations can cope with the pace that new pollutants are identified.

Distribution and Bioaccumulation of Chlorinated Diphenyl Ethers in a Contaminated Embayment of Lake Ontario

Polychlorinated diphenyl ethers (PCDEs) are halogenated aromatic hydrocarbons that have structural similarities to polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans. PCDEs have been detected in piscivorus fish, fish eating birds and humans, but little is known about the transfer of these compounds through aquatic ecosystems. At sampling stations in the contaminated area of Whitby Harbour on the north shore of Lake Ontario, mean concentrations of total PCDE congeners in sediment were between 622 and 1,929 ng/g dry weight. Analysis of semipermeable membrane devices (SPMDs) deployed at several stations around the harbor indicated that PCDEs were distributed homogeneously in the water. Mean total PCDE concentrations in biota were as high as 672 ng/g wet weight (105 μg/g lipid) in white sucker ( Catostomus commersoni) and 791 ng/g wet weight (55 μg/g lipid) in brown bullheads ( Ameiurus nebulosus). The patterns of 45 PCDE congener analytes differed among the SPMDs, sediment, and biota, but between invertebrates and fish the congener patterns were relatively homogeneous. Bioamagnification factors (BMFs) calculated for total PCDEs in a simple benthic food chain (oligochaetes to white suckers) and a simple pelagic food chain (plankton to pumpkinseed) indicated that there was biomagnification, with BMFs < 50 on a lipid-normalized basis and BMFs < 5 on a wet weight basis. For individual PCDE congeners, there was a slight trend to increasing BMFs with increasing chlorine substitution.

Maternal and developmental toxicity of polychlorinated diphenyl ethers (PCDEs) in Swiss-Webster mice and Sprague-Dawley rats

Polychlorinated diphenyl ethers (PCDEs) are industrial byproducts found in many ecosystems at low levels. PCDEs are not markedly toxic to adult rodents, but their developmental toxicity has not previously been examined. We evaluated the maternal and perinatal toxicity of nine PCDE congeners to outbred mice when compounds were administered from gestation day (GD) 6 through GD 15. 2,2′,4,4′,5,6′-hexaCDE and 2,3′,4′,6-tetraCDE decreased the number of pups born per female mated and the number of pups surviving per litter born. 2,2′,4,4′,5,5′-hexaCDE and 2,2′,4,5,6′-pentaCDE decreased the number of litters born per female mated, without decreasing postnatal survival. The other PCDEs did not decrease survival either pre- or postnatally. None of the PCDEs caused absence of Harderian glands in surviving offspring at the doses administered. Neither induction of cytochromes P450 nor tissue residues of individual congeners correlated well with developmental toxicity. Three PCDEs were also evaluated in outbred (Sprague-Dawley) rats: 2,2′,4,5,6′-pentaCDE and 2,3′,4′,6-tetraCDE, because of their toxicity to mice; 2,2′,4,4′,5,5′-hexaCDE, because it should exhibit PCB-like toxicity. Each congener was administered at three dose levels from GD 6 through GD 15. 2,2′,4,5,6′-pentaCDE decreased the number of litters born at 100 mg/kg/day, and the survival of pups in litters carried to term, at both 50 and 100 mg/kg per day. Postnatal weight gain was also reduced. In contrast to its action in mice, 2,3′,4′,6-tetraCDE decreased neither the numbers of litters born nor postnatal survival of rat offspring, but did suppress postnatal weight gain at least through PD 5. As in mice, induction of cytochromes P450 was not well correlated with the developmental toxicity of individual congeners.

Ethoxyresorufin-O-deethylase induction potency of polychlorinated diphenyl ethers in H4IIE rat hepatoma cells

Polychlorinated diphenyl ethers (PCDEs) are structurally similar to polychlorinated biphenyls (PCBs), and some PCDE congeners have been reported to cause toxic responses similar to those caused by some of the non-ortho-substituted PCBs, which are mediated by the aryl hydrocarbon receptor (AhR). Twenty-nine PCDEs were tested for their potency as AhR agonists relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) by measuring their ability to induce the cytochrome P-450 1A1-associated enzyme activity, ethoxyresorufin-O-deethylase (EROD), in the H4IIE rat hepatoma cell bioassay. All PCDE congeners tested were found to be inactive as EROD inducers except for PCDE 156, which was a weak EROD inducer with a 2,3,7,8-TCDD equivalency factor of about 1.2 {times} 10{sup {minus}5}. During this study the authors determined that small amounts of polychlorinated dibenzofurans (PCDFs) that occurred as impurities in the PCDE preparations were the cause of the apparent EROD induction initially measured in their experiments. Once the PCDF impurities were removed by purification on florisil, little or no activity could be attributed to the PCDEs.

Increased [3H]Phorbol Ester Binding in Rat Cerebellar Granule Cells and Inhibition of45Ca2+Sequestration in Rat Cerebellum by Polychlorinated Diphenyl Ether Congeners and Analogs: Structure–Activity Relationships

Our previous reports indicate thatortho-substituted non-coplanar polychlorinated biphenyl (PCB) congeners perturbed neuronal Ca2+-homeostasisin vitro,altered agonist-stimulated inositol phosphate accumulation, and caused protein kinase C (PKC) translocation. The structure–activity relationship (SAR) with 24 PCB congeners was consistent with a chlorination pattern that favored non-coplanarity while those with chlorination that favored coplanarity were less active. To test the hypothesis that coplanarity (or lack thereof) is a significant factor in the activity of PCBs, studies with related classes of chemicals such as the polychlorinated diphenyl ethers (PCDEs), in which coplanarity is more difficult to achieve regardless of degree and pattern of chlorination, were initiated. The selected PCDEs and their analogs are predicted to be active, since they are non-coplanar in nature. The effects of these chemicals were studied using the same measures for which PCBs had differential effects based on structural configuration. These measures include PKC translocation as determined by [3H]phorbol ester ([3H]PDBu) binding in cerebellar granule cells and45Ca2+sequestration as determined by45Ca2+uptake by microsomes and mitochondria isolated from adult rat cerebellum. All the PCDE congeners studied, increased [3H]PDBu binding in a concentration-dependent manner. The order of potency was 2,4,4′-trichlorodiphenyl ether > 4,4′-dichlorodiphenyl ether > diphenyl ether, 3,3′,4,4′-tetrachlorodiphenyl ether and, 2,2′,4,4′,5- and 2,3′,4,4′,5-pentachlorodiphenyl ethers. The structurally related diphenyl ether nitrofen and diphenyl ethaneso,p′-1,1,1-trichloro-2,2-bis[p-chlorophenyl]ethane (DDT) andp,p′-DDT increased [3H]PDBu binding to a similar extent (28–35% stimulation at 100 μM). All PCDE congeners and their analogs inhibited45Ca2+sequestration by microsomes and mitochondria. Of all the chemicals, unchlorinated diphenyl ether was the least active. These results are in agreement with previous SAR findings in which non-coplanar PCBs are active and support our hypothesis that the extent of coplanarity determined by a pattern of chlorination on certain aromatic hydrocarbons can weaken their potencyin vitro,although the extent of chlorination is also important.

Polychlorinated diphenyl ethers, dibenzo- p-dioxins and dibenzofurans in finnish human tissues compared to environmental samples

Finnish human samples from the Helsinki area and Arctic cod samples from Vestertana Fjord (Norway) were analyzed for polychlorinated diphenyl ethers (PCDE) and 2,3,7,8-chloro substituted dibenzo- p-dioxins (PCDD) and dibenzofurans (PCDF). The PCDE, PCDD and PCDF contents in human and animal samples from Finland and elsewhere were briefly reviewed. PCDEs were non-detectable in human liver and testis, but some PCDE congeners were identified in human adipose tissue and fat of boiled Arctic cod liver composite. The contents of PCDEs in Finnish human samples were similar to those reported in the literature for human tissues from North America. The estimated concentrations of PCDEs 99, 147+153 (coeluting) and 206 ranged between 2 and 8 ng/g lipid weight (Iw) in one Finnish human adipose tissue. The concentrations of PCDE congeners identified in the cod liver fat were between 0.4 and 5 ng/g Iw. Of toxic PCDEs and PCDEs, hepta- and octa-CDDs dominated in human. The concentrations of PCDD and PCDF congeners varied from< 2 to 7700 pg/g Iw in human. In Arctic cod samples analyzed (muscle tissues of an air dried cod and cod liver fat), 2,3,7,8-tetra-CDF was nearly the only congener of PCDD/PCDEs detected.

Contamination of Pike and Sediment from the Kymijoki River by PCDEs, PCDDs, and PCDFs: Contents and Patterns Compared to Pike and Sediment from the Bothnian Bay and Seals from Lake Saimaa

Sediment and pike from Kymijoki River and Bothnian Bay were analyzed for contents of polychlorinated diphenyl ethers (PCDE), 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF), and non-ortho-substituted polychlorinated biphenyls (coplanar PCBs). Both sites are located in the vicinity of pulp mills. The same compounds were measured in a chlorophenol formulation Ky-5, which used to be used as a wood preservative, and in four ringed seals from Lake Saimaa and in one seal from Lake Baikal. Results of this preliminary study indicated that spills from the manufacture of Ky-5 in the past have contaminated Kymijoki River sediments with PCDEs, PCDDs, and PCDFs. The same PCDE congeners that dominated in these sediments were abundant in Ky-5, pikes from Kymijoki River, and seals from Lake Saimaa. The TEQs of PCDD/PCDFs in the Kymijoki River sediments varied from 0.04 to 59 ng/g dry weight. The contents of PCDE, PCDD, and PCDF compounds were low in sediments and pikes from the Bothnian Bay.

Isomer-specific determination of 79 polychlorinated diphenyl ethers (PCDE) in cod liver oils, chlorophenols and in a fly ash

The occurrence of polychlorinated diphenyl ethers (PCDEs) has been investigated in two different cod liver oils produced in 1985 and 1993, respectively, from North-Atlantic fish. These samples mirror the distribution of PCDEs among other persistent organochlorine compounds in the marine environment. To elucidate the input of PCDEs in the environment, five possible sources of PCDEs have been analyzed, namely two wood preserving formulations containing approximately 10% pentachlorophenol, two technical chlorophenol products, and one fly ash from a municipal waste incinerator. The determination has been based on 106 available PCDE congeners. During sample preparation a 2-(l-pyrenyl)ethyldimethylsilylated silica column has been used in the normal phase mode to separate the PCDEs from possible PCDF interferences. The PCDEs have been quantified by high resolution gas chromatography/mass spectrometry on a SE 54 capillary column using electron ionization and selected ion monitoring. The total amount of PCDEs in 2,3,4,6-tetrachlorophenol have been determined to be 213 mg/kg. The lowest concentrations of PCDEs have been found in the more recently produced cod liver oil (sum PCDEs: 49 μg/kg) and in the fly ash sample (sum PCDEs: 93 µg/kg), respectively. The isomer-specific analysis has been employed to characterize the relationship between possible sources and the PCDEs found in the environment. PCDEs, like PCBs, can be indicator molecules for the global pollution of the environment.

Contents and origin of polychlorinated diphenyl ethers (PCDE) in salmon from the Baltic Sea, Lake Saimaa and the Tenojoki river in Finland

The presence of 26 congeners of polychlorinated diphenyl ethers (PCDEs) was investigated in salmon from three locations in Finland. In addition to salmon, one chlorophenol wood preservative (Ky-5) and one fly ash sample were analyzed for PCDEs. Concentrations of PCDE congeners in salmon muscle measured by high resolution gas chromatography/low resolution mass spectrometry ranged from < 0.02 to 2.4 ng/g fresh weight. The major components of tetra- to octachlorinated PCDEs in salmon were one TeCDE (22′44′-), two PeCDEs (22′44′5- and 23′44′5-) and three HxCDEs (22′44′56′-, 22′44′55′- and 22′344′5-). The Baltic salmon caught from the Simojoki River had higher levels of PCDEs than the Atlantic salmon from the Tenojoki River or salmon from Lake Saimaa in South-Finland. Same PCDE congeners which were abundant in the wood preservative were also detected in salmon, whereas PCDE congeners in the fly ash were different from those in salmon or in Ky-5.

Polychlorinated diphenyl ethers—A review

Polychlorinated diphenyl ethers (PCDEs) have been identified as by‐products formed in the synthesis of chlorinated phenols. Analytical surveys have shown that PCDE residues are present in sediments, fish, wildlife, and human tissues. The uptake and persistence of PCDEs in laboratory animals resembled that observed for the polychlorinated biphenyls (PCBs), however, in metabolic studies, ortho hydroxylation of the PCDEs was the dominant oxidative pathway. Studies indicate that PCDE congeners elicit a broad spectrum of toxic and biochemical responses in laboratory animals including the induction of several cytochrome P‐450‐dependent monooxygenase enzyme activities. In contrast with the coplanar PCBs which are significantly more toxic than their monoortho coplanar analogs, the coplanar PCDE congeners and their monoorthochloro‐substituted analogs were equipotent. These data suggest that the PCDEs may contribute significantly to the toxicity of halogenated aromatics associated with chlorinated phenol‐derived contaminated areas such as toxic chemical waste dumpsites.