PCDE in fish

Table 16. Chemical name, chemical structure, molecular formula, molecular mass, water solubility (WS), n-octanol/water partition coefficient (log Kow)> and estimated or predicted bioconcentration factors on a wet weight basis (BCF ) and on a lipid basis (BCFl) of Polychlorinated Diphenyl Ethers (PCDEs) in fish and mussel... 

The metabolism of PCDEs in fish has not been studied much, but apparently the metabolism in fish is low and similar to that of PCBs. Hydroxy-PCDEs were not detected in guppy (Poecilia reticulata) exposed to tri- and tetraCDEs [63]. Low metabolism and slow excretion leads to persistence and bioaccumulation. According to a study of Zitko and Carson [109], tri- through pentaCDEs are somewhat more persistent in fish than the corresponding PCBs. The excretion half-lives of one trichloro (PCDE 28 2,4,4 -), one tetrachloro (PCDE 66 2,3, 4,4 -) and one pentachloro (PCDE 99 2,2, 4,4, 5-) were 15,55, and 55 days in juvenile Atlantic salmon (Salmo salar), respectively. Half-lives of PCDEs were near to those of PCBs. The depuration half-lives of mono- through tetraCDEs have varied from 4 to 63 days in brook trout (Salvelinus fontinalis) [83] and those of tri- through decachlorinated PCDEs between 46 and 100 days in rainbow trout (Salmo gairdneri) [110]. 

Kuehl et al. [116] have extracted fish (dried with sodium sulfate) in a Soxhlet apparatus for 8 h with hexane dichloromethane (1 1) mixture. Birkholz et al. [120] extracted fish liver with the same solvent mixture, but used a longer extraction time (16 h). Acetone hexane (2 1) mixture [128] and dichloromethane [117-119,129] have also been used to extract PCDEs in fish. Jaffe et al. [117] and Jaffe and Hites [118] extracted fish with acetone hexane (1 1) in a Soxhlet for 24 h. Fish liver oil has been analyzed for PCDEs after being dissolved in hexane [43]. 

It is not surprising that PCDEs are detected in aquatic biota, because their reported half-lives are sufficient for bioaccumulation and near to those of PCBs. Tri- through pentaCDEs have been reported to be somewhat more persistent in fish than the corresponding PCBs [110]. Half-lives of PCDEs in fish have been higher than those in rats. 

Based on uptake and metabolism studies, the accumulation and tissue distribution patterns of PCDEs have been suggested to be similar to those of PCBs [63,109]. According to uptake studies of PCDEs in trout and Atlantic salmon, the uptake of PCDEs in fish is similar to that of PCBs [83,109]. When the uptake of mono through tetraCDEs was studied in brook trout, it was observed that the uptake of PCDEs was rapid ranging from 2.4 pg day"1 to 48.9 pg day"1 and did not reach a steady state during a seven day exposure [83]. The accumulation coefficients of PCDEs 28, 66, and 99 were 0.31,0.33, and 0.36 in Atlantic salmon, respectively [109]. 

Amino-PCDEs are impurities of Eulan Wa New and they have been detected as metabolites of Eulan Wa New in fish [53],... 

Toxicity of non-ortho- and mono-orfho-PCDEs to fish has recently been studied with early life stages of Japanese medaka [84], PCDEs 77, 105, and 118 were shown to be embryotoxic to medaka, but the potencies relative to 2,3,7,8-TCDD were low the toxic equivalency factors (TEF) were 0.00001-0.00056. The PCDE fraction isolated from a Lake Ontario lake trout was also embryotoxic and PCDEs in trout were suggested to have the potential to induce toxic effects in early life stages of fish, although not blue-sac disease. 

Metabolism studies of PCDEs in rats and fish have shown that PCDEs are metabolized more and excreted faster in rats compared to fish. When metabolism, tissue distribution and excretion of PCDEs was studied in male Sprague-Dawley rats with PCDE 99 (2,2, 4,4, 5-pentaCDE), 55% of PCDE 99 orally fed was excreted in feces in seven days and 64% of PCDE 99 was excreted unchanged [34]. Half-lives of hepta- through nonaCDEs in various tissues of rat have ranged between 5.7 days and 13.4 days [108]. 

Gel permeation chromatography (GPC) has been applied to remove lipids for PCDE analyses in fish muscle and human adipose tissue [110, 117-119, 129-131]. A mixture of dichloromethane cyclohexane is a typical eluent for automated GPC systems. GPC was used by Jaffe et al. [117] for fish extracts based on a method of Stalling et al. [135]. The column contained SX-2 (200-600 mesh) Biobeads swollen in the mixture which was used as an eluent (cyclohexane dichloromethane mixture (3 2)). 

PCDEs have also been measured in fish from other sites in Finland and in Baltic fish [33,36,57,122,136,139]. The Arctic environment has been suggested to be less polluted with PCDEs, since the concentrations of PCDEs have been lower in Atlantic salmon from the Tenojoki River compared to those in Baltic... 

PCDE profiles in juvenile and adult Baltic seals have been different and higher chlorinated PCDEs have dominated in old seals [113]. There have also been differences between gray seals and ringed seals most likely being due to differences in metabolism and/or diet. Because the isomer patterns were similar between juvenile gray seals and salmon, fish has been suggested as one of the most likely sources of PCDEs in seals [113]. 

PCDEs have been reported in birds from the US, Canada, and the Baltic Sea [36, 121, 124, 136]. Some PCDE congeners were measured between 11 ng g 1 and 900 ng g 1 fw in carcasses and eggs of fish-eating birds from the US and Canada [121]. The chemical industry was suggested as a source of PCDEs in common tern eggs and carcasses from Rhode Island. 

The occurrence of PCDE residues in biota shows that PCDEs have potential for bioaccumulation. The same PCDE congeners have been detected in biota compared to sediment from the same study area and elevated levels of PCDEs are detected in aquatic environment contaminated with PCDEs [33] (Fig. 5). Higher chlorinated PCDEs like octaCDEs seem to bioaccumulate, as well, since they have been measured in fish, seals, and birds [33, 57, 113,124] (Figs. 5 and 6). 

Since the toxicology data on PCDEs is still limited, PCDEs should be considered as compounds having possible adverse effects on wildlife and humans until more data is provided. PCDEs have shown low toxic potency in fish, but this is also true for PCBs, some of which are quite toxic in mammals. Mono-ortho-PCBs have not caused rainbow trout early life stage mortality and non-ortho-PCBs have shown unexpectedly low early life stage mortality when comparing Ah-receptor binding affinities in mammals [144],... 

In 1976 Sundstrom and Hutzinger [297] have suggested that leakage of PCDEs into the biosphere may cause bioaccumulation problems similar to those caused by PCB because of the similarity of their physico-chemical properties. It was also shown that PCDEs are relatively stable in the environment [305]. Therefore, it is not surprising that PCDEs are widespread in the environment and are found as environmental contaminants in sediments [303, 306], mussels [306], lobster [306], fish [307, 308], seals [286b, 303], and in human [286b, 309-311]. 

Polychlorinated diphenyl ethers (PCDE) are common impurities in chlorophenol formulations, which were earlier used as fungicides, slimicides, and as wood preservatives. PCDEs are structurally and by physical properties similar to polychlorinated biphenyls (PCB). They have low water solubility and are lipophilic. PCDEs are quite resistant to degradation and are persistent in the environment. In the aquatic environment, PCDEs bioaccumulate. These compounds are found in sediment, mussel, fish, bird, and seal. PCDEs show biomagnification potential, since levels of PCDEs increase in species at higher trophic levels. PCDEs are also detected in human tissue. Despite the persistence and bio accumulation, the significance of PCDEs as environmental contaminants is uncertain. The acute toxicity and Ah-receptor-me-diated (aryl hydrocarbon) activity of PCDEs is low compared to those of polychlorinated di-benzo-p-dioxins (PCDD) and dibenzofurans (PCDF). Due to structural similarity to thyroid hormone, PCDEs could bind to thyroid hormone receptor and alter thyroid function. Furthermore, PCDEs might be metabolized to toxic metabolites. In the environment, it is possible that photolysis converts PCDEs to toxic PCDDs and PCDFs. 

Fish-specific TEFs of halogenated diphenyl ethers have been low also in a rainbow trout early life stage mortality bioassay [85]. Halogenated diphenyl ethers were inactive in this bioassay, whereas polyhalogenated dibenzo-p-dio-xins, dibenzofurans, and biphenyls reduced growth and produced yolk sac edema and craniofacial malformations. PCDEs 71, 77, 102, 118, and 126 and PBDEs 47,85, and 99 were analyzed in this bio assay. 

Soxhlet extraction of PCDEs has been performed using one solvent or mixtures of different solvents. Fish and bird samples (muscle, egg) have been extracted for 6 h using a mixture of petroleum ether acetone hexane diethyl ether (PAHE) (18 11 5 2 by volume) [33, 57,58,114,122-124] in Finnish studies. This solvent mixture has been used since it was reported to give the best recoveries of PCBs in Soxhlet extraction when different solvent combinations were tested [127]. Soxhlet extraction gave better results for PCBs than those obtained by column extraction. 

Kuehl et al. [116] have used Celite-545 coated with concentrated sulfuric acid for lipid removal. They eluted fish extract using hexane through this column to a cesium silicate column. Acid treated silica gel is a common material for lipid removal of biota and abiota samples for PCDD/PCDF analyses [111, 112] and has been applied to human adipose tissue extracts for analysis of PCDE [132]. Silica impregnated with concentrated sulfuric acid packed on silica gel in a column has been applied as a second cleanup step [43,120,132]. A multi-silica gel column consisting of layers of silica (silica gel 60), silica impregnated with sulfuric acid (44%), silica, silica impregnated with sodium hydroxide (1 mol 1 ), silica, silica with silver nitrate (10%), and silica has been used for fish extracts by Birkholz et al. [120], The extract was eluted with 2% dichloromethane in hexane and was further purified on Florisil. 

It is difficult to conclude what the best analytical method is for PCDEs but, based on the literature, microcolumns such as Florisil [57] seem to be effective in separation of PCDEs from PCDDs and PCDFs. Furthermore they are fast and inexpensive. Before PCDEs can be analyzed by MS, however, an additional cleanup step is needed. This has been performed using column chromatography on carbon, since silica gel and neutral alumina microcolumns have not worked well with fish extracts for this purpose [57]. Activated silica and alumina microcolumns, however, could possibly be alternatives for a carbon column. An activated silica column has been used an additional cleanup step after Florisil and carbon column chromatography in the case of mussel extracts [123]. It is not necessary to separate PCBs from PCDEs, since PCBs have been reported not to interfere in the MS analysis of PCDEs [57,130],... 

Environmental levels of PCDEs have not been intensively studied like those of PCBs or PCDDs and PCDFs due to fact that model substances of PCDEs have not been commercially available until recently. Therefore, PCDEs have not been routinely monitored in any aquatic environment. Most data on PCDEs obtained using 17 or more PCDE standards are from Great Lakes fish [119] and from fish and sediment from a Finnish river, the Kymijoki River, [33,58,114]. Baltic Sea fish, birds, and seals have also been studied for PCDEs [113,124,139]. 

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