Polycyclic aromatic hydrocarbons (PAHs) reduce hepatic β-oxidation of fatty acids in chick embryos

Polycyclic aromatic hydrocarbons (PAHs) are widespread fused-ring contaminants formed during incomplete combustion of almost all kind of organic materials from both natural and anthropogenic sources. Some PAHs have been shown to be carcinogenic to humans, and a wide range of PAHs are found in wildlife all around the globe including avian species. The purpose of this project was to assess the effects of a standard mixture of 16 PAHs (United States Environmental Protection Agency) on the hepatic fatty acid β-oxidation in chicken embryos (Gallus gallus domesticus) exposed in ovo. The hepatic β-oxidation was measured using a tritium release assay with [9,10-³H]-palmitic acid (16:0) as substrate. Treated groups were divided into groups of 0.05, 0.1, 0.3, 0.5, and 0.8 mg PAHs/kg egg weight. The hepatic β-oxidation was reduced after exposure in ovo to the 16 PAHs mixture compared to control. The mechanisms causing reduced fatty acid oxidation in the present study are unclear, however may be due to deficient membrane structure, the functionality of enzymes controlling the rate of fatty acid entering into the mitochondria, or complex pathways connected to endocrine disruption. To the best of our knowledge, this is the first time a PAH-caused reduction of hepatic β-oxidation of fatty acids in avian embryos has been observed. The implication of this finding on risk assessment of PAH exposure in avian wildlife remains to be determined.     

Toxic and biochemical effects of 3,3',4,4'-tetrachlorobiphenyl (CB-77) and clophen A50 on eider duckling (Somateria mollissima) in a semi-field experiment

In this study the possible toxic and biochemical effects of one intraperitoneal dose of 5 or 50 mg kg(-1) of 3,3',4,4'-tetrachlorobiphenyl (CB-77) or 50 or 200 mg kg(-1) of Clophen A50 (CloA50) on 28-day-old eider ducklings (Somateria mollissima) were investigated. After ten days, no significant differences could be observed in any of the toxic and biochemical parameters studied, apart from ethoxyresorufin (EROD) activity, when comparing group average values of the dosed and control animals. However, significant correlations were observed at day 10 after exposure between the individual internal PCB concentration and body weight gain and beak length growth (negative correlations in the CloA50 groups); relative liver weight and cytochrome P4501A activity (positive correlations in CB-77 and CloA50 groups); plasma thyroid-hormone and hepatic retinoid levels (negative correlations in CB-77 groups); and plasma retinol levels and the ratio plasma retin/hepatic retinyl palmitate (positive correlations in CB-77 groups only). Animal activity was significantly reduced in the group that received 50 mg CB-77 kg(-1). These observations indicate that eider ducks are a sensitive species to PCB toxicity and may be at risk for development of adverse health effects in relatively highly contaminated areas such as the Waddenzee.     

The toxicity of tetrachlorobenzyltoluenes (Ugilec 141) and polychlorobiphenyls (Aroclor 1254 and PCB-77) compared in Ah-responsive and Ah-nonresponsive mice

The toxicity of the PCB substitute Ugilec 141, a mixture of tetrachlorobenzyltoluenes (TCBTs), is compared with the toxicity of a commercial mixture of polychlorobiphenyls (Aroclor 1254) and with the model toxic PCB-congener 3,3',4,4',-tetrachlorobiphenyl (PCB-77) as a positive control. Alterations in liver weight, hepatic cytochrome P450 content and EROD and PROD activity, plasma thyroxin and retinol level, hepatic retinoid level and liver and thyroid pathology, have been studied in Ah-responsive and Ah-nonresponsive mice. Ugilec 141 proved to induce similar toxicological changes, qualitatively and quantitatively, to Aroclor 1254. Therefore Ugilec may pose a similar environmental and health risk as PCBs. The criteria for acceptance of new substances, like Ugilec 141, on the European market are discussed.     

Biotransformation rates of Ugilec 141 (tetrachlorobenzyltoluenes) in rat and trout microsomes

In vitro biotransformation rates of tetrachlorobenzyltoluene (TCBT) isomers 3,3',4,4'-Cl4-2-Me (TCBT 87), 3,3',4,4'-Cl4-5-Me (TCBT 88), and 3,3',4',5-Cl4-4-Me (TCBT 94) were determined using trout and rat hepatic microsomes. The disappearance of the TCBTs from the in vitro system followed first-order kinetics. The estimated biotransformation constants (k) for the rat ranged from 0.96 to 4.14 h(-1). Biotransformation rates for trout microsomes were much lower and ranged from 0.009 to 0.017 h(-1).     

Persistency of highly toxic coplanar PCBs in aquatic ecosystems: uptake and release kinetics of coplanar PCBs in green-lipped mussels (Perna viridis Linnaeus)

The bioaccumulation potential of three highly toxic coplanar PCB isomers [3,3',4,4'-tetrachlorobiphenyl (T(4)CB); 3,3',4,4',5-pentachlorobiphenyl (P(5)CB); and 3,3',4,4',5,5'-hexachlorobiphenyl (H(6)CB)] was investigated using green-lipped mussels (Perna viridis Linnaeus) as a bioindicator, through a transplantation experiment at two locations in Hong Kong waters. By contrast to the relatively rapid uptake and release of many other PCB isomers, the non-ortho chlorine substituted coplanar PCB congeners exhibited slow uptake and clearance. The kinetic parameters of coplanar PCBs based on lipid weight-related data, and the degree of bioaccumulation based on the proportion of coplanar PCBs in total PCBs in mussels, clearly indicate that coplanar PCBs are highly bioaccumulative in lower organisms. On the assumption that mussels are unlikely to be particularly unusual with respect to their bioaccumulation of coplanar PCBs, it appears most likely that these highly toxic and persistent PCB congeners are concentrated by all aquatic organisms, and may reach higher consumers (including humans) in quantities of toxicological concern.     

Highly toxic coplanar PCBs: occurrence, source, persistency and toxic implications to wildlife and humans

Isomer-specific determinations of PCB congeners in a wide variety of animal species such as fish, marine mammals (whale, dolphin and porpoise) and terrestrial mammals (dog, cat and human) revealed the environmental occurrence of highly toxic coplanar 3,3',4,4'-tetrachlorobiphenyl (T(4)CB), 3,3',4,4',5-pentachlorobiphenyl (P(5)CB) and 3,3',4,4',5,5'-hexachlorobiphenyl (H(6)CB) within a range of few pg g(-1) to several ten ng g(-1) in fat tissues (except fish) on a wet weight basis. Detection of these toxic residues in wild specimens collected from remote areas such as the North Pacific suggests the already widespread distribution of coplanar PCBs as in the case of general PCB pollution. The clear positive correlations between concentrations of total PCBs and each of the three coplanar PCBs obtained in all mammals analysed suggest that the sources of coplanar PCB contamination to the environment are mainly commercial PCB preparations. Comparison of the composition of three toxic coplanar PCBs in commercial PCB mixtures and in the various animals indicates the relative metabolisability of these congeners as follows: 3,3',4,4'-T4CB>3,3',4,4',5-P5CB>3,3',4,4',5,5'-H6CB. Moreover, marine mammals seem to have lower potency to metabolise the coplanar PCBs in comparison with terrestrial mammals. In human adipose tissues, the concentrations of coplanar PCBs were found to be much higher than 2,3,7,8-tetrachlorodibenzo-p-dioxin (T(4)CDD), 2,3,4,7,8-pentachlorodibenzofuran (P(5)CDF) and other toxic congeners. 'T(4)CDD-equivalent' analysis based on the enzyme induction potencies and the residues of these toxic chemicals indicates that 3,3',4,4',5-P(5)CB may impose a greater toxic threat than dioxins and furans to the humans and probably to wildlife also.     

Multi-bioassay approach for assessing the potency of complex mixtures of polycyclic aromatic hydrocarbons

The chick embryotoxicity screening test (CHEST) and the Salmonella/microsome bioassay were used to evaluate embryotoxic and mutagenic endpoints from crude coal tar (CT) and its fractionated polycyclic aromatic hydrocarbon (PAH) mixtures (designated as A, B, C, D and E). In the CHEST assay, CT and PAH mixtures were injected into the egg yolk. A dose-dependent increase in embryo mortality was observed for all fractions. The E fraction resulted in 47% embryo mortality at a dose of 0.125 mg/kg and was more toxic than CT. At a dose of 1 mg/kg, 85-100% embryonic deaths occurred in fractions C and D and these two fractions were more potent than fractions A and B. The main visual toxic manifestations were liver lesions, discoloration of the liver, and edema. Both CT and fractionated PAH mixtures were also tested in the Salmonella/microsome plate incorporation assay with Salmonella typhimurium strain TA98 and were evaluated with and without metabolic activation at five dose levels. In the presence of S9, the CT and fractions C, D and E induced a dose-dependent positive response. Results from the Salmonella/microsome assay were in good agreement with findings from the CHEST assay suggesting that these two bioassays in combination may facilitate the rapid detection and ranking of complex PAH mixtures.     

Polychlorinated dibenzo-p-dioxins and related compounds in breast milk of Japanese primiparas and multiparas

We analyzed polychlorinated dibenzo-p-dioxins and related compounds in the breast milk of primiparas and multiparas, and estimated the levels transferred to newborns by breast milk in Western Japan. 2,3,7,8-TeCDD equivalents (TEQ) of the chemicals in primiparas decreased slightly from 1994 to 1996. In particular, decreases of the TEQs of total PCDDs and total coplanar PCBs were higher than that of total PCDFs. In 2,3,7,8-TeCDD, 1,2,3,7,8-PeCDD, 1,2,3,6,7,8-HxCDD, 1,2,3,7,8,9-HxCDD, 2,3,4,7,8-PeCDF, 1,2,3,6,7,8-HxCDF, 3,3',4,4',5-PeCB and 3,3',4,4',5,5'-HxCB concentrations, those in the breast milk of multiparas were significantly lower than those in the breast milk of primiparas (p < 0.05, lipid basis). Based on the assumption that newborns ingest 120 g of breast milk per kg body weight per day, the amounts converted to TEQ values were 121 pg/kg/day (primiparas) and 97.2 pg/kg/day (multiparas).     

Characterization of polycyclic aromatic hydrocarbons (PAHs) on lime spray dryer (LSD) ash using different extraction methods

In this study, traditional Soxhlet, automatic Soxhlet and ultrasonic extraction techniques were employed to determine the speciation and concentration of polycyclic aromatic hydrocarbons (PAHs) on lime spray dryer (LSD) ash samples collected from the baghouse of a spreader stoker boiler. To test the efficiencies of different extraction methods, LSD ash samples were doped with a mixture of 16 US EPA specified PAHs to measure the matrix spike recoveries. The results showed that the spike recoveries of PAHs were different using these three extraction methods with dichloromethane (DCM) as the solvent. Traditional Soxhlet extraction achieved slightly higher recoveries than automatic Soxhlet and ultrasonic extraction. Different solvents including toluene, DCM:acetone (1:1 V/V) and hexane:acetone (1:1 V/V) were further examined to optimize the recovery using ultrasonic extraction. Toluene achieved the highest spike recoveries of PAHs at a spike level of 10 microg kg(-1). When the spike level was increased to 50 microg kg(-1), the spike recoveries of PAHs also correspondingly increased. Although the type and concentration of PAHs detected on LSD ash samples by different extraction methods varied, the concentration of each detected PAH was consistently low, at microg kg(-1) levels.     

Effects of heterocyclic PAHs (N, S, O) on the biodegradation of typical tar oil PAHs in a soil/compost mixture

The interaction phenomena during the biodegradation of typical coal tar polycyclic aromatic hydrocarbons and their heterocyclic analogues (N, S, O) were investigated in an artificially contaminated AhA1-horizon/compost mixture. All compounds were partly or completely biodegraded. Degradation of two- to five-ring PAHs was inhibited by the presence of hetero-PAHs, whereas degradation of just some hetero-PAHs was inhibited by the presence of PAHs. Among the hetero-PAHs the sulphur-containing compounds were less susceptible to degradation than the corresponding oxygen- or nitrogen-containing analogues. The basic azaarene acridine showed an extreme persistence and strong sorption to the soil matrix proved by an increase of recovery after saponification of the soil matrix.     

Accumulation of weathered polycyclic aromatic hydrocarbons (PAHs) by plant and earthworm species

Experiments were conducted to assess the bioavailability of polyclycic aromatic hydrocarbons (PAHs) in soil from a Manufactured Gas Plant site. Three plant species were cultivated for four consecutive growing cycles (28 days each) in soil contaminated with 36.3 microg/g total PAH. During the first growth period, Cucurbita pepo ssp. pepo (zucchini) tissues contained significantly greater quantities of PAHs than did Cucumis sativus (cucumber) and Cucurbita pepo ssp. ovifera (squash). During the first growth cycle, zucchini plants accumulated up to 5.47 times more total PAH than did the other plants, including up to three orders of magnitude greater levels of the six ring PAHs. Over growth cycles 2-4, PAH accumulation by zucchini decreased by 85%, whereas the uptake of the contaminants by cucumber and squash remained relatively constant. Over all four growth cycles, the removal of PAHs by zucchini was still twice that of the other species. Two earthworm species accumulated significantly different amounts of PAH from the soil; Eisenia foetida and Lumbricus terrestris contained 0.204 and 0.084 microg/g total PAH, respectively, but neither species accumulated measurable quantities 5 or 6 ring PAHs. Lastly, in abiotic desorption experiments with an aqueous phase of synthetically prepared organic acid solutions, the release of 3 and 4 ring PAHs from soil was unaffected by the treatments but the desorption of 5-6 ring constituents was increased by up to two orders of magnitude. The data show that not only is the accumulation of weathered PAHs species-specific but also that the bioavailability of individual PAH constituents is highly variable.     

Examination of the bioaccumulation of halogenated dimethyl bipyrroles in an Arctic marine food web using stable nitrogen isotope analysis.

Concentrations of four possibly naturally produced organohalogens--1,1'-dimethyl-3,3',4-tribromo-4,5,5'-trichloro-2,2'-bipyrrole (DBP-Br3Cl3), 1,1'-dimethyl-3,3',4,4'-tetrabromo-5,5'-dichloro-2,2'-bipyrrole (DBP-Br4Cl2), 1,1'-dimethyl-3,3',4,4',5-pentabromo-5'-chloro-2,2'-bipyrrole (DBP-Br5Cl) and 1,1'-dimethyl-3,3',4,4',5,5'-hexabromo-2,2'-bipyrrole (DBP-Br6)--were quantitated and the extent of their magnification through an entire Arctic marine food web [measured as integrated trophic magnification factors (TMFs)] were calculated. The food web consisted of three zooplankton species (Calanus hyperboreus, Mysis oculata, and Sagitta sp.), one fish species [Arctic cod (Boreogadus saida)], four seabird species [dovekie (Alle alle), black guillemot (Cepphus grylle), black-legged kittiwake (Rissa tridactyla), and glaucous gull (Larus hyperboreus)], and one marine mammal species [ringed seal (Phoca hispida)]. Trophic levels in the food web were calculated from ratios of stable isotopes of nitrogen (15N/14N). All halogenated dimethyl bipyrrole (HDBP) congeners were found to significantly (P<0.02) biomagnify, or increase in concentration with trophic level in the invertebrate--fish--seabird food web. DBP-Br4Cl2 (TMF= 14.6) was found to biomagnify to a greater extent than DBP-Br3Cl3 (TMF = 5.2), DBP-Br5Cl (TMF = 6.9), or DBP-Br6 (TMF = 7.0), even though the Kow of DBP-Br4CI2 was predicted to be lower than those of DBP-Br5Cl and DBP-Br6. None of the four HDBP congeners in ringed seals followed the general trend of increasing concentration with trophic level, which was possibly due to an ability of the seals to metabolize HDBPs.     

Interspecies and spatial trends in polycyclic aromatic hydrocarbons (PAHs) in Atlantic and Mediterranean pelagic seabirds

PAHs were analyzed in the liver of 5 species of pelagic seabirds (Procellariiformes) from the northeast Atlantic and the Mediterranean. The main objective was to assess the trophic and geographic trends of PAHs in seabirds to evaluate their suitability as bioindicators of chronic marine pollution by these compounds. Although higher levels of PAHs have been described in the Mediterranean compared to other oceanic regions, we did not find significant spatial patterns and observed only minor effects of the geographic origin on seabird PAHs. However, we found significant higher PAH levels in petrel compared to shearwater species, which could be related to differences in their exploitation of mesopelagic and epipelagic resources, respectively, and the vertical dynamic of PAHs in the water column. Overall, although this study enhances the need of multi-species approaches to show a more comprehensive evaluation of marine pollution, seabirds emerged as poor indicators of pelagic chronic PAH levels.     

Accumulation pattern and distribution of polycyclic aromatic hydrocarbons (PAHs) in liver tissues of seven species of birds from Ahmedabad, India, during 2005–2007

Concentrations of polycyclic aromatic hydrocarbons (PAHs) were measured in liver tissues of seven species of birds collected from Ahmedabad, India during 2005–2007. All the samples collected were dead as victims of kite flying. Concentrations of ∑PAHs in livers of birds were ranged from 110?±?32.6 ng/g wet wt (1,078?±?320 lipid wt) in common myna Acridotheres tristis to 382?±?90.1 ng/g (2,388?±?563 lipid wt) in white-backed vulture. Statistically significant (p?<?0.05) differences in ∑PAHs were observed among species. However, year of collection and sex of birds did not show significant differences in concentrations of PAHs. The levels of ∑PAHs measured in the present study species were higher than the levels documented for a number of avian species and were lower than those reported to have deleterious effects on survival or reproduction of birds. Presence of PAH residues in birds of Ahmedabad city show the continuous input of PAHs through environmental exposure. Although no threat is posed by any of the hydrocarbons detected, continuous monitoring of breeding colonies of birds is recommended in unpolluted reference sites as well as polluted sites. It is also the first account of a comprehensive analysis of PAHs in various species of birds in India. Therefore, the values reported in this study can serve as baseline values for future research.     

Effects of polycyclic aromatic hydrocarbons on germination and subsequent growth of grasses and legumes in freshly contaminated soil and soil with aged PAHs residues

The relevance of germination trials for screening plants that may have potential for use in the phytoremediation of PAH contaminated land was evaluated. The germination and subsequent growth of 7 grass and legume species were evaluated in soil spiked with a pure PAH mixture or coal tar and soil from a former coking plant heavily contaminated with aged PAHs. None of these treatments adversely affected germination of the plants. However, apart from Lolium perenne all species exhibited reduced growth in the coking plant soil after 12 weeks growth when compared to the untreated soil. In the coal tar spiked soil 4 out of the 7 species showed reduced growth, as did 3 out of the 7 in the soil spiked with a mixture of 7 PAHs. Therefore, germination studies alone would not predict the success of subsequent growth of the species tested in the ranges of soil PAH levels studied.     

Comparative toxicities of the polychlorinated dibenzofuran (PCDF) and biphenyl (PCB) mixtures which persist in Yusho victims

The toxic Yusho oil contained a mixture of polychlorinated biphenyls (PCBs) which were contaminated by other halogenated aromatics including the highly toxic polychlorinated dibenzofurans (PCDFs). It has been reported that the PCBs and PCDFs which persist in the liver of victims still suffering from Yusho poisoning include the following compounds; 2,3′,4,4′,5-penta-,2,2′,4,4′,5,5′-,2,2′,3′,4,4′,5- and 2,3,3′,4,4′,5-hexa, 2,2′,3,4,4′,5,5′- and 2,2′,3,3′,4,4′,5-heptachlorobiphenyls and the 2,3,7,8-tetra-, 1,2,4,7,8-, 1,2,3,7,8- and 2,3,4,7,8-penta- and 1,2,3,4,7,8-hexachlorodibenzofurans. All of these PCBs and PCDFs have been synthesized and reconstituted to approximate their composition in human liver. A comparison of the dose-response effects of the reconstituted PCB and PCDF mixtures in causing weight loss, thymic atrophy and the induction of cytochrome P-448-dependent monooxygenases indicated that the PCDF mixture was at least 700 times more active than the PCBs. Since the ratio of PCBs/PCDFs persisting in Yusho patients' blood and liver was less than 600:1 and 5:1 respectively, the results suggest that the PCDFs are the major etiologic agent in Yusho poisoning.     

Polycyclic aromatic hydrocarbons affect survival and development of common snapping turtle (Chelydra serpentina) embryos and hatchlings

Polycyclic aromatic hydrocarbons (PAHs) are toxic compounds found in the John Heinz National Wildlife Refuge in Philadelphia, Pennsylvania. We assessed the impact of PAHs and crude oil on snapping turtle development and behavior by exposing snapping turtle eggs from the Refuge and from three clean reference sites to individual PAHs or a crude oil mixture at stage 9 of embryonic development. Exposure to PAHs had a significant effect on survival rates in embryos from one clean reference site, but not in embryos from the other sites. There was a positive linear relationship between level of exposure to PAHs and severity of deformities in embryos collected from two of the clean reference sites. Neither righting response nor upper temperature tolerance (critical thermal maximum, CTM) of snapping turtle hatchlings with no or minor deformities was significantly affected by exposure to PAHs.     

Polychlorinated biphenyls (PCBs) in sediments in Hong Kong: a congener-specific approach to the study of coplanar PCBs in aquatic ecosystems

Patterns of contamination by polychlorinated biphenyls (PCBs) were investigated in fourteen samples of coastal sediments from Hong Kong. Congener-specific analyses revealed nine sediment samples from Junk Bay to contain PCBs at concentrations ranging from 31 to 2200 ng g(-1) dry weight, concentrations generally increasing with distance north in the Bay. By contrast, five sediments from the Tolo area to the north-east of Hong Kong exhibited total PCB levels of only 6.6 to 45 ng g(-) dry weight. The patterns of relative abundance of PCB congeners in the northern Junk Bay sediments suggested the existence of ongoing source(s) of PCBs in this area; biphenyls of lower chlorination were present at high concentration in these samples. Three coplanar PCBs (3', 4, 4'-tetrachlorobiphenyl; 3,3',4,4',5-pentachlorobiphenyl; and 3,3',4,4',5,5'-hexachlorobiphenyl) were found to be present in Junk Bay sediments; these are highly toxic and are cause for concern in aquatic environments. The abundance of the three coplanar PCBs in the sediments studied was similar to that in commercial PCB mixtures, suggesting that these congeners are not enriched over other PCBs by the sediments of coastal ecosystems. It is concluded that the preferential enrichment of coplanar PCBs occurs in the biosphere, rather than in sediments.     

PAHs in background soils from Western Europe: influence of atmospheric deposition and soil organic matter

The levels and distribution of polynuclear aromatic hydrocarbons (PAHs) were determined in soil samples from background locations in the UK and Norway, to investigate their spatial distribution and the controlling environmental factors. Concentrations ranged between 42 and 11200 microg kg(-1) (geometric mean 640 microg kg(-1)) and 8.6 and 1050 microg kg(-1) (150 microg kg(-1)) dry weight in the UK and Norwegian soil, respectively. Proximity to sources and locations susceptible to high atmospheric depositional inputs resulted in higher concentrations. Statistically significant relationships were observed between PAH and total organic carbon (TOC) in the Norwegian samples. High molecular weight PAHs correlated with black carbon (BC) in UK-woodland soil. These observations support the hypothesis that TOC plays an important role in the retention of PAHs in soil and that PAHs are often combined with BC during combustion emissions. PAHs with 4 and more rings comprised approximately 90% of total PAHs in the UK soil, but only 50% in the Norwegian soil. The mixture of PAHs implied that fractionation occurred during long-range atmospheric transport and deposition. The lighter PAHs with lower K(ow) values more readily reached the most remote sites. The heavier PAHs with higher K(ow) values remained in closer proximity to sources.     

Toxicological assessment of chlorinated diphenyl ethers in the rat

Chlorinated diphenyl ethers are environmental contaminants that have been found in Great Lakes fish and birds. Because of their presence in the food chain, and potential for human exposure, the present short-term study was conducted to assess their toxicity. Groups of 10 male and 10 female rats were each given by gavage 2,2',4,4'6-pentachlorodiphenyl ether (CDE1), 2,2',4,4',5,6-hexachlorodiphenyl ether (CDE2) or 2,2',3,3',4,6'-hexachlorodiphenyl ether (CDE3) at dose levels of 0.04, 0.4, 4.0 or 40 mg/kg b.w./day for a period of 28 days. The control group received an equivalent volume of corn oil only (0.5 ml/100 g b.w.). Treatment with the three CDE congeners did not result in suppression of growth rate or food consumption. Increased liver weights were seen in the animals of both sexes fed 40 mg/kg CDE2, in males treated with 40 mg/kg CDE1, and in females with 40 mg/kg CDE3. Hepatic microsomal aminopyrine demethylase activity was significantly higher in the male rats administered 40 mg/kg CDE2, and aniline hydroxylase activity was elevated in the females following the same treatment. Serum glucose, calcium, protein and urea nitrogen of CDE1-treated males were higher than the control. Levels of uric acid, potassium and LDH of CDE3-treated females were also elevated. No hematological changes were observed. Histological examination revealed that the liver and thyroid were the target organs affected by CDE treatment but the morphological changes were mild even at the highest dose level. Changes in the liver consisted of nuclear vesiculation and increased cytoplasmic volume. Alterations in the thyroid were characterized by increased epithelial height and follicular collapse. Based on the data presented above, the 3 CDE congeners can only be considered moderately toxic in the rat.