Polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs): biochemistry, toxicology, and mechanism of action

Coplanar PCBs and the relative contribution of coplanar PCBs, PCDDs, and PCDFs to the total 2,3,7,8-TCDD toxicity equivalents in human serum

Coplanar PCBs in human serum were measured by high-resolution gas chromatography/isotope-dilution high-resolution mess spectrometry in 46 pulp and paper mill workers and 16 community residents with no specific known source of PCB exposure. The relative contribution of coplanar PCBs, PCDDs, and PCDFs to the total 2,3,7,8-TCDD toxicity equivalents (TEQs) were compared using the toxic equivalency factors proposed by Safe [1] and the factors recently proposed by WHO [2]. The mean concentrations of PCB-126 and PCB-169 were higher in paper mill workers than in community residents. However, these differences were not statistically significant. Serum PCB-126, but not PCB-169, was correlated with body mass index (Spearman's r = 0.40, p = 0.002). Serum PCB-169, but not PCB-126, was correlated with age (Spearman's r = 0.54, p = 0.0001). Multiple linear regression analysis for log-transformed combined PCBs showed that age (p = 0.008), body mass index (p = 0.031), and eating locally caught fish (p = 0.019) were statistically significant predictors. The majority of the total TEQ in serum is due to PCDDs (63%), whereas PCDFs account for 21% and coplanar PCBs account for 15% when calculated using the TEFs proposed by Safe. The percent contributions from PCDDs, PCDFs, and coplanar PCBs were 66%, 24%, and 10% respectively when calculated based on the TEFs proposed by WHO. Age, body mass index, and consumption of locally caught fish are significant predictors for coplanar PCB levels in human serum. Serum PCDDs were the major contributors to the total 2,3,7,8-TCDD equivalent toxicity in this study.

Hydroxylated polychlorinated biphenyls (PCBs) as estrogens and antiestrogens: structure-activity relationships

The effects of structure on the estrogenicity and antiestrogenicity of hydroxylated polychlorinated biphenyls were investigated using the following estrogen-sensitive assays: competitive binding to the rat and mouse cytosolic estrogen receptor (ER); immature rat and mouse uterine wet weight, peroxidase and progesterone receptor (PR) levels; induction of luciferase activity in HeLa cells stably transfected with a Gal4:human ER chimera and a 17mer-regulated luciferase reporter gene; proliferation of MCF-7 human breast cancer cells; induction of chloramphenicol acetyl transferase (CAT) activity in MCF-7 cells transiently transfected with a full-length human ER expression plasmid and a plasmid containing an estrogen-responsive vitellogenin A2 promoter linked to a CAT reporter gene. The chemicals synthesized for this study contained a 4-hydroxy group in one ring, a 2- or 3-chloro substituent meta or ortho to the hydroxyl group, and variable substitution (2',3',4',5'-, 2',3',4',6'-, 2',3',5',6'-tetrachloro and 2',4',6'-trichloro) in the chlorophenyl ring. The compounds included: 2,2',3',4',5'- (A), 2,2',3',4',6'- (B), and 2,2',3',5',6'-pentachloro- (C); 2,2',4',6'-tetrachloro-4-biphenylol (D); 2',3,3',4',5'- (E), 2',3,3',4',6'- (F), and 2',3,3',5',6'-pentachloro (G); and 2',3,4',6'-tetrachloro-4-biphenylol (H). With the exception of 2',3,4',6'-tetrachloro-4-biphenylol (H), all of the compounds competitively bound to the mouse and rat ER with relative binding affinities [compared to 17beta-estradiol (E2)] varying from 1.4 x 10(-3) to 5.3 x 10(-5). The structure-ER binding relationships for the hydroxy-PCB congeners were different in the rat and mouse, and no dose-dependent estrogenic activities were observed in the mouse or rat uterus. Several hydroxy-PCB congeners exhibited antiestrogenic activity (primarily in the mouse uterus) and two compounds, 2,2',3',5',6- and 2,2',3',4',6'-pentachloro-4-biphenylol, inhibited E2-induced uterine wet weight, PR binding, and peroxidase activity in the mouse uterus. 2,2',3',4',5'- and 2,2',3',4',6'-Pentachloro-4-biphenylol induced CAT activity in MCF-7 cells transiently transfected with the Vit-CAT plasmid; the remaining congeners did not induce CAT activity but exhibited antiestrogenic activity in MCF-7 cells cotreated with 10(-9) E2 plus 10(-5) M hydroxy-PCBs. Complementary structure-estrogenicity relationships were observed utilizing the HeLa cell luciferase induction and MCF-7 cell proliferation assays. The placement of the 2- or 3-chloro groups in the phenolic ring had minimal effects on estrogenic activity, whereas 2,4,6-trichloro- and 2,3,4,6-tetrachloro substitution in the chlorophenyl ring (B, D, F, and H) were required for this response. Substitution in the phenolic ring was also not important for structure-antiestrogenicity relationships, and the most active compounds (A, C, E, and G) contained 2',3',4',5'- and 2',3',5',6'-tetrachlorophenyl groups. Thus, structure-estrogenicity/antiestrogenicity relationships for this series of hydroxy-PCBs were complex and response-specific.

Chemical contaminants in harbor porpoise (Phocoena phocoena) from the north Atlantic coast: tissue concentrations and intra- and inter-organ distribution

Concentrations of chlorinated hydrocarbons (CHs), such as polychlorinated biphenyls (PCBs), were measured in subsamples taken from different anatomical locations of blubber and liver of three apparently healthy harbor porpoises (Phocoena phocoena) incidentally caught in a gill-net fishery along the northwest Atlantic coast; selected elements (e.g., mercury) were measured in subsamples of liver. The vertical distribution (skin to muscle) of contaminants within blubber was also determined. Additionally, the concentrations of CHs and elements were determined in individual samples of brain, lung, kidney, and testis to assess how the disposition of toxic chemicals may be dependent on the physiological characteristics of a specific organ. Statistical analyses of the results showed that the anatomical location of the blubber or liver sample had no significant effect on concentrations of either CHs in blubber and liver, or of selected elements in liver. However, there were statistical differences between strata of blubber (skin to muscle) for the concentrations of CHs. As expected, the results showed that the CH concentrations, based on wet weight, were considerably higher in the blubber than in the other tissues; however, the concentrations of CHs in the different tissues were more comparable when values were based on total lipid weight with the exception of the brain where lipid normalized concentrations were lower than in all other tissues: This low relative accumulation of lipophilic contaminants in the brain tissue may be due to the presence of the blood-brain barrier, or due to a lower proportion of neutral lipids, such as triglycerides, as analysis for percent lipid and for the proportion of specific lipid classes showed.

Comparative toxicity of polychlorinated biphenyls to Japanese quail (Coturnix c. japonica) and American kestrels (Falco sparverius)

Polychlorinated biphenyls (PCBs) and related halogenated hydrocarbons bioaccumulate to high concentrations in top predators, such as raptorial birds, yet little is known of PCB toxicity to such species. This study explored several aspects of both the acute and chronic response of American kestrels (Falco sparverius) to three purified PCB congeners and a commercial mixture, Aroclor 1254, and compared the response to that of the Japanese quail (Coturnix c. japonica), a more studied species known to be PCB sensitive. In one experiment, adult female birds were given single oral doses of either Aroclor 1254, 3,3',4,4'-TCB (PCB 77, IUPAC nomenclature), 3,3',4,4',5-PCB (PCB 126) or 2,2',4,4',5,5'-HCB (PCB 153) and sacrificed after 5 d. In kestrels, neither the pure compounds nor the mixture affected hepatic or renal porphyrin levels. There was slight but significant hepatic and renal ethoxyresorufin O-deethylase (EROD) induction in birds dosed with PCBs 77 and 126. A cytochrome P-4501A (CYP1A) cross-reactive protein was detected in liver and kidney of kestrels given PCBs 77 and 126, but not in Aroclor 1254-dosed birds. In quail, an acute dose of Aroclor 1254 caused significant liver weight increases, hepatic and renal EROD and aminopyrine n-demethylase (APND) induction, and dose-related hepatic and renal porphyria. Quail treated with PCB 126 developed hepatic and renal porphyria; EROD and APND were also induced. Administration of PCB 77 caused only slight induction of hepatic EROD activity. PCB 153 caused some hepatic and renal porphyria and induced EROD to the same degree as PCB 126. A hepatic CYP1A cross-reactive protein was induced about 200-fold in all individual quail that exhibited significant EROD induction and was also induced in kidney of 1 quail given Aroclor 1254. A second experiment examined chronic exposure to Aroclor 1254 by feeding adult females of both species a daily dose of 7 mg/kg/d for 4-, 8-, and 12-wk periods. There were no effects on hepatic porphyrins in kestrels. APND and aldrin epoxidase (AE) were induced; EROD was not induced, although a hepatic CYP1A-like protein was detected in 1 kestrel dosed for 12 wk. Chronic exposure of quail to Aroclor 1254 caused highly significant increases in mean hepatic porphyrin levels and in activity of EROD, APND, and 4-chlorobiphenyl hydroxylase; a CYP1A-like protein was also induced about 200-fold. In both studies, Aroclor 1254 residues accumulated in tissues of both species, but there was no significant relationship between residue levels and effects. In conclusion, adult American kestrels were relatively insensitive to the effects of PCBs, from both acute and chronic exposure, on hepatic and renal porphyrin levels. Although concentrations of a CYP1A-like protein were increased in some kestrels given PCBs, EROD activity was only marginally increased, suggesting that catalytic activity of this protein differed among the two species.

Aryl hydrocarbon receptor-mediated signal transduction

The aryl hydrocarbon (or dioxin) receptor (AhR) is a ligand-activated basic helix-loop-helix (bHLH) protein that heterodimerizes with the bHLH protein ARNT (aryl hydrocarbon nuclear translocator) forming a complex that binds to xenobiotic regulatory elements in target gene enhancers. Genetic, biochemical, and molecular biology studies have revealed that the AhR mediates the toxic and biological effects of environmentally persistent dioxins and related compounds. Cloning of the receptor and its DNA-binding partner, ARNT, has facilitated detailed efforts to understand the mechanisms of AhR-mediated signal transduction. These studies have determined that this unique receptor consists of several functional domains and belongs to a subfamily of bHLH proteins that share a conserved motif termed the PAS domain. In addition, recent genetic studies have revealed that expression of the AhR is a requirement for proper embryonal development, which appears to be a common function shared by many other bHLH proteins. This review is a summary of recent molecular studies of AhR-mediated gene regulation.

Toxicity of PCB 105 in the rat liver: an ultrastructural and biochemical study

PCB 105 (2,3,3',4,4'-pentachlorobiphenyl) congener was fed to weanling Sprague-Dawley rats in a diet combined with 4% corn oil. The animals were distributed randomly into 10 groups, each of which contained 10 males and 10 females, and rats in 8 groups received diets containing PCB at concentrations of 0.05, 0.5, 5, and 50 ppm. Animals in the other 2 groups served as controls. After 13 weeks, the animals were humanely killed and liver samples were obtained and prepared for transmission electron microscopy. Ultrastructural alterations revealed in the hepatocytes of animals fed the PCB included smooth endoplasmic reticulum proliferation, atypical mitochondrial cristae, and augmentation of peroxisome numbers (in animals fed high PCB concentrations). Biochemical alterations were estimated by using hepatic microsomal pentoxyresorufin-O-dealkylase (PROD) and ethoxyresorufin-O-deethylase (EROD) activities. A dose-dependent increase in EROD and PROD activities was discovered; only in the animals of highest PCB dose group, however, was EROD found to be significant (p < .05). Based on our previous work, this congener is relatively less toxic than PCB 126, 118, and 153 and is similar in toxicity to 156.

Inhibition of 3,3',4,4',5-pentachlorobiphenyl-induced fetal cleft palate and immunotoxicity in C57BL/6 mice by 2,2',4,4',5,5'-hexachlorobiphenyl

3,3',4,4',5-Pentachlorobiphenyl (pentaCB) caused a dose-dependent induction of fetal cleft palate in offspring from pregnant C57BL/6 mice exposed to a single dose (783 or 1044 micrograms/kg) of this compound on gestation day 10. In contrast, 2,2',4,4',5,5'-hexaCB did not cause cleft palate at a dose of 271 mg/kg and, in pregnant mice cotreated with 2,2',4,4',5,5'-hexaCB (271 mg/kg) plus 783 or 1044 micrograms/kg 3,3',4,4',5-pentaCB, fetal cleft palate formation was significantly inhibited. 3,3',4,4',5-PentaCB (6 micrograms/kg) also inhibited the splenic plaque-forming cell (PFC) response and serum IgM levels in C57BL/6 mice treated with the T cell-independent antigen trinitrophenyl-lipopolysaccharide. At doses as high as 72 mg/kg, 2,2',4,4'-5,5'-hexaCB was not immunotoxic; however, in mice cotreated with a immunotoxic dose of 3,3',4,4',5-pentaCB plus different doses of 2,2',4,4',5,5'-hexaCB (18, 36 and 72 mg/kg), there was a dose-dependent inhibition of 3,3',4,4',5-pentaCB-induced immunotoxicity. These non-additive (antagonistic) interactions of prototypical polychlorinated biphenyl (PCB) congeners may be an important consideration in development of a toxic equivalency factor approach for hazard and risk assessment of PCB mixtures.

Halogenated aromatic hydrocarbon-mediated porphyrin accumulation and induction of cytochrome P4501A in chicken embryo hepatocytes

Concentration-dependent induction of cytochrome P4501A (CYP1A) and intracellular porphyrin accumulation were observed following treatment of chicken embryo hepatocyte (CEH) cultures with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4'-tetrachlorobiphenyl (PCB 77, IUPAC nomenclature), 2,3',4,4',5-pentachlorobiphenyl (PCB 118), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169), and a commercial mixture of PCBs (Aroclor 1254). For these halogenated aromatic hydrocarbons (HAHs), or mixture, maximal CYP1A activity [measured as ethoxyresorufin-O-deethylase (EROD) activity] and immunodetectable protein were observed at concentrations just prior to, or coincident with, the concentrations at which porphyrin accumulation became evident. Both immunodetectable CYP1A protein and catalytic activity decreased at high concentrations of these compounds, but the rate and extent of decrease of immunodetectable CYP1A protein varied. Time-course studies with PCB 77 indicated a decrease in potency and an increase in maximal CYP1A induction between 24 and 48 hr of exposure which may indicate in vitro metabolism of this HAH. Intracellular accumulation of total porphyrins without CYP1A induction, was observed for 2,2',5,5'-tetrachlorobiphenyl (PCB 52), 2,2',6,6'-tetrachlorobiphenyl (PCB 54), 2,2',3,5',6-pentachlorobiphenyl (PCB 95), 2,2',4,5,5'-pentachlorobiphenyl (PCB 101), 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136), and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153). Overall, these results are consistent with a role for CYP1A induction and/or Ah receptor activation in porphyrin accumulation mediated by HAHs with a planar configuration, whereas those that are not planar may mediate porphyrin accumulation by a mechanism not involving induction of CYP1A.

Bioaccumulation profiles of polychlorinated biphenyls including coplanar congeners and possible toxicological implications in Baikal seal (Phoca sibirica)

Isomer specific concentrations of individual polychlorinated biphenyls (PCBs) including toxic non-ortho (IUPAC 77, 126, 169), mono-ortho (105, 118, 156) and di-ortho (137, 138, 153, 180) coplanar congeners were determined in the blubber of 40 Baikal seals (Phoca sibirica) and as their fish diet collected from Lake Baikal, Siberia. Residue levels of total PCBs in Baikal seals were noticeably high and comparable to those reported for seals from the North Sea, suggesting the recent usage of this compound in the watershed of Lake Baikal. Non-, mono-, and di-ortho coplanar congeners were also detected in Baikal seals and fish. An approach to estimate bioaccumulation profiles of PCB congeners revealed that the non-ortho PCBs, IUPAC 77, 126 and 169 seemed to be less persistent than other congeners. Furthermore, selective biotransformation of PCB congeners having either meta-para vicinal H atoms or both adjacent chlorinated meta-para and ortho-meta positions has been suggested. Comparison of 2,3,7,8-TCDD toxic equivalents (TEQ) of non-, mono- and di-ortho coplanar congeners in Baikal seals with those for other marine mammals suggested higher enrichment of mono-ortho congeners, particularly IUPAC 105 and 118, which contributed significantly to the total TEQs in Baikal seals. Results imply that the TCDD-like toxicity is relatively serious in Baikal seals, because of the enrichment of these toxic PCB congeners in tissues.

Metabolic degradation, inducing potency, and metabolites of fluorinated and chlorinated-fluorinated dibenzodioxins and dibenzofurans

The metabolic degradation of fluorinated, chlorinated-fluorinated and chlorinated congeners was measured in liver homogenate of NMRI mice. While in the time period between 0 and 240 min no degradation of the 2,3,7,8-TCDD/TCDF could be detected, for all fluorinated congeners a perceptible degradation was found, even for the 2,3,7,8-TFDD. Stepwise chlorination of the 2,3,7,8-fluorinated congeners leads to a decrease of the degradation rate. In the EROD test, the exchange of chloro- with fluorosubstituents in the 2,3,7,8-TCDF leads to a decrease of induction potency. 3,7-Dichloro-2,8-difluorodibenzofuran was about 1/1000th as potent as 2,3,7,8-TCDF, while 2,3,7,8-TFDF was complete inactive. Comparison of the metabolic rates of different TCDD with those of the analogous TFDD demonstrates that the order of enzymatic degradation of different TCDD and the analogous TFDD is identical. The TFDD are degraded slightly faster than the corresponding TCDD. Surprisingly 1,4,6,9-TXDD showed the second slowest metabolic rate of the fluorinated and chlorinated TXDD after 2,3,7,8-TXDD although none of the 2,3,7,8-positions were substituted. Judging from 2,3,7,8-TFDD and 1,7-dichloro-2,8-difluorodibenzofuran the metabolic pathway of fluorinated and chlorinated-fluorinated congeners seem to be comparable to the chlorinated congeners.

Organochlorines in polar bears (Ursus maritimus) at Svalbard

A comprehensive survey on organochlorine (OC) contaminants in polar bears at Svalbard has been undertaken. Subcutaneous tissue, blood and milk have been sampled from anesthetized free-ranging bears of both sexes and different ages in the period from 1990 to 1994. A number of sexually mature females have been fitted with satellite transmitters which make it possible to follow their reproductive behaviour pattern. We report on contamination levels and pattern of PCB congeners, chlordanes, DDT-compounds, HCB and HCH-isomers in the various tissues. The relation of age, sex and reproductive status to OC contamination has been described, and the capacity of polar bears in metabolising OCs has been discussed from the isomer/metabolite composition of residues. Finally, the possible association between OC contamination and reproduction success has been assessed. The PCB levels present in polar bears at Svalbard are extremely high. Especially high levels of higher chlorinated PCBs are found, and they accumulate with age, particularly in males. With females, considerable amounts of OCs are transferred to the offspring via milk. However, more efficient OC transfer between subcutaneous depot lipid and circulatory lipids than from the circulatory system to milk is found particularly for the most lipophilic compounds. The OC pattern in suckling yearlings reflects the low transfer of the highest chlorinated PCBs into maternal milk. The levels of most other OCs, however, are higher in depot lipid of yearlings than in that of their mothers. The polar bears have high capacity to metabolise several OCs. This may protect them against toxic action of the contaminants. No relation between OC levels in females and their ability to get pregnant is found in this preliminary investigation on OC effects on the polar bears at Svalbard.

Effects of polychlorinated biphenyls on dopamine release from PC12 cells

In PC12 cells, Aroclor 1254 produced a concentration-dependent decrease in basal and K(+)-evoked dopamine (DA) release, and cellular DA levels. Aroclor 1254 did not alter the fraction of cellular DA released, suggesting that the decreased release of DA was solely due to decreased cellular levels of DA, and not to decreased packaging of DA or inhibition of neurotransmitter release. The coplanar congener 3,3',4,4',5-pentachlorobiphenyl decreased cellular DA levels and release of DA at levels that produced cytotoxicity. Absent of any apparent cytotoxicity, the ortho-substituted PCB congeners 2,2',5,5'-tetrachlorobiphenyl, 2,2',3,3',4,4'-hexachlorobiphenyl, 2,3',4,4',5-pentachlorobiphenyl, and 2,2',4,4',5,5'-hexachlorobiphenyl were effective in decreasing the amount of DA released from PC12 cells. These results suggest that ortho-chlorinated PCBs can cause decreased K(+)-evoked DA release through non-Ah receptor-mediated mechanisms. Furthermore, the PCB-mediated decrease in DA release was not due to impairment of DA packaging or release, but only due to decreased cellular DA levels.

Effects of 3,3',4,4'-tetrachlorobiphenyl, 2,3,3',4,4'-pentachlorobiphenyl, and 3,3',4,4',5-pentachlorobiphenyl on the developing chicken embryo when injected prior to incubation

Great Lakes waterbird populations have experienced less-than-expected hatchability of eggs and a greater-than-expected incidence of developmental abnormalities. Such deleterious effects have been attributed to polyhalogenated hydrocarbons such as polychlorinated biphenyls (PCBs). PCBs are of primary concern since they are present in significant quantities in the environment. Specific PCB congeners, 3,3',4,4',5-pentachlorobiphenyl (IUPAC number 126), 3,3',4,4'-tetrachlorobiphenyl (IUPAC number 77), and 2,3,3',4,4'-pentachlorobiphenyl (IUPAC number 105), were injected (singly or in combination) into the yolks of White Leghorn chicken (Gallus domesticus) eggs prior to incubation. Teratogenicity was assessed in dead embryos and in hatchlings. Hatchlings were raised for 3 wk to assess body weight gain and mortality. At the end of the 3-wk period, chicks were subjected to necropsy and the brain, bursa, heart, liver, spleen, and testes were removed and weighed. All 3 congeners caused increased embryo mortality, with approximately 50% mortality occurring at 0.6, 8.8, and 5592 micrograms/kg egg for congeners 126, 77, and 105, respectively. All three congeners also produced significantly more abnormalities than the vehicle. Chicks from PCB-injected eggs had lower body weights at wk 2 and 3 of age. Congener 126 caused lower relative bursa weights, congener 77 caused greater relative spleen weights and lower relative liver weights, and all three congeners caused relative heart weights to be greater when compared to control.

Effect of dietary casein levels on activation of promutagens in the spiral Salmonella mutagenicity assay. II. Studies with induced rat liver S9

In the previous study (Mutation Res., this issue), we showed that increased levels of dietary casein as the sole protein source for male F344 rats decreased the ability of the uninduced liver S9s to activate 2-aminoanthracene (2AN) to a mutagen in strain TA98 using the spiral Salmonella mutagenicity assay. No effects of dietary casein levels were noted for the ability of uninduced liver S9s to activate the promutagens aflatoxin B1 (AFB) and benzo[a]pyrene (BAP). In the present study, we have extended this study to include liver S9s induced with either Aroclor 1254, phenobarbital or 3-methylcholanthrene (3MC). S9s were derived from individual male F344 rats fed for 6 weeks on semisynthetic diets containing 8%, 12% or 22% methionine-supplemented casein as the sole source of protein (diets were made isocaloric by adjusting the corn starch content). Rats were housed in large, raised-bed cages by groups of three/diet/inducing agent. S9 activation mixtures were prepared at 5 mg of S9 protein/ml of S9 mix. Slopes from the linear portions of the mutagenicity dose-response curves were analyzed by ANOVA comparisons. Assays used to elucidate the phase I activities of microsomal preparations were cytochrome P-450 content, cytochrome-c reductase activity, flavin-containing monooxygenase activity, 7-ethoxyresorufin O-deethylation (EROD) activity, N-demethylation of benzphetamine, and para-nitrophenol O-deethylation. Phase II activities were assayed by estimating glutathione (GSH) content and measuring the metabolism of 1-chloro-2,4-dinitrobenzene (CDNB) by glutathione S-transferase in cytosolic preparations. None of the phase I or phase II endpoints were significantly affected by dietary casein levels. In general, increasing levels of dietary casein resulted in increased body and liver wet weight and amount of S9 protein. Aroclor-induced S9s from rats fed the 22% or 12% casein diet were most effective at activating AFB, depending on the lot of Aroclor used for induction; these divergent results were replicated with two groups of rats for each lot of Aroclor. The observed differences between Aroclor lots are assumed to arise from variation in the mix of PCB isomers. The Aroclor-induced S9s did not exhibit any casein-related effects for the activation of BAP or 2AN. For 3MC-induced S9s, the 12% casein diets produced S9s with the highest ability to activate AFB and BAP when standardized for protein content. Phenobarbital-induced S9s did not demonstrate any dietary casein-related effects on the activation of the three model promutagens. These results illustrate the complex interaction between dietary levels of casein, enzyme inducing agent and promutagen.

Temporal induction pattern of hepatic cytochrome P450 1A in thermally acclimated dab (Limanda limanda) treated with 3,3',4,4'-tetrachlorobiphenyl (CB77)

Mature male dab (Limanda limanda) acclimated at 10 degrees and 16 degrees C were orally administered a single dose of 0.5 mg/kg 3,3',4,4'-tetrachlorobiphenyl (CB77). At both temperatures, levels of cytochrome P450 1A (CYP1A) protein and 7-ethoxyresorufin O-deethylase (EROD) activity showed a two to six fold induction 40 days after CB77 treatment compared to control groups. Maximum responses of both EROD activity and CYP1A protein for the warm-acclimated fish were observed at 5 days after treatment. For the cold-acclimated fish a slow, progressive elevation for both EROD activity and CYP1A protein was observed and maximum responses were measured 40 days after treatment. Absolute EROD activity and CYP1A protein levels of fish from both temperatures were equally high at 40 days after treatment. Since in the control groups EROD activity and CYP1A protein levels were higher in the cold-acclimated fish, the magnitude of induction was higher in the warm acclimated ones. The highest concentrations of CB77 in muscle of fish from both temperatures were found at 5 and 10 days after treatment. The liver somatic index (LSI) showed 1.5 fold significantly higher values for the fish acclimated at 10 degrees C.

Embryotoxicity of polychlorinated biphenyls (PCBS) for preimplantation embryos

In a previous study oral administration of a commercial PCB mixture (Aroclor 1,260) to female rabbits (4 mg/kg b.wt. for 14 weeks) resulted in a significant accumulation of PCBs in 6-d-old blastocysts and increased preimplantation embryo mortality (1). In the present study, the direct toxicity of PCBs on preimplantation rabbit embryos was investigated during in vitro culture. One-day-old cleavage stages and 3-d-old rabbit morulae were cultured in BSM II medium supplemented with 1.5% BSA in a reduced oxygen concentration of 5% O2. They were exposed to 50, 5, or 0.5 microgram Aroclor 1,260/mL culture medium for 24 h. PCB (50 micrograms) led to a complete degeneration of the exposed embryos. Following exposure to 5 micrograms only 16% of the morulae developed into blastocysts. The others were either arrested in the morulae stage or were degenerated. Cell proliferation of the nondegenerated embryos was approximately 20% of that of corresponding control embryos. Compared with nonexposed controls, addition of 0.5 microgram PCB/mL showed either no or only a slight impairment of development. Preliminary embryo transfer experiments showed that morulae exposed to 5 micrograms PCB with clear signs of degeneration after 24 h in vitro culture were able to implant. Aroclor 1,260 is embryotoxic in a dose-dependent manner in cultured rabbit preimplantation embryos.

Developmental neurotoxicity of PCBs in humans: what do we know and where do we go from here?

The potential neurotoxicity of PCBs was first recognized in 1968 when a number of Japanese people became ill after ingesting rice oil that was contaminated with PCBs during the manufacturing process (Yusho). Later a similar exposure occurred in Taiwan (YuCheng). Children born to Taiwanese mothers who consumed PCB-contaminated rice oil were followed and a number of developmental abnormalities, including lower body weight and height, higher activity levels, greater incidence of behavior problems, and lower IQ scores, were observed. However, interpretation of these findings is complicated by the fact that there did not appear to be any relationship between available indices of exposure and severity of effects, and by the fact that the PCBs to which the Taiwanese were exposed contained unusually high concentrations of dibenzofurans, which are many times more toxic than PCBs, and may have been responsible for some or all of the observed effects. Since the Yusho and YuCheng episodes, several studies have been initiated to study the neurobehavioral effects of exposure to the lower levels of PCBs present in the environment. The two studies published to date have yielded conflicting results. Jacobson, Jacobson, and colleagues reported that in utero PCB exposure was associated with decreased birth weight and head circumference, shorter gestation, and several adverse outcomes on the Brazelton Neonatal Assessment Battery. Later they reported that the body weight deficits associated with prenatal PCB exposure were still present at 5 months and 4 years of age. Deficits in memory function were observed at 7 months and 4 years. Rogan, Gladen, and colleagues did not find any evidence of decreased birth weight or head circumference. Nor did they find any evidence of deficits in memory function. However, they did observe some similar effects on the Brazelton Neonatal Assessment Battery. They also observed a small delay in psychomotor development in the most highly PCB-exposed children, but the effect did not persist beyond 2 years of age. A number of methodological concerns have been raised about the Jacobson study, including issues related to exposure assessment, sample selection, and control of potential confounding variables. However, it is not clear that these shortcomings can explain the discrepancies between their findings and those of Rogan and Gladen. Other possible explanations include differences in exposure levels or PCB congener patterns between the two cohorts, differences in sociodemographic variables between the two cohorts, or other problems inherent in trying to detect subtle neuropsychological deficits at exposure levels that are near the threshold for effects. Hopefully, several new studies that are currently underway will help to resolve the uncertainties regarding the risks of perinatal PCB exposure that have been created by the conflicting results of these early studies.

Milk transfer and neonatal uptake of coplanar polychlorinated biphenyl (PCB) congeners in mice

The selective accumulation of 3,3',4,4'-tetrachlorobiphenyl metabolites in late gestational foetal blood and soft tissues in mice as a result of administration of different coplanar polychlorinated biphenyl (PCB) congeners, is reported elsewhere. The situation in the nursing neonate after maternal exposure to the same congeners is now studied: The 14C-labelled congeners 3,3',4,4'-tetrachlorobiphenyl (IUPAC number CB-77),3,3',4,4'5-pentachlorobiphenyl (IUPAC number CB-126), 3,3',4,4',5,5'-hexachlorobiphenyl (IUPAC number CB-169) (all three non-ortho congeners) and 2,3,3',4,4'-pentachlorobiphenyl (IUPAC number CB-105) (mono-ortho congener) were injected intravenously in lactating mice at day 11 post partum. One day and four days later, milk and neonatal/maternal tissues and plasma radioactivity was monitored by liquid scintillation counting (dose: 2.0 mumol (20-50 microCi)/kg body weight). In milk, CB-126, -169 and -105 showed higher levels (1450-2520 pmol/ml; one day after administration) than did CB-77 (580 pmol/ml), and in neonates, the relative whole-body levels of radioactivity (CB-169 and -105 highest) were related to the levels seen in milk (probably the consequences of their metabolic persistence). The comparably high 14C-concentration found in neonatal liver (about 15,000 pmol/kg) after CB-126 administration and in plasma (880 pmol/ml) after CB-77 administration could be explained by binding to specific proteins. In general, neonatal mice had two to seven times higher plasma levels than those of their mothers. These results indicate that CB-126, -169 and -105 are transferred via milk to neonates in considerable quantity and are deposited mainly in neonatal liver, whereas CB-77 is transferred in a comparably lower amount and accumulated in neonatal plasma. The lower 14C-levels in the NMRI mothers and offspring (about half of C57BL values in maternal and neonatal plasma), could possibly be explained by a differentiated metabolism of CB-77 in these two strains.

Foetal uptake of coplanar polychlorinated biphenyl (PCB) congeners in mice

Earlier studies (Darnerud et al. 1986) have shown that the Ah-receptor binding polychlorinated biphenyl (PCB) congener 3,3',4,4'-tetrachlorobiphenyl (IUPAC number CB-77) accumulated as hydroxy and methylsulphone metabolites in late gestational mice foetuses. In the present paper the foetal accumulation potential in mice of other dioxin-like PCB congeners was studied: 3,3',4,4',5-pentachlorobiphenyl, 3,3',4,4',5,5'-hexachlorobiphenyl and 2,3,3',4,4'-pentachlorobiphenyl (IUPAC numbers CB-126, CB-169, CB-105, to some extent dioxin-like) were compared to results of CB-77 (all congeners 14C-labelled and in equimolar doses (2.0 mumol/kg body wt.)). CB-77 resulted in the comparatively strongest foetal 14C-accumulation, when measured in plasma or whole body homogenate four days after administration (day 17 of pregnancy); the plasma 14C-values (calculated as pmol/g wet wt.) were 760, 130, 60 and 40 for CB-77, -126, 105 and -169, respectively, and the CB-77 derived radioactivity in the foetal compartment was 3.6% of administered dose (i.e. a considerable portion of the remaining maternal body radioactivity). Thin-layer chromatography (TLC) results, suggesting extensive CB-77 metabolism and foetal metabolite uptake, support earlier findings. The effects of CB-77 and CB-169 on foetal 7-ethoxyresorufin-O-deethylase (EROD) activities (day 17 of gestation; two days after 5 mg/kg body wt. dose (14.0-17.0 mumol/kg body wt.)) was about 20 times lower than of CB-126. In the dam, high radioactivity levels were observed in the liver and fat (highest concentrations found in CB-126 and CB-105, respectively). Strain comparison-foetal 14C-uptake (four days after administration of CB-77) in C57BL mice was almost five times higher than in NMRI-may be correlated to earlier observed differences in EROD activities between these strains. The present results indicate that congener and strain differences exist regarding both foetal and maternal distribution patterns of coplanar PCB congeners and point out the difference in foetal disposition between CB-77 and the other studied congeners.

Transfer of PCBs via lactation simultaneously induces the expression of P450 isoenzymes and the protooncogenes c-Ha-ras and c-raf in neonates

At the first day of lactation, maternal rats were injected with a single i.p. dose of 100 or 250 mg/kg body weight of a mixture of polychlorinated biphenyls (Aroclor 1254). This treatment caused significant increases in both material and neonatal hepatic cytochrome P-450, cytochrome b5, and cytochrome-c-(P-450) reductase. Transfer of PCBs via lactation resulted in significant increases in hepatic enzyme activities catalysed by neonatal CYP1A1, CYP1A2, CYP2B1, CYP3A1, and CYP2E1 using a variety of substrates. In contrast, the metabolism of dimethylnitrosamine and aminopyrine was only marginally (up to 2-fold) increased in maternal animals four days post treatment. Further measurements showed significant increases in maternal and neonatal epoxide hydrolase, glutathione-S-transferase, and UDP-glucuronyl transferase activities, thus suggesting a coordinated response for an induction of CYP1A1, CYP1A2, CYP2A1, CYP2B1, CYP2E1, CYP3A1, and CYP4A1 in both maternal and neonatal CYP2C6, and at the higher dose the expression of neonatal CYP2E1 was significantly reduced. Northern blot analysis provided further evidence for significant increases in maternal and neonatal hepatic CYP1A1, CYP1A2, CYP2B1, and CYP2E1 mRNA, but reduced amounts of CYP2C7 and CYP4A1 mRNA. Additional Northern blot hybridization experiments may suggest an increased expression of the protooncogenes c-Ha-ras and c-raf in the mother and the neonate upon treatment of maternal rats with Aroclor 1254. Lactation itself may result in an increased expression of the latter protooncogenes, but the mRNA of the protooncogenes c-erb A and c-erb B was not detected in any of the tissues examined.

Detection of PCB adducts by the 32P-postlabeling technique

The purpose of this study was to determine whether lower chlorinated biphenyls would be bioactivated to electrophilic metabolites by microsomes alone or in combination with peroxidase. Monochloro- and dichlorobiphenyls were incubated with liver microsomes of rats treated with phenobarbital and beta-naphthoflavone, an NADPH-regenerating system, and deoxyguanosine 3'-monophosphate (dGp). The resultant adducts were analyzed by 32P-postlabeling either following microsomal incubation alone ("preoxidized") or coupled with subsequent oxidation with horseradish peroxidase/H2O ("oxidized"). The incubation of 4-monochlorobiphenyl (4-MCB) resulted in the formation of two minor adducts by microsomal activation alone. However, the oxidized sample showed two additional major adducts. Formation of the latter adducts was almost completely (> 80%) inhibited when the oxidation reaction was performed in the presence of ascorbic acid. The other test mono- and dichlorobiphenyls also formed 1-3 major adducts. Compared with microsomal activation alone, these adducts were enhanced after the oxidation reaction or detected only in the oxidized samples. These data suggest that (1) some adducts of the lower chlorinated biphenyls are derived from arene oxides and (2) many adducts may be formed by metabolism of the parent compounds to catechol and p-hydroquinone species, which are oxidized to semiquinones and/or quinones. The involvement of quinones and/or semiquinones was supported by UV/vis spectroscopic measurements, which showed that metabolites of 4-MCB can be oxidized to products with spectra characteristic of quinones. These data raise the possibility that lower chlorinated biphenyls may be genotoxic and may explain the fact that commercial polychlorinated biphenyl mixtures are complete rodent carcinogens.

Tissue distribution, metabolism, and excretion of 2,4,4'-trichlorobiphenyl (CB-28) in the rat

The tissue distribution, metabolism, and excretion of 14C-labeled 2,4,4'-trichlorobiphenyl (CB-28) were studied in the rat. Following intravenous administration, radioactivity was removed from the blood rapidly and distributed to tissues. The time-courses of varying concentrations of CB-28 in tissues and blood were described mathematically using nonlinear regression analysis. The highest concentrations of radioactivity were found in the adipose and skin, which showed distinct uptake phases. High levels were seen at 30 minutes in liver and brain, but quickly declined. Fifty-two percent of the given dose was excreted in feces within 14 days. Intraperitoneal administration to three female rats for five consecutive days provided tissues which were analyzed for metabolites.

Congener-specific effects of PCBs on contractions of pregnant rat uteri

Both increased and decreased gestation lengths have been reported following exposures to polychlorinated biphenyl (PCB) mixtures and congeners. Because oscillatory uterine contractions are essential for parturition, we hypothesized that the disparate findings on gestation length may be the result of distinct PCB congener-specific actions on oscillatory uterine contractions. This study examined the acute effects of PCB congeners on isometric contractions of isolated pregnant uteri and the structure-activity relationship for individual congeners. After cumulative exposure to individual PCB congeners (0.5 microM to 150 microM), oscillatory contractions were: 1) not altered by 2,4,5,2',4',5'-hexachlorobiphenyl, 3,4,5,3',4'-pentachlorobiphenyl, or 3,4,3',4'-tetrachlorobiphenyl; 2) significantly inhibited by 4-hydroxy-2',4',6'-trichlorobiphenyl; and 3) markedly increased by 2,4,6-trichlorobiphenyl and 2,4,2',4'-tetrachlorobiphenyl, when compared to solvent controls. The uteri were more sensitive to PCB congeners with ortho-substituted light chlorination than those highly chlorinated, or those interacting with the Ah-receptor.

Inhibition of microsomal and mitochondrial Ca2+-sequestration in rat cerebellum by polychlorinated biphenyl mixtures and congeners. Structure-activity relationships

Recent studies from our laboratory indicate that polychlorinated biphenyl (PCB) congeners in vitro perturbed signal transduction mechanisms including cellular Ca2+-homeostasis and protein kinase C translocation. We have now investigated the structure-activity relationship (SAR) of three PCB mixtures, 24 PCB congeners and one dibenzofuran for their effects on microsomal and mitochondrial Ca2+-sequestration in rat cerebellum. Ca2+-sequestration by these intracellular organelles was determined using radioactive 45CaCl2. All three mixtures studied, Aroclor 1016, Aroclor 1254 and Aroclor 1260, were equally potent in inhibiting microsomal and mitochondrial Ca2+-sequestration with IC50 values of 6-8 microM. 1,2,3,7,8-Pentachlorodibenzofuran had no effect on Ca2+-sequestration by these organelles. The SAR among the congeners revealed: (1) congeners with ortho-/meta- or ortho-, para-chlorine substitutions were the most potent in inhibiting microsomal and mitochondrial Ca2+-sequestration (IC50 = 2.4-22.3 microM); (2) congeners with only para- but without ortho-substitutions were not effective in inhibiting Ca2+-sequestration by microsomes and mitochondria; (3) increased chlorination was not related to the effectiveness of these congeners. The present SAR studies indicate that the effects of most PCB congeners in vitro may be related to an interaction at specific sites having preference for low lateral substitution or lateral content (meta- or para) in the presence of ortho-substitution.

Immunotoxicity of PCBs (Aroclors) in relation to Great Lakes

Polychlorinated biphenyls (PCBs) are among the most widespread environmental pollutants and a prominent contaminant of the Great Lakes basin. Due to their resistance to biodegradation and lipophilic properties, PCBs bioaccumulate in fish tissues and in fish-eating humans. PCBs are also known to cross the placenta and to be excreted into the mother's milk, thus predisposing the infant to potentially adverse health effects. For example, a higher incidence of bacterial infections was reported for breast-fed infants born to mothers who consumed large amounts of Great Lakes fish compared to the incidence in control infants whose mothers ingested low amounts of fish. While data regarding the PCB-induced immunotoxic effects in humans are scarce, data derived from the use of experimental animals, including nonhuman primates, indicate that the immune system is a potential target for the immunotoxic effects of PCBs. Such studies have used the commercially available PCB mixtures alone. However, PCBs have the potential of partially antagonizing the effects of other structurally related compounds including the highly toxic dioxins, which are also present in small amounts in the Great Lakes. Thus, to fully evaluate the magnitude of the immunotoxic risk PCBs pose to humans, consideration should be given to investigations in which the interactive effects of PCBs are combined with other contaminants present in the Great Lakes.

DNA adducts and P450 induction in human, rat and avian liver cells after exposure to polychlorobiphenyls

Polychlorinated biphenyls (PCBs) are industrial chemicals which have been detected in fish, birds and humans. They are known to exert marked effects on the liver. They induce hepatocellular carcinoma in rats and birds, and are suspected of being carcinogenic to humans. To better understand the genotoxic effects of PCBs, we used 32P-postlabelling to investigate DNA adduct formation, after exposure to PCBs (Aroclor 1254 and 3,3',4,4'-tetrachlorobiphenyl), in primary cultures of fetal hepatocytes from two animal species and in a human cell line (Hep G2). We also studied the induction of 7-ethoxyresorufin-O-deethylase (EROD) in these PCB-treated cells. The three cell types used are known to express different cytochrome P450 families. The aim was to see whether a correlation could be established between EROD activity (a CYP1A1-related activity) and DNA adduct formation. DNA adducts were found in all three models after exposure to 50 microM 3,3',4,4'-tetrachlorobiphenyl. The number of adducts was higher in quail hepatocytes (37 adducts per 10(9) nucleotides) than in rat hepatocytes or Hep G2 cells (20 adducts per 10(9) nucleotides in both cases). The major adduct was the same in all three cell types, but some adducts were found in only one or two species. These inter-species differences probably reflect metabolic differences leading to different ultimate carcinogens. Exposure to Aroclor 1254 failed to produce significant levels of DNA adducts, suggesting that pre-treated cells are required to magnify Aroclor 1254 metabolism. No correlation was found between adduct formation and the level of EROD induction.

Induction of cytochrome P-450 in the Norway rat, Rattus norvegicus, following exposure to potential environmental contaminants

Cytochrome P-450 (CYP) induction (consisting of increases in cellular RNA and protein content and associated catalytic activities) occurs predominantly in the liver, but also in small intestine, lung, kidney, and placenta, of Norway rats (Rattus norvegicus) exposed to certain types of potential environmental contaminants. The specific isoform(s) induced in the rat and the magnitudes of the increases observed depend upon the chemical nature of the xenobiotic. For instance, the predominant isoforms induced by nonhalogenated polycyclic aromatic hydrocarbons, such as petroleum derivatives and coal-tar constituents such as the benzopyrenes and the anthracenes, are those of the CYP1A subfamily. Polyhalogenated aromatic hydrocarbons, such as the halogenated dibenzodioxins, dibenzofurans, and biphenyls, may cause the induction of predominantly the CYP1A subfamily, predominantly the CYP2B subfamily, or mixed CYP1A- and CYP2B-type induction, depending upon the halogen substitution pattern. In contrast, the chlorinated hydrocarbon pesticides, such as DDT, dieldrin, chlordane, and mirex, cause almost exclusively the induction of isoforms of the CYP2B (and to a lesser extent the CYP3A) subfamilies. The commonly employed plasticizing agent di-(2-ethylhexyl)phthalate elicits predominantly induction of the CYP4A subfamily. Those xenobiotics that would be expected to be the most pervasive environmental contaminants are typically those that have also been found to cause the most profound CYP induction responses. Such chemicals are extremely lipophilic and tend to accumulate in animal tissues, especially fatty tissues such as the liver. The hepatic CYP induction response to such potential environmental contaminants is typical of the animals' response to lipophilic xenobiotics in general, and serves as a mechanism by which the excretion of such compounds from the body is facilitated.

CB pattern in the harbour porpoise: bioaccumulation, metabolism and evidence for cytochrome P450 IIB activity

Metabolism of chlorobiphenyls (CBs) was studied in harbour porpoise by comparing patterns of CB-X/CB-153 ratios in blood, brain, liver and blubber with the patterns in herring, the main food source. The CBs were classified in five groups, based on the presence/absence of vicinal H-atoms (vic. Hs) in meta,para (m,p) and/or ortho,meta (o,m) positions and the number of ortho-Cl-atoms (ortho-Cls). Plots of CB-X/CB-153 ratios in porpoise tissue vs the ratios in herring appeared to be linear for each CB group in all tissues. Slopes of these plots (metabolic slopes) were used as quantitative indicators of metabolic activity. In this way, activity of PB-type isozymes of the P450 monooxygenase system was apparent: in contrast to existing literature data, harbour porpoise appears to be able to metabolize congeners with m,p vic. Hs, even in the presence of more than 2 ortho-Cls. The presence of 3-MC-type (MC-type) isozymes was also detected. The metabolic slopes were also used as basis for risk assessment. Due to their metabolism the most toxic non-ortho CBs were not present in the tissues at detectable levels. We suggest a risk assessment approach which takes this into account. It is considered to be an alternative and more reliable basis for risk assessment than the use of toxic equivalent factors. The results support the model of equilibrium distribution of CBs in harbour porpoise and the role of blood as central transport medium. The model has been developed for persistent compounds; it appears to hold for metabolizable CB congeners as well.

Synthesis and characterization of hydroxylated polychlorinated biphenyls (PCBs) identified in human serum

Hydroxylated polychlorinated biphenyls (PCBs) have been identified in wildlife and human samples. Most of these compounds are highly chlorinated (penta-hepatachloro) and contain a single meta- or para-hydroxyl group. Using the Cadogan coupling procedure, the following hydroxy-PCBs congeners were synthesized: 2,3,3',4',5-pentachloro-4-biphenylol, 2,3',4,4',5-pentachloro-3-biphenylol, 2',3,3',4',5-pentachloro-4-biphenylol, 2,2',3',4,4'-pentachloro-3-biphenylol, 2,2',3,3',4',5-pentachloro-4-biphenylol, 2,2',3',4,4',5-hexachloro-3-biphenylol, 2,2',3,4',5,5'-hexachloro-4-biphenylol, 2,2',3,3',4',5,5'-heptachloro-4-biphenylol, 2,2',3',4,4',5,5'-hepatachloro-3-biphenylol, 2,2',3,4',5,5',6-heptachloro-4-biphenylol. Many of these compounds have been detected as residues in human serum and current studies are investigating their activities as agonists and antagonists for several endocrine-mediated responses.

Contaminant levels in harbor seals from the northeastern United States

The concentrations of polychlorinated biphenyls (PCBs), organochlorine pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzofurans (PCDF), polychlorinated dibenzo-p-dioxins (PCDD), and mercury (Hg) were determined in blubber and liver tissues of harbor seals (Phoca vitulina) collected along the northeast coast of the U.S. Average PCB concentrations in seal blubber (sum of congeners) were 12.0 micrograms/g (wet weight) with a range of 7.30 to 24.3 micrograms/g in 1980 and 6.66 micrograms/g (wet weight) with a range of 2.61 to 11.3 micrograms/g in 1990-1992. Comparisons between blubber data from this study and previous work indicated that the concentration of PCBs along the northeast coast of the U.S. may have decreased over the past twenty years. The average p,p'-DDE concentrations in seal blubber were 10.9 micrograms/g (wet weight) in 1980 with a range of 6.95 to 21.9 micrograms/g and 4.12 micrograms/g (wet weight) with a range of 1.83 to 7.84 micrograms/g in 1990-1992. Only trace amounts of PCDFs and PCDDs were found in a few blubber samples; levels in most tissues were below detection (3-5 pg/g) (wet weight). Trace amounts (< 30 ng/g) of phenanthracene, anthracene, and alkylated MW-178 compounds were found in some seal samples; all other PAH compounds were below the detection level (5-15 ng/g). Toxic equivalents (TEQ) of selected coplanar and mono-ortho PCB congeners and relative toxic equivalents (RTE) (pg total TEQ/microgram total PCB) were calculated, using recently proposed dioxin toxic equivalent factors (Ahlborg et al. 1994). The TEQs ranged from 41 to 315, and the RTEs ranged from 2.25 to 16.3.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicological consequences of aroclor 1254 ingestion by female rhesus (Macaca mulatta) monkeys. Part 2. Reproduction and infant findings

A group of 80 menstruating rhesus (Macaca mulatta) monkeys were randomly allocated to four similar test rooms (20 monkeys/room) and then randomly allocated within each room to one of five dose groups (four females/dose group/room). Each day, the monkeys self-ingested capsules containing doses of 0, 5, 20, 40 or 80 micrograms Aroclor 1254/kg body weight. After 25 months of continuous dosing, approximately 90% of the treated females had attained a qualitative pharmacokinetic steady state with respect to the concentration of polychlorinated biphenyl (PCB) in their adipose tissue. Commencing on test month 37, each female was paired with an untreated male until either an impregnation occurred or the 29-month breeding phase of the study was completed. The females continued to receive their daily test dose during mating and gestation. To preclude an infant ingesting the mother's dosing capsule, dosing of the dam was discontinued when a nursing infant was approximately 7 wk old. Treatment was restarted when the infant was weaned at 22 wk of age. At parturition, and every 4 wk until weaning, milk and blood samples were obtained from the dam and a blood sample was obtained from the infant for PCB analysis. When the infant was 20 wk old, immunological testing was initiated and an adipose sample was obtained from the infant and dam for PCB analysis. Subsequently, further adipose and blood samples were obtained from the infant and blood specimens were obtained from the dam for PCB analysis. Concurrently, each infant was subjected to anthropometric measurements and detailed clinical examinations until it was approximately 122 wk old. At 122 wk some of the control and all of the treated infants were killed humanely and autopsied. A statistical analysis of the reproduction data provided evidence for a significant decreasing dose-related trend in conception rates and a significant increasing dose-related trend in foetal mortality. Several comparisons between impregnated and non-impregnated females did not implicate 'age' as a confounding factor regarding these results. The major findings with the infants involved some immunological test differences and mild clinical manifestations of PCB ingestion.

Polybrominated biphenyl and diphenylether flame retardants: analysis, toxicity, and environmental occurrence

Data on two classes of brominated polyaromatic flame retardants are reviewed with emphasis on analytical aspects, occurrence, fate, and toxicity in the environment. Concentrations of brominated fire retardants are quantified as equivalents of commercial mixtures. Because different congeners behave differently in the environment and show large differences in toxicity, future studies would benefit from the availability of analytical standards of individual congeners. The main environmental properties and mechanisms of toxicity of the PBBs and PBDEs are similar to those of the structurally related PCBs and dibenzodioxins. Although the present concentrations of brominated fire retardants do not yet appear to represent a major environmental risk in marine food chains, their replacement by environmentally less harmful alternatives is recommended.

Atrazine treatment potentiates excretion of mutagenic urine in 2,6-dinitrotoluene-treated Fischer 344 rats

Atrazine (ATZ), an s-triazine herbicide, is a widespread environmental contaminant. The hepatocarcinogenic component of technical grade dinitrotoluene, 2,6-dinitrotoluene (2,6-DNT, 19.5%), is a byproduct of trinitrotoluene synthesis and is found at production sites. This study explores the effect of ATZ treatment on the bioactivation of the promutagen, 2,6-DNT. Male Fischer 344 rats (5 weeks old) were administered 50 mg/kg of ATZ by gavage for 5 weeks. At 1, 3, and 5 weeks, both DMSO-control and ATZ-pretreated rats were treated p.o. with 75 mg/kg of 2,6-DNT and were housed in metabolism cages for urine collection. Sulfatase- and beta-glucuronidase-treated, concentrated urine was bioassayed for urinary mutagens in a microsuspension modification of the Salmonella assay with and without metabolic activation. No significant change in mutagen excretion was observed in ATZ-treated rats; however, an elevation in direct-acting urine mutagens from rats receiving ATZ and 2,6-DNT at weeks 1 (359 +/- 68 vs. 621 +/- 96 revertants/ml) and 5 (278 +/- 46 vs. 667 +/- 109 revertants/ml) of treatment was observed. The increase in production of urinary mutagens was accompanied by an elevation in small intestinal nitroreductase activity. Increases in large intestinal nitroreductase and beta-glucuronidase were observed after 5 weeks. There was no apparent effect of ATZ following 5 weeks of treatment on the production of 2,6-DNT-derived hepatic DNA adducts. ATZ treatment modifies intestinal enzymes responsible for promutagen bioactivation, and potentiates the excretion of mutagenic urine in 2,6-DNT-treated animals.

Effects of polychlorinated biphenyls (PCBs) and dioxins on growth and development

Polychlorinated biphenyls (PCBs) and dioxins are potentially toxic compounds which occur widely in the environment. Their effects on the growth and development of infants at the levels currently found in highly industrialised western countries is not well known. This Dutch multicenter study, combining animal and human studies, tries to answer this question. Animal studies showed that PCB 169, given once during pregnancy at a dose of 1.8 g kg-1 bodyweight, has an effect on developmental parameters, dopamine regulation and fertility. Effects on thyroid hormones were also found in animals, probably due to both a competitive binding of PCB metabolites to the thyroxine binding protein and increased glucuronidation. Perhaps to compensate for this, an increased diodase activity in the brain was found. Human studies involved 400 mother-infant pairs, half of them being breast-fed, the other half were fed a formula devoid of PCBs and dioxins. PCB levels were measured in serum and dioxin and PCB levels in breastmilk. Levels were found to be as high as previously found in highly industrialised countries. Growth and development were carefully documented, but no data are as yet available. In pregnant women, a significant negative correlation was found between some dioxin and PCB congeners in milk and plasma thyroid hormones, while newborn infants showed higher thyroid stimulating hormone (TSH) at higher levels of dioxin exposure. In summary, data from this combined multicenter study involving animals and humans increases our insight into the potentially negative effects of PCBs and dioxins on growth and development.

Isomer specific analysis of PCBs and organochlorine pesticides in Finnish diet samples and selected individual foodstuffs

Twenty organochlorine pesticide compounds (OCPs) and 20 polychlorinated biphenyl (PCB) congeners known to be the most abundant or toxicologically significant were determined in samples of a representative Finnish diet and in individual foodstuffs. OCPs were isolated and cleaned-up by solvent extraction and concentrated sulphuric acid treatment according to the methods given by Moilanen et al. (1986) or Veierov and Aharonson (1980). Instrumental analysis was performed by gas chromatography-mass spectrometry using selected ion monitoring. PCBs were determined by a congener-specific method. There were very low levels of most OCPs and PCB congeners in the present Finnish market basket, hospital diet, milk, cheese and egg samples. The average total PCB intake from the diets was approximately 2.3 micrograms/day per capita, which represents 3% of the highest tolerable intake proposed by the US Food and Drug Administration.

Levels of PCBs and some organochlorine pesticides in the human population of selected areas of the Slovak Republic. I. Blood

Fifty samples of human blood collected in 1992 from the general human population living in five selected areas of the Slovak Republic (the Michalovce, Velký Krtís and Nitra District, Myjava area and Bratislava) were analysed for polychlorinated biphenyls (IUPAC Nos. 28, 52, 77, 101, 105, 114, 118, 123, 126, 138 (+163), 153, 156, 157, 167, 169, 180 and 189) and some organochlorine pesticides (HCB, gamma-HCH, p,p'-DDE and p,p'-DDT). PCB levels (the sum of the congeners analysed) in serum lipids averaged for all the samples analysed were 1.79 micrograms.g-1 (range: 0.53-9.20 micrograms.g-1, median: 1.33 micrograms.g-1), HCB 5.38 micrograms.g-1 (0.16-23.20 micrograms.g-1, 4.27 micrograms.g-1), gamma-HCH 0.012 microgram.g-1 (< 0.01-0.18 microgram.g-1), p,p'-DDE 6.05 micrograms.g-1 (1.30-34.80 micrograms.g-1, 4.39 micrograms.g-1) and p,p'-DDT 0.27 microgram.g-1 (< 0.01-0.79 microgram.g-1, 0.23 microgram.g-1). About three times higher levels of PCBs were found in the samples from the district where PCB formulations had been produced (the Michalovce District).

Differential effects of polychlorinated biphenyl congeners on phosphoinositide hydrolysis and protein kinase C translocation in rat cerebellar granule cells

Previous reports from our laboratory have suggested that the neuroactivity of some polychlorinated biphenyl (PCB) congeners is associated with perturbations in cellular Ca(2+)-homeostasis. We have characterized further the neurochemical effects of PCBs on signal transduction in primary cultures of cerebellar granule cells. The present experiments found that neither 2,2'-dichlorobiphenyl (DCBP), an ortho-substituted congener, nor 3,3',4,4',5-pentachlorobiphenyl (PCBP), a non-ortho-substituted congener, affected basal phosphoinositide (PI) hydrolysis in cerebellar granule cells. However, at concentrations up to 50 microM, DCBP potentiated carbachol-stimulated PI hydrolysis, while decreasing it at 100 microM. PCBP, on the other hand, had no effect on carbachol-stimulated PI hydrolysis in concentrations up to 100 microM. [3H]Phorbol ester ([3H]PDBu) binding was used to determine protein kinase C (PKC) translocation. DCBP increased [3H]PDBu binding in a concentration-dependent manner and a twofold increase was observed at 100 microM in cerebellar granule cells. PCBP had no effect on [3H]PDBu binding at concentrations up to 100 microM. The effect of DCBP on [3H]PDBu binding was time-dependent and was also dependent on the presence of external Ca2+ in the medium. To test the hypothesis that DCBP increases [3H]PDBu binding by acting on receptor-activated calcium channels, the effects of DCBP were compared to those of L-glutamate. The effects of DCBP (50 microM) and glutamate (20 microM) were additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential modulation of hepatic cytochrome P-450 enzymes in rat and Syrian hamster by 4'-trifluoromethyl-2,3,4,5-tetrachlorobiphenyl

The effects of a single injection (40 mg/kg) of 4'-trifluoromethyl-2,3,4,5-tetrachlorobiphenyl (CF3) on hepatic cytochrome P-450 monooxygenases were assessed in rat and syrian hamster. The CF3 treatment significantly increased the total amount of cytochrome P-450 in both species. In rats, CF3 treatment caused marked increases in ethoxyresorufin O-deethylase (EROD), arylhydrocarbon hydroxylase (AHH), and testosterone 7 alpha-hydroxylase activities but significantly reduced the activities of benzphetamine N-demethylase (BzND), erythromycin N-demethylase (ErND), testosterone 6 beta, 16 alpha, and 16 beta-hydroxylase, and formation of androstenedione. Administration of CF3 to hamsters strongly induced the activities of EROD, AHH, BzND, testosterone 15 alpha, and 16 alpha-hydroxylases, and androstenedione production, whereas ErND, testosterone 6 beta, and 7 alpha-hydroxylases were decreased. Administration of CF3 to rats induced the CYP1A family proteins and CYP2A1, while CF3 reduced the level of CYP2B1, and, to a lesser extent, of CYP6 beta 2. In hamsters, CF3 treatment significantly induced the CYP1A2, CYP2A1, CYP2A8, and CYP2B1 isozymes, whereas the CYP6 beta 2 level was decreased. The ability of hepatic microsomes to activate aflatoxin B1 and benzo(a)pyrene was elevated by CF3 treatment in hamsters, while activation of aflatoxin B1 was decreased in microsomes from CF3-treated rats. These results showed differences in the CF3-induced pattern of rat and hamster cytochrome P-450 monooxygenases.

Abnormally high polychlorinated biphenyl levels in striped dolphins (Stenella coeruleoalba) affected by the 1990-1992 Mediterranean epizootic

PCB concentrations and total lipid content were determined in the blubber and liver of striped dolphins affected by the 1990 morbillivirus epizootic in the Mediterranean Sea, and in the blubber of striped dolphins from the same area sampled with a biopsy dart in 1987-1989 and 1991. PCB levels were found to be significantly higher in the individuals that succumbed to the epizootic than in the 'healthy' population sampled before or after the event. Although recent mobilization of lipid reserves was found to have occurred in some of the diseased dolphins, this had little effect on their PCB blubber concentrations and cannot explain the observed difference with the healthy individuals. Three hypotheses are put forward to explain the apparent link between high PCB levels and mortality caused by the epizootic: (i) depressed immunocompetence caused by PCBs leading to an increase in individual susceptibility to the morbillivirus infection, (ii) mobilization of fat reserves leading to increased PCB levels in blood which, in turn, may produce a liver lesion capable of increasing the individual's susceptibility to the morbillivirus infection, and (iii) previous existence of an unspecific hepatic lesion producing impairment of the liver function which, in turn, could lead to an increase both in tissue PCB concentrations and in individual susceptibility to the morbillivirus infection.

Toxic chlorobiphenyls in adipose tissue and whole blood of an occupationally/accidentally exposed man and the general population

Individual polychlorinated biphenyl (CB) congeners in adipose and whole blood tissues of a capacitor manufacture worker (occupational/accidental exposure) and of the general population were determined. Nondestructive sample cleanup and multidimensional gas chromatography-electron capture detection (MDGC-ECD) techniques were applied. Special attention was given to the toxicologically relevant congeners CB-77, CB-126, CB-169, CB-105, CB-114, CB-118, CB-156, CB-167, and CB-189 (IUPAC). Lipid-based tissue contents of sigma CBs were higher in the occupationally/accidentally exposed worker (adipose = 7,000 ng/g; whole blood = 11 ng/g) than in the general population (adipose = 300 ng/g; whole blood = 1.9 ng/g). Among the non-ortho Cl CBs, CB-77 was below detection limit (< 1.0 pg/g). The contents of CB-126 for the capacitor manufacture worker were 2,000 and 3 pg/g, and in the general population were 100 and 2 pg/g for adipose and whole blood, respectively. The corresponding data for CB-169 were 3,500 and 4 for adipose and whole blood, respectively, in the exposed worker, and 40 and 2 for adipose and whole blood, respectively, in the general population. Congeners with highest contents were CB-153, CB-138, CB-180, CB-170, and CB-187. These congeners possess chlorine substitution patterns, making them resistant to metabolism. X/153 ratios suggest that both PB and 3-MC type cytochrome P-450 enzymes were induced in the exposed worker, as well as in the general population.