Postmortem tissue levels of polychlorinated biphenyls in female rhesus monkeys after more than six years of daily dosing with Aroclor 1254 and in their non-dosed offspring

Human Exposure to Polychlorinated Biphenyls and Health Effects

Polychlorinated biphenyls (PCBs) are a mixture of chemicals. Some congeners of the mixture are highly persistent both in the environment and in humans. Although PCBs have not been used commercially since about 1977 in the US, they can still be detected in human blood and tissues in this country. PCB levels are declining and are often no longer detectable in younger people. A cursory review of recent animal studies is provided. Studies to determine whether PCBs cause cancer in humans, neurobehavioural effects, abnormal thyroid and immune function in children and low birth weight are discussed in more detail. These studies are inconclusive and do not provide clinical evidence that PCBs at levels encountered with human exposure produce adverse health effects. The differences in PCB blood or tissue concentrations between controls and cases, or between the upper and lower end of various environmentally exposed groups of children or adults, are small. Although some effects are statistically significantly different, they do not appear to be biologically significant. Many studies on the effects of PCBs are difficult to interpret because the range of normal values for clinical and neurobehavioural tests are not provided or appropriately considered, there was no, or inadequate, control for potential confounders. In occupational mortality studies, exposures were much higher. In some studies, various specific cancers were elevated. However, these appear to be chance observations resulting from multiple comparisons since the increase of specific cancers was not consistent between studies and was no longer present in some cohorts when studies were repeated at a later date with longer follow-up. Overall, the data fail to demonstrate conclusive adverse health effects of PCBs at concentrations encountered with human exposures.

Integration of mechanistic data in the toxicological evaluation of endocrine modulators

Controversy has arisen concerning the likelihood of adverse health effects due to exposure to hormonally active agents or endocrine modulators such as environmental estrogens. With the aim to improve the basis for their toxicological evaluation, several chemicals of anthropogenic (bisphenol A, octylphenol, o,p'-DDT) and of natural origin (daidzein, genistein) were investigated with regard to their mode of hormonal action and potency as well as toxicokinetics. Experimental toxicodynamic and toxicokinetic data illustrate important points in a comparative assessment of environmental estrogens. A novel concept, the Hygiene-Based Margine of Safety (HBMOS), has been suggested to characterize the relative impact of these potential endocrine modulators on human health: It integrates exposure scenarios (i.a. those generated within the European Existing Chemicals Programme) and in vivo rodent potency data for xenoestrogens and for dietary phytoestrogens. On the basis of these informations, HBMOS values calculated for the alkylphenol and bisphenol A appear sufficiently high to ensure the absence of a practical risk to human health under the present exposure conditions. For slowly accumulating compounds (e.g. DDT) with much longer half-lifes than isoflavones, such comparison should be based on comparative blood levels rather than on scenarios of daily exposures.

The mammalian testis accumulates lower levels of organochlorine chemicals compared with other tissues

Tissues were obtained from three separate experiments in order to quantify the tissue distribution of organochlorine chemicals that are thought to be potential reproductive toxicants in males: 1) Sprague Dawley rats received 1 microCi of 14C-Aldrin or 14C-Dieldrin (20.6 microCi/micromole) i.p. once a week for three weeks. One week and four weeks after the last injection, tissues were harvested and stored at -80 degrees C. Tissue 14C levels were quantified by scintillation spectrometry. 2) Cis- or trans-nonachlor (0, 0.25, 2.5, 25 mg/kg body weight) were administered daily in corn oil to male rats by gavage for 28 days. Tissues were harvested and frozen at -80 degrees C on the 29th day. Organochlorine residues were extracted and quantified by gas chromatography with electron capture detection. 3) Technical grade toxaphene (0, 0.1, 0.4 or 0.8 mg/kg body weight) was ingested daily by female cynomolgus monkeys of reproductive age for 18 months prior to being mated with control males. Dosing continued during pregnancy and lactation. Their infants received toxaphene via breast milk, and upon weaning, they ingested the same dose as their mothers for 48 to 49 weeks until, at 77 to 80 weeks of age, tissues were harvested and stored at -80 degrees C. Organochlorine residues were extracted and quantified as previously stated. In all three experiments, organochlorine residues in the testis were lower than in most of the other reproductive tract and nonreproductive tract tissues we examined. For example, testicular aldrin and dieldrin levels were <5% the epididymal content; testicular cis- and trans-nonachlor were <25% the epididymal content and, testicular toxaphene levels were <15% of the epididymal content. The reasons for the low degree of accumulation by the testis in comparison with other tissues are unknown. However, the lower testicular content may afford germ cells some protection from the potentially toxic effects of these chemicals.

Dosing via gavage or diet for reproduction studies: a pilot study using two fat-soluble compounds-hexachlorobenzene and aroclor 1254

The choice of a dosing route for in vivo toxicological tests is often dictated by practical constraints. Reproduction studies are particularly challenging in this regard since the determination of no-effect levels and allowable daily intakes from reproduction data encompasses exposure of the dam to the test xenobiotic prior to pregnancy, during gestation and during lactation. The fetus/infant can be exposed to the xenobiotic as well as the dam's metabolic products of the test xenobiotic during gestation and lactation. We initiated a series of two-litter, pilot reproduction studies with Sprague-Dawley and Fischer 344 rats to specifically ascertain the amount of xenobiotic and its metabolites ingested by the nursing neonate on lactation days 4, 7, 12, 17 and 21, when its dam received the xenobiotic via its diet or by gavage. The xenobiotics studied in this initial series of experiments were hexachlorobenzene (HCB) and Aroclor(R) 1254 (polychlorinated biphenyls; PCBs). The dams were dosed for 28 days, mated to untreated males and then remated approximately 2 weeks after weaning their first litter to a second untreated male. Dietary levels of 10 ppm HCB or 10 ppm PCBs, and gavage doses of 0.9 mg HCB or 0.8 mg PCBs/kg body weight/day were chosen and resulted in similar doses of HCB and PCBs per unit of the body weight of the dam during the premating period. There were no apparent toxicological effects regarding the dam nor were any of the reproduction parameters (feed consumption, dam weight, litter size, pup weight, external anomalies and day 4 viability index) significantly different from control values. Following impregnation, the body weight of the dam increased appreciably during gestation, but its feed consumption increased only slightly. During lactation, the dam's feed consumption increased markedly while its body weight increased slightly. Consequently, when dams received the xenobiotic in their diet they consumed slightly less xenobiotic per unit of body weight during gestation when compared to the gavaged dams, whereas the situation was dramatically reversed during lactation. While the greater consumption of xenobiotic by the dietary-dosed dams during lactation did result in more HCB (P</=0.0001 for both litters) and PCBs/metabolites (litter one: P=0.05; litter two: P</=0.0001) in the suckling neonate's stomach contents in both generations, there was no evidence of any differences between the two litters when each sampling date was assessed separately, except for the day 4-HCB results when the litter one pups had more HCB in their stomachs (P=0.018). For the PCBs, the F344 neonates were found to have more PCBs in their stomachs (litter one P=0.0015; litter two P=0.002) than the Sprague-Dawley neonates. In addition, the amount of HCB, PCBs and fat in the neonates' stomachs decreased during lactation, as the pups age increased (P</=0.035). These preliminary results suggest that analogous amounts of HCB and PCBs given via diet or gavage may not result in similar lactational exposure by the suckling neonate.

Toxicological consequences of feeding PCB congeners to infant rhesus (Macaca mulatta) and cynomolgus (Macaca fascicularis) monkeys

In a study designed to minimize interspecies extrapolation of toxicological data, nine rhesus (Macaca mulatta) and 15 cynomolgus (M. fascicularis) day-old infant monkeys were separated from their dams following parturition and hand-reared using a liquid non-human primate formulation. The infants were randomly divided into a control and a treated group which received a mixture of polychlorinated biphenyl (PCB) congeners analogous to those found in breast milk from Canadian women. The concentration of congeners in the dosing media resulted in each infant receiving a total of 7.5 microg PCB congeners/kg body weight/day. The congeners were added either to the liquid formulation or to corn oil and administered to the back of the monkey's mouth for 20 weeks. Monthly blood and adipose specimens were obtained during the dosing period and then periodically until the monkey was necropsied or taken off test (minimum of 66 weeks on test) for congener analysis. Parameters such as body weight, formula consumption, tooth eruption, somatic measurements, haematology and serum biochemistry were monitored throughout the study. In addition, a qualitative evaluation of the absorption and depletion of the various congeners was undertaken as was an immunological evaluation. For the monitored parameters, very few differences were found to be statistically significant. For the immunological parameters, the only statistically differences found were a reduction over time for immunoglobulins M and G antibodies to sheep red blood cells (cyno, P = 0.025; rhesus, P = 0.002) and a treatment-related reduction in the levels of the HLA-DR cell surface marker (mean percent, P = 0.016; absolute levels, P = 0.027). There were some qualitative differences regarding absorption and depletion rates for the various congeners, but it could not be definitely ascertained whether these differences were due to species differences or dosing mode. However, statistically significant differences were found for treatment (P = 0.0293) as well as for species and vehicle regarding the concentration of PCB in blood (species;--P = 0.0399; treatment--P = 0.0001) and adipose tissue (species--P = 0.0489; treatment--P = 0.0001).

Effect of exposure to 3,3',4,4',5-pentachlorobiphenyl (PCB 126) throughout gestation and lactation on development and spatial delayed alternation performance in rats

There is evidence that polychlorinated biphenyl (PCB) congeners have differential effects on endpoints of neurotoxicity depending on their chemical structure: specifically, that ortho-substituted congeners are neurotoxic whereas coplanar (dioxin-like) congeners are relatively inactive in producing neurotoxic effects. The effects of the coplanar congener 3,3',4,4',5-pentachlorobiphenyl (PCB 126) on developmental endpoints, hematology, serum biochemistry, and performance on a spatial delayed alternation task were assessed in Long-Evans rats. Dams were dosed with 0, 0.25, or 1.0 microg/kg/day Monday to Friday beginning 5 weeks before and continuing through gestation and lactation. The first 2-week breeding period produced 10, 8, and 13 litters in the three dose groups, respectively. Breeding females from the control and low-dose group that did not conceive were rebred after 76 days of dosing, producing 7 and 6 litters, respectively. Reduction in weight gain from birth to weaning at 21 days of age (DOA) was observed in both dose groups of Cohort 1 but not in Cohort 2. Males in Cohort 1 exhibited a slight decrease in anogenital distance normalized for weight. Changes in hematological and some serum biochemical parameters were observed in the pups at DOA 21 and/or 60. PCB 126 was detected in fat sampled at both DOA 21 and 60. PCB 126 was not detected in brain samples at 60 DOA in any group; analysis of Cohort 2 at DOA 21 revealed levels in the treated group about 1/100 of those in fat. On the spatial delayed alternation task, there was no convincing evidence for impairment as a result of PCB exposure, as assessed by overall accuracy of performance and measures of perseverative and other types of inappropriate responding. These data provide further evidence for the lack of neurotoxicity of dioxin-like PCB congeners. However, assessment of performance on additional behavioral indices is required before definitive conclusions may be drawn.

Polychlorinated biphenyls in adipose tissue, liver, and brain from nine stillborns of varying gestational ages

We analyzed polychlorinated biphenyls (PCBs) in s.c. adipose tissue, liver, and brain of nine fetuses who died in utero. Their median (range) gestational ages and birth weights were 34 (17-40) wk and 2050 (162-3225) g. Three fetuses were small for gestational age. The levels of PCB congener nos. 118, 138, 153, and 180, and the sum of these (sigmaPCB), were calculated in terms of tissue total fat content (ng/g fat). The median (range) sigmaPCB (in ng/g fat) amounted to adipose tissue 235 (97-768), liver 198 (67-362), and brain 50 (22-122). Median (range) sigmaPCB levels in liver and brain were 0.8 (0.4-0.9) and 0.2 (0.1-0.3) times, respectively, as high as the sigmaPCB levels in adipose tissue. There were strong relations between sigmaPCB in adipose tissue and sigmaPCB in liver (r=0.98; p < 0.01), and between sigmaPCB in adipose tissue and sigmaPCB in brain (r=0.91; p < 0.01). Adipose tissue, liver, and brain did not show differences in the distribution of congeners 118, 138, 153, and 180, and there was no statistically significant association between tissue PCB levels and gestational age (r varied between 0.22 and 0.47). Median sigmaPCB levels in fetal adipose tissue proved to be comparable with our previously established sigmaPCB levels in mature breast milk of 93 Dutch women (median 414; range 158-969 ng/g of fat). The PCB congeneric distribution of fetal adipose tissue was not different from that of human milk. We conclude that maternal PCBs have a tendency to accumulate notably in fetal tissues with high triglyceride contents. They are easily transferred across the placenta and seem to become equilibrated among the apolar parts of maternal and fetal lipids.

Toxicological consequences of Aroclor 1254 ingestion by female rhesus (Macaca mulatta) monkeys and their nursing infants. Part 3: post-reproduction and pathological findings

A group of 80 menstruating rhesus (Macaca mulatta) monkeys were randomly allocated to four similar rooms (20 monkeys/room) and then 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 microg 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 nuchal fat pad. Concurrently, sebaceous glands were being examined for changes analogous to chloracne. Subsequently, the females were paired with untreated males. The infants' blood PCB levels at birth were not correlated with its dam's dose or blood PCB level. However, there was an association between an infants preweaning blood PCB levels and its dam's dose and PCB milk levels. After weaning, the infants were not dosed with PCB. The half-life for the PCB in the infants' blood was determined and found to be slightly more than 15 wk. After 6 yr on test, three monkeys from the 0, 5, 20 and 40 microg dose groups were randomly allocated to a depletion study to ascertain the half-lives of specific PCB congeners (Mes et al., Chemosphere 1995, 30, 789-800). Concurrently, necropsies began of the remaining females, and of seven infants from the treated dams and four infants from the control dams, which had attained an age of 2 yr. Approximately 3 yr later, the depletion monkeys were necropsied. The only statistically significant treatment-related pathological changes found during the study were in the adult females, in which an involution of the sebaceous glands and a dose related increase in liver weight due to hyperplasia were evident.