Toxic effects of brominated flame retardants in man and in wildlife

Brominated flame retardants (BFRs) are ubiquitous industrial chemicals, and many of them are produced in large volumes. Due to this fact, several BFRs are found in quantifiable levels in wildlife, as well as in humans. However, we are still lacking information on the effects of BFR in wildlife and, especially, in man. This review summarises the biological effects of polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA) and derivates, hexabromocyclododecane (HBCD) and polybrominated biphenyls (PBBs), however excluding other aspects such as environmental levels. These BFR groups were selected because of a large volume production (PBDEs, TBBPA and derivates), and availability of some toxicity data in spite of much lower production volumes (HBCD and PBBs). In addition, the increase in levels of PBDEs in human (breast milk) and wildlife samples during later time made it especially interesting to include this BFR group. PBDES: The commercial PBDE products predominantly consist of so-called penta-, octa- and decabromodiphenyl ether products. Each product consists of a rather narrow range of congeners and is named after the dominating congener as regards the bromination pattern. Generally, the PentaBDEs seem to cause adverse effects at the comparably lowest dose, whereas much higher doses were needed for effects of the DecaBDEs. The critical effects of PentaBDEs are those on neurobehavioural development (from 0.6 mg/kg body weight) and, at somewhat higher dose, thyroid hormone levels in rats and mice, of OctaBDEs on fetal toxicity/teratogenicity in rats and rabbits (from 2 mg/kg body weight), and of DecaBDEs on thyroid, liver and kidney morphology in adult animals (from 80 mg/kg body weight). Carcinogenicity studies, only performed for DecaBDEs, show some effects at very high levels, and IARC (1990) evaluates DecaBDEs not classifiable as to its carcinogenicity to humans. TBBPA: The toxicity of TBBPA in the experimental in vivo studies is suggested to be low. In most reported studies, only doses in g/kg body weight were effective, but at least one study suggested renal effects at around 250 mg/kg body weight. Although difficult to include and interpret in a quantitative risk assessment, the in vitro effects on immunological and thyroid hormones, as well as binding to erythrocytes should be noted. Before a solid standpoint could be reached on TBBPA toxicity additional studies must be performed. This statement is even more valid regarding the TBBPA derivates, where there is an almost complete lack of toxicity data. HBCD: Also in the case of HBCD, relevant toxicity studies are lacking. Based on the present animal studies, a critical effect is seen in the liver and on thyroid hormones (LOAEL 100 mg/kg body weight/day). However, in a recent short paper behavioural effects in mice pups were observed already at 0.9 mg/kg body weight, and behavioural effects may be a sensitive endpoint for HBCD, as well as for other BFRs. PBBS: Due to the Michigan accident in 1973-1974, many toxicity studies on PBBs are available. The critical experimental effects are those on reproduction and carcinogenicity, and a NOAEL of 0.15 mg/kg body weight/day could be suggested based on the cancer effects. In man no unequivocal effects have been observed, although in some studies neurological and musculoskeletal symptoms were suggested. Based on the carcinogenic effects in animals, a human TDI of 0.15 microg/kg body weight has been presented. To conclude, the toxicity data are almost entirely based on experimental models. There are differences among the BFR groups, as well as within these groups, both regarding type of toxic effect and at what dose it appears. As BFRs will continue to appear both in industrial applications and, even if the production has ceased, in our environment, there is a continued need for effects studies on BFRs.

Methyl mercury and inorganic mercury in Swedish pregnant women and in cord blood: influence of fish consumption

We studied exposure to methyl mercury (MeHg) in Swedish pregnant women (total mercury [T-Hg] in hair) and their fetuses (MeHg in cord blood) in relation to fish intake. The women were recruited at antenatal care clinics in late pregnancy to participate in an exposure study of environmental pollutants. Fish consumption was evaluated using food frequency questionnaires including detailed questions on fish consumption. In addition, we determined inorganic mercury (I-Hg) and selenium (Se) in cord blood. On average, the women consumed fish (all types) 6.7 times/month (range 0-25 times/month) during the year they became pregnant. They reported less consumption of freshwater fish--species that might contain high concentrations of MeHg--during than before pregnancy. T-Hg in maternal hair (median 0.35 mg/kg; range 0.07-1.5 mg/kg) was significantly associated (R2 = 0.53; p < 0.001) with MeHg in cord blood (median 1.3 microg/L; range 0.10-5.7 microg/L). Both hair T-Hg and cord blood MeHg increased with increasing consumption of seafood (r = 0.41; p < 0.001 and r = 0.46; p < 0.001, respectively). Segmental hair analysis revealed that T-Hg closer to the scalp was lower and more closely correlated with MeHg in cord blood than T-Hg levels in segments corresponding to earlier in pregnancy. We found a weak association between Se (median 86 microg/L; range 43-233 microg/L) and MeHg in cord blood (r = 0.26; p = 0.003), but no association with fish consumption. I-Hg in cord blood (median 0.15 microg/L; range 0.03-0.53 microg/L) increased significantly with increasing number of maternal dental amalgam fillings.

Organochlorines in Swedish women: determinants of serum concentrations

We studied associations between lifestyle/medical factors and lipid-adjusted serum concentrations of seven polychlorinated biphenyl (PCB) congeners and five chlorinated pesticides/metabolites among 205 Swedish women (54-75 years old). Serum concentrations were significantly associated with age, body mass index, body weight change, diabetes mellitus, consumption of fatty fish, and place of residence. The findings suggest that lifestyle/medical factors may confound results in epidemiologic studies when they are related to both serum concentrations and disease. Moreover, disease itself may influence serum concentrations of some organochlorines, as indicated by the negative associations between recent weight change and serum concentrations of some PCB congeners, p,p -dichlorodiphenyldichloroethylene (DDE), and hexachlorobenzene (HCB) and the positive association between diabetes mellitus and HCB concentrations. Age was the only determinant that showed a consistent association with all compounds studied (positive); otherwise associations with single determinants varied among compounds even within the PCB group. This shows that the studied organochlorines should not be treated as a homogeneous group of compounds in epidemiologic studies.

Polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and chlorinated paraffins (CPs) in rats-testing interactions and mechanisms for thyroid hormone effects

The effects of the polybrominated diphenyl ether (PBDE) congener 2,2'4, 4'-tetrabromodiphenylether (DE-47), and technical preparations of polychlorinated biphenyls (PCBs; Aroclor 1254) and chlorinated paraffins (CPs; Witaclor 171P) on thyroid hormone (TH) levels were examined in rats. To study possible interactive effects, also combinations of the three compounds were used. Thus, female Sprague-Dawley rats, 7 weeks old, were treated with approximately isomolar doses (ca. 30 micromol/kg bw per day) of DE-47 (6.0 mg/kg per day), Aroclor 1254 (4.0 mg/kg per day) and Witaclor 171P (6.8 mg/kg per day), alone or in combinations, daily for 14 days by gastric intubation. DE-47 was also administered in a higher (18 mg/kg per day) and lower (1.0 mg/kg per day) dose. In order to test possible mechanisms behind the TH effects, microsomal enzyme (cytochrome P-450 isozymes and uridine diphosphoglucuronyl transferase-UDPGT) activity (indicating both metabolic activation and/or biliary clearance), ex vivo-binding of 125I-T4 to plasma proteins (suggesting effects on peripheral TH transport) and light microscope morphology of the thyroid gland were studied. The observed degree of TH reduction after Aroclor 1254 and DE-47 exposure corresponded with a decrease in the ex vivo binding of 125I-T4 to the plasma TH-transporter transthyretin (TTR), and with induction of the microsomal phase I enzymes (ethoxy- and methoxy-resorufin dealkylases, EROD and MROD). The phase II enzyme UDPGT was also elevated, but only moderately. The thyroid morphology showed an activation of the epithelia, but no degenerative alternations, that was correlated to exposure to Aroclor 1254. In our model, the observed effects match the hypothesis that the T4 decrease is chiefly due to disturbances in serum transport, caused by binding of in vivo-formed Aroclor 1254 and DE-47 metabolites to TTR. However, decreased plasma TH levels due to increased glucuronidation activity may also be of some importance. The thyroid gland hyperactivity is probably a feed-back consequence of the T4 decrease, in spite of the lack of TSH alterations. In the mixed DE-47 and Witaclor 171P group synergistic effects were indicated on free T4 (FT4) and EROD induction levels, results that may suggest that such effects should be considered in risk assessment of mixtures of persistent organohalogens.

Polychlorinated biphenyl congeners as markers of toxic equivalents of polychlorinated biphenyls, dibenzo-p-dioxins and dibenzofurans in breast milk

In breast milk, concentrations of polychlorinated biphenyls (PCBs) are higher than those of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), making PCB analyses less time-consuming and expensive. We searched for PCB "markers" of PCDD/DF concentrations, by studying associations between concentrations of PCB and PCDD/DFs (expressed as toxic equivalents, TEQs) in breast milk from 27 women (primiparas, 22-35 years). These women donated breast milk in 1996-1999 together with 183 other primiparas from Uppsala County, Sweden. Regression analyses showed that both dioxin-like and non-dioxin-like penta- to hepta-chlorinated PCBs could be used as markers of TEQ concentrations in this group of women, in some cases after age adjustment of the regressions. The strong positive association between concentrations of dioxin-like PCB/DD/DFs and non-dioxin-like PCBs will in future epidemiological studies make it difficult to separate Ah receptor-dependent effects from non-Ah receptor-dependent effects. With the use of regression equations and concentrations in breast milk samples collected in 1994, TEQ concentrations were estimated in the 1994 samples. Comparisons between estimated and measured concentrations indicated that associations between concentrations of marker substances and TEQs should be determined separately within each study population, in order to obtain reliable TEQ exposure assessments from PCB markers.

Effects of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) on thyroid hormone and vitamin A levels in rats and mice

The ability of the commercial polybrominated diphenyl ether (PBDE) preparation Bromkal 70-5 DE to alter thyroid hormone and vitamin A levels as well as microsomal enzyme activities was compared with that of the commercial polychlorinated biphenyl (PCB) preparation Aroclor 1254 in orally exposed female rats (Sprague-Dawley) and mice (C57BL/6 N). Additional mice were exposed to the PBDE congener 2,2',4,4'-tetrabromodiphenyl ether (DE-47), or to the PCB congener 2,3,3',4,4'-pentachlorobiphenyl (CB-105). For 14 days the animals were given approximately isomolar daily oral doses of Aroclor 1254, CB-105 (both 10 mg/kg body weight), Bromkal 70-5 DE or DE-47 (both at 18 mg/kg body weight). In addition, further groups of rats and mice received a higher dose of Bromkal 70-5 DE, 36 mg/kg body weight. Bromkal 70-5 DE and DE-47 decreased plasma free and total thyroxine (T4) levels in both rats and mice, although with lower potency than that of Aroclor 1254 and CB-105. By contrast, thyroid-stimulating hormone (TSH) levels were not significantly changed in any of the groups. Reduction of hepatic vitamin A levels was seen in rats after Aroclor 1254 and Bromkal 70-5 DE exposure. A similar tendency was seen also in mice, but the effects were significant only for concentration data and not the total amount. Induction ofmicrosomal phase I enzymes, measured as ethoxy, methoxy and pentoxy resorufin O-dealkylase (EROD, MROD, PROD) activities, was greatest after exposure to Aroclor 1254/CB-105 but were also significant in the Bromkal 70-5 DE/DE-47-treated groups. However, induction of uridine diphosphoglucuronosyl transferase (UDPGT) was small and for most groups insignificant. In conclusion, the PBDE compounds studied, although having a lower potency than the PCB compounds, decreased thyroxine and vitamin A levels and induced microsomal enzyme activities. Rats were more sensitive to the observed effects than mice. Microsomal phase I activity might be related, directly or indirectly, to the T4 and vitamin A effects, whereas several factors (such as weak enzyme induction and lack of correlation with altered T4 and vitamin A levels) argue against any UDPGT-related effects.

Polybrominated diphenyl ethers: occurrence, dietary exposure, and toxicology

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in plastics (concentration, 5--30%) and in textile coatings. Commercial products consist predominantly of penta-, octa-, and decabromodiphenyl ether mixtures, and global PBDE production is about 40,000 tons per year. PBDEs are bioaccumulated and biomagnified in the environment, and comparatively high levels are often found in aquatic biotopes from different parts of the world. During the mid-1970--1980s there was a substantial increase in the PBDE levels with time in both sediments and aquatic biota, whereas the latest Swedish data (pike and guillemot egg) may indicate that levels are at steady state or are decreasing. However, exponentially increasing PBDE levels have been observed in mother's milk during 1972--1997. Based on levels in food from 1999, the dietary intake of PBDE in Sweden has been estimated to be 0.05 microg per day. Characteristic end points of animal toxicity are hepatotoxicity, embryotoxicity, and thyroid effects as well as maternal toxicity during gestation. Recently, behavioral effects have been observed in mice on administration of PBDEs during a critical period after birth. Based on the critical effects reported in available studies, we consider the lowest-observed-adverse-effect level (LOAEL) value of the PBDE group to be 1 mg/kg/day (primarily based on effects of pentaBDEs). In conclusion, with the scientific knowledge of today and based on Nordic intake data, the possible consumer health risk from PBDEs appears limited, as a factor of over 10(6) separates the estimated present mean dietary intake from the suggested LOAEL value. However, the presence of many and important data gaps, including those in carcinogenicity, reproduction, and developmental toxicity, as well as additional routes of exposure, make this conclusion only preliminary. Moreover, the time trend of PBDEs in human breast milk is alarming for the future.

Polybrominated diphenyl ethers: occurrence, dietary exposure, and toxicology

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in plastics (concentration, 5--30%) and in textile coatings. Commercial products consist predominantly of penta-, octa-, and decabromodiphenyl ether mixtures, and global PBDE production is about 40,000 tons per year. PBDEs are bioaccumulated and biomagnified in the environment, and comparatively high levels are often found in aquatic biotopes from different parts of the world. During the mid-1970--1980s there was a substantial increase in the PBDE levels with time in both sediments and aquatic biota, whereas the latest Swedish data (pike and guillemot egg) may indicate that levels are at steady state or are decreasing. However, exponentially increasing PBDE levels have been observed in mother's milk during 1972--1997. Based on levels in food from 1999, the dietary intake of PBDE in Sweden has been estimated to be 0.05 microg per day. Characteristic end points of animal toxicity are hepatotoxicity, embryotoxicity, and thyroid effects as well as maternal toxicity during gestation. Recently, behavioral effects have been observed in mice on administration of PBDEs during a critical period after birth. Based on the critical effects reported in available studies, we consider the lowest-observed-adverse-effect level (LOAEL) value of the PBDE group to be 1 mg/kg/day (primarily based on effects of pentaBDEs). In conclusion, with the scientific knowledge of today and based on Nordic intake data, the possible consumer health risk from PBDEs appears limited, as a factor of over 10(6) separates the estimated present mean dietary intake from the suggested LOAEL value. However, the presence of many and important data gaps, including those in carcinogenicity, reproduction, and developmental toxicity, as well as additional routes of exposure, make this conclusion only preliminary. Moreover, the time trend of PBDEs in human breast milk is alarming for the future.

Serum concentrations of organochlorines in men: a search for markers of exposure

Analysis of single marker substances in serum could provide cost-effective assessment of human exposure to complex mixtures of organochlorines. We studied the serum concentrations of 10 polychlorinated biphenyl (PCB) congeners and 11 chlorinated pesticides and some of their metabolites in samples collected from 120 Swedish men (mean age 63 years, range 40-74 years) from the general Swedish population. The median concentrations of individual PCB congeners increased in the order PCB 52 < PCB 101 < or = PCB28 < PCB 105 < PCB 167 < PCB 156 < PCB 118 < PCB 138 < PCB 180 < PCB 153. The concentrations of o,p'-DDT, o,p'-DDE, p,p'-DDD, alpha-HCH and gamma-HCH were in most cases below the quantification limit (2-4 ng/g lipid). Among the other chlorinated pesticides the median concentration increased in the order oxychlordane (12 ng/g lipid) < p,p'-DDT < trans-nonachlor < beta-HCH < HCB < p,p'-DDE (586 ng/g lipid). The observed concentrations of PCB and chlorinated pesticides were in the same range as those found in similar groups of men from Sweden and Norway, but lower than those found in male populations with recent occupational exposure or high environmental exposure. Strong relationships were found between the concentrations of single mono- and di-ortho PCB congeners and groups of PCB congeners in serum. In our group of men PCB 153 was a good marker substance for the concentration of sigma PCB and sigma di-ortho PCB concentrations in serum. Moreover, among the mono-ortho PCB congeners analyzed, PCB 156 could be used as a marker for the sigma mono-ortho PCB TEQ concentrations in serum in the studied group. No useful marker substances were found among DDT compounds and other chlorinated pesticides and metabolites, except for trans-nonachlor which predicted the concentration of the metabolite oxychlordane fairly well.

PCB and chlorinated pesticide concentrations in swine and bovine adipose tissue in Sweden 1991-1997: spatial and temporal trends

Results from the Swedish control programme regarding organochlorines in food were used to determine time trends of organochlorine concentrations in adipose tissues from swine (4-8 months old) and bovines (non-dairy, 12-36 months) slaughtered between 1991 and 1997. Moreover, possible regional differences in concentrations were studied, as well as differences in concentrations depending on sex and age of the slaughtered animals. Multiple linear regression indicated that the concentrations of PCB, p,p'-DDE, HCB and alpha-HCH decreased by 4-17% per year, suggesting that the decline in organochlorine concentrations in the Swedish environment and biota reported during the 1970s-1990s also has occurred in meat-producing animals during the 1990s. The concentrations of PCB, DDE and HCB in bovines and PCB and DDE in swine were 1.4-3.8-fold higher in the southern parts of Sweden than in the northern parts of the country, indicating a regional difference in exposure of the animals. The organochlorine concentrations were higher in bovines than in swine, and declined faster in swine than in bovines. Moreover, the concentrations of CB 153 and p,p'-DDE were similar in bovines, but in swine the average concentrations of the two compounds differed two-fold. Apart from possible species differences in metabolism of organochlorines, this may be due to differences in the age at slaughter between swine and bovines, and differences in husbandry of the animals. In the latter case, swine are generally kept inside during their whole life span, whereas bovines are kept outside grazing during the summer period. Finally, a sex-dependent difference in concentrations was indicated in swine, but not in bovines. Our study shows that a lot of information can be 'extracted' from control program results.

Organochlorines and bone mineral density in Swedish men from the general population

Persistent organochlorines (POCs), such as polychlorinated biphenyls (PCBs) and DDT, are present at relatively high concentrations in food and show estrogenic, anti-estrogenic or anti-androgenic activity in biological test systems. Because bone mineral density (BMD) in men is influenced by sex hormones, we looked for associations between BMD and serum concentrations of POCs in 115 men (mean age 63 years, range 40-75 years) from the general Swedish population. Ten PCB congeners, five DDT isomers, hexachlorobenzene, three hexachlorocyclohexane isomers, trans-nonachlor and oxychlordane were analyzed by gas chromatography. Quantitative bone measurements were performed by dual-energy X-ray absorptiometry at three sites: whole body, the L2-L4 region of the lumbar spine, and the neck region of the proximal femur, as well as by quantitative ultrasound on the left os calcis (broadband ultrasound attenuation (BUA) and speed of sound (SOS)). After adjustment for confounding factors in linear regression analyses we found no strong association between serum concentrations of single POCs and the five BMD and ultrasound variables. When POCs were grouped according to hormonal activity (estrogenic, anti-estrogenic, anti-androgenic) and the study subjects were divided into organochlorine concentration quartiles, a weak association was indicated between increased serum concentrations of p,p'-DDE (antiandrogenic) and decreased BMD, BUA and SOS. This may suggest that p,p'-DDE could cause negative effects on bone density, but the findings might also be due to chance since multiple comparisons were made in the statistical analysis. Overall our results do not suggest that the studied POCs caused major effects on bone density in our study group.

Hydroxylated polychlorinated biphenyls: distribution in the pregnant mouse

1. In the pregnant C57BL mouse the disposition of a single, intravenous low dose of 14C-labelled 4-hydroxy-3,5,3',4'-tetrachlorobiphenyl (4-OH-TCB) or 4-hydroxy-3,5,2',3',4'-pentachloro-biphenyl (4-OH-PeCB1) was monitored by liquid scintillation counting and whole-body autoradiography. The compounds were placentally transferred and accumulated in the foetal tissues (e.g. plasma and liver). Also, maternal accumulation was observed in selected tissues, including liver, adrenal gland, adipose tissue and yolk sac placenta. 2. The foetal concentration of both hydroxy-PCBs increased with time up 24 h post-exposure and the foetal plasma concentration with at this time-point two-fold of that in maternal plasma. Chemical analysis of maternal plasma and liver showed no metabolism of the administered compounds. 3. In the pregnant C57BL mouse at late gestation, exposure to 4-OH-TCB generally resulted in a higher foetal and maternal tissue retention than did 4-OH-PeCB1. The estimated elimination half-lives (t 1/2) of 4-OH-TCB in maternal liver and plasma were 69 and 13 h respectively, and for 4-OH-PeCB1 were 17 and 13 h. 4. No differences in foetal tissue concentration of 4-OH-TCB were observed between the C57BL, and NMRI mouse. In contrast, earlier studies have shown that the PCB congener CB-77, the parent compound of 4-OH-TCB, resulted in a C57BL/NMRI foetal ratio of 1:5.

Hydroxylated polychlorinated biphenyls: placental transfer and effects on thyroxine in the foetal mouse

1. At day 17 of pregnancy, 1 day after maternal intravenous administration (5-50 mumol/kg body wt) of 4-OH-3,5,3',4'-tetrachlorobiphenyl (4-OH-TCB; a CB-77 metabolite), a limited dose-dependent decrease was found both in foetal and maternal total thyroxine (T4) levels (76-81% of control at 50 mumol/kg). Similarly, a 50 mumol/kg dose of a 4-OH-3,5,2',3',4'-pentachlorobiphenyl (4-OH-PeCB1) decreased total T4 levels, whereas 4-OH-2,3,5,3',4'-pentachlorobiphenyl (4-OH-PeCB2) showed no clear effect (both 4-OH-pentaCBs are CB-105 metabolites). Earlier administration (gestation day 10 or 13) of the 4-OH-PCBs had no effect on total T4 at day 17. 2. Placental transfer of 14C-4-OH-TCB to the foetal compartment was dose-related and accumulated mainly in foetal plasma at levels 2-fold those in the maternal plasma at the dose interval 0.5-5.0 mumol/kg body wt, whereas at higher doses (20 and 50 mumol/kg body wt) the foetal and maternal plasma levels were similar. A break-point in the foetal dose/plasma concentration curve at 5.0 mumol/kg indicates saturation of a high-affinity ligand binding above this dose. 3. There was an extensive accumulation of radioactivity in the maternal liver after 14C-4-OH-TCB administration (20-30% of the administered dose). In spite of this the investigated compounds resulted in a small or no effect on EROD/MROD activity in maternal liver and these enzyme activities were not detectable in either exposed or control foetal liver.

Lack of effects of some individual polybrominated diphenyl ether (PBDE) and polychlorinated biphenyl (PCB) congeners on human lymphocyte functions in vitro

The structural similarities between polybrominated diphenyl ethers and immunotoxic halogenated aromatic compounds suggest that the polybrominated diphenyl ethers might affect the immune system. The present study was undertaken to investigate the immunological effects of some purified PBDE-congeners on human lymphocyte function in vitro. Polychlorinated biphenyl congeners were also included in the study. Mitogen-induced DNA synthesis and immunoglobulin synthesis by lymphocytes from blood donors were examined following polybrominated diphenyl ether or polychlorinated biphenyl exposure in vitro in order to determine the immunotoxic potential of these substances. No effects on mitogen-induced proliferation or immunoglobulin synthesis were observed after exposure of cells to concentrations up to 10(-5) M. The negative findings in this study indicate that certain functions of human peripheral lymphocytes, i.e. proliferation and immunoglobulin synthesis, are insensitive to the direct action of polybrominated diphenyl ethers and polychlorinated biphenyls. Our results are in accordance with other recent studies in which no effects on immunological parameters were demonstrated by exposure of lymphocytes to polyhalogenated aromatic hydrocarbons in vitro.

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.

Binding of a 3,3', 4,4'-tetrachlorobiphenyl (CB-77) metabolite to fetal transthyretin and effects on fetal thyroid hormone levels in mice

The present study was conducted in order to study the effect of the PCB congener 3,3', 4,4'-tetrachlorobiphenyl (CB-77) on fetal thyroxin homeostasis in the mouse, and to examine a possible underlying mechanism behind the effect. C57BL mice were treated with 14C-labelled or unlabelled CB-77 (1 or 10 mg/kg body wt.) on day 13 of gestation, and control animals were treated with corn oil. The experiment was terminated at 4 days after exposure. Maternal and fetal plasma and livers, and whole fetuses for homogenate preparation, were collected and analysed for total radioactivity, in vitro binding of 125I-thyroxin to plasma transthyretin (TTR; a thyroxin-transporting protein), and free and total thyroxin (FT4, TT4) levels. Maternal plasma, fetal plasma and homogenates were also analyzed for presence of CB-77 and metabolites. Results showed a dose-dependent uptake of radioactivity in plasma and liver, fetal plasma 14C-levels being about five-times higher in 10 mg/kg dosed animals as after 1 mg/kg. Fetal; plasma levels of total radioactivity were four- to nine-times above maternal levels and corresponded to only one compound, the metabolite 4-OH-3,3', 4',5-tetrachlorobiphenyl (4-OH-tCB). 4-OH-tCB was the major metabolite also in whole fetuses, with only small amounts of the parent compound (approximately 15% of the 4-OH-tCB) and traces (approximately 6%) of two other metabolites, 2-OH-3,3, 4,4'-tetrachlorobiphenyl and 5-OH-3,3', 4,4'-tetrachlorobiphenyl. Polyacrylamide gel electrophoresis confirmed that the 14C-radioactivity in fetal plasma was bound to TTR, and revealed that in vitro binding of 125I-T4 to fetal TTR was reduced to 50% of control values in treated animals (10 mg/kg body wt.). Fetal plasma FT4 and TT4 levels were significantly decreased (64 and 55% of control fetuses) after 10 mg/kg treatment. In conclusion, exposure of pregnant mice to CB-77 results in the accumulation of the metabolite 4-OH-tCB in fetal mouse plasma. The metabolite binds to TTR and is accompanied by a significant decrease in fetal plasma T4 levels. A causative correlation between TTR binding and effects on T4 levels is suggested.

Liver accumulation of 2,3,7,8-tetrachloro-[3H]dibenzofuran in mice: modulation by treatments with polychlorinated biphenyls

The distribution of 2,3,7,8-tetrachloro-[3H]dibenzofuran ([3H]TCDF; 40 micrograms/kg) resembled that earlier reported for 2,3,7,8-tetrachlorodibenzo-p-dioxin, with a strong accumulation in the liver and a selective uptake in the nasal olfactory mucosa of adult and fetal mice. Pretreatments with a series of selected congeners of polychlorinated biphenyls (PCBs), i.e.. I (IUPAC)-77, I-105, I-118, I-126, I-153, I-156, I-169, and a commercial preparation, Aroclor 1254 (25-100 mg/kg body wt. i.p.), were found to modulate the hepatic uptake of [3H]TCDF (24 h post-3H-injection). At a short pretreatment time (4 h), non-ortho-chlorinated congeners decreased the uptake of [3H]TCDF equivalents in the liver (e.g., I-126 = 3,3',4,4',5-pentachlorobiphenyl: 34% of control), while several mono- and di-ortho PCB congeners and Aroclor 1254 increased the hepatic uptake of [3H]TCDF (e.g., I-156 = 2,3,3',4,4',5-hexachlorobiphenyl: 183% of control). At a longer pretreatment time (48 h), both a non-ortho (I-169 = 3,3',4,4',5,5'-hexachlorobiphenyl) and mono-ortho PCB congener(s) (e.g. I-156) markedly increased the hepatic 3H-uptake (190%), a probable effect of an induction of hepatic binding sites for TCDF. Ethoxyresorufin-O-deethylase activities, regarded to mirror the metabolic activity of cytochrome P-450 IA1 (CYP IA1), were strongly and time-dependently induced after I-169, but not after I-156, pretreatment (25 mg/kg). The initial liver concentrations of the two PCB congeners were similar and increased for I-169 but not for I-156 at later time points. In conclusion, the results show a selective uptake of [3H]TCDF in the mouse liver and nasal olfactory mucosa of both dam and fetus. The uptake of [3H]TCDF in the liver is influenced both by dose and pre-exposure with PCBs. The presence of a PCB-sensitive, but CYP IA1-independent, hepatic binding site for TCDF is suggested. Consequently, pharmacokinetic interactions with PCBs complicate the toxicity assessment of TCDF in complex mixtures.

Nephrotoxicity and covalent binding of 1,1-dichloroethylene in buthionine sulphoximine-treated mice

Autoradiography of mice injected i.p. with 14C-labelled 1,1-dichloroethylene (vinylidene chloride, VDC) in C57B1/6 mice revealed a selective covalent binding of radioactivity in the proximal tubules, in the midzonal parts of the liver lobules and in the mucosa of the upper and lower respiratory tract. Since VDC is a renal carcinogen in male mice the effects of compounds modulating biotransformation and glutathione (GSH) levels on the renal covalent binding were examined following a single i.p. dose of 14C-VDC. Most pretreatments did not influence the level of binding but treatment with buthionine sulphoximine (BSO), an irreversible inhibitor of gamma-glutamylcysteine synthetase and glutathione (GSH)-depleting agent, increased the renal covalent binding of VDC three-fold. Histopathological examination of kidneys in BSO-pretreated male mice given single i.p. injections of subtoxic doses of VDC (25 and 50 mg/kg) showed necrosis in the proximal tubules (S1 and S2 segments) 24 h following administration. In mice given VDC only, no significant lesions in the kidneys were observed. The severe renal toxicity of VDC in BSO-pretreated mice is suggested to be related to metabolic activation of VDC in the proximal tubules, resulting in further GSH depletion and covalent binding.

Induction of 7-ethoxyresorufin-O-deethylase (EROD) activity in mice foetuses by the PCB-congener 3,3',4,4'-tetrachlorobiphenyl

1. 3,3',4,4'-Tetrachlorobiphenyl (TCB) induces liver microsomal 7-ethoxyresorufin-O-deethylase (EROD) activity, and this P450 isoform, i.e. CYP 1, is involved in the metabolism of TCB. 2. TCB administered i.p. to pregnant mice (5-25 mg/kg) induced foetal as well as maternal hepatic EROD activity; in all cases the maternal induced activity was higher than the foetal activity. EROD activity of TCB-induced foetuses increased with developmental age, but decreased with the length of time after treatment. 3. Strain differences were seen; in control mice and TCB-treated dams NMRI > C57BL in EROD activity, but in transplacentally TCB-treated foetuses, C57BL > NMRI. EROD activity in non-pregnant control C57BL mice was higher than in pregnant ones, whereas no activity was seen in control foetuses. 4. Results indicate that TCB at a certain dose can induce foetal metabolism, but that earlier observed foetal accumulation at lower TCB doses is probably a consequence of transplacental transport of maternally-produced metabolites.

Age- and sex-dependent dichlorovinyl cysteine (DCVC) accumulation and toxicity in the mouse kidney: relation to development of organic anion transport and beta-lyase activity

The age- and sex-dependent changes in mouse kidney accumulation and toxicity of S-1,2-dichlorovinyl cysteine (DCVC) was investigated. The results were compared to developmental changes in the basal activities of organic anion transport in vitro (PAH uptake) and of cysteine conjugate beta-lyase (substrate: benzothiazolyl cysteine). Following 14C-DCVC (5 mg/kg body wt. orally), the renal 14C-accumulation increased with age, whereas the degree of tubular DCVC lesions was about the same at all time points. Regarding the sex differentiation in adult mice, both the kidney 14C-accumulation levels and the kidney lesion (5 mg/kg DCVC) were most accentuated in the female mouse. However, at a higher dose (25 mg/kg), the male kidney was most affected. Changes in the anion transport and beta-lyase activities did not directly mirror the age-dependent increase in kidney radioactivity. Sex differences in anion transport and beta-lyase activities were also seen, the former activity being highest in the male mouse and the latter in the female. The conflicting results of 14C-accumulation and histopathology in developing mice, may be explained by the ongoing development of the kidney; increase in the number of functionally active nephrons may result in an increased 14C-accumulation (in d.p.m./mg wet wt.) but still the same degree of lesion, when estimated per nephron. In the adult mice, the higher susceptibility of the female may be correlated to the higher beta-lyase activity in the same sex. Regarding the inversed results at a higher dose, rate limitations of transport and bioactivation systems may play a role.

Transplacental passage and fetal kidney binding of 14C-dichlorovinyl cysteine (DCVC) in mice

In order to assess the potential hazard of the nephrotoxic compound S-1,2-dichlorovinyl-L-cysteine (DCVC) during gestation, studies on its disposition and degenerative effects were performed in pregnant mice. In late gestation, binding of 14C-DCVC (spec. act. 1.01 microCi/mumol) equivalents was observed by autoradiography in the inner cortex of the kidney, in the liver and gastrointestinal tract of the fetuses. The uptake of radioactivity in the fetal kidney increased from day 13 to day 18 of gestation when measured by liquid scintillation. When fetuses were injected in utero, a distinct binding of 14C-DCVC was present in the kidney cortex. This fact suggests that bioactivation occurs in situ, as the reactive products are not likely to be transported far from their site of formation. The concentration of radioactivity in the fetal kidney at day 18 of gestation was about 10% of that found in the maternal kidney. Limiting factors for fetal kidney uptake may be both transplacental transfer, and renal bioactivation and transport activities. No distinct histopathological changes in the fetal kidney were observed when a nephrotoxic dose (25 mg/kg) of DCVC was given to the dam. These results suggest that the fetal kidney during late gestation is able to activate and bind DCVC. However, the degree of fetal binding seems too low to cause any visible histopathological effects.

Dichlorovinyl cysteine (DCVC) in the mouse kidney: tissue-binding and toxicity after glutathione depletion and probenecid treatment

The kidney binding of dichloro[14C]vinyl cysteine (14C-DCVC, 8 mg/kg body wt) and the kidney histopathology of DCVC (5 mg/kg body wt) were examined and compared in female C57BL mice subjected to various treatments. To evaluate the roles of organic anion transport and glutathione (GSH) status, mice were pretreated with probenecid (inhibitor of organic anion transport), L-buthionine-S,R-sulfoximine (BSO; inhibitor of GSH synthesis) or with diethyl maleate (DEM; GSH-depleting agent). In addition, the sites of 14C-DCVC binding in BSO-treated and control mice were monitored by microautoradiography. Probenecid was found to inhibit both kidney binding and toxicity of DCVC. In BSO-treated mice, DCVC binding remained roughly unchanged, whereas nephrotoxicity was severely increased and topographically extended to the subcapsular region. Microautoradiography showed that the site of DCVC binding in the straight portion of the proximal tubule was not changed by BSO. In DEM-treated mice, a clearly decreased DCVC binding was observed, while the effect on nephrotoxicity was minute. The effects of probenecid on DCVC binding and toxicity support a role for carrier-mediated transport of DCVC equivalents into the target cells. The BSO result suggests a protective function of GSH towards the nephrotoxicity of DCVC. Moreover, they support our previous contention that a primary lesion occurs at the site of DCVC binding, followed by a secondary, dose-dependent lesion localized outside the DCVC-binding region. In the case of DEM it is proposed that a DEM-GSH conjugate might compete for the uptake and/or activation of DCVC in the target cells.

3,3',4,4'-Tetrachlorobiphenyl. Excretion and tissue retention of hydroxylated metabolites in the mouse

The coplanar 3,3',4,4'-tetrachlorobiphenyl (TCB) was given orally to mice and the metabolite patterns in feces, urine, liver, and adipose tissue were examined. In feces, 80% of the dose was excreted within 5 days. 5-Hydroxy-, 6-hydroxy-TCB, 4-hydroxy-3,3',4',5-tetrachlorobiphenyl, and unmetabolized TCB were identified by comparison to synthetic standards (GC/MS). 4-Hydroxy-trichlorobiphenyl and a dihydroxy-trichlorobiphenyl were indicated by the fragmentation pattern of the corresponding methylated derivatives by GC/MS. In urine, 4.9% of the TCB dose was excreted mainly as conjugates. After hydrolysis, TCB and seven hydroxylated metabolites were detected; 2-, 5-, and 6-hydroxy-TCB and 4-hydroxy-3,3',4',5-tetrachlorobiphenyl were identified and two dihydroxy-tetrachlorobiphenyls were indicated. The major compound detected after hydrolysis of urine was a dihydroxy-trichlorobiphenyl. TCB was the major compound present in the liver, while a minor portion was due to 4-hydroxy-3,3',4',5-tetrachlorobiphenyl. TCB, 4-hydroxy-3,3',4',5-tetrachlorobiphenyl, and 5- and 6-hydroxy-TCB were present in adipose tissue. In addition, radiolabeled material was present in a lipid fraction obtained after gel permeation chromatography of all samples except urine, indicating the presence of TCB metabolites with lipid characteristics.

1,2-Dibromoethane and chloroform in the rainbow trout (Salmo gairdneri): studies on the distribution of nonvolatile and irreversibly bound metabolites

The disposition of metabolites from 14C-labeled 1,2-dibromoethane (DBE) and chloroform (CF) in juvenile rainbow trout was studied by autoradiography and quantitation of tissue radioactivity. Whole-body autoradiography of heated tissue sections showed a considerable level of nonvolatile metabolites of DBE and CF in the liver and certain areas of the body kidney. A lower level of metabolites appeared in the gills, intestinal mucosa, and olfactory rosettes in trouts exposed to DBE- or CF-containing water. Unlike previous studies in rodents, no specific uptake or binding of DBE or CF occurred in the surface epithelia of the upper alimentary tract. Microautoradiography and exhaustive tissue extraction confirmed a high irreversible binding of DBE metabolites in the liver and in a proximal tubular segment of the body kidney in fish exposed to DBE-containing water. A high level of radioactivity in the bile indicated fecal excretion of metabolites from both compounds. The results suggest that there is marked metabolism of DBE and CF in the liver and kidney, whereas the metabolism in the surface epithelia is low. The liver and kidney are proposed to be target organs of toxicity in fish.

S-(1,2-dichloro-[14C]vinyl)-L-cysteine (DCVC) in the mouse kidney: correlation between tissue-binding and toxicity

Uniformly 14C-labeled DCVC and unlabeled DCVC were synthesized and used for autoradiographical and histopathological studies. Four hours after administration of [14C]DCVC (25 mg/kg body wt), a strong binding of radioactivity was observed in the straight proximal tubular cells. Later, the radioactivity was redistributed from the proximal tubules to scattered foci in the kidney medulla, suggesting desquamation and tubular transport of labeled epithelial cells. The redistribution was less pronounced at a lower [14C]DCVC dose (5 mg/kg body wt). Localization of [14C]DCVC was also observed in the liver, exocrine pancreas, and stomach (fundal part), although at a lower level than in the kidney. While the low dose (5 mg/kg body wt) produced a moderate lesion in the straight proximal tubules 24 hr after DCVC, the high dose (25 mg/kg body wt) not only induced a more pronounced lesion in this tubular segment but also extended the lesion to other tubular segments, including the subcapsular region. The results indicate binding of (a) vinyl-containing metabolite(s) to the straight portion of the proximal tubules, where a primary lesion is subsequently developed. Depending on dose, a "secondary" lesion appears in the subcapsular region, topographically different from the DCVC-binding region.

3,3'4,4'-Tetrachlorobiphenyl in pregnant mice: embryotoxicity, teratogenicity, and toxic effects on the cultured embryonic thymus

3,3',4,4'-Tetrachlorobiphenyl (TCB) is a known ligand of the Ah-receptor. When TCB was given to Ah-responsive C57BL/6 mice at gestation day 11, 12 or 13, a pattern of embryotoxic effects similar to those of TCDD was produced. This pattern included death and resorptions of the conceptus (peak sensitivity at day 11), as well as characteristic malformations such as cleft palate, dilated kidney pelvis (peak sensitivity day 12), and thymus hypoplasia (peak sensitivity day 13). The ED50 for cleft palate induction was found to be about 100 mg/kg, as compared to 30 micrograms/kg for TCDD (earlier results). The binding affinity of TCB for the Ah-receptor has been reported to be two orders of magnitude lower than that of TCDD. When TCB was introduced into a thymus organ culture (thymi taken from day-14 embryos), the lymphoid cell development was inhibited with an approximate EC50 of 5 X 10(-8) M. This is approximately 100 times higher than that of TCDD and in good agreement with the receptor binding affinities of both compounds. The difference in in vivo toxicity between TCB and TCDD can be explained by a more rapid metabolism and excretion of TCB.

3,3',4,4'-tetrachloro[14C]biphenyl in pregnant mice: enrichment of phenol and methyl sulphone metabolites in late gestational fetuses

The distribution of radioactivity after injection of 3,3',4,4'-tetrachloro[14C]biphenyl (14C-TCB) in pregnant mice was determined by autoradiography and computer-assisted densitometric analysis. TCB metabolites in fetal tissue were analysed by g.l.c. and g.l.c.-mass spectrometry and compared to the synthesized reference compounds 2-, 5- and 6-methoxy-3,3',4,4'-tetrachlorobiphenyl. The concentration of radioactivity was high in the uterine fluid, and in the fetuses in late gestation. Fetal radioactivity decreased after pretreatment with a high dose of unlabelled TCB. Radioactivity was reversibly bound to fetal tissues. A phenolic metabolite, 3,3',4,4'-tetrachloro-2-biphenylol, and a methylsulphonyl-tetrachlorobiphenyl were found in fetuses in late gestation. No unmetabolized TCB was detected in the fetuses.

O-dealkylation of phenacetin in the olfactory rosette in rainbow trout (Salmo gairdneri)

Olfactory rosettes from trout (Salmo gairdneri) were found to metabolise (14C-ethyl)-phenacetin to 14CO2 in vitro. Based on wet weight, the rate of metabolism was lower than that in liver and gills. Based on protein content, the rate of metabolism was about equal to that in liver and gills. Addition of the cytochrome P-450 inhibitors metyrapone, 9-hydroxyellipticine and piperonyl butoxide significantly decreased the formation of 14CO2 from (14C-ethyl)-phenacetin in olfactory rosettes. Microautoradiography of rosettes incubated with (14C-ethyl)-phenacetin showed the presence of non-extractable metabolites in the sensory and indifferent epithelium. Addition of metyrapone decreased the binding of radioactivity in the epithelia considerably. When olfactory rosettes were incubated with (14C-dimethylamine)-aminopyrine, no formation of 14CO2 was observed. The results are concluded to indicate that cytochrome P-450 dependent enzyme activity is present in the epithelia of the trout olfactory rosette.

Chlorinated paraffins: formation of sulphur-containing metabolites of polychlorohexadecane in rats

A uniformly 14C-labelled polychlorinated hexadecane (14C-PCHD; 65% chlorine by wt) was injected into the portal vein in bile duct-cannulated rats (5-6 mg/kg) and the bile was collected for two or three days. Less than 3% of the total amount of radioactivity excreted in the bile was due to unchanged 14C-PCHD. The radioactivity was separated by ion-exchange chromatography into two major fractions: one acidic, the other amphoteric. Comparison with a similar fractionation of propachlor metabolites indicates that the fractions contain 14C-PCHD conjugates of N-acetylcysteine (mercapturic acid) and glutathione, respectively. The tentative 14C-PCHD-mercapturic acid on t.l.c. had an RF value similar to that of a synthetic PCHD-mercapturic acid, and chlorine and divalent sulphur were shown to be present.

Distribution and retention of some chlorinated hydrocarbons and a phthalate in the mouse brain during the pre-weaning period

In a quantitative retaining study and a whole-body autoradiographic study 5 14C-labelled compounds, bis-(4-chlorophenyl)trichloroethane (DDT), 2,2',4,4',5,5'-hexachlorobiphenyl (6-CB), hexachlorophene (HCP), polychlorohexadecane (PCHD) and diethylhexylphthalate (DEHP) were each administered to mice at the age of 3, 10 and 20 days. The mice were killed 24 h or 7 days after treatment and the amount of radioactivity in the whole brain was measured and its distribution studied. The retention of radioactivity was most pronounced in mice receiving DDT, PCHD, and 6-CB during the tenth day of life. Here the level of radioactivity 7 days after treatment was nearly as high as that observed after 24 h (ratio between 0.86 and 0.74). In contrast, HCP showed a rapid elimination from the brain and was hardly retained at all in the 20-day-old mouse brain. The retention of DEHP in the brain was minimal. Some of the autoradiographic sections were also subjected to myelin staining. Large amounts of radioactivity were found in the myelinated areas of the brain after HCP and PCHD administration. DDT and 6-CB showed a more even distribution within the brain and were not particularly concentrated in the myelin. There was no obvious relationship between the lipophilicity of the parent compounds and their retention in the brain.

Pitfalls in the interpretation of whole-body autoradiograms: long-time retention in brain and adrenal cortex caused by metabolic incorporation of 14C from various labelled xenobiotics

The long-time retention of radioactivity in mice was studied by whole-body autoradiography after administration of 1-14C-alkanes (C12 and C16), 1-14C-polychlorododecanes (56 and 68% Cl w/w), U-14C-polychlorohexadecane (23% Cl w/w), ethyl-14C-phenacetin and ring-3H-phenacetin. All the labelled xenobiotics, except the high-chlorinated (68% Cl) polychloroalkane and the ring-3H-phenacetin, gave rise to long-time (12-60 days) retention of radioactivity in the central nervous system and in the adrenal cortex; the distribution of radioactivity within the brain corresponded to the stain intensity of myelin stained sections. Administration of 1-14C-fatty acids (C12 and C16) and 1-14C-acetylcoenzyme A gave a similar distribution pattern. The lipophilic radioactivity in brain and adrenal tissue was extracted and separated with thin-layer chromatography. In the adrenal extracts, the label co-chromatography mainly with cholesteryl ester, and in the brain extracts with cholesterol and with more polar lipids (mainly phosphatidyl-choline and -ethanolamine). The brain homogenate contained a non-extracted, probably proteinaceous, residue, with comparably high radioactivity. The results show that several 14C-labelled xenobiotics which give long time retention of radioactivity in the adrenal cortex and brain, are degraded to intermediates with the possibility to become incorporated into endogenous substances. The high-chlorinated alkane (1) and ring-3H-phenacetin (2) did not give such long time retention due to its persistance towards degradation (1), and lack of labelling of the degradable part of the molecule (2). It is concluded that erroneous interpretations can be drawn from distribution studies if the routes of degradation and positions of label of the 14C-labelled compounds are not considered.

Chlorinated paraffins: effect of some microsomal enzyme inducers and inhibitors on the degradation of 1-14C-chlorododecanes to 14CO2 in mice

The degradation of 1-14C-chlorododecanes to 14CO2 in C57BL mice was studied. 1-14C-Chlorododecane-injected mice were transferred to an all-glass metabolism cage and the exhaled air was monitored for 14CO2. Pretreatment with cytochrome P-450 inhibitors resulted in a marked decrease in the rate of 14CO2-formation, when measured as peak 14CO2-exhalation rate (PER): After piperonyl butoxide pretreatment the degradation rate of a high-chlorinated 14C-dodecane (PCDD II; 68% Cl w/w) to 14CO2 was 16% of control, and after metyrapone pretreatment 40%. It was also shown that piperonyl butoxide pretreatment decreased the rate of 14CO2-formation, and the amount of 14CO2 formed, in proportion to the chlorine content of four differently chlorinated dodecanes. The cytochrome P-450 inducer phenobarbital moderately (PER 152%) increased the rate of 14CO2-formation from PCDD II, whereas 3-methylcholanthrene and several technical grade chlorinated paraffins generally gave less or no inductive effects. Also the cumulative 14CO2-exhalation, measured during six hours (CE-6), was inhibited and induced after the above pretreatments. The results indicate a cytochrome P-450-dependent degradation of C12-chloroalkanes to 14CO2 in vivo. The degradation via cytochrome P-450 seems to be relatively more important for higher chlorinated alkanes.

A simple method for collecting 14CO2 in fish

A simple apparatus was designed for continuous collection of excreted 14CO2 in fish. Carp (Cyprinus carpio; body wt. about 400 g) were intraarterially injected with [14C]acetate (44 mmol) and transferred to a test chamber (21 +/- 1 degrees C). Within 48 h, 65.4 +/- 2.7% of the dose was recovered as 14CO2. A small amount of 14CO2 was retained in the water of the test chamber. Control experiments using [14C]acetate-injected mice as '14CO2-generators' showed that this 14C residue in the water could be recovered almost completely as 14CO2 upon acidification. In the carp experiments, some radioactivity remained in the acidified test chamber water; this residue may represent unchanged [14C]acetate and/or metabolites other than 14CO2.

Chlorinated paraffins: disposition of a polychloro-[1-14C]-hexadecane in carp (Cyprinus carpio) and bleak (Alburnus alburnus)

The disposition of polychloro-[1-14C]hexadecane (PCHD, 34% chlorine w/w) was studied in carp (Cyprinus carpio) and bleak (Alburnus alburnus). After intra-arterial (i.a.) injection in carp about 6% of dose was excreted as 14CO2 in 96 h. The autoradiographic distribution pattern after administration of PCHD to carp (i.a.) and bleak (up to 14 days of exposure in PCHD-contaminated water) was characterized by a strong labelling in the bile/intestinal contents. High radioactivity also appeared in the kidney, liver, gills and, particularly in bleak, in the nasal cavity, lens and skin.

Toxicity and distribution in chick embryos of 3,3',4,4'-tetrachlorobiphenyl injected into the eggs

3,3',4,4'-Tetrachlorobiphenyl (3TCB) was injected into the yolk of embryonated hens' eggs in doses of 4, 20 or 100 micrograms/kg egg. Twenty and 100 micrograms/kg resulted in the death of all the embryos. The hatching rate of the eggs treated with 4 micrograms/kg was 60% while that of the control eggs was 88%. This means that 3TCB is at least 10 000 times more toxic in chick embryos than a previously studied isomer, 2,2',4,5'-tetrachlorobiphenyl (2TCB). 3,3',4,4'-Tetrachlorobiphenyl might be teratogenic in chick embryos since eye and beak deformities were seen in 3 unhatched tetrachlorobiphenyl-treated embryos. In addition rump edema and excess fluid in the body cavity was observed in some embryos. The distribution of the 2 tetrachlorobiphenyls in chick embryos was studied by means of whole-body autoradiography. No differences in distribution, which could explain the extreme difference in toxicity, were detected. High amounts of radioactivity were found in the bile of the embryos, indicating a capacity of the embryos to metabolize and excrete the tetrachlorobiphenyls.

Chlorinated paraffins: disposition of a highly chlorinated polychlorohexadecane in mice and quail

Uniformly 14C-labelled 1-chloro-polychlorohexadecane (PCHD) of high chlorine content (69% w/w) was given to Japanese quail and to C57Bl mice perorally (p.o.) and intravenously (i.v.). The degradation of PCHD to 14CO2, measured during 8 h, was found to be minute (about 1% of dose) in both species after either route of administration. In mice 66 and 43% of dose was eliminated in the feces during 96 h following p.o. and i.v. administration, respectively; the urinary excretion was about 3% in both cases. In quail, the combined fecal and urinary excretion during 96 h after p.o. administration was 58% of dose. The autoradiographic distribution following p.o. administration showed some general similarities between mice and quail; high radioactivities were present in bile, liver, kidney, and intestinal contents up to 24 h after administration. In addition, in quail high radioactivity was present in the hypophysis, retina, blood, and egg yolk. In mice strong accumulation and retention was observed in the corpora lutea up to 30 days after administration. A long time retention in fat occurred in both species.

Metabolic fate of chlorinated paraffins: degree of chlorination of [1-14C]-chlorododecanes in relation to degradation and excretion in mice

The disposition of three [1-14C]-chlorododecanes (MCDD, PCDD I and PCDD II; 17.4%, 55.9%, and 68.5% chlorination) was studied in C57Bl mice. [1-14C]-lauric acid (LA) was studied as reference compound. Fifty-two percent (MCDD), 32% (PCDD I), and 8% (PCDD II) of the radioactive doses were exhaled as 14CO2 during 12 h after i.v. injection. Similar results were obtained after p.o. administration. In addition to a marked labelling of the liver and fat, the distribution patterns observed at 24 h after administration revealed an uptake of radioactivity in tissues with high cell turnover/high metabolic activity, e.g., intestinal mucosa, bone marrow, salivary glands and thymus. The concentration of radioactivity in these sites and the exhalation of 14CO2, which were inverse to the degree of chlorination, indicate that the chloroalkanes are degraded to metabolites which can be utilized in the intermediary metabolism. A similar, although more pronounced, distribution pattern and 14CO-2-exhalation (70% of i.v. dose) was observed after LA administration. The long time retention of heptane-soluble radioactivity in liver and fat (indicating unmetabolized substance) increased with degree of chlorination. On the contrary, the administration of LA and the chlorododecanes MCDD and PCDD I, but not of PCDD II, resulted in a selective labelling of the central nervous system 30-60 days after injection.

Metabolism of 2,4'5-trichlorobiphenyl: enrichment of hydroxylated and methyl sulphone metabolites in the uterine luminal fluid of pregnant mice

Autoradiography of 2,4',5-trichloro-[14C] biphenyl ([14C] triCB) in mice at different stages of gestation indicated a strong accumulation of radioactivity in the uterine luminal fluid at gestation day 9 and later. From day 10 an uptake of radioactivity occurred also in the yolk sac epithelium. In order to identify the suspected metabolites in the fluid pregnant mice were dosed with unlabelled triCB on gestation day 9. Gas chromatographic (GC) and mass fragmentographic (MF) analysis of extracts of uterine fluid obtained on day 12 showed that hydroxylated, methyl sulphone and conjugated metabolites were present in the fluid. The unchanged triCB could not be detected in the extracts of the fluid. The site of release of the metabolites to the fluid may be the endometrium or, possibly, the yolk sac epithelium. The mechanism behind the concentration of water-insoluble methyl sulphone and hydroxylated metabolites of triCB in an aquatic phase is discussed.

Metabolism of 2,2',5,5'-tetrachlorobiphenyl: formation of mono- and bis-methyl sulphone metabolites with a selective affinity for the lung and kidney tissues in mice

1. Distribution in mice of 2,2',5,5'-tetrachloro[14C]biphenyl has been studied by autoradiography. Radioactivity was specifically localized in the bronchial epithelium, the lung parenchyma, the kidney cortex and the adipose tissue. 2. Bis(methylsulphonyl)-2,2',5,5'-tetrachlorobiphenyl, a hitherto unknown metabolite of 2,2',5,5'-tetrachlorobiphenyl, has been identified in lung, kidney and liver of mice. 3- and 4-Methylsulphonyl-2,2'5,5'-tetrachlorobiphenyl were also present. 3. The ratio of the contents of 3- and 4-methylsulphonyl-2,2',5,5'-tetrachlorobiphenyl in the liver was 1.12 after 12 days. A lower ratio in lung and kidney indicates a high affinity of these tissues for the 4-methyl isomer.

Effects of cold stress on rats fed different levels of docosenoic acids

Male Sprague-Dawley rats, 4 weeks old, were subjected to an ambient temperature of 4 C for periods up to 24 days and fed a synthetic diet containing one of the following oils: peanut oil (PO), rapeseed oil (RO), low erucic acid rapeseed oil (LO), and partially hydrogenated marine oil (HO), each at 20% w/w. A parallel experiment using the same oils was performed at room temperature (23 C). During cold stress, animals on the RO diet showed higher mortality than all other groups; all 20 animals in this group died within 5 days. At room temperature, however, all animals survived. The lipid accumulation in the heart reached its peak in all groups after 3 days and then gradually declined. The accumulation was most pronounced in the RO animals and coincided with the high mortality at 4 C. The fatty acid composition of the cardiac triglycerides reflected that of the diet, while the composition of the cardiac lecithin was only marginally modified.