Toxicology of chlorinated dibenzo-p-dioxins

Reversible inhibition of in vitro epithelial cell proliferation by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Subconfluent cultures of a mouse epithelial cell line, which after prolonged subculturing exhibited an elevated saturation density as compared to the original cell line, were treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Cultures of cells with or without TCDD grew at equal rates until confluency was reached. At confluency, cultures treated with as little as 10(-11) M TCDD showed a decline in cell proliferation relative to controls as demonstrated by cell enumeration and supported by reduced [3H]thymidine incorporation (both by liquid scintillation spectrometry of whole culture and autoradiography of individual cells). After 14 days of exposure, the saturation density of the treated culture was about 50% of the control culture. This TCDD-induced, increased sensitivity to density-dependent inhibition of replication ( DDIR ) was accompanied by a change from a fusiform morphology in the high-saturation-density control cells to a flat cobblestone appearance in the treated low-saturation-density cells. The nondividing cultures treated for 14 days with 10(-11) M TCDD had the same viability as control cultures. Upon trypsin suspension and reseeding , these formerly quiescent cultures were again capable of growing to high cell density and of again showing susceptibility to TCDD-induced changes in cell growth and morphology. Evidence is presented to suggest that this reversible increase in sensitivity to DDIR and the morphological change are not a consequence of cell growth inhibition. This system may provide the basis for an in vitro model to study the effect of TCDD on the control of replication of these cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induces hyperplasia in confluent cultures of human keratinocytes

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the prototype for a group of halogenated aromatic hydrocarbons which can be potent modulators of growth and differentiation of epithelial tissues. TCDD causes chloracne and can act as a skin tumor promoter, but these actions have been demonstrated only in animals in which TCDD causes epidermal hyperplasia. Study of the hyperplastic response to TCDD has been hampered by lack of an in vitro model; all previous investigations indicated that TCDD had no in vitro effect on cell growth. We show here that nanomolar concentrations of TCDD cause hyperplasia in confluent cultures of human keratinocytes and suggest that this model system will be useful for analyzing mechanisms of TCDD-induced epithelial hyperplasia and genetic differences in responsiveness to TCDD.

Studies on the metabolic fate of [14C]2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the mouse

Studies on the Metabolic Fate of [14C]2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in the Mouse. KOSHAKJI, R. P., HARBISON, R. D., and BUSH, M. T. (1984). Toxicol. Appl. Pharmacol. 73, 69-77. After a single po dose (135 micrograms/kg; 62 microCi/kg) of 14C-labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in male ICR/Ha Swiss mice, 67 to 76% of the administered dose was eliminated via the feces and 1 to 2% in the urine during the first 24 hr following treatment. It seems likely that most of this material was simply not absorbed. Much of the remaining chemical was then excreted slowly in the urine (2%) and feces (7%) during the next 10 days, partly as the unchanged compound and partly as metabolites. One of the metabolites (Fraction II) appears to be a single polar, acidic metabolite characterized in urine (0.4 +/- 0.1%) and feces (2.2 +/- 0.2%), and is also likely excreted as a glucuronide conjugate. The rest of the radioactivity was in the form of unchanged TCDD in the animal body (17 +/- 2%). Steady rates of decline in the concentrations of the 14C as well as of the unchanged TCDD were reached in the feces and urine after the fifth day following the administration of the chemical. Based on this steady rate, the half-life of the radioactivity in the body was approximately 20 days. Urine, feces, and whole body were analyzed by solvent extraction, 14C counting, thin-layer chromatography, and countercurrent distribution.

Teratogenicity of 2.3.7.8-tetrachlorodibenzofuran (TCDF) in mice

Treatment of pregnant C57BL/6N mice with 2,3,7,8-tetrachlorodibenzofuran (TCDF) (0, 250, 500, and 1000 micrograms/kg on gestation day 10 or 0, 10, 30, 50, and 100 micrograms/kg on gestation days 10-13) results in dose-related increases in isolated cleft palates and hydronephrotic kidneys in the offspring. TCDF is teratogenic in 100% of the fetuses at dose levels that are not maternally toxic. The fetal kidney is the most sensitive target organ but the kidney lesions may be reversible.

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) causes reduction in the low density lipoprotein (LDL) receptor activities in the hepatic plasma membrane of the guinea pig and rat

Administration of 1 micrograms/kg (single intraperitoneal injection and studied after 10 days) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to young male guinea pigs was found to cause a significant reduction in binding of low-density lipoprotein (LDL) to its receptor on the hepatic plasma membrane. This reduction in LDL binding is not caused by the decrease of food intake by treated animals since pair-fed control animals had significantly higher LDL binding than treated animals. It was also found that primary hepatocytes from treated animals had a reduced ability to internalize LDL than controls. Such a change in the plasma membrane function may explain the resulting hyperlipidemia particularly hypercholesterolemia which occurs in this species as a result of TCDD administration.

Decreased induction of aryl hydrocarbon hydroxylase activity in hyperproliferative hairless mouse epidermis

Hairless mice were treated topically with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to induce experimental chloracne. The aryl hydrocarbon hydroxylase (AHH) activity in the epidermis was monitored. TCDD is a potent inducer of AHH activity in normal skin. However, as continued TCDD application induced hyperproliferative and hyperkeratotic changes in the epidermis, the AHH activity decreased. Similar suppression in AHH activity was demonstrated in epidermis made hyperplastic by (a) tape stripping of stratum corneum and (b) repeated application of 50% oleic acid. This suggests that the epidermal AHH response varies with the state of epidermal differentiation. In the hairless mouse, AHH activity in hyperplastic epidermis is lower than that in normal epidermis.

Sensitivity to suppression of cytotoxic T cell generation by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is dependent on the Ah genotype of the murine host

Susceptibility of mice to a variety of toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is genetically determined by the Ah locus. To determine if immunotoxicity following TCDD exposure was also regulated by the Ah locus, we tested the ability of low dose TCDD (4 ng/kg) to suppress the generation of allospecific cytotoxic T cells (CTL) by lymphocytes from "susceptible" C57B1/6, and "resistant" DBA/2, and from C57B1/6XDBA/2J F1 hybrid mice in vitro. To determine if TCDD acted directly on the "susceptible" lymphoid cells, the immune response of C57B1/6 leads to DBA/2 and DBA leads to C57B1/6 bone marrow chimeras was also measured. C57B1/6 and F1 mice proved susceptible to suppression consistent with the dominant effect of Ah. Susceptibility to suppression in chimeric mice, however, was determined by the Ah genotype of the host and not by the genotype of the grafted lymphomyeloid cells. Mixing experiments demonstrated that suppression of CTL generation by TCDD was due to suppressor T cells. The frequency of CTL precursors was not affected by TCDD. These results are consistent with the idea that TCDD acts by an Ah locus-dependent mechanism to indirectly promote development of suppressor T cells that block the generation of CTL from their precursors.

Health status of workers with past exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin in the manufacture of 2,4,5-trichlorophenoxyacetic acid: comparison of findings with and without chloracne

Chloracne was found in 52% of 226 workers in a 1979 cross-sectional survey at a plant where 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) had been manufactured from 1948 to 1969. Mean duration of residual chloracne was 26 years, and in 29 subjects, it had been present for 30 years. A significant increased prevalence of abnormal gamma-glutamyl transpeptidase (GGT) and higher mean GGT were found in those with chloracne, compared to those without. Although mean triglyceride values were higher in those with chloracne, the difference was not statistically significant. Neurological examination showed a statistically significant higher prevalence of abnormal sensory findings in those with chloracne. Increased prevalence of angina and reported myocardial infarction in those with chloracne was not significant when age-adjusted. Increased prevalence of reported sexual dysfunction and decreased libido in those with chloracne compared to those without was statistically significant after age adjustment. No differences were found between those with and without chloracne in serum cholesterol, total urinary porphyrins, or in reproductive outcome.

Excretion and distribution of two occupational toxicants, tetrachloroazobenzene and tetrachloroazoxybenzene in the rat

The clearance profile and tissue distribution of 2 occupational toxicants, 3,3',4,4'-tetrachloroazobenzene (TCAB) and 3,3',4,4'-tetrachloroazoxybenzene (TCAOB), were examined in male Sprague-Dawley rats. TCAB was found to be cleared from the body more rapidly than TCAOB when a single dose of 14C-labeled TCAB or TCAOB was administered orally. While 66% of the administered TCAB dose was excreted via the urine and feces within the first 24 h, TCAOB-treated animals were only able to clear 37% of the administered dose by the same elimination route. The half-lives for elimination of TCAB and TCAOB were estimated to be 18 h and 34 h, respectively. Examination of the tissue distribution of the remaining radioactivity indicated that, for both compounds, the adipose tissue contained the highest level of radioactivity. The rapid elimination of TCAB and TCAOB by rats may explain in part the reduced toxicity of these 2 compounds to whole animals in comparison to the isosteric 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Hypothyroxinemia and hypothermia in rats in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin administration

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treatment on body temperature and serum and tissue levels of thyroid hormones, glucose, glucagon, insulin, and somatostatin were investigated. Within 7 days following TCDD administration (45 micrograms/kg), rats exhibited hypothyroidism compared to pair-fed controls and rats fed ad libitum. Body temperature was maintained in the pair-fed and ad libitum-fed controls but was significantly decreased in TCDD-treated rats at 2 days. Within 2 weeks of the administration of 90 micrograms TCDD/kg, body temperature was below 35 degrees C with the lowest mean value of 34.5 degrees C recorded on Day 16. Mean body temperatures for control rats ranged from 36.8 to 37.5 degrees C. One week after TCDD administration (45 micrograms/kg), serum thyroxine (T4) declined to 46% of pair-fed controls. The decreased free-thyroxine index indicated that the measured decrease in thyroxine reflected decreased hormone concentrations as opposed to altered protein binding. Hypoglycemia occurred in TCDD-treated rats subsequent to hypothyroxinemia and hypothermia, but it did not develop in the pair-fed controls. At 1 week after administration of 45 micrograms TCDD/kg, serum and pancreatic insulin levels were reduced to 25 and 76% of ad libitum-fed controls, respectively. Hypophagia was determined to be responsible for the decreased growth rate and hypoinsulinemia but did not account for hypothyroxinemia, hypothermia, and hypoglycemia following the administration of TCDD. No significant alterations were detected in serum glucagon or in pancreatic, hepatic, or serum somatostatin levels. Decreased somatostatin in the gastric antrum coincided with a 29% increase in stomach dry weight. The delayed toxicity of TCDD may result, in part, from these hormonal alterations.

Subchronic oral toxicity in guinea pigs of soot from a polychlorinated biphenyl-containing transformer fire

We have previously described the acute po toxicity in guinea pigs of soot from a transformer fire at the State Office Building in Binghamton, New York. The soot was determined to contain polychlorinated biphenyls, biphenylenes, dibenzodioxins, and dibenzofurans. The present study evaluates soot toxicity in guinea pigs receiving 0, 0.2, 1.9, 9.3, or 46.3 ppm soot in the feed for 90 days or 231.5 ppm for 32 days. At 231.5 ppm, body weight loss, thymic atrophy, bone marrow depletion, skeletal muscle and gastrointestinal tract epithelial degeneration, and fatty infiltration of hepatocytes were observed. Mortality had reached 35% by Day 32 (when survivors were killed), with total soot consumption of approximately 400 mg/kg. At 46.3 or 9.3 ppm soot, a reduced rate of body weight gain was observed, and at 46.3 ppm, the mortality by Day 90 was 30%. Relative (to body) thymus weights were decreased in both groups, while relative spleen weights were increased at 46.3 ppm soot only. Salivary gland interlobular duct squamous metaplasia and focal lacrimal gland adenitis were detected histopathologically, while bone marrow depletion was noted only in females at the higher dose. Diminished serum alanine aminotransferase (ALT) activity in both sexes and decreased serum sodium levels in male and potassium levels in female animals were detected at both dose levels. decreased gamma-glutamyl transferase activity and red blood cell count and elevated serum creatinine and triglycerides were observed only in animals fed 46.3 ppm soot. At 1.9 ppm soot, salivary gland duct metaplasia was observed in both sexes, along with decreased relative thymus weights, ALT activity, and serum sodium levels in male animals only. No effects attributable to soot exposure were noted in animals receiving 0.2 ppm soot for 90 days. Total average soot consumption for male and female animals in the 0.2, 1.9, 9.3, and 46.3 ppm dosage groups was 1.2, 12, 55, and 275 mg/kg, respectively. Although many of the observed effects were typical of acute exposure of guinea pigs to the Binghamton soot or to polychlorinated aromatic hydrocarbons in general, salivary gland duct metaplasia has not been previously reported. Toxic effects of this subchronic exposure were observed at lower total doses than with acute exposure, although variations in absorption due to the effects of different vehicles (aqueous in the acute study versus the feed in this study) could account for some or all of this difference.

Liver morphology in guinea pigs administered either pyrolysis products of a polychlorinated biphenyl transformer fluid or 2,3,7,8-tetrachlorodibenzo-p-dioxin

A transformer cooled and insulated with a mixture of 65% Aroclor 1254 and 35% chlorinated benzenes located in the Binghamton State Office Building in Binghamton, New York, was involved in a fire, which produced soot containing polychlorinated biphenyls, biphenylenes, dioxins, and dibenzofurans. A single dose of either soot or 2,3,7,8-tetrachlorodibenzo-p-dioxin in aqueous methyl cellulose was administered by gavage to Hartley guinea pigs of both sexes. The liver tissue was examined 42 days after administration. By light microscopy hypertrophy of hepatocytes, steatosis, focal necrosis, and cytoplasmic hyalin-like bodies were observed as a result of both treatments. Bile duct proliferation (adenofibrosis) was observed only in the guinea pig groups administered soot. These animals also showed proliferation of the smooth endoplasmic reticulum, concentric membrane arrays (CMA), mitochondrial alterations, decreased rough endoplasmic reticulum, and autophagolysosomes by electron microscopy. The CMAs, which corresponded to the hyalin-like bodies, surrounded lipid droplets and cytoplasmic matrix containing mitochondria and degenerating organelles.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-mediated depression of rat testicular heme synthesis and microsomal cytochrome P-450

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces hirsutism, alopecia, and chloracne, symptoms that suggest a possible alteration of endocrine function. Therefore, the effects of TCDD on rat testicular cytochrome P-450 content were investigated. Forty-eight hours after a single, oral dose of TCDD (25 microgram/kg) testicular microsomal cytochrome P-450 levels were depressed by approximately 24%. Microsomal cytochrome P-450 continued to decrease to 62% of control levels at 4 days and remained at approximately the same levels 7 days following treatment. Testicular microsomal heme content exhibited a similar pattern after administration of TCDD. No alterations in testicular delta-aminolevulinic acid (ALA) synthase were detected. The incorporation of [14C]ALA into microsomal heme was decreased to approximately 36% of control values at 24 hr after TCDD administration. Testicular weights were not altered during the 7-day experimental period. These data suggest that TCDD depresses cytochrome P-450 levels in the rat testis through an inhibition of the synthesis of testicular heme.

Inhibition of ornithine decarboxylase activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the activity of rat liver ornithine decarboxylase (ODC) were investigated. Sixteen hours after partial hepatectomy, rats that had been pretreated with TCDD for 1 week exhibited a 3- to 4-fold increase in ODC activity, while vehicle controls exhibited to 8- to 10-fold increase. This inhibition of ODC induction by TCDD was time dependent since TCDD administration at the time of partial hepatectomy did not produce inhibitory effects on the subsequent ODC induction. ODC induction after either aminophylline or dexamethasone administration, agents which act via cAMP-mediated and direct nuclear events, respectively, also was inhibited by pretreatment with TCDD. It was concluded that TCDD pretreatment decreased the ability of the liver to respond to hormonal stimulation as reflected in the attenuation of ODC induction. RNA polymerase I activity, which positively correlates with ODC activity in growth and development, decreased concomitantly with decreased induction of ODC. In unstimulated liver RNA polymerase I activity, as well as protein, DNA, and RNA levels, remained unchanged 1 week after TCDD. However, TCDD administration resulted in decreased liver concentrations of putrescine and spermidine, but not spermine. This suggests that TCDD pretreatment results in a time-dependent decrease in hormone responsivity.

Fate of 2,3,7,8-tetrachlorodibenzo-p-dioxin metabolites from dogs in rats

1. Metabolites of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were extracted from the bile of TCDD-treated dogs and administered by gavage to bile-duct-cannulated rats and also to an intact rat. 2. Radioactivity of the TCDD metabolites was rapidly cleared from the body of the rats, indicating that bioaccumulation of these compounds does not occur. 3. Biliary excretion was the most important route of elimination in the cannulated rats and amounted to greater than 30% of the administered dose within 24h. TCDD metabolites were also eliminated to a minor extent by the kidneys. The combined recovery of radioactivity in faeces, bile and urine after 24h accounted for greater than 85% of the dose. 4. The intact animal exhibited a somewhat different kinetic behaviour in that only 13% dose was excreted in faeces and urine after 24h, which indicates enterohepatic circulation. The administered radioactivity was completely recovered after 72h. 5. Results from the present experiments indicate that metabolism of TCDD is the rate-limiting step in elimination of TCDD from the liver. Interspecies variability in the toxicity of TCDD may in part be attributable to different rates at which the species metabolize and excrete TCDD.

Induction of porphyria in the rat by chronic versus acute exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

Chronic oral administration of 1 microgram . kg-1 . week-1 of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to female rats for 16 weeks resulted in hepatic porphyria. In contrast, administration of single oral doses as high as 30 micrograms/kg did not produce porphyria, either acutely or 16 weeks later. Activities of hepatic drug-metabolizing enzymes [aryl hydrocarbon hydroxylase (AHH) and glucuronyl transferase] were increased by chronic oral doses of TCDD as low as 0.01 microgram . kg-1 . week-1. When animals were dosed with TCDD chronically and then allowed to recover for 6 months, AHH and glucuronyl transferase activities returned toward normal (98 and 86% recovery). However, animals showed only partial recovery from TCDD-induced porphyria. Hepatic porphyrin levels did decrease during this period, but urinary porphyrins and the rate-limiting enzyme in porphyrin synthesis, delta-aminolevulinic acid synthetase, remained maximally elevated during the 6-month recovery period. It is concluded that single doses of TCDD do not produce porphyria in the rat, but that TCDD is porphyrogenic when given chronically. Moreover, when TCDD administration is stopped, recovery from the porphyrogenic effects of TCDD is very slow and does not correlate with the biological half-life of TCDD in the rat.

Structure elucidation of mammalian TCDD-metabolites

Thin layer and gas chromatographic examination of the bile of dogs which were given tritium-labelled TCDD revealed the presence of several polar biotransformation products. The structure of 5 phenolic metabolites was elucidated by combined gas chromatography-mass spectrometry. A metabolic breakdown scheme for TCDD in the dog is proposed.

Toxicity of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD)

In summary, the toxicity of TCDD has been comprehensively examined in multiple acute, subchronic, and chronic studies. Acute toxicity studies have shown marked species differences, with up to a 10,000-fold difference between the single oral LD50 dose for the guinea pig and hamster. TCDD is capable of causing an acnegenic response in man and a similar skin response in certain animals. It is also a potent inducer of microsomal enzymes in some but not all species. A dose-related suppression of cell-mediated immunity has been observed at higher dose levels in laboratory animals but not in humans manifesting TCDD-induced acnegenic response. TCDD causes a dose-related teratogenic response in mice, with the no-adverse-effect level of 0.1 micrograms TCDD/kg/day. In rats, TCDD causes embryo- and fetotoxicity above the no-adverse-effect level of 0.03-0.125 micrograms/kg/day. Dose-related reproductive effects have also been noted in monkeys at doses that elicit maternal toxicity, and additional long-term studies are presently underway. A multigeneration reproduction study as well as a lifetime chronic toxicity study have been completed with TCDD in rats; in both studies, the no-adverse-effect level was found to be 0.001 microgram TCDD/kg/day. Numerous mutagenic studies have been performed using in vitro plant and microbial test systems as well as in vivo tests in mammals and man. A mutagenic response was noted in a few of the vitro test systems, but there are no definitive in vivo correlates of TCDD mutagenicity in higher mammals or man. TCDD has been studied for carcinogenic potential in rats and mice. There is good correlation of the results, with a carcinogenic response noted in both species only after long-term ingestion of higher dose levels that induce toxicity. No carcinogenic response occurred at continuous dose levels of 0.001-0.0014 micrograms/kg/day in rats and 0.001-0.03 micrograms/kg/day in mice. Data presently available are more supportive of a nongenetic (?promotor) rather than a genetic mechanism of carcinogenesis. The most recent research, some of which is still underway, indicates that the biologic uptake and toxicity of TCDD may be significantly decreased if the TCDD is adsorbed onto carbon or soil particles. This information is helpful in hazard assessment of exposure to TCDD.

A new synthesis of tetrachlorofluorodibenzo-p-dioxin

The 1,2,3,4-tetrachloro-7-fluorodibenzo-p-dioxin has been synthesized via condensation of 4-fluorocatechol and pentachloronitrobenzene. This compound could be used as an internal standard for the analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin by chromatographic methods.

Evidence of degradation of polybrominated biphenyls in soil samples from Michigan

Soil samples obtained from the former polybrominated biphenyls (PBB) manufacturing site in Michigan were analyzed by gas chromatography and gas chromatography with mass spectrometric detection. The results indicate significant degradation of the PBB residue in the soil sample. The soil sample with the highest concentration of PBB had the greatest degree of degradation. Principal degradation products include 2,3', 4,4', 5-pentabromobiphenyl, 2,2', 4,4', 5-pentabromobiphenyl and two unidentified tetrabromobiphenyls. The degradation pattern observed supports a photochemical decomposition mechanism. These degraded residues may be more toxic than the original Firemaster residues. The implications of the results are discussed.

Acnegenic activity of 3-methylcholanthrene and benzo[a]pyrene, and a comparative study with 2,3,7,8-tetrachlorodibenzo-p-dioxin in the rabbit and hairless mouse

The non-halogenated hydrocarbons 3-methylcholanthrene (MC) and benzo[a]pyrene (BP) were tested for acnegenic activity using the rabbit ear test. Both compounds induced characteristics follicular hyperkeratosis, although their acnegenic potency was approximately 4 orders of magnitude lower when compared to the potent acnegen 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). These results are discussed in view of the hypothesis that the acnegenic activity of TCDD and its congeners is mediated through stereospecific binding to a cytosolic receptor protein. In an experiment with hairless (hrhr) mice, which mutant has been described as an animal model for testing acnegenic potency, reduction in sebaceous gland tissue but no follicular hyperkeratosis was observed after application of a total dose of 0.4 microgram TCDD on the back skin. At a 10 times lower dose, no effects were seen. The hairless mouse strain used was responsive to TCDD as judged from the dose-related increase in the activity of aryl hydrocarbon hydroxylase (AHH) in liver microsomes, the increased liver weight and the histopathological changes in the liver. In comparison, a total dose of 0.12 microgram TCDD produced a strong follicular hyperkeratosis in the rabbit ear. From these results and from literature data, the adequacy of the hairless mouse for the testing of compounds for acnegenic potency is questioned.

Intestinal absorption of nutrients in rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Impairment of active intestinal absorption of glucose and leucine was observed in rats 2-3 wk after oral treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (5 and 100 mg/kg). At the higher dose level used this response was complicated by the effects of severely reduced food consumption. Malabsorption of specific nutrients may help occasion the body wasting seen in many animals after acute exposure to TCDD.

Hyperkeratosis induced by sunlight degradation products of the major polybrominated biphenyl in Firemaster

Sunlight photodegradation of 2,2', 4,4', 5,5' -hexabromobiphenyl, the major component of Firemaster, gave a mixture that produces severe hyperkeratosis of the rabbit ear. This component in its pure state does not cause hyperkeratosis. One or more of the four major photolysis products must be responsible for this activity. A similar photodegradation pattern was observed for 2,2', 3,4,4', 5,5' -heptabromobiphenyl, the second largest component of Firemaster.

Agent Orange toxicity: a quantitative perspective

1 The minimum toxic dose of tetrachloro-dibenzo-p-dioxin (TCDD) for man has been calculated from monkey and human data to be 0.1 microgram kg-1. 2 The amount of TCDD which man takes in from his environment is about 1/2050 of that present in one square metre of his immediate environment. 3 The average concentration of TCDD present in Vietnam immediately after spraying Agent Orange was 8 microgram m-2. 4 A soldier directly sprayed would attain an internal body concentration of 7 X 10(-5) microgram kg-1 or 1/1750 of the minimum toxic dose; soldiers moving through previously sprayed areas would ingest much less. 5 These quantitative aspects indicate that the dioxin sprayed with Agent Orange in Vietnam cannot have caused systemic illnesses in Vietnam veterans or birth defects in their children.

The influence of malnutrition on the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rats

A single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (20 or 40 microgram/kg body wt) administered to rats resulted in reduced body weight gain, water intake, degenerative changes in the liver and involution of the thymus. Although a restricted diet alone caused thymic involutions it was shown that TCDD at 10 or 20 microgram/kg body wt accentuated this atrophy. Microscopically, a marked atrophy of the thymus and swelling and necrosis of the liver were found in the malnourished animals. The effects of TCDD were also tested in rats fed either 3.5%, 26% or 55% protein. There was no clear relation between the protein level and the influence of TCDD on the thymus. However, the effect of TCDD on body weight and the liver was more severe in rats given low protein diet. These effects were not reversed by high protein diet. Since it is unlikely that the influence of TCDD on the thymus is related to malnutrition, other mechanisms, such as depletion of energy reserves, a direct effect of TCDD on the thymus or a mediation by the hepatotoxic action may be involved.

Review of the dioxin problem. Mass spectrometric analyses of tetrachlorodioxins in environmental samples

Major concern over the chemical group of chlorodioxins has arisen since 2,3,7,8-tetrachlorodibenzo-p-dioxin with its extremely toxic and teratogenic properties has been found in widely distributed pesticides such as the herbicide 2,4,5-trichlorophenoxy acetic acid. Because of its chemical stability and lipophilic nature, 2,3,7,8-tetrachlorodibenzo-p-dioxin released into the environment has the potential of accumulation in the food chain. Mass spectrometry in its various forms has been the method of choice to detect and confirm low parts per billion of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Recently, a Consensus Forum held at the National Center for Toxicological Research amongst the various United States Government agencies (Food and Drug Administration, Environmental Protection Agency, US Department of Agriculture and National Institute of Environmental Health Sciences), eloquently demonstrated the potential, as well as the shortcomings, of the various techniques applied. In particular, the availability of a stable 13C labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin has proved to be an essential component to achieve low level quantitation. A brief review of the findings of the Consensus Forum is presented together with a detailed survey of the application of atmospheric pressure ionization mass spectrometry to TCDD analysis at the National Center for Toxicological Research/Food and Drug Administration.

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the hepatic storage of retinol in rats with different dietary supplies of vitamin A (retinol)

The effect of various dietary sources of vitamin A on liver storage of retinol has been investigated in Sprague-Dawley rats treated with single oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): 0,0.1,1.0, or 10 microgram.kg-1. Each dose group consisted of 3 subgroups, each comprising 10 rats which received a diet with normal, low or high retinol content. The animals were killed 4 weeks after TCDD administration. Analyses of retinol were performed by high pressure liquid chromatography and glucuronosyltransferase activities were determined spectrophotometrically. A dose-dependent decrease in hepatic storage of retinol was evident. The high retinol diet did not fully compensate for the reduction caused by the highest TCDD-dose. Glucuronosyltransferase activity increased directly in relation to the TCDD-dose but in inverse proportion to the retinol content of the diet.

Long-term hazards of polychlorinated dibenzodioxins and polychlorinated dibenzofurans

During January 10-11, 1978 in Lyon, France, a joint National Institute of Environmental Health Sciences/International Agency for Research on Cancer ad hoc Working Group considered and discussed the feasibility of coordinating epidemiological studies on the long-term hazards associated with the chlorinated dibenzo-p-dioxins and chlorinated dibenzofurans (PCDDs and and PCDFs). Nineteen invited scientists from eight countries presented introductory working papers summarizing the most up-to-date and relevant information available from their individual programs. This report represents the collective views and scientific opinions of the Working Group. The greater part of this document comprises epidemiological studies related to episodes of human exposures. The review begins with a brief section concerning possible routes of human exposure, an overview of the pertinent chemical characteristics, and the salient toxicological properties of the structurally similar PCDDs/PCDFs. The Working Group report ends with recommendations for future activities.