Mutagenicity of commercial hair dyes in Salmonella typhimurium TA98

Commercial permanent hair-dye formulations containing p-phenylenediamine, resorcinol and aminophenols were incubated with hydrogen peroxide and then tested for their ability to induce reverse mutations in Salmonella typhimurium TA98. Approximately half of the formulations (12 out of 25) gave positive results. The activity varied widely in degree and was observed only in the presence of an S-9 microsomal fraction from Aroclor-induced male rats. Five of the 12 positive formulations and one negative dye were administered topically to male rats; with one exception the urines of animals treated with the mutagenic hair dyes gave positive results in the presence of the S-9 mix.     

Toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the Golden Syrian hamster

Lethality, pathology, and various clinical chemical parameters were assessed in the hamster following a single ip or po treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). A single dose, 50-day LD₅₀ of greater than 3000 μg TCDD/kg, ip, was obtained for male and female hamsters while the LD₅₀ of orally administered TCDD was found to be 1157 μg/kg. Thus, the hamster appears to be the least sensitive mammalian species to the lethal effect of TCDD that has yet been investigated. TCDD treatment generally reduced the rate of body weight gain, with orally treated hamsters exhibiting the greatest reduction in rate. Thymic atrophy was the most consistent pathologic finding in TCDD treated hamsters. No histopathological changes were seen in the liver, spleen, kidneys, adrenals, or heart. Moderate to severe ileitis and peritonitis were found in many of the hamsters which died following oral treatment with TCDD. This lesion usually affects the distal ileum and consists of a marked hyperplasia of the mucosal epithelium with mild to severe hemorrhaging and necrosis. The intestinal lesion probably contributed in part to the greater lethality of TCDD in orally treated hamsters. A significant increase in serum alkaline phosphatase, bilirubin, protein, iron, cholesterol, and a decrease in serum albumin, chloride, urea nitrogen, and triglycerides were found in hamsters following both ip and po treatment with TCDD.     

Mutagenicity of a halocarbon refrigerant monochloro-difluoromethane (R-22) in Salmonella typhimurium

Commercially available refrigerant R-22 was found to produce a reproducable positive response in the Salmonella reverse mutation assay (Ames' test) modified for testing gases. The positive response was shown to be dependent neither on the presence of rat post-mitochondrial supernatant in the incubation medium nor on the presence of known mutagenic gases contaminating the commercial grade refrigerant.     

Transplacental induction of mixed-function oxygenases in extra-hepatic tissues by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Treatment of pregnant rats with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in a dose-dependent induction of a mixed-function oxidase system in fetal and maternal extra-hepatic tissues. At doses of 6 μmg/kg, aryl hydrocarbon hydroxylase (AHH) activity was increased 24-, 22- and 4-fold in fetal lung, kidney and skin, respectively, while maternal lung, kidney and adrenal AHH activity was increased 4-, 2- and 2-fold respectively. High-pressure liquid chromatographic (H.P.L.C.) analysis of benzo(a)pyrene (BP) metabolism after TCDD induction indicated that fetal lung, kidney and skin produced significant quantities of benzo(a)pyrene-7,8-dihydrodiol (BP-7,8-diol), benzo(a)pyrene-4,5-dihydrodiol (BP-4,5-diol) and 9- and 3-phenols of BP. The fetal liver produced benzo(a)pyrene-9,10-dihydrodiol (BP-9,10-diol), BP-4,5-diol, BP-7,8-diol and 9- and 3-phenols of BP. Maternal lung also produced BP-9,10-diol, while maternal adrenal gland yielded primarily the 9-phenol of BP. Epoxide hydratase activity was increased 2- to 3-fold in maternal lung, fetal lung and skin after TCDD pretreatment, but was not affected significantly in liver, kidney or placenta. Treatment of pregnant rats with TCDD increased the covalent binding of BP to DNA in preparations containing maternal liver, lung and placenta as well as fetal liver, lung and skin. Pretreatment with TCDD resulted in increased epoxide hydratase and AHH activities in extra-hepatic tissues but only AHH was increased in hepatic tissues, indicating that the inducing capabilities of TCDD differ from, but share some similarities with, both phenobarbital (PB) and 3-methylcholanthrene (MC). Thus, TCDD appears to provide an exceptionally potent and broad-spectrum transplacental induction of carcinogen-transforming enzymes in extra-hepatic tissues.     

Increased epidermal transglutaminase activity following 2,3,7,8-tetrachlorodibenzo-p-dioxin: In vivo and in vitro studies with mouse skin

In previous studies it has been shown that topical treatment of hairless mice with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) induces hyperproliferation and hyperkeratinization in the epidermis of hairless mice. The present investigation demonstrated that such TCDD-induced morphological changes in skin in vivo are accompanied by increased levels in activity of epidermal transglutaminase (ETG), the enzyme associated with terminal epidermal differentiation. Exposure of mouse epidermal cells in tissue culture to 10^?9m TCDD also resulted in a significant increase in ETG activity, despite the fact that morphologically these cultures (grown at 0.07 mm ionic calcium concentrations) exhibited no signs of terminal differentiation. Thus one mechanism of action of TCDD in inducing cutaneous changes appears to relate to the stimulation of increased ETG levels.     

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

Chronic oral administration of 1 μg. kg^?1. week^? 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 μg/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 μg. kg^?1. week^?. 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, δ-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.     

Three-generation reproduction study of rats given 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the diet

A three-generation reproduction study was conducted to evaluate the effects of chronic, low-level ingestion of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Sprague-Dawley rats were maintained continuously on diets providing dose levels of 0, 0.001, 0.01, or 0.1 μg TCDD/kg/day. No significant toxicity was noted in the f₀ rats of either sex during the 90 days of TCDD ingestion prior to mating. Significant decreases in fertility and neonatal survival were observed in the f₀ generation rats receiving 0.1 μg TCDD/kg/day; these effects precluded continuation of this high dose level in subsequent generations. At 0.01 μg TCDD/kg/day, fertility was significantly decreased in the f₁ and f₂ but not f₀ generations. Other indications of toxicity seen at 0.01 μg TCDD/kg/day included decreases in litter size at birth, gestation survival (proportion of pups born alive), and neonatal survival and growth. Among the rats receiving 0.001 μg TCDD/kg/day, no effect on fertility, litter size at birth, or postnatal body weight was observed in any generation. No consistent effect on neonatal survival was observed at 0.001 μg TCDD/kg/day. In summary, the reproductive capacity of rats ingesting TCDD was clearly affected at dose levels of 0.01 and 0.1 μg TCDD/kg/day, but not at 0.001 μg TCDD/kg/day, through three successive generations.     

Cytotoxicity and mitochondrial dysfunction of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in isolated rat hepatocytes

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmental contaminant that induces hepatic and extrahepatic oxidative stress and the mechanisms of TCDD-induced reactive oxygen species are not fully investigated. Moreover, the potential toxicity of TCDD in isolated rat hepatocytes is not fully explored. The aim of the current study was to explore the possible cytotoxic effect of TCDD on primary rat hepatocytes and to explore the impact of mitochondria in TCDD-induced toxicity. Hepatocytes were isolated from adult rat liver and incubated with 0, 5, 10 or 15 nM of TCDD for 24, 48 and 72 h. Cell viability, lactate dehydrogenase (LDH) leakage into media along with reactive oxygen species (ROS) generation and hydrogen peroxide (H₂O₂) production, mitochondrial membrane potential (Δψ_m), superoxide dismutase (SOD), catalse (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), total thiol contents, hepatic aryl hydrocarbon hydroxylase (AHH), and ethoxyresorufin O-deethylase (EROD) were performed in hepatocytes. In addition, superoxide anion generation, lipid peroxidation (LPO), mitochondrial protein carbonyl content and respiratory chain complexes II and IV were assayed in hepatocyte mitochondria. Cell viability was significantly decreased while LDH leakage into media was significantly increased in a dose and time related manner. ROS generation and H₂O₂ production along with EROD and AHH activities were significantly increased in hepatocytes in the same pattern. The antioxidant enzymes SOD, CAT, GPx and GR and the non-enzymatic protein thiols, in addition to Δψ_m were significantly decreased in hepatocytes in a concentration and time dependent pattern. On the other side, mitochondrial superoxide anion along with LPO and mitochondrial protein carbonyl content were significantly increased while the respiratory chain complexes II and IV activities were significantly decreased in hepatocyte mitochondria. This effect may lead to disruption in the functional integrity of hepatocytes and hepatocyte mitochondria. In conclusion, our data clearly show that TCDD induces hepatocyte toxicity and mitochondrial dysfunction by a mechanism involving generation of ROS. Mitochondria might be the primary source of (or at least contribute to) the oxidative stress response and resulting toxicological outcomes elicited by TCDD.     

Nature of the enhancement of hepatic uridine diphosphate glucuronyltransferase activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin in rats

After single low-level oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to rats, hepatic microsomal p-nitrophenol (PNP) glucuronyltransferase activity was elevated approximately 6-fold, whereas the hepatic glucuronyltransferase conjugating testosterone or estrone was unaffected. Solubilized and purified PNP glucuronyltransferase and steroid glucuronyltransferases from control and TCDD-treated rats exhibited the same relative activities (TCDD:control) as when the enzymes were bound to the endoplasmic reticulum. Elevation of PNP glucuronyltransferase was still evident 73 days after a single oral dose of 25 μg TCDD/kg. Female rats were more susceptible to TCDD actions on liver microsomal PNP glucuronyltransferase than males. The effects of TCDD treatment on PNP glucuronyltransferase appeared to be related to increased amounts of liver enzyme for the following reasons: (1) K_m values for PNP and UDPGA were unchanged by TCDD treatments; (2) the magnitude of the TCDD-induced increase of PNP glucuronyltransferase activity was the same whether enzyme activity was measured in the presence or absence of Mg²⁺ or Triton X-100; (3) TCDD, when added in in vitro, had no detectable effect on enzyme activity; (4) TCDD treatment of rats did not change total hepatic microsomal phospholipid or cholesterol contents: (5) pH optima were unaffected by TCDD treatment; (6) solubilization of enzyme was not accompanied by a change in the TCDD induction effect: and (7) actinomycin D appeared to block the initial phase of induction.     

The effect of total parenteral nutrition on the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the rat

The effects of total parenteral nutrition (TPN) upon the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rats has been studied. At doses of 50 or 100 μg/kg, TPN-fed, TCDD-treated rats demonstrated a weight gain similar to that of TPN-fed controls, but died at Days 13–17 following treatment. Gross examination of moribund animals revealed icterus, thymic atrophy, increased adipose tissue depots, and enlarged livers. The liver weights ranged from two to three times those from TPN-fed control animals. Histologically the livers were severely necrotic. Most cells which were not necrotic were markedly swollen and disorganized. Extensive vacuolization of hepatocytes and cystic areas containing cell debris were also prominent features. Whereas glycogen stores were depleted, the total content of water, lipid, protein, RNA, and DNA in the livers was increased. Alterations in cytochrome P-450-associated monooxygenase activities were also observed. Statistically significant increases in serum iron, bilirubin, alkaline phosphatase, serum glutamic-oxaloacetic transaminase and cholesterol were found in the TPN-fed, TCDD-treated animals. Serum protein, glucose, and triglycerides were significantly decreased except in a few severely moribund animals in which hyperglycemia was observed. The results in the TPN-fed, TCDD-treated rats were compared with TCDD-treated rats fed a chow diet ad libitum. At the same dose of TCDD, the liver damage in the TPN-fed, TCDD-treated rats was histologically more severe.     

Interpretation of studies on the developmental reproductive toxicology of 2,3,7,8-tetrachlorodibenzo-p-dioxin in male offspring

There have been several studies on the maternal administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and effects in the reproductive tract of male offspring, subsequent to risk assessments undertaken in 2001. This review compares the methodology and results to examine key methodological features, and consistency in reported outcomes. Maternal dosing at >0.8 μg TCDD/kg causes lethality and weight loss, and it is difficult to distinguish between direct and indirect effects of TCDD at these dose levels. Statistically significant effects of maternal doses of <1 μg TCDD/kg (i.e. the dose levels relevant for risk assessment) on prostate weight or epididymal sperm counts in offspring were reported in the minority of studies. The pharmacokinetics of TCDD differs considerably between acute and chronic dosing, and with dose level of TCDD. On the basis of body burden, TCDD had different potency at inducing adverse effects in the only comparison study between acute and chronic dosing. Understanding of the pharmacokinetics of TCDD and relationship to adverse effects in offspring is required. These analyses identify key features of TCDD developmental toxicity in male offspring, and identify data needs for future risk assessment.     

Antimutagenic effect of Phellinus rimosus (Berk) Pilat against chemical induced mutations of histidine dependent Salmonella typhimurium strains

Mutations are one of the important factors contributing to oncogenesis. Somatic mutations have been detected in oncogenes and tumor suppressor genes in various types of cancers. In vitro antimutagenic activity of ethyl acetate extract of macro fungus, Phellinus rimosus was evaluated by Ames’ mutagenicity assay. The effect was evaluated against the direct acting mutagens (sodium azide, N-methyl-N′-nitro-N-nitrosoguanidine, doxorubicin and 4-nitro-o-phenylenediamine) and mutagen needing activation (2-acetyl aminofluorine, and benzo[a]pyrene). The extract was significantly (p < 0.05) and dose dependently effective against direct acting mutagens and mutagen needing activation. Among the antimutagenic activity against directly acting mutagens, effect was found to be highest against doxorubicin-induced mutation. The antimutagenic effect of the extract against indirect acting mutagen in the presence of mammalian metabolic activation system was also found to be significant (p < 0.01). The background bacterial growth and number of revertant colonies in the extract alone treated plate with or with out metabolic activator was almost same as that of spontaneous revertants. This indicated the non-toxic nature of the extract. The effect was partially ascribed to the antioxidant activity. The results of the study suggest the possible antitumor mechanisms of P. rimosus.     

Role of the endocrine system in the action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the thymus

Several experiments were conducted to study the involvement of the adrenal and the pituitary gland in the acute toxic effects of TCDD.Adrenalectomized or hypophysectomized rats were treated with a single oral dose of 10 or 20 μg or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg body weight. The reduced growth rate, the hepatotoxic effects and thymic involution induced by TCDD were not prevented by the adrenalectomy.The pituitary gland did not appear to be involved in causing thymic involution. In fact, the thymic effects of TCDD intoxication were even somewhat increased in hypophysectomized rats. Treatment with growth hormone failed to prevent thymic involution or the influence of TCDD on the liver.     

Toxic interaction of specific polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin: Increased incidence of cleft palate in mice

The induction of cleft palate in $\text{C57BL}\text{6N}$ mice is an extremely reproducible and sensitive indicator of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity. This endpoint was used to look for potential interactions between two polychlorinated biphenyl (PCB) congeners and TCDD. Both 2,3,4,5,3′,4′-hexachlorobiphenyl (HCB) and 2,4,5,2′,4′,5′-HCB are of relatively low toxic potency, but their biological properties differ. Pregnant mice were treated with TCDD and either HCB on gestation Days 10 through 13, and the fetuses examined for the presence of cleft palate and renal abnormalities on gestation Day 18. At a dose of TCDD which caused a low level of cleft palate, moderate hydronephrosis was observed. No renal or palatal anomalies were detected after 2,4,5,2′,4′,5′-HCB treatment, and the combination of this isomer with TCDD had no effect on the incidence of TCDD-induced cleft palate. 2,3,4,5,3′,4′-HCB caused mild renal toxicity, but no cleft palate. However, treatment of pregnant mice with a combination of TCDD and 2,3,4,5,3′,4′-HCB resulted in a 10-fold increase in the incidence of cleft palate. Thus, the toxicity of compounds such as TCDD may be enhanced by compounds of relatively low acute toxicity such as selected PCBs. The widespread environmental occurrence of such combinations suggests a need for further evaluation of the mechanism of this interaction.     

Tissue distribution,excretion, and metabolism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the Golden Syrian hamster

The hamster has been reported to be the least sensitive mammalian species to the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The fate of a single dose of [³H]- or [¹⁴C]TCDD (650 μg/kg, ip or po) was assessed in male hamsters for up to 35 days following treatment. The greatest content (percentage dose/g tissue) of radioactivity was found in the liver, adipose tissue, and adrenals. The radioactivity in liver and adipose tissue was identified as unmetabolized TCDD. The rate of ³H or ¹⁴C elimination in urine and feces suggested a first-order process. Similar half-life of elimination ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) values of 12.0 ± 2.0 and 10.8 ± 2.4 days (mean ± SD) were obtianed with ip administered [³H]- and [¹⁴C]TCDD, respectively. With both [³H]- and [¹⁴C]TCDD, approximately 35 and 50% of the radioactivity was eliminated in urine and feces, respectively. The $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for po administered [³H]TCDD was 15.0 ± 2.5 days. High-pressure liquid chromatography of the urine and bile of animals receiving [¹⁴C]TCDD revealed one major and several minor radioactive peaks, none of which corresponded to [¹⁴C]TCDD. The apparent absence of TCDD metabolites in extracts of liver or adipose tissue indicates that the biotransformed products of TCDD are readily excreted in urine and bile. The enhanced rate of metabolism and excretion of TCDD in hamsters relative to other species may in part contribute to, but not totally explain its unusual resistance to TCDD toxicity.     

Immunosuppressive effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in strains of mice with different susceptibility to induction of aryl hydrocarbon hydroxylase

Mouse strains with different susceptibility to aryl hydrocarbon hydroxylase (AHH) induction and with different levels and/or affinity for a specific cytosolic binding protein (“receptor”) were used to investigate the immunosuppressive effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Humoral antibody production was strongly inhibited in $\text{C57B1}\text{6}$ and $\text{C3H}\text{HeN}$ mice (more susceptible strains) with very low, single doses of TCDD (1.2 μg/kg), while other strains ($\text{DBA}\text{2}$ and AKR) required higher doses (at least 6 μg/kg) to be partially suppressed. Longer exposure (8 weeks) did not increase the sensitivity of $\text{DBA}\text{2}$ mice. A good correlation between the degree of enzyme inducibility and immunosuppression was observed in studies with B6D2F1 mice and backcrosses. Similar results were obtained with 2,3,7,8-tetrachlorodibenzo-furan (TCDF), the most powerful competitor for TCDD “receptor” in vitro and in vivo. TCDD immnotoxic effects appeared to be associated with the presence of a specific cytosolic binding protein which mediates AHH induction.     

The influence of phenobarbital, 3-methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin on glutathione s-transferase activity of rat liver cytosol

Specific activities and apparent Michaelis-Menten kinetic parameters were determined for glutathione (GSH) S-transferase activity (E.C. 2.5.1.18) in rat liver cytosol, towards styrene oxide (STOX), 1,2-butylene oxide (BOX) and 1-chloro-2,4-dinitrobenzene (CDNB) as electrophilic substrates, before and after pretreatment with the drug-metabolizing enzyme inducers phenobarbital (PB), 3-methylcholanthrene (MC) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The measured GSH S-transferase activities appear to obey Michaelis-Menten kinetics. In non-induced animals the apparent K_m values of the transferase activities were equal for STOX vs GSH, but they differed by a factor of 2 for CDNB vs GSH and by a factor of 14 for BOX vs GSH. The apparent V_max values in each combination of GSH and electrophilic substrate were equal, but differed by one order of magnitude for the mutual substrate combinations. Pretreatment of the rats with MC resulted in enhancement of all measured activities expressed in terms of cytosol protein, while TCDD only enhanced the activities expressed as per gram body wt. PB enhanced both activities when STOX was employed as substrate, but when CDNB was used as the substrate, only the activity per gram body wt increased. All pretreatments increased the V_max values using CDNB as the substrate, while PB and MC had an enhancing effect using STOX; the V_max using BOX was enhanced after TCDD administration only. The K_m values using BOX as the substrate was lowered after MC pretreatment; TCDD pretreatment decreased the K_m using STOX, while it increased the K_m using CDNB. It is concluded that the GSH S-transferase system is inducible, but in contrast to the induction of the mixed function oxidase system, qualitative differences between the inducing effects of PB and MC were not observed. Use of TCDD as inducing agent, however. resulted in a different induction pattern, which may indicate that during induction with this agent different types of GSH S-transferases are involved.     

Porphyrogenic effect of chronic treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin in female rats. Dose-effect relationship following urinary excretion of porphyrins

The porphyrogenic effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was evaluated in female rats treated chronically for 45 weeks with 0.01, 0.10, and 1.00 μg/kg TCDD per week. The time course of the urinary porphyrin pattern was followed in order to determine the qualitative and quantitative composition in urine and to test the sensitivity of a parameter such as porphyrins in urine as an indication of exposure to TCDD. The results showed that the dose of 0.01 μg/kg/week resulted in significantly enhanced excretion of coproporphyrin from 6 months onward; with the dose of 0.10 μg/kg/week coproporphyrinuria was observed after 3 months and was associated at 10 months with a significant rise in uroporphyrin. The highest dose (1.00 μg/kg/week) caused enhanced excretion of coproporphyrin from 2 months onward. This effect was associated, at 6 months, with an increase in heptacarboxylic porphyrin and uroporphyrin excretion. A marked porphyric state was established in this group of animals from 8 months onward as indicated by massive enhancement of total urinary porphyrin excretion (about 70 times higher than the control group) with a large prevalence of porphyrins with a high number of carboxyl groups and reversal of the coproporphyrin/uroporphyrin ratio. Accumulation of porphyrins was also observed in liver, spleen, and kidneys of this group of animals. Terminal livers of rats treated with 0.01, 0.10, and 1.00 μg/kg/week contained 1050, 4740, and 30,700 ppt, respectively. Comparison of our data with the literature on the porphyrogenic effect of hexachlorobenzene indicated that TCDD can be considered 1400 times more potent.     

Elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxine in goat milk

2,3,7,8-tetrachlorodibenzo-p-dioxine (TCDD) 200 ng/day, was given orally to 7 goats for 2 months, followed by an elimination period of 1 month. Then a daily dose of 400 ng TCDD was given for 1 month to the same animals. Two animals were killed and the rest of the animals were observed for several months. The excretion of TCDD in milk was studied by glass capillary gas fragmentography, where the minimal detectable concentration was below 5 ppt. After the first feeding the concentration of TCDD in milk achieved a maximum of 20.8 ±6.6 ppt while a similar value 19.3 ±6.6 ppt was observed after the second feeding. After this period, the concentration of TCDD decreased slowly with values, after 18 weeks, of 4, 2±, 3 and 6 ppt. The concentration of TCDD in the liver in the two animals killed was 1039.0 and 898.0 ppt. There were no differences in clinical observations or blood and urine analyses when experimental animals were compared with controls.