Acute toxicity in guinea pigs and rabbits of soot from a polychlorinated biphenyl-containing transformer fire

A fire involving a polychlorinated biphenyl (PCB)-containing transformer extensively contaminated the State Office Building in Binghamton, New York, with a sootlike material containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), 2,3,7,8-tetrachlorodibenzofuran, and high concentrations of numerous other polychlorinated dibenzodioxins, dibenzofurans, and PCBs. The oral LD50s of the soot and of its benzene extract, each administered to female guinea pigs in 0.75% aqueous methyl cellulose, were 410 mg of soot/kg and 327 mg of soot equivalent/kg, respectively. Serum triglycerides were elevated in males at 100 and 500 mg/kg and in females at 500 mg/kg. Alkaline phosphatase was lowered in females at 500 mg/kg. Histopathology revealed dose-related pancreatic duct hyperplasia and salivary gland duct metaplasia in males. Body weight loss was observed in both sexes at 500 mg/kg. Thymus weight decreased in both sexes at 100 and 500 mg/kg, and kidney weights decreased in males at these doses. Dermal application of soot to rabbits for 24 hr caused no overt toxicity, although hepatic centrilobular hypertrophy was observed in both sexes. Similar application of soot extract caused a local serous inflammation in addition to the hepatic centrilobular hypertrophy. The oral LD50 for 2,3,7,8-TCDD in female guinea pigs was 19 μg/kg in aqueous methyl cellulose and 2.5 μg/kg in corn oil. We concluded that the soot matrix alters the dermal but not the oral toxicity of its components, that the toxic effects were consistent with those reported after exposure to dibenzodioxins and dibenzofurans, and the aqueous vehicle markedly diminished the acute toxicity of 2,3,7,8-TCDD relative to that in corn oil vehicle.     

Subchronic Oral Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in the Guinea Pig: Comparisons with a PCB-Containing Transformer Fluid Pyrolysate

Subchronic Oral Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxinin the Guinea Pig: Comparisons with a PCB-Containing TransformerFluid Pyrolysate. DECAPRIO, A. P., MCMARTIN, D. N., O'KEEFE,P. W., REJ, R., SILKWORTH, J. B., AND KAMINSKY, L. S. (1986).Fundam. Appl. Taxicol. 6,454–463. In contrast to the well-characterizedacute toxicity of the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin(2,3,7,8-TCDD) in the guinea pig, the effects of prolonged poexposure in this species are unknown. The present report describesthe results of administration to guinea pigs of 2,3,7,8-TCDDin the feed at levels of 0,2, 10, 76, or 430 ppt for up to 90days. Additional aims were to examine recovery following prolonged2,3,7,8-TCDD exposure in the guinea pig and to generate datato facilitate comparison of the previously reported toxicityof a transformer fluid pyrolysate with that of pure 2,3,7,8-TCDD.Animals receiving 430 pot 2,3,7,8-TCDD exhibited body weightloss, thymic atrophy, liver enlargement, and 60% mortality byDay 46 (males) and by Day 60 (females), when surviving animalsin this group were sacrificed. Total 2,3,7,8-TCDD consumptionwas approximately 1.3 and 1.9 µg/kg, respectively. Animalsreceiving 76 ppt 2,3,7,8-TCDD for 90 days (total 0.44 µg/kg)exhibited a decreased rate of body weight gain and increasedrelative (to body) liver weights. Male animals also displayeda reduction in relative thymus weights and elevated serum triglycerides,while females exhibited hepatocellular cytoplasmic inclusionbodies and lowered serum alanine arninotransferase activities.Toxic effects were generally similar to those observed afteracute 2,3,7,8-TCDD administration. No dose-related alterationswere seen in animals receiving either 10 ppt (total 0.06 µg/kg)or 2 ppt (total 0.01 µg/kg) for 90 days, establishinga no-observed-effect level of approximately 0.65 ng 2,3,7,8-TCDD/kg/day.In the recovery study, groups of guinea pigs were administered430 ppt 2,3,7,8-TCDD for 11,21, or 35 days and then allowedto recover for an additional 79,69, or 55 days, respectively.Treatment-related mortality in each group was 0, 10, and 70%,respectively, by Day 90. An effective LD5O of 0.8 µg 2,3,7,8-TCDD/kgfor prolonged exposure was calculated on the basis of theseresults, a value lower than those previously reported from thislaboratory for acute exposure. The results also suggested apossible lowering of the body weight "set point" following 2,3,7,8-TCDD exposure. Comparison of the present findings with thosepreviously reported for a trans former fluid pyrolysate containinga mixture of polychlorinated aromatic species indicated botha greater variety of toxic effects and flatter dose-responserelationships for the pyrolysate in the guinea pig.     

The development of an aquatic bivalve model: evaluating the toxic effects on gametogenesis following 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) exposure in the eastern oyster (Crassostrea virginica)

The objective of this study is to develop a gametogenesis protocol to serve as a model for evaluating the toxic effects of chemicals on oogenesis and spermatogenesis in the eastern oyster (Crassostrea virginica). The compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) was selected as a "proof of principle" toxicant to examine developmental toxicity in this invertebrate system. The studies were designed to: (1) test the model using 2,3,7,8-TCDD and (2) to use histopathological evaluations to characterize the effects on oocyte and sperm development during stages of gametogenesis. 2,3,7,8-TCDD at 10 pg/g resulted in significant histopathological gonadal lesions by day 14 of gametogenesis in both female and male oysters. These lesions resulted in complete inhibition of gonadogenesis. Studies also showed that a total body dose of 2 and 10 pg/g 2,3,7,8-TCDD caused adverse responses resulting in abnormal gametogenesis in female and male oysters, respectively, such as: (1) incomplete oocyte division, (2) inhibition of oocyte growth and maturation, (3) unsynchronized sperm development, and (4) inhibition of spermatogenesis. The eastern oyster is one of the most responsive invertebrate models tested to date for reproductive effects of chemicals. Therefore, the eastern oyster can be used as a sensitive toxicological model for examining the effects of dioxin-like compounds and other xenobiotics on gametogenesis. The reported studies show that environmentally relevant concentrations of 2,3,7,8-TCDD (2-10 pg/g) have a significant adverse effect on oyster gametogenesis.     

Effects of commercial chlorophenolate, 2,3,7,8-TCDD,and pure phenoxyacetic acids on hepatic peroxisome proliferation,xenobiotic metabolism and sister chromatid exchange in the rat

The induction of hepatic peroxisome proliferation and drug metabolizing enzymes and of sister chromatid exchange (SCE) in lymphocytes was studied in male Han/Wistar rats after exposing them for 2 weeks to a commercial chlorophenolate formulation (Ky-5) (100mg/kg/ day), to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD; 0.05–5 g/kg/wk) and to the pure phenoxyacetic acids, 2,4-dichlorophenoxyacetic acid (2,4-D; 100 mg/kg/day) and 2-chloro-4-methylphenoxyacetic acid (MCPA; 100 mg/kg/day). The chlorophenolate formulation and pure 2,4-D and MCPA caused significant increases in the number of peroxisomes in liver cells, although the average size of peroxisomes was not affected, whereas the effect of even the highest dose of 2,3,7,8-TCDD remained small. This finding indicates that dioxin impurities do not account for the peroxisome proliferation induced by chlorophenolate. The relative weight of the liver increased significantly in rats treated with the chlorophenolate formulation and with 2,3,7,8-TCDD (5.0 and 0.5 g/kg). The pattern of induction of xenobiotic metabolizing enzymes showed some differences between chlorophenolate treatment and 2,3,7,8-TCDD treatment. Furthermore, the effects of pure phenoxyacetic acids were different from that seen with chlorophenolate and 2,3,7,8-TCDD. The highest dose of 2,3,7,8-TCDD increased the frequency of SCE in circulating lymphocytes slightly, but significantly.     

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on hepatic and uterine estrogen receptor levels in rats

Administration of a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 20 or 80 micrograms/kg) resulted in significantly decreased hepatic and uterine estrogen receptor (ER) levels in 25-day-old female Long-Evans rats. By contrast, estradiol (5 and 15 micrograms/kg) administration increased hepatic and uterine ER levels, while a combination of 2,3,7,8-TCDD plus estradiol resulted in uterine and hepatic ER levels which were similar or lower than those observed after treatment with only 2,3,7,8-TCDD. In addition, 2,3,7,8-TCDD significantly decreased the effects of estradiol on uterine wet weight increase. Competitive binding studies showed that estradiol did not bind to the aryl hydrocarbon (Ah) receptor and that 2,3,7,8-TCDD did not bind to the ER. The effects of structure on the activity of polychlorinated dibenzo-p-dioxin congeners on their activity to down-regulate hepatic and uterine ER levels were determined by using 2,3,7,8-TCDD, 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 1,3,7,8-TCDD, and 1,2,4,7,8-PeCDD. Both 2,3,7,8-TCDD and 1,2,3,7,8-PeCDD exhibit high affinities for the Ah receptor and at dose levels of 80 micrograms/kg the hepatic ER levels were decreased 42 and 41%, respectively, and uterine ER levels were decreased 53 and 49%, respectively. 1,3,7,8-TCDD and 1,2,4,7,8-PeCDD bind less avidly to the Ah receptor and at dose levels of 400 micrograms/kg these compounds decreased hepatic ER levels 36 and 40%, respectively, and uterine ER levels 21 and 24%, respectively. These results support a role for the Ah receptor in the down-regulation of uterine and hepatic ER levels in the female rat by 2,3,7,8-TCDD and this effect may be associated with the decrease in spontaneous mammary and uterine tumors observed in female rats treated with 2,3,7,8-TCDD.     

Aroclor 1254 as a 2,3,7,8-tetrachlorodibenzo-p-dioxin antagonist: effects on enzyme induction and immunotoxicity

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Aroclor 1254 induced the cytochrome P-450 dependent monooxygenases, aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) in rat hepatoma H-4-II E cells and C57BL/6J mice. It has been proposed that both Aroclor 1254 and 2,3,7,8-TCDD induce these enzymes via a common mechanism which features initial binding to the aryl hydrocarbon (Ah) cytosolic receptor protein. The major difference between these compounds was the relative potency (i.e. 2,3,7,8-TCDD much greater than Aroclor 1254). Cotreatment of rat hepatoma H-4-II E cells or C57BL/6J mice with a dose of 2,3,7,8-TCDD which submaximally induces AHH and EROD and a dose of Aroclor 1254 which exhibited little or no induction activity resulted in significant antagonism of the induction effects of 2,3,7,8-TCDD. For example, cotreatment of C57BL/6J mice with 2,3,7,8-TCDD (15 nmol/kg) and Aroclor 1254 (25, 75 and 150 mumol/kg) resulted in up to 23% antagonism of AHH induction by 2,3,7,8-TCDD. Moreover, cotreatment with a higher dose of the 2,3,7,8-TCDD agonist (30 or 50 nmol/kg) partially reversed some of the antagonism by Aroclor 1254. In vivo antagonism was observed only at Aroclor 1254/2,3,7,8-TCDD molar ratios of 1667:1, 5000:1 and 10,000:1. Administration of 2,3,7,8-TCDD (3.72 nmol/kg) to C57BL/6J mice resulted in a 76% decrease in the splenic plaque forming cell response to sheep red blood cells. This T-cell mediated immunotoxic effect of 2,3,7,8-TCDD segregates with the Ah locus. In contrast, administration of 5, 15, 75 and 150 mumol/kg of Aroclor 1254 resulted in impairment of the immune response only at the highest dose level. However, cotreatment of mice with 2,3,7,8-TCDD (3.72 nmol/kg) and Aroclor 1254 (5, 15 or 75 mumol/kg) resulted in no significant decrease in the plaque forming cell response and complete protection from the immunotoxicity of 2,3,7,8-TCDD. Cotreatment of the mice with Aroclor 1254 (75 mumol/kg) and a higher dose of the 2,3,7,8-TCDD agonist resulted in partial reversal of the protective effects of Aroclor 1254. The in vitro and in vivo data suggest that within specific antagonist/agonist dose ratios, Aroclor 1254 can antagonize at least 2 Ah receptor-mediated effects of 2,3,7,8-TCDD, namely AHH induction and immunotoxicity.     

Aroclor 1254 as an antagonist of the teratogenicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 20 micrograms/kg) to pregnant C57BL/6J mice (on day 10) resulted in 62% fetuses with cleft palate per litter without any observable maternal toxicity. In contrast, Aroclor 1254 administered at a dose of 750 mumol/kg was not teratogenic. Cotreatment of the pregnant mice with both Aroclor 1254 (244 mg/kg) and 2,3,7,8-TCDD (20 micrograms/kg) resulted in an 8.2% incidence of cleft palate per litter. In contrast, Aroclor 1254 did not afford any protection from the teratogenicity of dexamethasone in C57BL/6J mice. Previous studies have shown that Aroclor 1254 can act as a partial antagonist of the microsomal enzyme induction and immunotoxic effects of 2,3,7,8-TCDD in C57BL/6J mice and this paper demonstrates that the commercial polychlorinated biphenyl mixture also antagonizes 2,3,7,8-TCDD-mediated teratogenicity in this strain of mice.     

Induction of terminal differentiation in cultured human keratinocytes by polychlorinated aromatic hydrocarbons as measured by cell size analysis.

Polychlorinated aromatic hydrocarbons modulate the proliferation and differentiation of human epidermal cells in vivo and in culture. One of the earliest events in the process of terminal differentiation is the increase in cell size. In this report the usefulness of morphometric cell size analysis as a quantifiable marker for chemical-induced differentiation was examined. Concentration-related increases in cell size distribution were induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and 2,3,4,7,8-pentachlorodibenzofuran in normal human keratinocytes and cells from an SV40-transformed keratinocyte cell line (SVK14) whereas the analog 1,2,3,4-tetrachlorodibenzo-p-dioxin did not affect the cell size distribution up to a concentration of 100 nM. The minimal effective concentrations of five 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins/dibenzofurans and a coplanar polychlorbiphenyl necessary to induce an increase in cell size distribution were determined in SVK14 cells. It was found that the potency of these compounds relative to that of 2,3,7,8-TCDD correlated well with the toxicity equivalency factors observed in other test systems. This indicates that the keratinocyte cell assay is a useful method for establishing the relative potency of various "dioxins" and their mixtures.     

Immunosuppressive activities of polychlorinated dibenzofuran congeners: quantitative structure-activity relationships and interactive effects

The dose-response immunosuppressive effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8- and 1,2,3,7,9-pentachlorodibenzofuran (PeCDF), 2,3,7,8- and 1,3,6,8-tetrachlorodibenzofuran (TCDF) on the splenic plaque-forming cell (PFC) response to sheep red blood cells were determined in C57BL/6 mice. The ED50 values for immunosuppression were 2.4, 3.0, 14.0, 710, and 35,700 nmol/kg for 2,3,7,8-TCDD, 2,3,4,7,8-PeCDF, 2,3,7,8-TCDF, 1,2,3,7,9-PeCDF, and 1,3,6,8-TCDF, respectively, and the results confirmed that lateral chlorine substitutions were important structural determinants for the toxicity of the polychlorinated dibenzofuran congeners. Interaction of both 2,3,7,8-TCDD and 2,3,4,7,8-PeCDF with subimmunotoxic doses of 1,3,6,8-TCDF resulted in significant antagonism of the immunotoxic effects of both 2,3,7,8-TCDD and 2,3,4,7,8-PeCDF. Previous studies have also demonstrated that 1,3,6,8-TCDF also antagonizes the induction of aryl hydrocarbon hydroxylase by 2,3,7,8-TCDD and analysis of competitive receptor binding studies suggests that 1,3,6,8-TCDF acts as a competitive partial antagonist of the action of 2,3,7,8-TCDD. The antagonism of 2,3,7,8-TCDD immunosuppression was found to be dependent on the timing of administration of 1,3,6,8-TCDF. Using a protocol in which 2,3,7,8-TCDD is administered 5 days prior to the antigen and 9 days prior to assessing the splenic PFC response, it was possible to partially antagonize the immunosuppressive effects of 2,3,7,8-TCDD by administering the antagonist up to 5 days after the initial dose of the toxin. Administration of 1,3,6,8-TCDF after the antigen does not afford any significant protection from the effects of 2,3,7,8-TCDD and these results are consistent with the hypothesis that 2,3,7,8-TCDD modulates some early event in B-cell differentiation. However, these results do not exclude a role for 2,3,7,8-TCDD in modulating other cellular processes associated with the PFC response.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin as an antiestrogen: effect on rat uterine peroxidase activity

Treatment of 25-day-old female Sprague-Dawley rats with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) significantly lowered constitutive uterine peroxidase activity and decreased uterine wet weights in a dose-response fashion. In cotreatment studies with 17 beta-estradiol, 2,3,7,8-TCDD antagonized the increase in uterine peroxidase activity and uterine wet weights, and these effects persisted for up to 156 hr. In the rat uterus, the antiestrogenic affects of two potent Ah receptor agonists, 2,3,7,8-TCDD and 2,3,4,7,8-pentachlorodibenzofuran, were comparable at a dose of 80 micrograms/kg, whereas the weaker Ah receptor agonist, 1,2,4,7,8-pentachlorodibenzo-p-dioxin, was relatively inactive at this dose. These results show that 2,3,7,8-TCDD antagonizes a well-characterized estrogen-induced response (uterine peroxidase activity), and the structure-activity data suggest that the Ah receptor is involved in mediating the antiestrogenic responses in target cells/organs.     

The toxicological significance of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds in human adipose tissue

Reports of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs) in human tissues were reviewed to assess their toxicological significance. The predominance of 2,3,7,8-chlorinated congeners in human tissues and in the food chain, but not in other environmental matrices, suggests that the food chain is the major source of human residues. Exposures to unique distributions of congeners can result in recognizable patterns of excess 2,3,7,8-chlorinated PCDDs/PCDFs in humans. Current levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) in the general population can be accounted for by an average level of 133 or 27 ppq (parts per quadrillion) in food based on an estimated half-life in humans of 1 or 5 yr, respectively. 2,3,7,8-TCDD is more persistent in humans than in rodents or lagomorphs, resulting in higher body burdens in humans at comparable levels in the diet. Taken alone, this toxicokinetic difference would increase risks estimated for humans from toxicity in laboratory animals. However, humans appear to be less susceptible due to the following: less food is ingested per body mass, more 2,3,7,8-TCDD is sequestered in adipose tissue and away from target organs, and tissue susceptibility appears to be lower than in the most sensitive rodents and lagomorphs. The body burden of 2,3,7,8-TCDD in a Seveso woman receiving an apparently nontoxic dose was approximately 180 times the average body burden of 2,3,7,8-TCDD equivalents in the general population of industralized societies. The body burden of prisoners who were exposed dermally to a suspension of 2,3,7,8-TCDD and who developed severe chloracne was estimated to be as much as 38 times that of the Seveso woman. These comparisons suggest a considerable margin of safety for the general population.     

Comparative activities of 2,3,7,8-tetrachlorodibenzo-p-dioxin and progesterone as antiestrogens in the female rat uterus

The comparative antiestrogenic effects of progesterone and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on cytosolic and nuclear estrogen (ERc and ERn, respectively) and progesterone (PRc and PRn, respectively) receptor levels were determined in female Long Evans rats. Estradiol treatment typically increases ER and PR levels in target cells or tissues and these proteins have been proposed as markers of estrogen action. 2,3,7,8-TCDD causes a dose-dependent decrease in uterine ERc, ERn, PRc, and PRn levels which persist up to 7 days. Progesterone treatment caused significant decreases in uterine ERc, ERn, and PRn levels; however, after 7 days, the effects of the hormone on receptor levels were diminished. The effects of 2,3,7,8-TCDD and progesterone on hepatic ER and PR levels were comparable to those observed in the uterus. Treatment of the rats with estradiol (5 micrograms/kg), estradiol (5 micrograms/kg) plus progesterone (1 mg/animal), or 2,3,7,8-TCDD (80 micrograms/kg) showed that both progesterone and 2,3,7,8-TCDD significantly antagonized the estradiol-mediated increases in uterine (and hepatic) ERc, ERn, PRc, and PRn levels and for 2,3,7,8-TCDD the decreased receptor levels persisted for up to 7 days. In vitro studies with freshly isolated uterine strips demonstrated that both 2,3,7,8-TCDD and progesterone antagonized the estradiol-mediated increases in ER and PR levels. Previous studies suggest that the antiestrogenic activity of progesterone is due, in part, to the induction of proteins which are involved in decreasing ERn levels in target cells. Moreover in the uterine strip assay procedure, it was previously shown and reproduced in this study that the decrease in uterine ERn by progesterone was inhibited by both protein and RNA synthesis inhibitors over a 4-hr incubation period. In contrast, the 2,3,7,8-TCDD-mediated decrease in uterine ERn was inhibited only by actinomycin D and not by cycloheximide or puromycin. These in vitro studies thus confirm that both progesterone and 2,3,7,8-TCDD exhibit comparable antiestrogenic effects in vivo and in vitro; however, the results suggest that these effects are expressed through different mechanisms.     

Comparative dermal absorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin and three polychlorinated dibenzofurans

Polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) are toxic environmental contaminants which have the potential to accumulate in human tissues. In order to examine the potential for systemic exposure following dermal exposure, the absorption, distribution, and elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 1,2,3,7,8-pentachlorodibenzofuran (1PeCDF), and 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF) were evaluated in male F344 rats. TCDD (0.00015, 0.001, 0.01, 0.1, 0.5, and 1.0 mumol/kg) and the three PCDFs (0.1, 0.5, and 1.0 mumol/kg) were applied to a preclipped region on the back of the rat and covered with a perforated cap. The rats were held in individual metabolism cages for 3 days. In animals administered 0.1 mumol/kg, the absorption of TCDF was greater than that of 4PeCDF, 1PeCDF, and TCDD. Relative absorption (percentage of administered dose) declined with increasing dose while the absolute absorption (microgram/kg) increased nonlinearly with dose. Absorption of TCDF at 0.1 mumol/kg was 48% of the administered dose which was significantly greater than that of the other compounds. At this dose, absorption of 4PeCDF was greater than that of TCDD. Absorption at the higher doses was similar for all four compounds. Maximum relative absorption of TCDD (approximately 40% of the administered dose) was obtained at 0.001 and 0.00015 mumol/kg. Major tissue depots for these four chemicals included liver, adipose, skin, and muscle tissue; however, the liver:fat ratio for 4PeCDF was approximately fourfold higher than that for the other three compounds. When normalized to 100% of dose absorbed, the distribution of 4PeCDF-derived radioactivity in liver and adipose tissue was similar to that previously observed after oral and iv administration. In animals administered 0.1 mumol TCDF or 1PeCDF/kg, 56 and 32% of the respective absorbed dose was excreted as polar metabolites within 3 days. Very little of the absorbed dose of either TCDD (approximately 10%) or 4PeCDF (approximately 2%) was eliminated. Results indicate that the dermal absorption of these compounds is incomplete and that systemic toxicity following acute dermal exposure to levels found in the environment is unlikely.     

Comparative developmental toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the hamster, rat and guinea pig

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent environmental contaminant capable of causing a wide variety of adverse health effects including teratogenesis and altered development. The objective of this study was to compare the developmental toxicity of TCDD in the hamster, rat and guinea pig, which in mature animals exhibit a relatively low, medium and high sensitivity to TCDD, respectively. A single oral dose of TCDD was administered to pregnant rats (0, 1.5, 3.0, 6.0 or 18.0microg/kg) on gestation day 10, pregnant hamsters (0, 1.5, 3.0, 6.0 or 18.0microg/kg) on gestation day 9 and pregnant guinea pigs (0, 0.15 or 1.5microg/kg) on gestation day 14 with fetal analysis on gestation day 20, 15 and 56, respectively. The developmental toxicity of TCDD in the three species included increased fetal mortality, alterations to fetal body weight, body length, organ weight and significant changes to the fetal white blood cell differential counts. Additionally, teratogenic responses were observed in the hamster and rat consisting of cleft palate, kidney congestion, hydronephrosis and intestinal hemorrhaging. Furthermore, the results from this study demonstrate that despite the up to 5000-fold interspecies variability to the acute lethal potency of TCDD observed in mature guinea pigs, rats and hamsters, the developing fetus is uniquely vulnerable to gestational TCDD exposure and displays approximately a 10-fold variability in fetal lethal potency in these species. Together, these results will assist efforts to reduce the uncertainty in the risk assessment for TCDD in sensitive populations, such as the developing embryo and fetus.     

Toxicity assessment of thiodiglycol

Sulfur mustard (HD) undergoes hydrolysis to form various products such as thiodiglycol (TG) in biological and environmental systems. TG is a precursor in the production of HD and it is also considered as a "Schedule 2" compound (dual-use chemicals with low to moderate commercial use and high-risk precursors). Several toxicological studies on TG were conducted to assess environmental and health effects. The oral LD(50) values were >5000 mg/kg in rats. It was a mild skin and moderate ocular irritant and was not a skin sensitizer in animals. It was not mutagenic in Ames Salmonella, Escherichia coli, mouse lymphoma, and in vivo mouse micronucleus assays, but it induced chromosomal aberrations in Chinese hamster ovarian (CHO) cells. A 90-day oral subchronic toxicity study with neat TG at doses of 0, 50, 500, and 5000 mg/kg/day (5 days/week) in Sprague-Dawley rats results show that there are no treatment-related changes in food consumption, hematology, and clinical chemistry in rats of either sex. The body weights of both sexes were significantly lower than controls at 5000 mg/kg/day. Significant changes were also noted in both sexes in absolute weights of kidneys, kidney to body weight ratios, and kidney to brain weight ratios, in the high-dose group. The no-observed-adverse-effect level (NOAEL) for oral toxicity was 500 mg/kg/day. The developmental toxicity conducted at 0, 430, 1290, and 3870 mg/kg by oral gavage showed maternal toxicity in dams receiving 3870 mg/kg. TG was not a developmental toxicant. The NOAEL for the developmental toxicity in rats was 1290 mg/kg. The provisional oral reference dose (RfD) of 0.4 mg/kg/day was calculated for health risk assessments. The fate of TG in the environment and soil showed biological formation of thiodiglycalic acid with formation of an intermediate ((2-hydroxyethyl)thio)acetic acid. It was slowly biodegraded under anaerobic conditions. It was not toxic to bluegill sunfish at 1000 mg/L and its metabolism and environmental and biochemical effects are summarized.     

The Effects of Love Canal Soil Extracts on Maternal Health and Fetal Development in Rats

The Effects of Love Canal Soil Extracts on Maternal Health andFetal Development in Rats. SILKWORTH, J.B., TUMASONIS, C, BRIGGS,R.G., NARANG, A.S., NARANG, R.S., REJ, R., STEIN, V., MCMARTIN,D.N., AND KAMINSKY, L.S. (1986). Fundam. Appl. Toxicol. 7,471-485.The effects of a solvent extract of the surface soil of theLove Canal chemical dump site, Niagara Falls, New York, andof a natural extract, or leachate, which is drained from thecanal for treatment, on the maternal health and fetal developmentwere determined in rats. The solvent extract, which was contaminatedwith 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) at 170ppb and numerous other chlorinated organic compounds with theprimary identified components being the isomers of benzenehexachloride(BHC), was dissolved in corn oil and administered by gavageto pregnant rats at 0,25,75, or 150 mg crude extract/kg/dayon Days 6-15 of gestation. A 67% mortality was observed at thehighest dose. The rats were sacrificed on Day 20. Dose-relatedincreases in relative liver weight accompanied by hepatocytehypertrophy were observed at all dose levels. Fetal birthweightwas decreased at 75 and 150 mg extract/kg/day. No major treatment-relatedsoft tissue or skeletal malformations, except for delayed ossification,were observed. Based on literature values for BHC, all of theobserved toxicity could be accounted for by the BHC contaminantsof the extract. The crude organic phase of the leachate wasadministered to pregnant rats at 0, 10, 100, or 250 mg/kg/dayas described above. Maternal weight gain decreased at 100 and250 mg/kg/day, accompanied by 5 and 14% maternal mortality,and 1 and 3 dead fetuses, respectively. Early resorptions andthe percentage of dead implants increased whereas fetal birthweightswere decreased at 250 mg/kg/day. No major treatment-relatedsoft tissue or skeletal malformations, except for delayed ossification,were observed. The primary components of the complex leachateby mass were tetrachloroethanes; however, 2,3,7,8-TCDD, whichwas present at 3 ppm, probably accounted for all the observedtoxicity.     

A review of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced changes in immunocompetence: 1991 update

2,3,7,8-tetrachlorodibenzo-p-dioxin, more popularly called dioxin or TCDD and referred to in this review as 2,3,7,8-TCDD, is considered the prototype of the polychlorinated dibenzo-p-dioxins (PCDD). The PCDD are true contaminants and are formed primarily as byproducts in the manufacture of materials requiring the use of chlorinated phenols and during the combustion of chlorinated chemical products. From an environmental perspective, the PCDD have been most closely associated with the use of a number of phenolic herbicides, including Agent Orange, which is a 1:1 mixture of the butyl esters of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). 2,3,7,8-TCDD and related PCDD are not produced commercially except in small amounts for research purposes and to date, have no known human benefit. 2,3,7,8-TCDD has been demonstrated to be the most potent and the most biologically active congener among the halogenated aromatic hydrocarbons (HAH), which include polychlorinated and polybrominated biphenyls (PCB and PBB, respectively) and the polychlorinated dibenzofurans (PCDF), in addition to the PCDD. An updated review on the effects of 2,3,7,8-TCDD on immunocompetence is timely from a number of perspectives. First, effects on immune function have been demonstrated to be among the earliest and most sensitive indicators of 2,3,7,8-TCDD-induced toxicity. Second, recent evidence indicates that exposure to 2,3,7,8-TCDD causes changes in innate immunity in addition to the changes in acquired immunity (i.e., which include effects on both cell-mediated and humoral immunity) previously shown to be associated with this chemical. Third, effects on immune function are almost universally observed among the animal species in which it has been evaluated, including some non-human primates. Fourth, effects of 2,3,7,8-TCDD on specific indicators of immune function have been correlated with changes in host resistance capabilities, which are often considered to be more holistic indicators of immunocompetence. Fifth, there are several reports which describe possible effects of 2,3,7,8-TCDD and related compounds (i.e., primarily PBB and PCB) on immune function in humans. It is important to emphasize at the onset that these studies have triggered much controversy, both political and scientific. However, it is equally important to speculate that at least part of the controversy associated with man's sensitivity to the immunological effects of 2,3,7,8-TCDD may be that the most appropriate approaches have heretofore not been applied. This possibility is discussed further in this review.(ABSTRACT TRUNCATED AT 400 WORDS)     

The biologic and toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in chickens

The administration of 2,3,7,8-TCDD to 2-week-old White Leghorn cockerels produced a dose-dependent induction of hepatic microsomal ethoxyresorufin O-deethylase (EROD) and benzo[alpha]pyrene (B[alpha]P) hydroxylase activities with induction EC50 values of 778 and 302 ng/kg, respectively. In addition, 2,3,7,8-TCDD also induced 4-dimethylaminoantipyrine (DMAP) N-demethylase (EC50 = 561 ng/kg), this result contrasting with studies reported for other animal species in which 2,3,7,8-TCDD either does not induce or inhibits this cytochrome P-450 dependent monooxygenase enzyme activity. However, the reduced cytochrome P-450:CO binding difference spectral absorption maxima for the 2,3,7,8-TCDD induced microsomes was observed at 448 nm which was similar to that reported for most animals which have been investigated. Electrophoresis of control and 2,3,7,8-TCDD induced microsomal proteins using SDS polyacrylamide slab gels showed intensification of 3 protein staining bands at Mr 53 000, 56 000 and 58 000. Incubation of the 2,3,7,8-TCDD-induced microsomes with SKF-525A and alpha-naphthoflavone showed that both compounds inhibited DMAP N-demethylase, EROD and AHH and that alpha-naphthoflavone was the more potent inhibitor of all 3 microsomal monooxygenases. 2,3,7,8-TCDD treatment caused significant involution of the Bursa of Fabricius when administered at a dose level of 10 micrograms/kg for 3 days and this result confirmed the extreme sensitivity of the immature White Leghorn cockerel to the biologic and toxic effects elicited by 2,3,7,8-TCDD. However, in contrast to other sensitive species, no high affinity cytosolic receptor protein for [3H]2,3,7,8-TCDD could be detected in the liver of chick embryos or 2-week-old birds.     

Polychlorinated dibenzo-p-dioxins: quantitative in vitro and in vivo structure-activity relationships

There were marked effects of structure on the activities of 14 polychlorinated dibenzo-p-dioxins (PCDDs) as competitive ligands for the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) receptor and as inducers of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) in rat hepatoma H-4-II E cells in culture. 2,3,7,8-TCDD was the most active compound in both assays and several PCDD congeners which were fully substituted in the lateral 2, 3, 7 and 8 positions but also contained additional chlorosubstituents in non-lateral 1, 4, 6 and 9 positions were less active. It was also evident that there was a decrease in in vitro binding and induction activities with decreasing lateral chlorine substitution. Although comparable structure-activity relationships (SARs) for the PCDDs were observed for the induction and receptor binding assays, there was not a linear or rank order correlation between the 2 sets of data. Several in vivo biologic and toxic activities of 2,3,7-trichloro-, 2,3,7,8- and 1,3,7,8-tetrachloro-, 1,2,4,7,8- and 1,2,3,7,8-pentachloro- and 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin were determined in a dose-response fashion in immature male Wistar rats. The ED50 values for hepatic microsomal AHH and EROD induction, body weight loss and thymic atrophy were obtained. There was an excellent linear correlation between the -log EC50 values for AHH or EROD induction in cell culture and the -log ED50 values for enzyme induction, body weight loss and thymic atrophy in the rat. The in vitro enzyme induction data could be used to quantitatively estimate the toxicity of the PCDD congeners in the rat: this latter correlation has previously been observed for a series of polychlorinated dibenzofurans.     

Modeling and assaying dioxin-like biological effects for both dioxin-like and certain non-dioxin-like compounds.

13C NMR data have been correlated to Toxic Equivalency Factors (TEFs) of the 29 PCDDs, PCDFs, or PCBs for which non-zero TEFs have been defined. Such correlations are called quantitative spectrometric data-activity relationship (QSDAR) models. An improved QSDAR model predicted TEFs of 0.037 and 0.004, respectively, for 1,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 1,2,3,4,7-pentachlorodibenzo-p-dioxin (PeCDD), both among the 390 congeners for which zero value TEFs are assumed. A QSDAR model of Relative Potency (REP) values estimated the corresponding values as 0.115 and 0.020. Results from both models indicated that these two congeners may exhibit significant dioxin-like toxicity. If other such congeners have non-zero toxicity, TEF-based risk assessments of some dioxin-, furan-, or PCB-contaminated sites or foods may underestimate toxicity. Both models were extensively cross-validated and the TEF model was externally validated. We confirmed the predictions by an independent in vitro method, a luciferase gene expression assay based on mouse liver cells that found REPs of 0.027 and 0.013, respectively, for 1,3,7,8-TCDD and 1,2,3,4,7-PeCDD. The QSDAR-estimated and gene-expression assayed values agreed. The models were used to predict activity for an applicability domain including 108 non-2,3,7,8 dioxin, furan, or PCB congeners and 2,3,7,8-tetrachlorophenothiazine, a dioxin analog proposed as a drug candidate. This study showed that QSDAR prediction followed by a relatively inexpensive in vitro assay could be used to nominate a few candidates among hundreds for further investigation. It suggested that in silico and in vitro nomination protocols may facilitate practical risk assessment when chemical family members exhibit different degrees of toxicity operating via a common mechanism.