Abstract  The Report on Carcinogens (RoC) is a scientific and public health document mandated by Congress in 1978. The RoC identifies and discusses substances, chemicals, mixtures, or exposure circumstances (collectively called substances) that may pose a cancer hazard to human health and to which persons in the United States are exposed. Nominations to the RoC go through a rigorous review process with multiple opportunities for public comment. The RoC is a compilation of substance profiles and each new edition replaces the previous one. Each substance profile in the RoC identifies a substance as known or reasonably anticipated to be a human carcinogen and provides information on (1) the scientific evidence that supports the listing (human epidemiological studies, cancer studies in experimental animals, and toxicokinetic, genotoxic, and mechanistic data), (2) the potential for human exposure, such as data on use, production, environmental occurrence, occupational exposure, and exposure to the general population, and (3) current Federal regulations to limit exposure.

Abstract  1. Pentachloroethane and tetrachloroethylene were major metabolites of hexachloroethane in sheep.2. Concentrations of hexachloroethane, pentachloroethane and tetrachloroethylene were determined by gas-liquid chromatography in blood, bile, faeces, urine and tissues after oral administration of hexachloroethane emulsions to sheep.3. Increased blood concentrations of sorbitol dehydrogenase, glutamate dehydrogenase, and ornithine carbamoyl transferase were found to follow oral administration of hexachloroethane or pentachloroethane.4. The rate of bromsulphthalein transfer from liver cells to bile was found to decrease after oral administration of hexachloroethane.

Abstract  A physiologically based pharmacokinetic model which describes the behavior of inhaled styrene in rats accurately predicts the behavior of in baled styrene in humans. The model consists of a series of mass-balance differential equations which quantify the time course of styrene concentration within four tissue groups representing (1) highly perfused organs, (2) moderately perfused tissues such as muscle. (3) slowly perfused fat tissue, and (4) organs with high capacity to metabolize styrene (principally liver). The pulmonary compartment of the model incorporates uptake of styrene controlled by ventilation and perfusion rates and the blood:air partition coefficient The metabolizing tissue group incorporates saturable Michaelis-Menten metabolism controlled by the biochemical constants Vmax and Km. With a single set of physiological and biochemical constants, the model adequately simulates styrene concentrations in blood and fat of rats exposed to 80, 200, 600, or 1200 ppm styrene (data from previously published studies). The simulated behavior of styrene is particularly sensitive to changes in the constants describing the fat tissue group, and to the maximum metabolic rate described by Vmax, The constants used to simulate the fate of stvrene in rats were scaled up to represent humans. Simulated styrene concentrations in blood and exhaled air of humans are in good agreement with previously published data. Model simulations show that styrene metabolism is saturated at inhaled concentrations above approximately 200 ppm in mice, rats, and humans. At inhaled concentrations below 200 ppm, the ratio of styrene concentration in blood to inhaled air is controlled by perfusion limited metabolism. At inhaled concentrations above 200 ppm. This ratio is controlled by the blood:air partition coefficient and is not linearly related to the ratio attained at lower (nonsaturating) exposure concentrations. These results show that physiologically based pharmacokinetic models provide a rational basis with which (1) to explain the relationship between blood concentration and air concentration of an inhaled chemical, and (2) to extrapolate this relationship from experimental animals to humans.

Abstract  The metabolism of carbon-14(C-14) labeled hexachloroethane(C2-C116) (67721) was studied in experimental rabbits. Three days after feeding the animals 0.5 g/kg C2-C116 containing C-14 in both carbon (7440440) atoms, 5 percent of the radioactivity appeared in the urine and 14-24 percent in the expired air. Analysis of labeled metabolites in the urine and the expired air by chromatography and isotope-dilution techniques yielded a number of chlorinated and other compounds, including the highly toxic urinary metabolite monochloroacetic-acid (79118).

Abstract  Studies were conducted to assess hazards to personnel exposed to hexachloroethane (HCE) in an industrial setting. Acute testing in laboratory animals indicated HCE was moderately toxic orally and could produce reversible eye irritation and mild skin irritation. Percutaneous absorption appeared to have no practical significance. The subchronic vapor inhalation toxicity was determined in rats, guinea pigs, Japanese quail and dogs in a 6-week test, monitoring pulmonary function changes, teratogenicity and operant behavioral changes in addition to clinical chemistry, hematology and histopathology. Concentrations of 260 ppm HCE vapor caused severe systemic effects in dogs, moderate effects in guinea pigs and rats and almost no responses in quail. No differences were found between exposed and control animals at 3 months after termination of these exposures. Minimal toxic effects were found following similar 6-week tests at levels of 48 ppm with no detectable changes at 15 ppm of HCE.

Abstract  The distribution and elimination of hexachloroethane (HCE) was evaluated in male and female Fischer 344 rats after oral ingestion of the test material. The rate at which HEC is cleared from tissue was evaluated in twenty male rats after receiving the test material for 57 days in the diet at a estimated concentration of 100mg/kg/day. Three to four animals were sacrificed 0, 3, 6, 13, 22 and 33 days after the last day of treatment. Fat, liver, kidney and whole blood were taken for analysis. The highest concentration of HCE was found in the fat (303 +/- 50 ug/g). The concentration of HCE in the fat was approximately three times the concentration found in the kidney, and over 100 times that found in the liver and blood. HEC cleared from the fat, liver, kidney and blood in an apparent first order manner, with half-lives between 2-3 days. A second experiment evaluated the concentration of HCE in the tissues of male and female rats (4/sex/group) after receiving the test material for 111 days in the diet at a estimated concentration of 3, 30 or 100mg/kg/day. The concentration of HCE in the male kidneys was higher than the female kidneys and the difference was most noticeable at the high dose level. As the dose rate increased, the relative increases in the levels of HCE was greater in the fat and less in the liver for both sexes.

Abstract  The Report on Carcinogens (RoC) is an informational scienti.c and public health document that identifies and discusses agents, substances, mixtures, or exposure circumstances (hereinafter referred to as substances) that may pose a hazard to human health by virtue of their carcinogenicity. For each listed substance, the RoC contains a substance profile which provides information on (1) the listing status, (2) cancer studies in humans and animals, (3) studies of genotoxicity (ability to damage genes) and biologic mechanisms, (4) the potential for human exposure to these substances, and (5) Federal regulations to limit exposures. The RoC does not present quantitative assessments of the risks of cancer associated with these substances. Thus, the listing of substances in the RoC only indicates a potential hazard and does not establish the exposure conditions that would pose cancer risks to individuals in their daily lives.

Abstract  Chlorinated compounds such as chlorinated ethylenes and ethanes are serious environmental pollutants. In the present study, we examined whether or not a recombinant strain of Saccharomyces cerevisiae that expresses rat liver cytochrome P450 1A2 (P450 1A2) wild-type and mutant proteins can efficiently catalyze oxidative and reductive dehalogenations of trichloroethylene, pentachloroethane, and hexachloroethane. Mutations at putative heme distal and protein surface sites of P450 1A2 greatly enhanced turnover values toward those substrates under both aerobic and anaerobic conditions. For example, a Thr319Ala mutation at the putative heme distal site enhanced the degradation rate of trichloroethylene and pentachloroethane by 2- and 2.7-fold, respectively, under aerobic conditions. The Thr319Ala mutation also strongly facilitated the reaction with hexachloroethane up to 13- and 4.5-fold under aerobic and anaerobic conditions, respectively. The Thr319Ala mutation increased dechlorinated over protonated product ratios by 3-fold as well when either pentachloroethane or hexachloroethane was used as a substrate. A Lys250Leu mutation on the putative protein surface site enhanced the dehalogenation rate of hexachloroethane up to 4.8-fold under anaerobic conditions. In contrast, a Glu318Ala mutation at the putative distal site markedly decreased the activities with trichloroethylene and pentachloroethane substrates under aerobic conditions. Conserved amino acids Thr319 and Glu318 at the heme distal site have been suggested to be important in the O2 activation during monooxidation reactions of P450s. However, the present study indicates that Thr319 is likely to be an inhibitor of dechlorination of trichloroethylene and penta- and hexachloroethanes. The roles of Thr319, Glu318, and Lys250 in the catalysis with chlorinated hydrocarbons are discussed in association with reaction mechanisms.

Abstract  Environmental chemicals are thought to adversely affect human reproductive function, however there are no studies that have explored the association between failed fertilization and exposure of both partners to environmental contaminants. Therefore, we collected blood and follicular fluid from the female partner and seminal plasma from the male partner of 21 couples attending an in vitro fertilization (IVF) program, in order to determine the extent of the existence of environmental chemicals in these fluids. Any relationship to the outcome of IVF was also considered. Sera and fluids were analysed for a variety of contaminants, including polychlorinated biphenyls, pesticides, cotinine, and the steroids progesterone and estradiol. Of the couples examined, 18 had fertilizations, three of whom became pregnant. There were no fertilizations in three other couples. The contaminants most frequently found in follicular fluid, more than 50% of the samples tested, were p,p'-DDE, mirex, hexachloroethane, 1,2,4-trichlorobenzene, PCB 49, PCB 153, and PCB 180. Cadmium was detected in eight of 21 (38.1%) samples of follicular fluid whereas cotinine was detected in 18 (85.7%). Residue levels of p,p'-DDE, endosulfan I, PCB 99, PCB 138, PCB 153, PCB 180 were quantified in more than 50% of the sera samples examined. Seminal plasma was relatively free of pollutants with mirex being the most frequently detected contaminant found in seven of 21 (33.3%) samples. Mirex could not be detected in the seminal plasma of the husbands whose partner's oocytes failed to fertilize whereas significant levels of mirex were found in the seminal plasma of all couples who had a pregnancy. Cadmium was also found in the follicular fluid of these pregnant subjects. No relationship was found between follicular fluid cotinine in pregnant and non-pregnant subjects. Where identical contaminants were found in both sera and follicular fluids, the levels were about twofold higher in serum and were positively correlated in both fluids. Fertilization was negatively correlated with serum and follicular fluid p,p'-DDE whereas pregnancy was positively correlated with follicular fluid PCB 49. These data reveal that more than 50% of the population of women attending a fertility program have had exposure to environmental chemicals sufficient to produce detectable concentrations in their serum and ovarian follicular fluid. Of the chemical contaminants detected in the serum and follicular fluid of these women, p,p'-DDE was the most frequently detected, had the highest residue levels, and was associated with failed fertilization.

Abstract  The rate and mechanisms of degradation of three hexachlorocyclohexane (HCH) isomers were studied with rat liver cytochrome P450, which is known to react with chlorinated compounds in the presence and absence of molecular oxygen. In addition, P450 is produced from HCH metabolites which are found aerobically and anaerobically during microbial biodegradation of this compound in a complex soil system. Conversion assays with P450 were carried out with alpha-, beta-, and gamma-HCH. Hexachloroethane served as a reference compound for bioconversion kinetics. Under anaerobic conditions, gamma-HCH was readily dechlorinated (r0 = 0.31 nmol/min.nmol cyt.P450) to tetrachlorocyclohexene and monochlorobenzene. gamma-HCH was also reductively dechlorinated, but at a much slower rate (r0 = 0.03 nmol/min.nmol cyt.P450). Both substrates followed Michaelis-Menten kinetics (gamma-HCH: Vmax = 1.87 nmol/min.mg and Km = 47 mumol/liter; gamma-HCH: Vmax = 0.24 nmol/min.mg and Km = 201 mumol/liter). Under aerobic conditions, bioconversions of gamma-HCH (r0 = 0.05 nmol/min.nmol cyt. P450) and alpha-HCH (r0 smaller than detection limit) were slower. beta-HCH proved to be recalcitrant under both aerobic and anaerobic conditions. The differences in bioconversion rates between the three HCH isomers could be related to the differences in spatial chlorine configuration of the three isomers. beta-HCH recalcitrance was explained by the absence of axial-orientated chlorines.

Abstract  1. Caffeine metabolism was studied in human liver microsomes from foetuses (n = 10), neonates (n = 10), infants (n = 9) and adults (n = 5). Caffeine and its metabolites, 1-3-7-trimethyluric acid, paraxanthine, theophylline and theobromine, were assayed by h.p.l.c. Methoxyresorufin-O-demethylase activity (MEROD) was determined and immunoquantifiable levels of CYP1A2 were measured. 2. The formation of the dimethylxanthines by N-3, N-7 or N-1-demethylation was significantly less in foetuses, neonates and infants than in adults, as shown previously in vivo. The formation of 1-3-7-trimethyluric acid (C-8-hydroxylation) was not significantly different between age groups. The production of total dimethylxanthines, paraxanthine and theophylline increased significantly with age within the neonate-infant group over at least the 0-300 day range (rs = 0.739, 0.667, 0.682, respectively). These data differ from those reported in vivo which suggested that N-3 and N-7-demethylations matured at about 120 days. The difference in maturational profiles of each metabolic pathway suggests that the reactions depend on different isoenzymes. The delay in the maturation of N-1 compared with N-3 and N-7-demethylation is in agreement with previous in vivo data. 3. In the neonate-infant group, only N-3-demethylation correlated with both MEROD activity (rs = 0.681; P < 0.05) and CYP1A2 microsomal concentration (rs = 0.454; P approximately 0.05), suggesting that, as in adults, this reaction depends on CYP1A2. 4. In the foetal samples, the production of total dimethylxanthines, paraxanthine and theobromine decreased significantly (rs = -0.879, -0.767, -0.708, respectively) with increasing gestational age.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract  The clinical and histopathological distinction between benign and malignant pheochromocytomas and paragangliomas is difficult, and reliable diagnostic markers are lacking. Here we have evaluated the prognostic value of human telomerase reverse transcriptase (hTERT) gene expression detected by reverse transcription PCR (RT-PCR); telomerase activity (TA) measured by TRAP (telomeric repeat amplification protocol) assay; immunohistochemical staining for Ki-67/MIB-1; and the mRNA expression of matrix metalloproteinase (MMP)-2 and EMMPRIN (extracellular matrix metalloproteinase inducer) analyzed by in situ hybridization in 32 primary pheochromocytomas or abdominal paragangliomas. hTERT was expressed in 7/11 malignant tumors (defined as presence of metastasis and/or extensive local invasion) as compared with in 2/21 benign tumors. All of the benign tumors showed <1% proliferative activity, as measured by Ki-67/MIB-1 staining. In all three patients with malignant tumors who developed metastases and/or invasive local recurrence during follow-up, the tumors were positive for either hTERT expression or Ki-67/MIB-1 immunoreactivity. TA was not a significant discriminator between benign and malignant tumors, and the value of EMMPRIN and MMP-2 as predictive markers was limited. In conclusion, the findings imply that the combined use of Ki-67/MIB-1 and hTERT, in addition to histopathology, provides a highly specific tool to identify benign pheochromocytoma and abdominal paraganglioma cases that are not at risk of developing recurrent or metastatic disease.

Abstract  CYP3A isoforms are responsible for the biotransformation of a wide variety of exogenous chemicals and endogenous steroids in human tissues. Two members of the CYP3A subfamily display developmentally regulated expression in the liver; CYP3A7 is expressed in the fetal liver, whereas CYP3A4 is the major cyrochrome P-450 isoform present in the adult liver. To gain insight into the descriptive ontogenesis of CYP3A isoforms during the neonatal period, we have developed several approaches to explore a neonatal liver bank. Although CYP3A4 and CYP3A7 are structurally closely related, they differ in their capacity to carry out monooxygenase reactions. We have cloned CYP3A4 and CYP3A7 and established stable transfectants in Ad293 cells to investigate their substrate specificities. The 16alpha hydroxylation of dehydroepiandrosterone is catalyzed by both proteins, but CYP3A7 has a higher affinity and maximal velocity than CYP3A4. Conversely, the conversion of testosterone into its 6beta derivative is essentially supported by CYP3A4. We used these two probes to determine the ontogenic evolution at the protein level; CYP3A7 was very active in the fetal liver and its activity was maximal during the first week following birth before to progressively decline and reached a very low level in adult livers. Conversely, the activity of CYP3A4 was extremely weak in the fetus and began to raise after birth to reach 30-40% of the adult activity after one month. CYP3A4 RNA accumulation displays a similar pattern of evolution; when probed with an oligonucleotide, its concentration increased rapidly after birth to reach a plateau as soon as the first week of age. These data supports the assumption that CYP3A4 expression is transcriptionally activated during the first week after birth and is accompanied by a simultaneous decrease of CYP3A7 expression, in such a way that the overall CYP3A protein content and the level of pentoxyresorufin dealkylase catalyzed by the two proteins remain nearly constant.

Abstract  The ATSDR toxicological profile succinctly characterizes the toxicologic and adverse health effects information for the hazardous substance described here. Each peer-reviewed profile identifies and reviews the key literature that describes a hazardous substance's toxicologic properties. Other pertinent literature is also presented, but is described in less detail than the key studies.

Abstract  The ATSDR toxicological profile succinctly characterizes the toxicologic and adverse health effects information for the hazardous substance described here. Each peer-reviewed profile identifies and reviews the key literature that describes a hazardous substance's toxicologic properties. Other pertinent literature is also presented, but is described in less detail than the key studies.

Abstract  A series of halogenated compounds was tested by oral intubation in 200 Osborne-Mendel rats and 200 B6C3F1 mice of both sexes. Carbon tetrachloride, used as a positive control, induced liver and adrenal tumors in mice and neoplastic nodules in the livers of rats. 1,2-Dibromoethane and 1,2-dibromo-3-chloropropane caused stomach tumors with many metastases in both rats and mice. Chloroform, known to cause hepatocellular carcinomas in mice, led in addition to kidney tumors in male rats. 1,2-Dichloroethane was much weaker than the analog, 1,2-dibromoethane, and induced only a few stomach tumors in rats. It increased liver and lung tumors in mice. Most of the compounds, namely, trichloroethylene, 1,1-dichloroethane, 1,1,2-trichloroethane, hexachloroethane, and tetrachloroethylene, increased hepatocellular carcinomas in mice but had little or no action in rats. Iodoform tended to increase thyroid tumors in male rats and hepatocellular carcinomas in male mice. The action of 3-chloropropene was questionable. No tumors could be attributed to 1,1,1-trichloroethane (methylchloroform).

Abstract  Sixteen halogenated aliphatic hydrocarbons were assayed for genotoxicity using the Ara mutagenicity assay with Salmonella typhimurium. Seven substances (1,2-dibromo-3-chloro-propane, 1,2-dibromoethane, 1,2-dichloroethane, vinyl bromide, hexachloro-1, 3-butadiene, iodoform and vinilydene chloride) were mutagenic at non-lethal doses. Comparatively, nine compounds (chloroform, carbon tetrachloride, 1,1,1-trichloroethane, 1,1,2-trichloroethane, tetrachloro-ethylene, trichloroethylene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrahloroethane and hexachloroethane) were non-mutagenic after being assayed both in the presence and absence of metabolic activation with a rat liver microsomal fraction (S9). All negative compounds (except hexachloro-ethane) gave a lethal response, which could be an indication that bacteria were adequately exposed. The concordance between mutagenicity in the Ara test and carcinogenicity in rodents for this group of halogenated hydrocarbons was (31%) significantly lower than the concordance (72%) previously found in the Ara test with respect to a wider range of chemical classes. This result is in agreement with data reported for other genotoxicity assays. The presence of non-genotoxic carcinogens versus genotoxic non-carcinogens is discussed as a possible explanation. Five positive compounds (1, 2-di-bromo-3-chloropropane, 1, 2-dibromoethane, 1, 2-dichloro-ethane, vinyl bromide and hexachloro-1, 3-butadiene) were analyzed for a quantitative relationship between carcinogenic potency in rats and the potency of response in the Ara mutagenicity test. This was possible because the Ara test, for volatile compounds (such as vinyl bromide), did not require the use of special vaporization techniques, which are difficult to evaluate quantitatively for mutagenic activity. A highly significant correlation was found between the mutagenic efficiencies of the five compounds in the Ara test and their carcinogenic potencies in rats. These results suggest that the Ara test might be capable of reflecting the relative potency of genotoxic animal carcinogens beyond the group of direct acting monofunctional alkylating compounds previously studied by our group.

Abstract  Investigation of covalent DNA binding in vivo provided evidence for whether a test substance can be activated to metabolites able to reach and react with DNA in an intact organism. For a comparison of DNA binding potencies of various compounds tested under different conditions, a normalization of the DNA lesion with respect to the dose is useful. A covalent binding index, CBI = (mumol chemical bound per mol DNA nucleotide)/(mmol chemical administered per kg body weight) can be determined for each compound. Whether covalent DNA binding results in tumor formation is dependent upon additional factors specific to the cell type. Thus far, all compounds which bind covalently to liver DNA in vivo have also proven to be carcinogenic in a long-term study, although the liver was not necessarily the target organ for tumor growth. With appropriate techniques, DNA binding can be determined in a dose range which may be many orders of magnitude below the dose levels required for significant tumor induction in a long-term bioassay. Rat liver DNA binding was proportional to the dose of aflatoxin B1 after oral administration of a dose between 100 micrograms/kg and 1 ng/kg. The lowest dose was in the range of general human daily exposures. Demonstration of a lack of liver DNA binding (CBI less than 0.1) in vivo for a carcinogenic, nonmutagenic compound is a strong indication for an indirect mechanism of carcinogenic action. Carcinogens of this class do not directly produce a change in gene structure or function but disturb a critical biochemical control mechanism, such as protection from oxygen radicals, control of cell division, etc. Ultimately, genetic changes are produced indirectly or accumulate from endogenous genotoxic agents. The question of why compounds which act via indirect mechanisms are more likely to exhibit a nonlinear range in the dose-response curve as opposed to the directly genotoxic agents or processes is discussed.