Abstract  Delayed (or incomplete) ossification of developing fetal bones and wavy ribs are some of the most common skeletal variations encountered in regulatory guideline developmental toxicity studies. Although they tend to be regarded as minor effects, they can be quite sensitive and consequently may influence the study lowest-observed-adverse-effect levels (LOAELs), and thus, impact classification, labeling, and risk assessment. In this study, we review the underlying mechanisms of these skeletal variations, evaluate different scenarios in which they have been observed, offer guidance for their interpretation, and comment on their use for risk assessment. Both minor delays in ossification and wavy ribs seem to be readily repairable via postnatal skeletal remodeling, are not mechanistically linked to malformation, and often are seen in the presence of maternal or fetal toxicity. As such, these minor variations would not generally be considered adverse in and of themselves but should be interpreted in the context of other maternal and fetal findings, information available on normal skeletogenesis patterns, mode of action of the test agent, and historical control incidence using a weight of evidence approach.

Abstract  TLV Recommendation Although no thresholds for safe worker exposure can be estimated from currently available reports of plant surveys, they indicate the serious consequences of heavy and prolonged exposure to biphenyl. For this reason, reliance should be placed on the responses of the most susceptible animal species, the mouse, which showed respiratory difficulties following repeated inhala¬tion exposure at 5 mg/m3, or about 1 ppm. Accordingly, a TWA-TLV of 0.2 ppm is recommended until evidence indicating the need for a change is forthcoming. At this time, no STEL is recommended until additional toxicological data and industrial hygiene experience become available to provide a better base for quantifying on a toxicological basis what the STEL should be. The reader is encouraged to review the section on Excursion Limits in the "Introduction to the Chemical Substances" of the current TLV/BEI Booklet for guidance and control of excursions above the TLV-TWA, even when the 8-hour TWA is within the recommended limits.

Abstract  Peroxisome proliferator-activated receptor alpha (PPARalpha) is responsible for peroxisome proliferator-induced pleiotropic responses, including the development of hepatocellular carcinoma in rodents. However, it remains to be determined whether activation of PPARalpha only in hepatocytes is sufficient to induce hepatocellular carcinomas. To address this issue, transgenic mice were generated that target constitutively activated PPARalpha specifically to hepatocytes. The transgenic mice exhibited various responses that mimic wild-type mice treated with peroxisome proliferators, including significantly decreased serum fatty acids and marked induction of PPARalpha target genes encoding fatty acid oxidation enzymes, suggesting that the transgene functions in the same manner as peroxisome proliferators to regulate fatty acid metabolism. However, the transgenic mice did not develop hepatocellular carcinomas, even though they exhibited peroxisome proliferation and hepatocyte proliferation, indicating that these events are not sufficient to induce liver cancer. In contrast to the transgenic mice, peroxisome proliferators activate proliferation of hepatic non-parenchymal cells (NPCs). Thus, activation of hepatic NPCs and/or associated molecular events is an important step in peroxisome proliferators-induced hepatocarcinogenesis.

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  In a continuing review of long-term toxicology and carcinogenesis studies in rats and mice, the National Toxicology Program (NTP) is confronted with many problems concerning the interpretation of tumor data. A frequently raised question is: "Should certain neoplasms be combined for overall assessment of rodent carcinogenesis data?" NTP policy is that certain neoplasms may be combined for statistical assessment of tumor data and that hyperplastic responses may be used as supportive evidence. The primary reason for combining neoplastic lesions is to gain more insight into the evidence of the carcinogenicity of a given chemical in that species of animal. This report gives the rationale, criteria, and guidelines used by the NTP for combining neoplasms for the evaluation of long-term rodent toxicology and carcinogenesis studies. The guidelines are based mainly on lesions occurring in the F344/N inbred rat and (C57BL/6 X C3H)F1 mouse and may or may not be appropriate for other strains or species. The concepts of combining neoplasms and sites should be viewed in terms of the study as a whole, since tumor formation is only one of many responses caused by chemicals in mammals. The resulting information becomes part of the "weight of the evidence" for estimating the potential hazard of a given chemical.

Abstract  Chronic toxicity of diphenyl and its ability to promote carcinogenesis by N-ethyl-Nhydroxyethylnitrosamine (EHEN) in the kidney, were studied in Wistar rats. In the study of chronic toxicity, diphenyl at doses of 0, 0.25. and 0.5% was given in the diet to Wistar rats of both sexes for 75 weeks. Diphenyl dose-dependently induced urolithiasis, and stones, accompanied by hematuria. were observed in the kidney, ureter, and urinary bladder as early as 16 weeks after the beginning of the experiment. At the dose of 0.5% of diphenyl, the incidence of stones in the kidney and urinary bladder was 46.2 and 15.4%, respectively, in females and 31.9 and 27.7%, respectively, in males. Kidney stones were black and composed of protein, but urinary bladder stones were yellowish-white and composed of ammonium magnesium phosphate. In the promotion experiment, EHEN, at a dose of 0.1%. was given in the diet for 2 weeks as the initiator of carcinogenesis, and then diphenyl, at doses of 0, 0.125, and 0.5% was supplied in the diet for 34 weeks, to male Wistar rats. Neither doses of diphenyl affected the incidences of dysplastic foci and renal cell tumors induced by EHEN in the kidney. However, 0.5% of diphenyl, in spite of inducing urolithiasis, significantly decreased the mean numbers of both dysplastic foci and renal cell tumors per cm2 of the kidney. These results indicated that diphenyl induced urolithiasis but exhibited rather inhibitory effect on the induction of kidney carcinogenesis by EHEN in rats.

Abstract  Carcinogenicity and Chronic Toxicity in Mice and Rats Administered Vinyl Acetate Monomer in Drinking Water: Yumi Umeda, et al. Japan Bioassay Research Center, Japan Industrial Safety and Health Association-Carcinogenicity and chronic toxicity of vinyl acetate monomer (VA) were examined in male and female Crj:BDF1 mice and F344/DuCrj Rats. Groups of 50 mice and 50 rats of each sex were orally administered VA in drinking water containing 0, 400, 2,000 or 10,000 ppm (g/g) VA for 104 wk. Squamous cell tumors were clearly evident in the upper digestive tract of treated mice and rats, and in the larynx of treated mice of both sexes. In mice, squamous cell carcinomas and papillomas were observed in the oral cavity, esophagus, forestomach and larynx of the 10,000 ppm group, together with basal cell hyperplasia, squamous cell hyperplasia and epithelial dysplasia. In rats, incidences of squamous cell carcinomas and papillomas were increased in the oral cavity of the 10,000 ppm group of both sexes, and an esophagus squamous cell carcinoma was observed in a 10,000 ppm female. Pre-neoplastic hyperplasias were also noted. Mapping of the neoplastic and pre-neoplastic lesions in the oral cavity of the 10,000 ppm group revealed that both the lesions occurred predominantly at Level V in mice and at Level VI in rats. A lower confidence limit of a benchmark dose (BMDL10) of 477 mg/kg/d was obtained from a dose-response relationship between combined incidence of squamous cell carcinomas and papillomas in the oral cavity of mice and rats and the estimated daily VA intakes per body weight, and compared with literature values.

Abstract  This study was designed to investigate the possible genotoxic and teratogenic actions of diphenyl (DP), diphenyl ether (DPE), and their eutectic mixture, in a comparative approach including different test systems. Two microbial systems and a metazoan model were used: (1) diploid D7 strain of Saccharomyces cerevisiae; (2) Salmonella typhimurium strains TA100, TA98, TA1535, TA1537, TA1538, TA1532, TA2636; and (3) sea urchins (Paracentrotus lividus and Sphearechinus granularis). Both compounds resulted in severe toxicity in all of test organisms at levels greater than or equal to 10(-5) M (approximately 2 ppm). DP caused genetic effects in yeast with and without activating system, while the two chemicals appeared to be ineffective in Salmonella up to toxic levels. The action of DP and DPE on sea urchins resulted in developmental defects and mitotic abnormalities, following exposure of embryos or by pretreatment of sperm or eggs. In this system DPE appeared to be more effective than DP by about one order of magnitude (minimal active concentrations: 10(-5) M vs 10(-4) M). The eutectic mixture, industrially used as a heat transfer medium, was tested in its virgin and used form, for genotoxicity and embryotoxicity. The latter appeared to be more effective than the virgin eutectic. This increase in the embryo- and genotoxicity of the used eutectic may be related to the appearance of newly formed compounds in the heat transfer process. These compounds have been separated by high-pressure liquid chromatography and detected by fluorimetry.

Abstract  The effects of dietary exposure to sodium L-ascorbate (Na-AsA), butylated hydroxyanisole (BHA), and diphenyl on the development of urinary bladder tumors in a mouse two-stage carcinogenesis model were examined. Male B6C3F1 mice received 0.05% N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in the drinking water for 4 weeks and were then treated with 5% Na-AsA, 1% BHA, or 1% diphenyl for 32 weeks. None of these chemicals enhanced the development of either preneoplastic or neoplastic lesions in the urinary bladder. Furthermore, DNA synthesis levels of urinary bladder epithelium in mice treated with each substance alone for 8 weeks were not elevated significantly, although Na-AsA was associated with a significant increase in the urinary pH value and Na+ concentration. The results indicate that Na-AsA, BHA, and diphenyl do not exert an enhancing influence on mouse bladder carcinogenesis, in clear contrast to the case in the rat.

Abstract  Carcinogenicity and chronic toxicity of biphenyl was examined in the male and female BDF1 mice fed a diet containing biphenyl at 667, 2,000 or 6,000 ppm for 2 years. There was no difference in survival rate between any biphenyl-containing diet-fed group of either sex and the respective control. Body weights of the males and females fed 6,000 ppm diet were significantly lower than the respective control. Incidences of hepatocellular carcinomas and hepatocellular adenomas in the females fed diets containing biphenyl were significantly increased in a dose-related manner, and exceeded a range of the historical control data in the Japan Bioassay Research Center. Incidences of basophilic cell foci in the liver were increased in the females fed 2,000 and 6,000 ppm diets. There was no increase in tumor or tumor-related lesion in the males fed diets containing biphenyl. Chronic toxicity of biphenyl was characterized by increased incidences of urothelial desquamation in the renal pelvis in males and females and mineralization in the inner stripe of renal outer medulla in females, as well as changes in serum levels of BUN, ALP and some electrolytes in males and females. In conclusion, the 2-year oral administration of biphenyl-containing diets induced pre-neoplastic and neoplastic lesions in the liver of females and non-neoplastic lesions in the kidney of males and females. Causative factors for the biphenyl-induced hepatocarcinogenicity were discussed in light of our published finding of peroxisome proliferation.

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 metabolic conversion of biphenyl to phenolic metabolites was studied in the rat. The metabolites were identified by mass spectrometry and quantified by gas chromatography following conversion to their trimethylsilyl (TMS) ethers. The main route of excretion was via the urine, and the major part (22.3 %) of the biphenyl metabolites was excreted in the first 24 hrs. The total urinary recovery 96 hrs after administration was 29.5 % of the dose and the metabolites detected were conjugates of mono–, di– and tri–hydroxy derivatives of biphenyl as well as the meta– and para–methyl ethers of the catecholic compounds. The two main urinary metabolites were 4–hydroxybiphenyl (7.7 %) and 4,4′–dihydroxybiphenyl (11.4 %). The experiments also showed that biphenyl has to be hydroxylated and then conjugated before it appears in the rat bile. Thus, 5.2% of the dose was found in the 24 hrs bile as conjugates, mainly of 4–hydroxy–, 4,4′–dihydroxy– and 3,4,4′–trihydroxy–biphenyl. Faecal excretion of phenolic biphenyl derivatives was found to be of minor importance, but 4.7 % of the dose was detected during the first 24 hrs after dosing. The following previously undetected metabolites of biphenyl were found: 3,4′–dihydroxy–, 3,4,4′–trihydroxy–, 3,4′–dihydroxy–4–methoxy– and 4,4′–dihydroxy–3–methoxy–biphenyl.

Abstract  A comparative study of the effects of biphenyl and Kanechlor-400 (KC-400) on the respiratory and energy linked activities of rat liver mitochondria was made, and some differences in effects caused by the chlorination of biphenyl were clarified. The inhibition of state 3 respiration with succinate by biphenyl was less than that observed with alpha-ketoglutarate/malate. By contrast, KC-400 exhibited the opposite trend; state 3 respiration with succinate was more sensitive to inhibition than that observed with alpha-ketoglutarate/malate. Thus the inhibition of state 3 respiration with NAD+-linked substrate was decreased, whereas the inhibition of state 3 respiration with succinate was increased by the chlorination of aromatic rings. Biphenyl also instantaneously stimulated state 4 respiration. The extent of stimulation with succinate by biphenyl was larger than with alpha-ketoglutarate-malate. On the other hand, there was about a 1-2 minute lag period before stimulation of state 4 respiration by KC-400 became obvious. Furthermore, state 4 respiration in the presence of alpha-ketoglutarate/malate was more intensely stimulated by KC-400 than by succinate. Biphenyl and KC-400 dissipated the membrane potential across the mitochondrial membranes. The dissipation of membrane potential by biphenyl was instantaneous whereas that caused by KC-400 was preceded by a lag period (1-2 min). Biphenyl and KC-400 altered the permeability properties of mitochondrial membranes as evidenced by the release of endogenous K+. The release of K+ due to biphenyl was instantaneous but KC-400 induced K+-release was preceded by a lag period (1-2 min). Thus membrane perturbation by biphenyl was faster than that induced by KC-400. Therefore, it is clear that the chlorination of aromatic rings delays the perturbation in the state of membrane lipids.

Abstract  Groups of rats were fed biphenyl at various dose levels in a semisynthetic diet and in a commercial chow. The effect levels for induction of polycystic kidney lesions were established by means of urinalysis, organ weight changes, light and electron microscopy, and enzyme histochemistry. The no-effect level, was less than 50 mg/kg bw./day and 300 mg/kg bw./day, when feeding the semisynthetic diet and the commercial chow respectively. This difference in effect level due to the diet is an indication that the diet is of great influence on the results of toxicological experiments.

Abstract  The short-term test has been considered to be the most practical method for the rapid screening of carcinogens. Under a project of the Ministry of Health and Welfare, 182 compounds were examined by short-term tests over six years (1973-1978), using Salmonella typhimurium TAlOO and TA98 (mutations), Bacillus subtilis (rec assay), hamster lung fibroblast cells (chromosome aberrations, sister-3 23-324 KAWACHI ET AL. chromatid exchanges), human embryo fibroblasts (chromosome aberrations, sister chromatid exchanges), bone-marrow cells (chromosome aberrations in vivo) and silk worms (mutations). Compounds were selected by a research group organized by the Ministry and included carcinogens, noncarcinogens and compounds not previously tested for carcinogenicity. They were selected from the following categories: (1) structural analogues of known carcinogens; (2) food additives widely used in Japan; (3) drugs administered for long periods to patients; and (4) industrial intermediates with a high annual production. The object of the programme is not to screen possible carcinogens in our environment but to improve the tests and to investigate the validity of newly developed rapid screening techniques. Data from short- term assays for carcinogenicity are shown in Table 1: all data c ited as 'Salmonella test' are from the Salmonella/microsome assay system. Rec assays performed during 1973 did not include metabolic activation; however, from 1975-1978, a metabolic activation system was included. The chromosome aberration test in hamster fibroblasts in vitro included a metabolic ac tivation system between 1977 and 1978: among 65 compounds tested in this way, chlorpyrifos, cochineal and Eulan U-33 were the only ones t hat required metabolic activation. The chromosomal aberration test in human fibroblasts and the sister chromatid exchange assay in human fibroblasts and hamster fibroblasts were not activated metabolically. The validation of the short- term assays is summarized in Table 2. In the Salmonella/microsome test, of 49 compounds that showed mutagenic activity, 33 (67%) were found to be carcinogenic. On the other hand, of 66 nonmutagenic compounds, 48 (73%) were noncarcinogenic. Detailed data from the Salmonella/microsome tests are given in Table 3. Results from a combination of the Salmonella/microsome test and the chromosome aberration test (in vitro, in vivo) showed better validity than other combinations of short- term assays.

Abstract  The toxic action of environmental chemicals on reproduction and the toxiclike effects of ovarian hormones have been shown by numerous investigators. Some toxic effects of environmental chemicals on reproduction are through their action on hormonal secretion. Such effects on the endocrine system could provide additional approaches to investigations of toxicity of compounds. A better understanding of interactions of environmental chemicals with the endocrine system is needed. Therefore, it becomes important for a greater exchange of information and more interaction between toxicologists and endocrinologists.

Abstract  Practically all lipid-soluble xenobiotics enter the conceptus through placental transfer. Many xenobiotics, including a number of clinically used drugs, are known to cause unwanted effects in the embryo or fetus, including in utero death, initiation of birth defects, and production of functional abnormalities. It is well established that numerous xenobiotics are not necessarily toxic as such, but are enzymatically transformed in the body to reactive and toxic intermediates. The cytochrome P450 (CYP) enzymes are known to catalyze oxidative metabolism of a vast number of compounds, including many proteratogens, procarcinogens, and promutagens. About 20 xenobiotic-metabolizing CYP forms are known to exist in humans. Most of these forms are most abundant in the liver, but examples of exclusively extrahepatic CYP forms also exist. Unlike rodents, the liver of the human fetus and even embryo possesses relatively well-developed metabolism of xenobiotics. There is experimental evidence for the presence of CYP1A1, CYP1B1, CYP2C8, CYP2D6, CYP2E1, CYP3A4, CYP3A5, and CYP3A7 in the fetal liver after the embryonic phase (after 8 to 9 weeks of gestation). Significant xenobiotic metabolism occurs also during organogenesis (before 8 weeks of gestation). Also, some fetal extrahepatic tissues, most notably the adrenal, contain substantial levels of CYP enzymes. The full-term human placenta is devoid of many CYP activities present in liver. Placental CYP1A1 is highly inducible by maternal cigarette smoking. Other forms present in full-term placenta include CYP4B1 and CYP19 (steroid aromatase), which also contribute to the oxidation of some xenobiotics. At earlier stages of pregnancy, the placenta may express a wider array of CYP genes, including CYP2C, CYP2D6, and CYP3A7. Due to the small size of the fetus and low abundance of CYPs in placenta, the contribution of feto-placental metabolism to overall gestational pharmacokinetics of drugs is probably minor. In contrast, several toxic outcomes have been ascribed to altered metabolic patterns in the feto-placental unit, including a putative association between reduced placental oxidative capacity and birth defects. Examples of human teratogens that are substrates for CYP enzymes include thalidomide, phenytoin, ethanol, and several hormonal agents. Recent studies have improved our understanding of the expression and regulation of individual CYP genes in the fetus and placenta, and the stage is set for applying this knowledge with more precision to the role of xenobiotic metabolism in abnormal intrauterine development in humans.

Abstract  The Toxic Substances Control Act (TSCA) became law on October 11, 1976. The Act authorized EPA to secure information on all new and existing chemical substances, as well as to control any of the substances that were determined to cause unreasonable risk to public health or the environment. The current PCB regulations were published pursuant to this act. Current PCB regulations can be found in the Code of Federal Regulations (CFR) at 40 CFR 761.