Carcinogenic effects of acrylamide in Sencar and A/J mice.

Acrylamide structurally resembles vinyl carbamate, a proposed proximate carcinogenic form of ethyl carbamate. To test the hypothesis that acrylamide should possess carcinogenic properties, it was tested in the Salmonella-microsome assay for point mutation, as a skin tumor initiator in the Sencar mouse, and for its ability to induce lung adenomas in the A/J mouse. Acrylamide was found to be without activity as a mutagen in Salmonella strains TA 1535, TA 1537, TA 98, and TA 100 both in the presence and absence of rat liver microsomes using both the plate and liquid suspension assays. However, acrylamide was found to approximate ethyl carbamate in potency as a tumor initiator in the skin of the female Sencar mice. As with ethyl carbamate, acrylamide was more potent by systemic routes of administration relative to topical application. Acrylamide was also found to induce lung adenomas in male and female A/J mice using both the p.o. and i.p. routes of administration. Acrylamide was approximately one-seventh as potent as ethyl carbamate in the induction of lung adenomas. These data confirm the hypothesis that acrylamide possesses carcinogenic properties similar to ethyl carbamate.

Carcinogenic effects in A/J mice of particulate of a coal tar paint used in potable water systems.

Coal tar paints are among the products used as inside coatings for water pipes and storage tanks to retard corrosion in potable water supply systems. Four different formulations of these paints were tested in earlier work by this laboratory in the Ames mutagenesis and the mouse skin carcinogenesis bioassays. The paint most active in these assays were then tested in a particulate form in the lung adenoma assay with A/J mice. The paint was applied to clean glass plates, cured, collected and homogenized in 2% Emulphor. Doses of this coal tar suspension were administered by gavage at 1.0, 10.0 and 55.0 mg in 0.2 ml per mouse 3X weekly for 8 weeks. The total doses of coal tar paint were 24, 240, and 1320 mg/mouse. Benzo[a]pyrene (BaP), administered in a parallel schedule to a total dose of 6 mg/mouse, served as positive control. A negative control group received an equivalent volume of 2% Emulphor. Animals were killed at 9 months of age (8 months after first dose) and lung adenomas counted. A dose-related response, in the average number of lung tumors per mouse, was observed with the coal tar particulate. There were also squamous cell tumors of the forestomach in 42% of the mice receiving 55.0 mg coal tar paint per application.

Association of carcinoma yield with early papilloma development in SENCAR mice.

The responsiveness of SENCAR mouse skin to 20 different chemicals with known carcinogenic properties was assessed in initiation/promotion experiments. The purpose of these experiments was to evaluate the extent of false negative responses in mouse skin initiation/promotion protocols and to determine the extent to which early papilloma development can be used to predict the eventual development of malignant tumors. The chemicals were administered as initiators by four different routes: oral, intraperitoneal, subcutaneous, and topical. Following the initiating dose of carcinogen, the animals were subjected to topical applications of 1 microgram 12-O-tetradecanoylphorbol-13-acetate (TPA) 3 times per week for a period of 20 weeks. The yield of papillomas at 24 weeks was selected as a potential predictor of carcinoma yields at 52 weeks following the start of the promotion schedule. Positive responses were observed with only eight of the compounds tested. Where positive results were observed, there was some evidence that the response could depend both qualitatively and quantitatively on the route of administration. However, no route was clearly superior, i.e., different chemicals gave greater responses by different routes. Papilloma yield at 24 weeks following the start of the promotion schedule was clearly related to the development of carcinomas at 52 weeks. No simple linear relationship existed between papilloma yield and carcinoma development, since the number of malignant tumors per papilloma decreased with increasing papilloma yields. The relationship between papilloma and carcinoma yields appeared to be independent of the carcinogen used. These data indicate that there are some limitations in using mouse skin initiation/promotion experiments as the sole basis for identifying substances with carcinogenic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of the toxic interactions of disinfection by-products.

A large number and variety of compounds are formed in the process of chlorinating drinking water. The classes of compounds formed include trihalomethanes, haloacetic acids, haloacetonitriles, halophenols, and halopropanones. Many of the compounds have been shown to be toxic and are currently being further evaluated by the U.S. Environmental Protection Agency (EPA). One group of the halopropanones found in chlorinated drinking water is the dichloropropanones. The toxicological properties of this group have not been well characterized. In addition, a number of investigators have shown that ketones potentiate the hepatotoxicity of haloalkanes. We conducted a series of studies to explore both the toxicity of the dichloropropanones and their potential interactions with a well-characterized haloalkane, carbon tetrachloride. A variety of toxicological and biochemical endpoints were used to evaluate the toxicity of the dichloropropanones and their interaction with CCl4, including cytochrome P-450 concentration, reduced glutathione levels, pentane generation, serum enzyme activities, and histopathology. Administration of 1,1-dichloropropanone (DCP) resulted in elevated serum enzymes associated with periportal necrosis. Glutathione levels were reduced by the administration of 1,1-DCP; pentane generation was not increased. When 1,1-DCP was given prior to CCl4, the data were consistent with additivity. Administration of 1,3-DCP did not result in elevated serum enzymes, nor was there histopathologic evidence of necrosis. Glutathione levels and pentane generation in the 1,3-DCP-treated groups were the same as those of controls. Inhibition of the toxicologic effects of CCl4 in a dose-related manner was observed when 1,3-DCP was administered prior to CCl4.

Effect of trichloroethylene on the exploratory and locomotor activity of rats exposed during development.

Trichloroethylene (TCE) is a common contaminant of underground water supplies. To examine the effect of TCE on the developing central nervous system, rats were exposed to TCE throughout gestation until 21 days postpartum via their dams' drinking water. TCE concentrations of 312 mg/l, 625 mg/l and 1250 mg/l were tested. Exploratory behavior was higher in 60- and 90-day old male rats which were exposed to any level of TCE. The effect of TCE-exposure on locomotor activity (running wheel) was also examined in 60-day old males (625 and 1250 ppm exposure groups). Locomotor activity was significantly higher in rats exposed to 1250 ppm TCE. These data suggest that TCE has long-term effects on behaviour.

Subchronic toxicology of humic acid following chlorination in the rat.

A subchronic 90-d study was conducted with chlorinated and nonchlorinated humic acids using male Sprague-Dawley rats. Body weight gain, terminal organ and body weights, food and fluid consumption, clinical chemistries, hematological parameters, and urinalyses were determined for all animals. Selected organs were examined microscopically. Significant findings were confined to those rats given the high dose of chlorinated humic acid (1.0 g/l total organic carbon). The terminal body weight and average weekly body weight gain were significantly lower (p less than 0.05) in the high-dose group as compared to the distilled-water control group. This difference can be partially explained by a 16% lower daily fluid consumption. The average weight of the kidneys was significantly higher in the 1.0-g/l chlorinated humic group as compared to distilled-water controls. Hematological parameters and clinical chemistry values were normal in all treatment groups. The most significant finding was the increased incidence and severity of hematuria in the 1.0-g/l chlorinated humic acid group. A thorough histopathological examination of the entire urinary tract indicated that the most likely cause of the more severe incidences of hematuria in the rats was caused by crystalline deposits in the renal pelvis.

Comparative renal and hepatotoxicity of halomethanes: bromodichloromethane, bromoform, chloroform, dibromochloromethane and methylene chloride.

The renal and hepatotoxicities of five selected halomethanes, which are drinking water contaminants, were evaluated following a 14-day exposure. Bromodichloromethane, bromoform, chloroform, dibromochloromethane and methylene chloride were administered at three dose levels. Toxicity was evaluated by measuring changes in total body weight, uptake of p-aminohippurate into renal cortical slices, blood urea nitrogen, serum creatinine, and serum glutamate-pyruvate transaminase levels and by performing a histopathologic examination of liver and kidney tissues. Dose-related effects on the liver and kidney were detected with the uptake of p-aminohippurate into kidney slices and with the histopathologic evaluation of tissues. Treatment-related effects seen in the methylene chloride exposed mice were less pronounced as compared to the other halomethane treatment groups. In general, histopathological changes were the most sensitive indicators of both liver and kidney damage.

Effects of chlorine dioxide on thyroid function in neonatal rats.

Chlorine dioxide (ClO2), an alternative to chlorine for drinking water disinfection, has been implicated as a potential antithyroid agent (Bercz et al., 1982). Because antithyroid compounds are known to alter neurobehavioral development, the present study was designed to determine if perinatal exposure to ClO2 affects behavioral activity in rat pups. The activity cage system was designed to monitor the development of locomotor activity of a litter of pups between ages 14-21 d. Pups were exposed to ClO2 either directly, by gavaging 14 mg/kg . from age 5 to 20 d, or indirectly via their dams' drinking water in concentrations of 2, 20, or 100 mg/l from gestation to weaning (21 d postpartum). Although the activity of the indirectly exposed group was not different from controls, the gavaged group showed significantly depressed activity for d 18 and 19 postpartum. The T4 levels of the 21-d-old pups was significantly depressed in the 100-mg/l ClO2 group. The gavaged pups showed an even greater T4 depression, which correlates with their activity levels. These data support the hypothesis that ClO2 affects thyroid function and suggests that a slight depression in T4 can result in developmental delays.

Effect of gavage vehicle on hepatotoxicity of carbon tetrachloride in CD-1 mice: corn oil versus Tween-60 aqueous emulsion.

This investigation was conducted to evaluate the effect of gavage vehicles on altering the severity of the subchronic hepatotoxicity of carbon tetrachloride (CCl4). Male and female CD-1 mice were gavaged with 0, 1.2, 12, and 120 mg/kg CCl4 in either a corn oil or 1% Tween-60 vehicle once daily for 5 consecutive days per week for 90 days. The study revealed that the hepatotoxicity was greater in the mid- and high-dose groups of mice that had received CCl4 administered in corn oil. Increases in serum enzyme activities were detected in the mid-dose groups of mice that were gavaged with CCl4 in corn oil. The serum enzyme activities were significantly higher in the high-dose groups of animals in which CCl4 was administered in corn oil. Histopathological findings indicated that hepatocellular changes following the administration of CCl4 at the mid- and high-dose levels were more frequent and more severe when CCl4 was given in corn oil than when it was administered in Tween-60. The experimental findings indicate that the no-observed-adverse-effect level from CCl4 exposure was lowered by an order of magnitude (from 12 to 1.2 mg/kg) and that the hepatotoxicity of CCl4 was enhanced in the high-dose treatment groups when corn oil was employed as the gavage vehicle.

Evaluation of mutagenic and carcinogenic properties of brominated and chlorinated acetonitriles: by-products of chlorination.

The present study was undertaken to determine if chlorinated and brominated acetonitriles formed during the chlorination of drinking water possess mutagenic and/or carcinogenic properties. Chloroacetonitrile (CAN), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), bromochloroacetonitrile (BCAN), and dibromoacetonitrile (DBAN) were tested for their ability (1) to produce point mutations in the Salmonella/microsome assay, (2) to induce sister chromatid exchanges (SCE) in Chinese hamster ovary (CHO) cells in vitro, (3) to produce micronuclei in polychromatic erythrocytes in CD-1 mice, and (4) to act as tumor initiators in the skin of Sencar mice. DCAN and BCAN were found to be direct-acting mutagens in Salmonella. All five haloacetonitriles induced SCE in CHO cells in vitro. This activity paralleled the extent of chlorine substitution and was further enhanced in the dihaloacetonitrile series when bromine was substituted for chlorine. None of the haloacetonitriles showed evidence of activity in the mouse micronucleus assay. DBAN, BCAN, and CAN initiated tumors in the mouse skin with topical applications followed by a 20-week promotion schedule of 12-O tetradecanoylphorbol-13-acetate applications (p less than 0.02). These data indicate that the haloacetonitriles do display mutagenic and carcinogenic properties in some test systems and the hazard associated with their occurrence in drinking water and production within the gastrointestinal tract require further evaluation.

Subacute and subchronic toxicity of ethylene glycol administered in drinking water to Sprague-Dawley rats.

Subacute (10-day) and subchronic (90-day) toxicity studies of ethylene glycol (EG) were conducted in male and female Sprague-Dawley rats to provide the U.S. Environmental Protection Agency's (EPA) Office of Drinking Water with toxicity data for final preparation of a Health Advisory for the chemical. Ethylene glycol was administered in drinking water at concentrations of 0.5, 1.0, 2.0, and 4.0% for both sexes in the 10-day study. Based on a projected consumption rate of 100 ml/kg/day, the respective doses on a mg/kg/day basis would be 554, 1108, 2216, and 4432. These dose levels were also used in the 90-day study for females, but dose levels for the males in the 90-day study were 0.25, 0.5, 1.0, and 2.0% (227, 554, 1108, and 2216 mg/kg/day). At time of sacrifice necropsies were performed and tissues were prepared for histological evaluation. Blood samples were taken for hematology and clinical chemistry determinations. Body weights were measured weekly. Water and food consumption were determined three times weekly. No mortality occurred in the 10-day study. In the 90-day study 8/10 females and 2/10 males in the high dose group died prior to sacrifice. Body weights were suppressed in a dose response fashion for males and females. Hemoglobin, hematocrit, erythrocytes, and leukocytes were all significantly decreased in female rats receiving 4% EG for 10 days. The most significant histopathological findings, seen predominantly in males, were kidney lesions which included calcium oxalate crystals in tubules and pelvic epithelium; tubular dilation and degeneration; intratubular proteinaceous material; and inflammation in tubules and pelvic epithelium. At the same dose of ethylene glycol, males had more kidney lesions and much higher incidence and severity of lesions than the females.