Carbon tetrachloride appears as a clear colorless liquid with a characteristic odor. Denser than water (13.2 lb / gal) and insoluble in water. Noncombustible. May cause illness by inhalation, skin absorption and/or ingestion. Used as a solvent, in the manufacture of other chemicals, as an agricultural fumigant, and for many other uses.
Fasted male rats were given six doses of (14)CCl4 ranging from non-hepatotoxic (0.1 mmole/kg) to severely hepatotoxic (26 mmoles/kg). Time-course and pharmacokinetics of CCl4, (14)CO2 and CHCl3 elimination by exhalation were monitored by measuring amounts recovered in breath during discrete 15-min intervals for 8-12 hr. Amounts of (14)C-labeled metabolite recovered bound to liver macromolecules at 24 hr and excreted in urine or feces for 24 hr were also determined. Comparison pharmacokinetic studies were done with (14)CHCl3 and Na(2)14CO3. After all doses of (14)CCl4, the major metabolite was CO2, twenty to thirty times less metabolite was recovered bound to liver macromolecules, and intermediate amounts of metabolite were excreted in urine and feces. CHCl3 was the least abundant metabolite at low CCl4 doses, but the second most abundant at high doses. Stronger associations were found between the magnitude of liver injury at 24 hr (quantitated as serum glutamate-pyruvate transaminase activity) and the extent or rate of CCl4 metabolism by pathways leading to CO2 and CHCl3 than by pathways leading to (14)C-metabolites bound in liver or excreted in urine. Time-course and pharmacokinetic data indicated that a major pathway of CCl4 metabolism leading to CO2 became impaired within 2 hr after administration of hepatotoxic doses of CCl4.
No study has comprehensively compared the rate of metabolism of carbon tetrachloride (CCl4) across species. Therefore, the in vivo metabolism of CCl4 was evaluated using groups of male animals (F344 rats, B6C3F1 mice, and Syrian hamsters) exposed to 40-1800 ppm CCl4 in a closed, recirculating gas-uptake system. For each species, an optimal fit of the family of uptake curves was obtained by adjusting Michaelis-Menten metabolic constants Km (affinity) and Vmax (capacity) using a physiologically based pharmacokinetic (PBPK) model. The results show that the mouse has a slightly higher capacity and lower affinity for metabolizing CCl4 compared to the rat, while the hamster has a higher capacity and lower affinity than either rat or mouse. A comparison of the Vmax to Km ratio, normalized for milligrams of liver protein (L/hr/mg) across species, indicates that hamsters metabolize more CCl4 than either rats or mice, and should be more susceptible to CCl4-induced hepatotoxicity. These species comparisons were evaluated against toxicokinetic studies conducted in animals exposed by nose-only inhalation to 20 ppm (14)C-labeled CCl4 for 4 hr. The toxicokinetic study results are consistent with the in vivo rates of metabolism, with rats eliminating less radioactivity associated with metabolism ((14)CO2 and urine/feces) and more radioactivity associated with the parent compound (radioactivity trapped on charcoal) compared to either hamsters or mice. The in vivo metabolic constants determined here, together with in vitro constants determined using rat, mouse, hamster, and human liver microsomes, were used to estimate human in vivo metabolic rates of 1.49 mg/hr/kg body weight and 0.25 mg/L for Vmax and Km, respectively. Normalizing the rate of metabolism (Vmax/Km) by milligrams liver protein, the rate of metabolism of CCl4 differs across species, with hamster > mouse > rat > human.
To estimate the rate of CCl4 metabolism in vivo by using an inhalation pharmacokinetic approach based on arterial blood:air concentration ratios, the blood CCl4 concentrations (Cart) at the end of 5-hr exposure to varying concentrations of CCl4 in inhaled air (Cinh) were determined in male, naive rats and in rats pretreated with po administration of 100 or 200 microliters CCl4/100 g body weight 24 hr before exposure. Hepatic cytochrome P-450 content during and at the end of exposure was also determined. The biphasic nature of the Cart-Cinh curve for naive rats, with a transition at Cinh of about 100 ppm, indicated that CCl4 metabolism is perfusion-limited below 100 ppm and is saturated above 100 ppm. In 100 microliters CCl4-pretreated rats, Cinh at the transition point decreased from 100 to 50 ppm; this percentage decrease was consistent with the decreased cytochrome P-450 content induced by administration of 100 microliters CCl4. In 200 microliters CCl4-pretreated rats, where CCl4 metabolizing enzyme activity was completely inhibited, the Cart-Cinh curve gave a single line with a shallower slope than that of the steeper part of the curve for naive rats, reflecting a loss of cytochrome P-450 content during exposure. The curves of calculated uptake rate showed continued uptake in completely inhibited rats, representing the contribution of fat loading only. The rate of metabolism was approximated by the uptake rate for naive rats minus that for 200 microliters CCl4-pretreated rats, and decreased gradually with increasing Cinh over the range of saturable metabolism. From this rate curve, Vmax and Km for naive rats were 2.7 mg/kg/hr and of the order of 0.3 mg/liter, respectively. The gradual decrease in the rate of metabolism could be interpreted in terms of the rapid loss of cytochrome P-450 content. The Vmax for 100 microliters CCl4-pretreated rats decreased by about 57%, which was in good agreement with the decrease of cytochrome P-450 content. These experiments suggest the usefulness and validity of this approach for studying metabolism of a volatile compound.
Liver tissue reduces carbon tetrachloride to chloroform, and it was suggested that homolytic cleavage of carbon-chlorine bond yields free radicals which can then alkylate the sulfhydryl groups of enzymes.
Carbon tetrachloride is absorbed readily from the gastrointestinal and respiratory tracts, and more slowly through the skin. It is distributed to all major organs, with highest concentrations in the fat, liver, bone marrow, adrenals, blood, brain, spinal cord, and kidney. Once carbon tetrachloride is absorbed, it is metabolized by cytochrome P-450 enzymes, with the production of the trichloromethyl radical. Aerobically, metabolism of the trichloromethyl radical can eventually form phosgene. Anaerobically, the radical can undergo reactions to form chloroform, hexachloroethane, or carbon monoxide. Carbon tetrachloride is excreted primarily in exhaled air and in the feces, with relatively minimal amounts in the urine. (L129)
IDENTIFICATION AND USE: Carbon tetrachloride is a colorless, heavy liquid. It is used in refrigerants, metal degreasing, in chlorinating organic compounds, in the production of semiconductors, and as a solvent (fats, oils, rubber, etc). It was formerly used as anthelmintic. HUMAN STUDIES: Potential symptoms of overexposure are CNS depression, drowsiness, dizziness, incoordination, nausea, and vomiting as well as liver and kidney injury. Direct contact may cause skin and eye irritation, and dermatitis through defatting action. Liver damage appears after 24 hrs or more. Kidney damage is evident often only 2 to 3 weeks following the poisoning. Three case reports describe the occurrence of liver tumors associated with cirrhosis in people who had been exposed to carbon tetrachloride. Covalent binding to macromolecules and lipid peroxidation occur via metabolic intermediates of carbon tetrachloride. Carbon tetrachloride did not demonstrate the DNA damaging activity in a short-term in vitro system which utilized human lymphocytes. ANIMAL STUDIES: The liver and kidney are target organs for carbon tetrachloride toxicity. The severity of the effects on the liver depends on a number of factors such as species susceptibility, route and mode of exposure, diet or co-exposure to other compounds, in particular ethanol. Furthermore, pretreatment with various compounds, such as phenobarbital and vitamin A, enhances hepatotoxicity, while other compounds, such as vitamin E, reduce the hepatotoxic action of carbon tetrachloride. Moderate irritation after dermal application was seen and there was a mild reaction after application into the rabbit eye. Increased fetal mortality was observed in pregnant mice given single doses of 150 mg carbon tetrachloride per animal during the last part of pregnancy. Cause of death was failure of peripheral circulation, mainly due to fetal liver damage. Moreover, circulatory disturbances and necroses were found in the placentas, which probably also contributed to the death of the fetuses. Carbon tetrachloride was not teratogenic to rats exposed orally, subcutaneously, or via inhalation. Carbon tetrachloride produced testicular toxicity in the rat at dose levels where hepatic damage is evident. After 25 wk of inhalation exposure to 200 and 400 ppm, male rats show germ cell degeneration in the testes along with liver toxicity and a high mortality rate. Testicular damage was also observed in rats when carbon tetrachloride was administered ip at a dose level of 1.5 mg/kg. A single injection caused testicular atrophy, a decrease in testes and seminal vesicle weights, and histological evidence of abnormal spermatogenesis. Carbon tetrachloride may have estrogenic properties that can alter male fertility. Its estrogenicity is evidenced by (a) inhibition of hepatic microsomal hydroxylation of estrogens in immature female rats, (b) potentiation of the uterotrophic responses of estrogens, and (c) increased estrogen uterine uptake. Carbon tetrachloride was not mutagenic in bacteria. It was mutagenic in yeast at almost lethal doses. It did not induce chromosomal damage in cultured rat liver epithelial cells and did not induce unscheduled DNA synthesis in the hepatocytes of rats exposed in vivo. Carbon tetrachloride induced hepatomas and hepatocellular carcinomas in mice and rats. The doses inducing hepatic tumors were higher than those inducing cell toxicity. ECOTOXICITY STUDIES: Carbon tetrachloride is considerably more toxic to the embryo-larval stages of several species of fish and amphibians than it is to the adults.
Unmetabolized carbon tetrachloride, depresses the central nervous system. All other toxic effects of carbon tetrachloride are related to its biotransformation via cytochrome P-450 enzymes, specifically CYP2E1. Metabolism of carbon tetrachloride by CYP2E1 may result in the destruction of the enzyme during the metabolic process, either by direct attack of radicals on the cytochrome(s) or highly localized lipid peroxidation resulting in detachment of P-450 proteins from the microsomal membranes. Reactive metabolites of carbon tetrachloride causes hepatic damage via haloalkylation of cellular macromolecules and lipid peroxidation. Carbon tetrachloride also perturbs the intracellular calcium homeostasis. Increased cytosolic levels of calcium may result from an influx of extracellular calcium caused by plasma membrane damage and decreased intracellular calcium sequestering. Higher levels of calcium activate enzymes such as proteases, which hydrolyze proteins in neighboring cells, leading to a progression of the lesion. Carbon tetrachloride's carcinogenicity is likely the result of certain reactive metabolites that bind to nuclear proteins, lipids, and DNA. (T10, L129)
Under the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a), carbon tetrachloride is "likely to be carcinogenic to humans" based on: (1) inadequate evidence of carcinogenicity in humans and (2) sufficient evidence in animals by oral and inhalation exposure, i.e., hepatic tumors in multiple species (rat, mouse, and hamster) and pheochromocytomas (adrenal gland tumors) in mice.
Evaluation: There is inadequate evidence in humans for the carcinogenicity of carbon tetrachloride. There is sufficient evidence in experimental animals for the carcinogenicity of carbon tetrachloride. Overall evaluation: Carbon tetrachloride is possibly carcinogenic to humans (Group 2B).
This paper reports a fatality involving a 75-year-old white male, who ingested an unknown quantity of carbon tetrachloride (CCl4) - a toxic agent able to induce central nervous system depression and severe renal and hepatic damage - and who died after two days of intensive care. The analytical assessment of CCl4 concentration was performed on several biological fluids and tissues employing gas chromatography-flame ionization detection (GC-FID) head space method. Both urine (328.5 mg/L) and bile (169.8 mg/L) had high concentrations of CCl4, proving that the chemical undergoes extensive urinary and biliary excretion. In accordance with the high clearance power of lungs, systemic venous blood, (143.4 mg/L) had a concentration of CCl4 almost two and half times greater than in arterial blood (57.5 mg/L), representing the best specimen to correlate CCl4 blood concentration with the deep of narcosis. Vitreous humor, (170.5 mg/L) concentration of CCl4 proves the capability of the chemical to enter eyes and its relatively slow release into the systemic blood. Pancreas (657.9 mg/kg), brain (243 mg/kg) and testis (237.3 mg/kg) have great affinity for CCl4. The concentrations of the chemical in brain are cortex: 243.2 mg/kg, basal ganglia: 216.1 mg/kg, medulla oblongata: 243.3 mg/kg and cerebellum: 175.3 mg/kg. As the depth of narcosis is correlated with CCl4 concentration, brain represents the most suitable tissue for toxicologic analysis. Lower concentrations of the chemical are found in lungs (127.3 mg/kg), kidneys (150.5 mg/kg), muscle (71.1 mg/kg), myocardium (78.5 mg/kg) and spleen (68.3 mg/kg). Liver (58.6 mg/Kg), a frequently analyzed tissue in forensic toxicology, shows the lowest concentration.
The target organ toxicity, mechanisms of toxicity, and metabolism of carbon tetrachloride (CCl4) have been studied extensively. However, there is a paucity of information concerning its elimination. Previous inhalation studies showed that a significant amount of (14)C appeared in the feces of rats and monkeys exposed to (14)CCl4. The nature of the compound(s) excreted in the feces has not been well characterized. Fecal excretion is a major route of elimination for many lipophilic compounds that are resistant to metabolism. A mechanism of excretion for these compounds is the direct exsorption from the blood to the lumen of the intestinal tract. The primary purpose of this study was to determine if fecal elimination contributes significantly to the elimination of CCl4. The secondary purpose was to determine the mechanism (biliary and/or nonbiliary, i.e., direct exsorption) of fecal elimination of CCl4 and/or its metabolite(s) in Sprague-Dawley rats. The results indicate that both biliary and nonbiliary mechanisms contribute to the fecal elimination of CCl4 following a single iv dose (1 mmol/kg), but this route accounts for less than 1% of the administered dose. The results also indicate that CCl4 is not eliminated unchanged in the feces following either acute treatment (iv or ip) or repeated inhalation exposures. Fecal elimination of CCl4 does not significantly contribute to the overall elimination of CCl4.
Carbon tetrachloride (CCl4) has been studied extensively for its hepatotoxic effects. There is a paucity of information, however, about its tissue deposition following administration by different routes and patterns of exposure. The specific objective of this study was to delineate the uptake, distribution, and elimination of CCl4 in tissues of rats subjected to equivalent oral and inhalation exposures. Male Sprague-Dawley rats (325-375 g) were exposed to 1000 ppm CCl4 for 2 hr. The total absorbed dose (179 mg CCl4/kg bw) was administered to other groups of rats as a single oral bolus or by constant gastric infusion over a period of 2 hr. Animals were terminated at selected time intervals during and post-exposure and tissues (liver, kidney, lung, brain, fat, skeletal muscle, spleen, heart, and GI tract) removed for measurement of their CCl4 content by headspace gas chromatography. CCl4 levels in all tissues were much lower in the gastric infusion group than in the oral bolus and inhalation groups. Inhalation resulted in relatively high tissue CCl4 concentrations, because inhaled chemicals enter the arterial circulation and are transported directly to organs throughout the body. It seems logical that the liver should accumulate more CCl4 following ingestion than following inhalation. This did not prove to be the case when comparing liver AUC values for the gastric infusion and inhalation groups. Substantially lower CCl4 concentrations in the liver of animals in the gastric infusion group appeared to be due to very rapid metabolic clearance of the relatively small amounts of CCl4 entering the liver over the 2-hr infusion period. It was hypothesized that the capacity of first-pass hepatic and pulmonary elimination could be exceeded, if CCl4 were given as a single, large oral bolus. Indeed, deposition of CCl4 in all tissues was greater in the oral bolus group than in the gastric infusion group. The time courses of uptake and elimination of CCl4 appeared to be governed largely by a tissue's rate of blood perfusion and lipid content. CCl4 was rapidly taken up, for example, by the brain and liver. These organs' CCl4 content then diminished, as CCl4 was metabolized and redistributed to adipose tissue. CCl4 accumulated slowly, but to very high concentrations, in fat and remained elevated for a prolonged period. Thus, concentrations of CCl4 in some tissues may not be reflective of blood levels. The most appropriate measure of internal dose for CCl4 acute hepatotoxicity appears to be the area under tissue concentrations versus time curve from 0 to 30 min. Tissue time-course data sets are essential for the refinement and validation of physiological models for CCl4 and other volatile organic chemicals.
[(14)C]-Carbon tetrachloride (CCl4) entered extensively into the liver and, to the small extent, into the brain 3 hr following the intragastric administration of the hepatotoxic dose. Although thiobarbituric acid (TBA) in the liver homogenates increased 12 hr after CCl4 administration, the brain showed little TBA values probably due to very low levels of chytochromes P-450 and b5 in the brain. These results suggest that CCl4 have no direct toxic effect upon the brain.
