Appendix A

Supporting Documentation for The Exposure Guidance Levels For Hydrochlorofluorocarbon-123

Prepared by

S. Channel, D. Dodd, J. Fisher, M. George, J. Lipscomb, J. McDougal, A. Vinegar, and J. Williams

Armstrong Laboratory

Toxicology Division and Toxic Hazards Research Unit

Wright-Patterson Air Force Base



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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 Appendix A Supporting Documentation for The Exposure Guidance Levels For Hydrochlorofluorocarbon-123 Prepared by S. Channel, D. Dodd, J. Fisher, M. George, J. Lipscomb, J. McDougal, A. Vinegar, and J. Williams Armstrong Laboratory Toxicology Division and Toxic Hazards Research Unit Wright-Patterson Air Force Base

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 BACKGROUND INFORMATION Physical and Chemical Properties1 Chemical name: 1,1-Dichloro-2,2,2-Trifluoroethane Chemical formula: CHCl2CF3 Molecular weight: 152.9 Synonym: HCFC-123, Genetron-123 CAS no.: 306-83-2 Physical state: Liquid at normal temperatures Boiling point: 27.9°C @ 760 mm Hg Freezing point: −107°C Vapor pressure: 11 psi (20°C) Vapor density: (Air = 1) 3.6 Solubility in water: 0.21% (wt) @ 70°F Flash point: N. A. - No flash point Auto ignition: Unknown, probably not applicable Flame limits: (In air, % by vol), none Occurrence and Use Hydrochlorofluorocarbon (HCFC) 123 is used primarily as a foam-blowing agent, as a refrigerant, and as an ingredient in cleaning solvents. The Air Force is considering the use of HCFC-123 as a fire extinguishant, replacing Halon 1211. Halon 1211 has been used as a fire extinguishant in streaming systems, where the extinguishant is manually discharged through a nozzle of small portable units that are commonly found in industry, military, and office settings. Jarabek et al. (1994) reviewed the process of searching for CFC substitutes with HCFC-123 as a specific example. Personnel with potential military occupational exposure to 1   Allied-Signal Inc., Material Safety Data Sheet (Attachment 1).

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 HCFC-123 as a fire extinguishant include maintenance personnel (crew chiefs) responding to aircraft fires on the flight line or in indoor structures, such as aircraft hangars, and trained fire fighters responding to alarms. The fire-fighter-exposure scenario deals with military personnel who don appropriate fire-fighting gear, including respirators, immediately before fighting fire. Thus, the exposure scenario of concern in setting emergency exposure guidance levels (EEGLs) involves the emergency situation where maintenance personnel attempt to put out a fire without the appropriate fire-fighting equipment. The exposure duration of concern involves a 1-min period to simulate personnel discharging either the entire contents of a small (1- or 3-lb) extinguisher or the partial contents of a large (150-lb) extinguisher while attempting to put out an aircraft fire (usually an engine fire) from upwind of the fire (C. Kibert, Tyndall Air Force Base, Fla., personal commun., 1994). The potential for repeated exposures to a streaming agent such as Halon 1211 has been estimated to be minimal. According to D. Vickers (Tyndall Air Force Base, Fla., personal commun., 1994), there are about three aircraft fires per Air Force wing per year. An average wing has 60 crew chiefs assigned; therefore, the probability that a crew chief will experience a fire in any one year is 1 in 20 or 0.05. The probability of experiencing two fires in a 20-year career is 0.1887 or about 1 in 5, according to the multiplication rule: The probability of experiencing three fires in a career is about 1 in 20. Probabilities of experiencing more than three fires are much less. The expectation of any crew chief for number of fires over a 20-year career is 1.

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 Probability of Aircraft Crew Chief Experiencing Multiple Fires in a 20-Year Career Fires, no. Probability 2 0.1887 3 0.0596 4 0.0133 5 0.0022 6 0.0003 TOXICOKINETICS Brashear et al. (1992) exposed F344 and Sprague-Dawley rats to HCFC-123 and detected the metabolites 2-chloro-1,1,1-trifluoroethane (HCFC-133a) and 2-chloro-1,1-difluoroethylene in the liver immediately following exposure. The most abundant metabolite in the urine was TFA. Additionally, Harris et al. (1991) and Martin et al. (1992) exposed rats to 1% HCFC-123 and, via 19F nuclear magnetic resonance spectrometry, observed the formation of reactive TFA intermediates with liver proteins. These newly formed TFA proteins have been implicated in halothane-induced hepatitis (Harris et al., 1991; Owen and Van der Veen, 1986). (See Attachment 2 for toxicity information on halothane and a comparison of HCFC-123 and halothane.) Both oxidative and reductive pathways participate in the metabolism of HCFC-123. The reductive pathway occurs only under conditions of very low oxygen tension and would not be expected to be a common route in man (Dodd et al., 1993). It begins with reductive dehalogenation to produce a radical intermediate that either can accept a hydrogen atom from a protein or a phospholipid to form HCFC-133a or can lose a fluorine to yield chlorodifluoroethylene. The oxidative pathway catalyzed by cytochrome P-450 produces a dichloro geminal halohydrin, which is unstable, and releases HCl to form trifluoroacetylchloride, which is hydrolyzed to TFA. These pathways are similar to those for the structur-

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 ally related compound halothane where TFA, HCFC-133a, and chlorodifluoroethylene have been detected as metabolites (Stier, 1964; Mukai et al., 1977; Sharp et al., 1979). It is unknown whether different isoforms of P-450 are responsible for differential metabolism of HCFC-123 or halothane via the oxidative or reductive pathways. The metabolism of halothane and several other halogenated hydrocarbons has been shown to be catalyzed primarily by the P-450IIE1 isoform. This isoform is expressed differentially in the sexes and is induced by such substances as ethanol, acetone, and isoniazid. The metabolism of HCFC-123 in vitro has been determined by using rat liver microsomes and aerobic conditions. Preliminary results of in vitro rat microsomal studies conducted at Wright-Patterson Air Force Base by C.S. Godin (personal commun.) indicate that the rate of formation of TFA from HCFC-123 is approximately 0.2 nmol/nmol P-450 per min. Urban and Dekant (1993) compared the metabolism of HCFC-123 and halothane in rat and human liver microsomes. For rat liver microsomes, the rate of formation of TFA from HCFC-123 was 3.1 nmol/mg per 20 min and the formation of TFA from halothane was 2.1 nmol/mg per 20 min. For human liver microsomes, rates of formation of TFA from HCFC-123 ranged from 5.4 to 41.9 nmol/mg per 20 min. TOXICITY INFORMATION Effects in Humans No literature citations were found of studies on HCFC-123 exposure to humans. Effects in Animals Single-Exposure Studies Attachment 3 of this supporting doumentation provides an out-

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 line of acute-toxicity results for HCFC-123 and lists the references. Acute Toxicity and CNS Depression. Potential toxicity during acute exposure to HCFC-123 includes severe central nervous system (CNS) depression and cardiac sensitization. The liver might be a target organ of concern following acute exposure to HCFC-123. All animal species exposed to HCFC-123 show CNS depression, and in rodent LC50 studies, death is attributed to severe CNS depression. Rodent LC 50 values are comparable across species and average 37,000 ppm for exposures of 4- to 6-hr durations (Darr, 1981; Hall and Moore, 1975; Coate, 1976; Waritz and Clayton, 1966). For exposures of ≤30 min duration in mice, concentrations of 74,000 ppm and higher produced mortality (Burns et al., 1982; Raventos and Lemon, 1965); 40,000 to 50,000 ppm was nonlethal. The lowest HCFC-123 concentration causing CNS depression (inactivity or altered response to auditory stimuli) in rats is 5,000 ppm (Mullin, 1976). A concentration of 1,000 ppm does not produce narcosis in rats or dogs (Mullin, 1976; Trochimowicz and Mullin, 1973). Cardiac Sensitization. The standard cardiac-sensitization protocol as defined by Reinhardt et al. (1971) has been applied to Halon and many of the Halon-replacement chemicals. [This protocol has been reviewed in detail in Chapter 2 of this report.] Briefly, the male beagle dogs are exposed to vapor concentrations of the test substance diluted in air via face mask following a “priming” dose of epinephrine (0.008 mg/kg given i.v. in 1 mL saline over 9 sec; rate = 50 µg/kg/min). After 5 min of exposure to the test agent, a “challenge” dose of epinephrine is administered under the same conditions as the priming dose. Cardiac activity is followed by electrocardiography and “marked” responses are tabulated. A “marked” response is defined as “those arrhythmias considered to pose a serious threat to life or which ended in cardiac arrest.” The only data available for HCFC-123 are reported by Trochimowicz and Mullin (1973). They used a “staircase-method” modifi-

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 cation of the standard protocol to study vapor concentrations (% vol/vol in air) and obtained an estimate of the EC50. A summary of the results follows: Concentration (% vol/vol) Marked Response Percent 1.0 0/3 0 2.0 4/6a 67 4.0 3/3a 100 aSix of seven marked responses ended in death. Statistical interpretation of the data indicated an EC50 of 1.9% with a 95% confidence interval of 1.29% ≤ EC50 ≤ 2.82%. These authors suggest that the unusually high percentage of fatal marked responses might reflect the nature of the staircase modification, which requires more test concentrations above the initial estimate of the EC50. Additionally, the extremely rapid onset of ventricular fibrillation, within 3 to 6 sec of the challenge dose, implies an effect that is specific to the compound itself. The table on the following page summarizes the cardiac-sensitization results for other chemicals under the same experimental conditions. Repeated exposures do not change the cardiac-sensitization effects of chemicals. Beck et al. (1973) studied the pharmacological actions, including cardiac arrhythmias and cardiac sensitization, of bromochlorodifluoromethane (BCF) in laboratory animals. BCF was selected as a prototype of halogenated hydrocarbons that produces CNS and cardiac effects. The authors (Beck et al., 1973) concluded from their results that cardiac sensitization occurred at the end of very brief exposures to BCF, but the concentration of BCF has to be high. Exposure (5 min/day, 3 days/week for 4 weeks) to BCF at a concentration that caused minimal cardiac sensitization did not make the heart more susceptible to epinephrine arrhythmias.

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 Test Compound Concentrationn (% vol/vol) Marked Responses Percent Fluorocarbon 11 0.13 0.61 0.96 0/12 1/12 5/12 0 8.3 41.7 Fluorocarbon 12 2.5 5.0 0/12 5/12 0 41.7 Fluorocarbon 22 2.5 5.0 0/12 2/12 0 16 Fluorocarbon 114 2.5 5.0 1/12 7/12 8.3 58.3 Fluorocarbon 1301 5.0 7.5 15 20 0/62 1/18 8/69 2/7 8/13 0 5.5 11.6 28.6 61.5 Fluorocarbon 142b 2.5 5.0 10.0 0/6 5/12 12/12 0 41.7 100.0 Fluorocarbon 152a 5.0 15.0 0/12 3/12 0 25.0 Propane 5.0 10.0 20.0 0/6 2/12 7/12 0 16.7 58.3 Isobutane 2.5 5.0 10.0-20.0 0/12 4/12 6/6 0 33.3 100.0 Vinyl chloride 2.5 5.0 10.0 0/12 6/12 6/6 0 50.0 100.0 Dimethyl ether 10.0 20.0 30.0 0/6 2/12 2/6 0 16.7 33.3 Source: Adapted from Reinhardt et al. (1971) and Trochimowicz (1975).

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 Malignant Hyperthermia. HCFC-123 has not been tested for its potential to produce malignant hyperthermia in the Pietrain malignant hyperthermia-susceptible pig model. Hepatotoxicity. The potential for acute HCFC-123 exposure to produce hepatotoxicity in the guinea pig has been evaluated recently at Wright-Patterson Air Force Base (G. Marit, A. Vinegar, and M. George, unpublished material, 1994). The use of a guinea pig model for examining the mechanisms of acute liver injury produced by halothane (Lunam et al., 1985; Lind et al., 1987) has received considerable attention, because the spectrum of liver injury observed in guinea pigs exposed to anesthetic concentrations (1%) of halothane resembles that observed in nonfatal halothane hepatitis in humans (Lunam et al., 1989). Exposure-related liver alterations were observed in guinea pigs exposed for 4 hr to HCFC-123-vapor concentrations of 3%, 2%, 1%, or 0.1%. In agreement with the results of Lunam et al. (1985, 1989) and Lind et al. (1987), there were wide variations in individual sensitivity based on lesion morphology, severity, and incidence. Liver lesions observed in guinea pigs exposed to 3% or 2% HCFC-123 included centrilobular necrosis and degeneration and were comparable to those observed in guinea pigs exposed to 1% halothane (G. Marit, A. Vinegar, and M. George, unpublished material, 1994). Hepatic lesions observed in guinea pigs exposed to 1% or 0.1% HCFC-123 were mild in severity (altered hepatocytes and lymphoid infiltrates) and multifocal or random in distribution. All liver lesions observed in guinea pigs exposed for 4 hr to HCFC-123 at concentrations of 0.1-3% were considered reversible. Repeat-Exposure Studies Attachment 3 of this supporting documentation provides an outline of repeat-exposure toxicity results for HCFC-123 and lists the references.

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 For evaluating general toxicity due to repeated exposure to HCFC-123, the 90-day (Malley, 1990a) and 1-year (Malley, 1990b) studies in rats are thorough and well documented. The exposure concentrations used in these studies were 0 (control), 300, 1,000, and 5,000 ppm. Malley states that a no-observed-effect level (NOEL) was not established in these studies owing to exposurerelated changes in select serum chemistry values and hepatic betaoxidation enzyme activity at all HCFC-123 concentrations. The liver is a target organ of toxicity following HCFC-123 exposure. Hepatic degenerative changes, including hypertrophy, clear cytoplasm, and necrosis with inflammatory cell infiltrates, were observed in the 90-day dog study at an exposure concentration of 10,000 ppm (Crowe, 1978). However, rats exposed to the same HCFC-123 concentration for 90 days (Crowe, 1978), or even higher concentrations for shorter exposure periods (Lewis, 1990; Kelly, 1989), did not produce similar hepatic effects, although some indexes of liver toxicity (liver weight, hepatocellular hypertrophy and fatty vacuolation, and hepatic peroxisomal activity) were observed to be of greater magnitude or incidence when compared with control values. For a no-observed-adverse-effect level (NOAEL), dogs exposed to 1,000 ppm for 90 days did not have liver damage. A study on the oncogenic potential of HCFC-123 in rats has been completed recently (Malley, 1992). Exposure concentrations were 5,000, 1,000, 300, and 0 (control) ppm. Consistent with the 90-day and 1-year studies (Malley, 1990a,b), exposure-related changes were observed in select serum chemistry values (e.g., triglyceride, glucose, and cholesterol) and in hepatic beta-oxidation enzyme activity at all HCFC-123 concentrations. In this study, a NOEL was not achieved using clinical chemical values —lower body weight and body-weight gain, increased incidence of neoplastic and non-neoplastic morphological changes, and higher hepatic betaoxidation activity—at all concentrations. The tumor incidences of concern were increases in benign hepatocellular adenomas or hepatic cholangiofibromas or both, increases in benign pancreatic acinar cell adenomas, and increases in interstitial cell adenoma in

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 the testes. Diffuse retinal atrophy was increased in all test groups of both males and females. Also noteworthy was the observation that the survival index was higher in HCFC-123-exposed rats in comparison to control rats. The potential for HCFC-123 to produce developmental toxicity or reproductive toxicity has not been evaluated fully. Developmental toxicity studies in rabbits (Bio-Dynamics, 1989a,b) and rats (Culik and Kelly, 1976; IBT, 1977) indicate that a concentration of 5,000 ppm is a NOAEL for the development of terata, but maternal toxicity effects were not studied in dogs exposed to HCFC-123 at 500 ppm. Only minimal toxicity was observed at 500 ppm in the Cullick and Kelly (1976) study. No evidence for maternal or fetal toxicity was seen in the IBT (1977) study. Testicular effects were observed in rats exposed to HCFC-123 at 20,000 ppm for 4 weeks (Kelly, 1989), although testicular lesions have not been observed in rats exposed to lower HCFC-123 concentrations (Kelly, 1976, 1989; Crowe, 1978; IBT, 1977; Malley et al., 1990a,b). The observation of benign testicular tumors in the rat 2-year bioassay might be coincidental. EXPOSURE ASSESSMENT Fire training exercises have been performed routinely by Air Force personnel. In 1991, the Air Force directed the Midwest Research Institute (MRI) to assess the hazards associated with the inhalation of selected Halon-replacement compounds and determine the fate and effects of the Halon-replacement-chemical and jet-fuel combustion products. To accomplish this directive, a detailed air-monitoring survey of representative training-exercise test burns was conducted by using Halon-replacement candidates, including HCFC-123, and by burning jet fuel. This fire-fighter training scenario differs from anticipated flight-line exposures to the crew chief in two ways: (1) fire fighters wore protective gear and used respirators, and (2) they applied the fire-fighting agent at a

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 oroethane. Acute Inhalation Toxicity. Report No. 426-75. Haskell Laboratory. Henry, J.E., and A.M. Kaplan. 1975. 1,1-Dichloro-2,2,2 trifluoroethane. Acute oral test. Report No. 638-75. Haskell Laboratory. IBT (Industrial Bio-test Laboratories). 1977. Ninety-Day Inhalation Study and Teratology Study with Genetron 123 in Rats. Report No. 8562-09344. Industrial Bio-test Laboratories , Decatur, Ill. Kelly, D.P. 1976. Two-Week Inhalation Toxicity Studies (FC-21 and FC-123). Report No. 149-76. Haskell Laboratory. Kelly, D.P. 1989. Four-Week Inhalation Study with HCFC-123 in Rats. Report No. 229-89. Haskell Laboratory. Lewis, R.W. 1990. HCFC 123: 28-Day Inhalation Study to Assess Changes in Rat Liver and Plasma. Report No. CTL/T2706. Central Toxicology Laboratory, Imperial Chemical Industries. Malley, L.A. 1990a. Subchronic Inhalation Toxicity: 90-Day Study with HCFC-123 in Rats . Report No. 594-89. Haskell Laboratory. Malley, L.A. 1990b. Combined Chronic Toxicity/Oncogenicity Study with HCFC-123. Two-Year Inhalation Toxicity Study in Rats (One-Year Interim Report). Report No. 260-90. Haskell Laboratory. Malley, L.A. 1992. Combined Chronic Toxicity/Oncogenicity Study with HCFC-123. Two-Year Inhalation Toxicity Study in Rats. Report No. 669-91. Haskell Laboratory. Müller, W., and T. Hofmann. 1988. HCFC 123 micronucleus test in male and female NMRI mice after inhalation . Report No. 88.1340. Pharma Research Toxicology and Pathology, Hoechst , Hattersheim, Germany. Mullin, L.S. 1976. Behavioral Toxicity Testing. Fluorocarbon 123. Report No. 941-76. Haskell Laboratory. Raventos, J., and P.G. Lemon. 1965. The impurities in fluothane: Their biological properties. Br. J. Anaesth. 37:716-737. Trochimowicz, H.J., and L.S. Mullin. 1973. Cardiac sensitization potential (EC50) of trifluorodichloroethane. Report No. 132-73. Haskell Laboratory. Waritz, R.S., and J.W. Clayton. 1966. Acute Inhalation Toxicity(FC-123). Report No. 16-66. Haskell Laboratory.

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 Attachment 4 Summary of Acute Pharmacokinetic Study Of HCFC-123 in Dogs by Inhalation 1 OBJECTIVE The objective of this study was to evaluate the pharmacokinetic behavior of HCFC-123 in an exposure scenario that mimics the cardiac-sensitization test in dogs and to use the data to support the development of a physiologically based pharmocokinetics model. Specific emphasis was placed on the measurement of blood and tissue samples following exposure of 1% or 5% HCFC-123 for 1-5 min. MATERIALSAND METHODS Two male beagle dogs per time-point were exposed to HCFC-123 at either 1% or 5% for various exposure durations (Table 1). 1   Vinegar, A., D. Dodd, D. Pollard, R. Williams, and J. McDougal. 1995. Pharmacokinetics of HCFC-123 in Dogs. Technical Report No. AL/OE-TR-1995-0025, Armstrong Laboratory, Wright-Patterson Air Force Base, Ohio.

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 Exposure was “nose-only” via a specially adapted canine anesthesia mask equipped with a two-way non-rebreathing valve. The exposure system was designed to provide instantaneous exposure of the dogs to the target concentrations and permit the drawing of blood samples. Blood samples were collected (as applicable) at 0 (pre-exposure), 1, 2, 3, 4, 5, 7.5, 10, 15, 30, 45, and 60 min during exposure and 1, 3, 6, 16, and 31 min after exposure and analyzed for HCFC-123. At the end of the exposure periods, animals were euthanized and samples from selected tissues (heart, liver, fat, and skeletal muscle) were collected as rapidly as possible for analysis of HCFC-123. TABLE 1 Experimental Design Number of Dogs Dog I.D. Number Exposure Concentration Exposure Time After Exposure 2 1974 1999 1% 1 min na 2 1975 1986 1% 5 min na 2 1992 1995 1% 60 min na 2 1993 1994 1% 60 min 30 min 2 1979 1990 5% 1 min na 2 1983 1997 5% 5 min na na = not applicable. Exposure System The dog nose-only exposure system set up is presented schematically in Figure 1. Liquid HCFC-123 was evaporated by heating a glass reservoir while air passed across the test article surface. The HCFC-123 was first brought to target concentrations in a 500-liter NYU-type inhalation chamber, then supplied to the animal via a sideport. Concentrations in the exposure chamber were monitored with a Miran 1A gas analyzer. Chamber air flow, temperature, relative humidity, and oxygen were monitored as well. Each animal

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 was exposed individually. The animal was first secured in a sling, and the snout placed in a modified dog anesthesia mask. The snout went through a small hole in a rubber diaphragm to provide a seal. The animal breathed either chamber atmosphere or room air via a valve on the exposure line sideport (Figure 1). The animal breathed the HCFC-123 through a two-way non-rebreathing valve to maintain a unidirectional flow of chemical. FIGURE 1 Dog nose-only exposure system setup.

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 Blood and Tissue Sampling A 5.0-cm over-the-needle Teflon catheter was inserted into a saphenous vein. The catheter was attached to a three-way valve so that heparinized saline could be used to flush the catheter. A 3-mL glass syringe was used to draw blood samples. Three ≈ 100-µL samples were place into preweighed headspace vials and reweighed for analysis of HCFC-123 concentration. For tissue sampling, animals were euthanized by lethal injection. The dead animals were transferred as rapidly as possible to a necropsy suite to harvest tissues for HCFC-123 analysis. The intact heart was removed first, followed by samples of fat (perirenal), liver, and skeletal muscle. For each tissue, three subsamples of ≈ 500 mg were weighed and sealed in headspace vials. In general, the entire necropsy procedure was completed in less than 5 min. Analysis of Blood and Tissue Samples Blood and tissue samples were stored in a ≄80°C freezer until analysis. Headspace vials containing blood or standards were loaded onto a Tekmar 7050 static headspace sampler for injection onto a Varian 3700 gas chromatograph. The gas chromatograph was equipped with a 0.53-mm 25-m PoraPlot Q column and an electron capture detector. Tissue samples were first digested with sodium hydroxide solution to release the HCFC-123 into the head-

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 space. The digestion process occurred within the headspace vial. The digested samples were analyzed in the same manner as the blood. Sample headspace HCFC-123 concentrations were calculated from a standard curve. RESULTS The blood and tissue (heart, muscle, liver, and fat) concentrations for all exposure scenarios are given in Table 2 and Table 3, respectively. In animals exposed for 60 min (n = 4), the maximum venous blood concentrations (mean values) were attained within 30 min, with less than a 3% increase over the next 30 min (Figure 2 and Table 2). Animals allowed to recover for 30 min (n = 2) had rapid decreases in the venous blood concentrations within the first 16 min with concentrations approaching the limits of detection by 31 min after exposure (Figure 3 and Table 2). Figure 4 and Figure 5 are graphs of the triplicate blood concentrations at the early time points for all animals exposed to 1% and 5% HCFC-123, respectively. The experimental design allowed for the sampling of eight animals at 1.0-min during the 1% exposure concentrations. Due to problems in sampling, half of the 1.0-min samples were not available for analysis. The plot of data was tightly clustered, with a gradual increase in the blood concentrations during the first 5-6 min of the 1% exposure. This was not the case for the 5% exposure. The plot of data showed two parallel groupings of data (each a different dog) that increased in concentration from 1 to 5 min. More than two dogs would be required to know the blood concentrations with greater certainty. Difference in behavioral reaction to the 5% exposure concentration between dogs is the most plausible reason for differences in blood concentration. The rise and fall in tissue concentrations paralleled that of blood. Heart, liver, and muscle tissue appeared to take up HCFC-123 much quicker than fat tissue (Table 3). It should be noted that the concentration of chemical in fat, in animals exposed for 60

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 min, was two- to three-fold higher than the other tissues as expected. The solubility of HCFC-123 in fat (partition coefficient = 52.9) is approximately 25 times greater than muscle (2.3), liver (1.9), or heart (2.5) tissues. Subsequently, the washout of chemical in fat tissue was much slower than any other tissue. In general, the blood and tissue concentrations of HCFC-123 both increased with exposure time and increasing concentration. TABLE 2 Blood Concentrations in Dogs Exposed by Inhalation to HCFC-123   Time of Exposure (min)     1 2 3 4 5 7.5 10 15 30 45 60 Animal I.D. 1% Exposure Concentration Blood Concentration (mg/L) 7.6 10.0 11.0 11.7 9.5 7.6 7.2 10.3 22.7 13.8 15.7 1993   – 3.3 8.8 6.6 9.1 8.2 13.6 26.1 31.3 36.1 34.5 1994   4.4 4.4 3.8 4.9 5.4 10.2 12.0 24.7 33.2 33.5 33.6 1992   4.1 10.6 16.5 18.2 18.4 17.2 14.3 21.1 22.9 27.3 29.1 1995   – 0.7 1.5 2.3 2.7 – – – – – – 1975   – 3.3 6.0 7.3 – – – – – – – 1986   4.7 – – – – – – – – – – 1999   – 3.8 – – – – – – – – – 1974 Mean 5.2 5.2 4.6 8.5 9.0 10.8 11.8 20.6 27.5 27.8 28.2   5% Exposure Concentration Blood Concentration (mg/L) 5.8 13.0 21.5 40.5 84.4 – – – – – – 1997   7.8 109.9 131.2 125.2 145.4 – – – – – – 1983   43.2 – – – – – – – – – – 1979   28.9 – – – – – – – – – – 1990 Mean 21.4 61.4 76.3 82.8 114.9 – – – – – –     Time After 60-Min 1% Exposure (min)     1 3 6 16 31   1% Exposure Concentration Blood Concentration (mg/L) 14.0 9.4 7.6 5.3 4.0 1993   30.6 27.8 25.1 6.7 – 1994 Mean 22.3 18.6 16.3 6.0 4.0

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 TABLE 3 Tissue Concentrations in Dogs Exposed by Inhalation to HCFC-123   Tissue Concentrations (mg/L)   Exposure Concentration and Exposure Time Heart Muscle Liver Fat Animal I.D. 1% for 1 min 14.7 6.7 13.8 7 12.9 5.1 2.1 0.6 1999 1974 1% for 5 min 15.8 18.6 5.5 7.2 14.6 19.5 15.9 13.9 1975 1986 1% for 60 min 39.4 37.9 34.7 66.6 51.1 46 199.1 182.2 1992 1995 1% for 30 min after 60-min exposure 2.5 2.6 5.3 10.2 2.2 3.6 118.5 195.3 1993 1994 5% for 1 min 107.4 94.8 24.9 29.1 75.8 48.2 3.9 9.7 1979 1990 5% for 5 min 141 179.8 39.5 36.4 81.8 174.9 78.3 46.2 1997 1983 FIGURE 2 1% HCFC-123 dog blood levels for 60-min exposure.

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 FIGURE 3 1% HCFC-123 dog blood levels after 60-min exposure. FIGURE 4 1% HCFC-123 dog blood levels for all exposed animals.

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 FIGURE 5 5% HCFC-123 dog blood levels for all exposed animals. DISCUSSION Analysis of the pharmacokinetics from this study facilitates extrapolating the 5-min cardiac-sensitization level to the 1-min level. As expected, both blood and tissue concentrations increased with exposure time and increasing concentration. See Table 4. Blood and tissue concentrations of HCFC-123 after a 5-min exposure to 1% HCFC-123 (the no-effect level) can be assumed to be the con-

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Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 centrations at which there would be no cardiac arrhythmias. Blood and heart-tissue concentrations are considered to be most relevant to the end point of cardiac sensitization. This table shows that Haber's law is not appropriate for this situation because, according to Haber's law, 1% HCFC-123 for 5 min should be equivalent to 5% HCFC-123 for 1 min. The results of this study were that the blood concentration of 5% HCFC-123 for 1 min was approximately 2.5 times greater than that of 1% HCFC-123 for 5 min, and the heart-tissue concentration of 5% HCFC-123 for 1 min was approximately 6 times greater than that of 1% HCFC-123 for 5 min. TABLE 4 Blood and Tissue Concentrationsa in Dogs Exposed by Inhalation to 1% or 5% HCFC-123   1% HCFC-123 5% HCFC-123 Sample 1 min 5 min 1 min 5 min Blood 5.2 (4.1-7.6)b 9.0 (2.7-18.4)c 21.4 (5.8-43.2)b 114.9 (84.4-145.4) Heart 10.7 (6.7-14.7) 17.2 (15.8-18.6) 101.1 (94.9-107.4) 160.4 (141.0-179.8) Muscle 10.4 (7.0-13.8) 6.4 (5.5-7.2) 27.0 (24.9-29.1) 38.0 (36.4-39.5) Liver 9.0 (5.1-12.9) 16.8 (14.4-19.2) 62.0 (48.2-75.8) 128.3 (81.8-174.9) Fat 1.36 (0.6-2.1) 14.9 (13.9-15.9) 6.8 (3.9-9.7) 62.3 (46.2-78.3) a Concentrations in milligrams per liter expressed as mean (range). b Four dogs. c Five dogs. Note: Number of dogs was two unless noted otherwise.