Perfluoro-n-Butyl Iodide: Acute Toxicity,Subchronic Toxicity and Genotoxicity Evaluations

Abstract

Perfluoro-n-butyl iodide (PFBI) is a promising alternative to chlorofluorocarbon solvents used in aircraft ground maintenance operations and other military and commercial operations, because it cleans well, has zero ozone depletion potential, and has extremely low global warming properties. Toxicity tests were performed with PFBI to determine and evaluate its health hazard. Using standard testing guidelines (e.g., Organization for Economic Cooperation and Development [OECD]), tests included acute (4-h) and 4-week (6 h/day, 5 days/week) inhalation (nose-only) toxicity studies in rats, acute (10-min) inhalation cardiac sensitization study in dogs, in vitro chromosomal aberrations experiments in human lymphocytes, and in vitro mutagenic experiments in Salmonella typhimurium and Escherichia coli. There were no mortalities in rats (n = 10) exposed for 4 h to 10,000 ppm PFBI, but all rats (n = 10) died within 2 h when exposed to 20,000 ppm PFBI. The 4-h LC₅₀ (95% confidence limits) was 14,000 ppm (13,000 ppm to 16,000 ppm). Signs (nasal discharge and labored breathing) observed in the rats exposed to 10,000 ppm returned to normal within 48 h. PFBI has the potential to cause cardiac sensitization in epinephrine-challenged dogs at 6200 ppm. A concentration of 3900 ppm was a no-observed-adverse-effect level (NOAEL) in the cardiac sensitization study. In the 4-week inhalation study (5 rats/sex/group), respiratory mucosal hypertrophy/hyperplasia was observed in rats of the 10,000-ppm group. A NOAEL of 1000 ppm was selected for the 4-week study on the basis that the mild increase in T₄ observed at 1000 ppm was considered adaptive, not adverse, because of the absence of frank effects in the thyroid. In the in vitro studies, PFBI showed no evidence of either mutagenic or clastogenic activity. The toxicity profile of PFBI was compared to trifluoroiodomethane. In conclusion, the results of these studies indicate a low order of general toxicity and an absence of genotoxicity following PFBI exposure.

The Montreal Protocol agreements initiated in 1987 continue to be the regulatory driver for finding suitable substitutes for currently used and globally distributed chlorofluorocarbons (CFCs). Perfluoro-n-butyl iodide (PFBI), CAS no. 423–39–2, is a liquid at room temperature with a boiling point of 67°C and a vapor pressure of 143 torr at 20°C. It is one of several fluoroiodocarbons that is being considered as a replacement for CFCs in aircraft ground maintenance operations and other military and commercial operations. Specifically, PFBI is being considered as an alternative cleaner for critical liquid and gaseous oxygen aerospace systems. Cleaning evaluations conducted by the Air Force have shown PFBI to be a superior wipe solvent cleaner. In addition to its performance, compatibility (e.g., reactivity) with existing aerospace systems, and environmental effects, the toxicity potential of PFBI must be assessed before PFBI can be considered to be a desirable replacement candidate. There are limited citations in the public domain that investigate the toxicity of fluoroiodocarbons. One example is a series of studies with trifluoroiodomethane, a replacement candidate for trifluorobromomethane (Halon 1301) conducted by Dodd et al. (1997a, 1997b, 1998b, 1999). The U.S. Air Force initiated the effort to evaluate PFBI toxicity by requesting and subsequently funding small business innovative research (SBIR) proposals to investigate the development of nonflammable, environmentally compliant (i.e., negligible ozone depletion potential, low global warming potential, and low toxicity) fluoroiodocarbon solvents. Under the U.S. Clean Air Act of 1990, the U.S. Environmental Protection Agency’s (EPA) Significant New Alternatives Policy (SNAP) program makes decisions on the end-use (e.g., household refrigerators) within a sector (e.g., refrigeration and air conditioning) of proposed CFC substitutes. The SNAP program has evaluation criteria for making decisions on health and safety, environmental impact, efficacy, and market potential. Included in the SNAP’s health hazard evaluation criteria is information on a substitute’s acute toxicity, including cardiac sensitization potential (primarily for halogenated hydrocarbons), genotoxicity, and subchronic toxicity. Preliminary ecotoxicity studies (acute toxicity to Daphnia magna and fat-head minnow) were performed with PFBI (Bell et al. 1996a, 1996b).

The objective of the proposed PFBI studies was to collect pertinent toxicity information that would be of value to SNAP’s health hazard evaluation process. Specifically, general toxicity was evaluated in rats following two exposure scenarios, a single (4-h) exposure and a repeated (4-week) exposure regimen. The general toxicity studies followed regulatory guidelines, such as those of the Organization for Economic Cooperation and Development (OECD). A cardiac sensitization study was performed, because PFBI is a fully halogenated carbon molecule. There are no regulatory guidelines for cardiac sensitization testing, but the study design that is widely accepted by pharmacologists and toxicologists is that of Reinhardt et al. (1971, 1973). For genotoxicity potential of PFBI, two in vitro assays were conducted, both of which are commonly part of an initial battery of tests required by regulatory agencies for assessing genotoxicity. Mutagenic potential of PFBI was determined in bacteria (Ames, McCann, and Yamasaki 1975; Maron and Ames 1983; Green 1984), and chromosomal aberration (clastogenic) potential was determined in human lymphocytes (Evans and O’Riordan 1975; Scott et al. 1990).

MATERIALS AND METHODS

All studies were conducted by Huntingdon Life Sciences (HLS) at East Millstone, New Jersey, USA, or at Huntingdon Life Sciences Ltd., Cambridgeshire, England. Acceptable practices of good animal husbandry were followed in all studies using laboratory animals (National Research Council 1996; United Kingdom Home Office Code of Practice for Housing and Care of Animals Used in Scientific Procedures). Regulatory guidelines followed included OECD Guidelines for Testing of Chemicals, Part 403 (1981a), Part 412 (1981b), No. 471 (1983a), No. 472 (1983b), and No. 473 (1983c). Principles of Good Laboratory Practices (GLP) followed included OECD GLP [C(81)30 (Final) Annex 2] (1981c) and OECD Environment Monograph No. 45 (1992). Complete details of all studies are available in the following HLS reports: HLS Study No. 97–5318 (1997a), Report No. IKE 14/973369 (1997b), HLS Study No. 97–6111 (1998), Report No. IKE 12B/960730 (1996b), and Report No. IKE 13B/960744 (1996a).

Acute Inhalation Study

Fischer 344 rats (5/sex/group), 8 to 11 weeks of age, were exposed to PFBI vapor for 4 h in nose-only inhalation exposure chambers. Exposure concentrations of 10,000, 20,000, 35,000, and 100,000 ppm were monitored hourly using a Wilks MIRAN 1A-CVF analyzer (infrared spectrophotometry) and a TSI Aerodynamic Particle Sizer. PFBI (>99% pure) was vaporized using a heated coiled glass rod insert in a glass volatilization chamber. Detailed observations for signs of toxicity were recorded pre-, during, and postexposure and daily during the 14-day postexposure observation period. Body weights were determined prior to exposure and weekly thereafter. Macroscopic necropsy examination was performed on all animals either upon spontaneous death or at the end of the postexposure period. The median lethal concentration (LC₅₀) and 95% confidence limits were calculated using the method of Litchfield and Wilcoxon (1949).

Cardiac Sensitization Study

The study design followed that of Reinhardt et al. (1971, 1973). Six pure-bred male beagle dogs (11 to 16 kg) were used in the study as the beagle dog is considered the most appropriate species for cardiac sensitization testing. All dogs had been used for previous studies of the same type. Epinephrine was injected intravenously (i.v.) before and during the inhalation exposure period. More specifically, the exposure procedure began with air only at 0 min, the administration of epinephrine at 2 min (to obtain baseline response), the beginning of PFBI exposure at 7 min, the administration of epinephrine challenge at 12 min (to obtain sensitization response, if any), and the conclusion of PFBI exposure at 17 min. Target exposure concentrations were 1000, 4000, and 6000 ppm PFBI vapor (specifically scheduled from low- to high-exposure sessions). At least 1 calendar day was allowed between exposure sessions to allow the dogs to recover. A snout-only exposure system was used that includes a Halls face mask (Phoenix Medical Ltd.) held in place with a muzzle and connected to a nonreturn valve that is used to control the introduction of either air or PFBI vapor. Test atmospheres of PFBI vapor were produced by measuring known volumes of air and liquid PFBI into a reservoir gas bag. Atmosphere samples were removed before and after animal exposure and analyzed directly by capillary gas chromatography with a flame ionization detector. Dogs were acclimatized to the exposure apparatus (face mask and canvas sling restrainer) for 3 days prior to initiation of the PFBI exposure procedure. In addition, individual responses to epinephrine alone were selected for each dog prior to the testing regimen for the purpose of establishing an epinephrine dose at which there was a clear but minimal effect on the electrocardiogram (ECG) ideally with a few ectopic beats. The maximum i.v. dose used was 12 μg epinephrine per kilogram body weight. Interpretation of results was made for each dog, taking into account the response of each dog to epinephrine alone. The criterion for a positive effect during exposure to PFBI was the appearance of a burst of multifocal ventricular ectopic activity (MVEA) or ventricular fibrillation (VF). Ventricular tachycardia alone was not necessarily considered definitive evidence of a positive response.

Four-Week Inhalation Study

Fischer 344 rats (5/sex/group; males weight range at initiation of exposure was 172 to 194 g; females weight range at initiation of exposure was 118 to 131 g) were exposed to PFBI vapor for 4 weeks (6 h/day, 5 days/week for a total of 20 exposures) in nose-only inhalation exposure chambers. Results from the acute inhalation study in rats indicated no mortality following 4 h exposure to 10,000 ppm PFBI (see Table 1). Lethality was observed at 20,000 ppm. Thus, 10,000 ppm was selected as the high target concentration for the 4-week study. Reduction factors of 10 and 100 were used to select the intermediate and low target concentrations, respectively. Exposure concentrations of 0 (control), 100, 1000, and 10,000 ppm were monitored four times a day using a Wilks MIRAN 1A-CVF analyzer (infrared spectrophotometry) and once a day with a TSI Aerodynamic Particle Sizer. PFBI (>99% pure) was vaporized using a heated coiled glass rod insert in a glass volatilization chamber.

Animals were observed for abnormal signs during daily exposures. Because the rats were restrained in clear plastic horizontal tubes during exposure, activities observed were limited to the following examples: twisting or turning of the whole body, pushing backward from the front end of the tube, and movement and/or pushing of limbs against the tubular wall. In addition, detailed observations for signs of toxicity were performed on all animals twice preexposure and weekly upon initiation of the 4-week exposure regimen. Body weights and food consumption were determined prior to the exposure regimen and weekly thereafter. Prior to animal sacrifice, body weights were recorded and blood samples were withdrawn (via orbital sinus under light CO₂/O₂ anesthesia) for analysis of hematology and clinical chemistry parameters. In addition to standard hematology (Technicon H-1, Bayer Corporation) and clinical chemistry (Hitachi 717, Boehringer Mannheim Corporation) measurements, serum thyroid hormones (thyroid-stimulating hormone [TSH], triiodothyronine [T₃], and thyroxine [T₄]) were determined using radioimmunoassay kits. Urine samples were collected prior to sacrifice for iodide analysis. Organs weighed at terminal sacrifice were adrenal glands, brain, kidneys, liver, lungs with mainstem bronchi, testes with epididymides, and thyroid/parathyroids. Macroscopic necropsy examination was performed on all animals either upon spontaneous death or at the end of the 4-week exposure period. Tissues preserved in 10% neutral-buffered formalin include the organs weighed and esophagus, heart, larynx, nasopharygeal tissue, ovaries, spleen, trachea, urinary bladder, and all tissues with macroscopic findings. Histopathological examination (hematoxylin and eosin–stained slides) was performed on all preserved tissues (except esophagus and spleen) of the control (air only) and 10,000 ppm PFBI–exposed animals. Also, adrenal glands, liver, and testes were examined microscopically in rats of the 100- and 1000-ppm groups.

Means and standard deviations were calculated for results in each exposure group. In general, further statistical analyses included Bartlett’s test for homogeneity of group variances (Snedecor and Cochran 1967), one way analysis of variance (Snedecor and Cochran 1967), Dunnett’s test (Dunnett 1955, 1964), Kruskal-Wallis test for nonparametric data (Hollander and Wolfe 1973) followed by Dunn’s summed rank test (Hollander and Wolfe 1973), if necessary, and tests for trend in dose levels using either standard regression procedures (Snedecor and Cochran 1967) or Jonckheere’s test (Hollander and Wolfe 1973).

Bacterial Mutation Assay

Four strains of Salmonella typhimurium (TA 98, TA 100, TA 1535 and TA 1537) and one strain of Escherichia coli (WP2 uvrA) were used for testing mutagenicity in the absence and presence of S-9 fraction with appropriate positive-control compounds. Aroclor 1254 was administered to rats as a single intraperitoneal injection in arachis oil at a dosage of 500 mg/kg body weight to stimulate liver mixed function oxidase systems. On the fifth day after injection, rats (fasted overnight) were killed and their livers aseptically removed. The efficacy of each batch of S-9 fraction was tested with 7,12-dimethylbenzanthracene and 2-aminoanthracene before use.

A preliminary toxicity test (up to 5000 μg PFBI/plate) was conducted prior to the mutation test procedure. The solvent used to administer PFBI was dimethyl sulfoxide. Toxicity can be detected by a substantial reduction in revertant colony counts or by the absence of a complete background bacterial lawn. In the absence of any toxic effects the top concentration used in the mutation test is the same as that used in the preliminary toxicity test. Doses for the mutation test ranged from 312.5 to 5000 μg PFBI/plate with or without S-9. Doses were carried out in triplicate, and the mutation test was duplicated. The mean number of revertant colonies for all treatment groups was compared with those obtained for the solvent control groups. In general, an increase in revertant colony numbers of at least twice the concurrent solvent control with some evidence of a positive dose-relationship in two separate experiments (with any bacterial strain in the presence or absence of S-9) is needed to show evidence of mutagenic activity.

Chromosomal Aberration Assay

Human lymphocytes in whole blood culture were stimulated to divide by addition of phytohemagglutinin and treated with PFBI (dissolved in dimethyl sulfoxide) in the presence and absence of S-9 fraction (derived from rat livers as described above). Solvent and positive-control cultures were prepared and carried out simultaneously. Incubation periods were either 21 h (tests 1 and 2) or 45 h (test 2). Cell division was arrested by the addition of Colcemid (Sigma). The cells were harvested and slides prepared (Giemsa staining) so that metaphase figures could be examined for chromosomal damage. In test 1, dose levels of PFBI were 39 to 5000 μg/ml in the absence of S-9 and 39 to 313 μg/ml in the presence of S-9. In test 2, concentrations of PFBI were 20 to 500 μg/ml in the absence of S-9 and 39 to 313 μg/ml in the presence of S-9. In all tests, duplicate cultures were used for treatment. Toxicity of PFBI to the cultured cells was assessed by calculating the mitotic index. Metaphase analysis was performed on cultured cells that showed no greater than an approximate 50% decrease in the mitotic index of the solvent control value. One hundred metaphase figures per culture were identified using a magnification of ×160 followed by ×1000 using oil immersion. Only cells with 44 to 46 chromosomes were analyzed. Vernier readings were recorded of all aberrant metaphase figures. Fisher’s test (Fisher 1973) was used to compare the number of aberrant metaphase figures in each treatment group with the solvent control value.

RESULTS

Acute Inhalation Study

Mean ± standard deviation (if applicable) analytical exposure concentrations were 10,000 ± 500, 20,000 ± 710, 35,000, and 100,000 ppm PFBI. No aerosol formation of PFBI was detected during any exposure. Mortality results are shown in Table 1. Exposure concentrations ≥20,000 ppm PFBI resulted in 100% mortality prior to the completion of the 4-h exposure period. No rats died following the 10,000-ppm exposure. Signs of treatment during or immediately following exposure included secretory and respiratory responses (clear or red nasal discharge, chromodacryorrhea, and labored breathing). Recovery from these effects was observed within two days post exposure. Surviving animals gained body weight, and there were no macroscopic abnormalities noted at necropsy. The 4-h LC₅₀ (95% confidence limits) for the combined sexes was 14,000 ppm (13,000 ppm to 16,000 ppm).

Cardiac Sensitization Study

The analytical concentrations (mean ± standard deviation) for the three PFBI exposures were 900 ± 300, 3900 ± 100, and 6200 ± 230 ppm. A summary of cardiac responses to epinephrine challenge during PFBI exposure is shown in Table 2. Individual responses to epinephrine alone were selected for each dog prior to the testing regimen for the purpose of establishing an epinephrine dose at which there was a clear but minimal effect on the ECG, ideally with a few ectopic beats. The range of i.v. doses used was 2 to 12 μg epinephrine per kg body weight (Table 2). There were no indications of cardiac sensitization to epinephrine at 900 and 3900 ppm PFBI. A positive response would not be expected in dog 1165 at 900 ppm in spite of equipment failure during exposure. At 6200 ppm, two dogs responded positively. Dog 1361 (Table 2) responded with a burst of consecutive unifocal beats approximately 3 s after the second epinephrine challenge. Dog 1353 responded with two bursts of unifocal ectopic activity. The first burst occurred approximately 14 s after the second challenge, and the second burst occurred 6 s later. Clinical signs observed in some dogs, but not all dogs exposed to PFBI included salivation, limb and/or muscle tension, and nonspecific signs of agitation. These results indicate that the cardiac sensitization no-observed-adverse-effect level (NOAEL) for PFBI is 3900 ppm, and the lowest-observed-adverse-effect-level (LOAEL) is 6200 ppm.

Four-Week Inhalation Study

The analytical concentrations (mean ± standard deviation) for the four PFBI exposure groups were 0 ± 0, 102 ± 7, 997 ± 28, and 10,000 ± 230 ppm. There was no PFBI aerosol formation during PFBI exposures. There was no mortality during the 4 weeks of study, and the only clinical sign of treatment was reduced activity during exposure in rats of the 10,000 ppm group. Body weight gain was reduced in male rats only of the 10,000-ppm group (Table 3). Food consumption was not different between control and PFBI exposed groups.

Results of blood sampling indicated mean hematology values were similar between all study groups. Except for triglycerides and T₄ levels, all other serum chemistries were either similar for all study groups or the changes observed were not related to PFBI concentration. Serum triglycerides increased significantly in a concentration-related manner in male rats of the 1000-and 10,000-ppm groups and in female rats of the 10,000-ppm group (Table 4). The increase in triglycerides was approximately twofold greater in rats of the 10,000-ppm group compared to control rats. Urine iodide levels were increased in male rats of the 1000-ppm group and in male and female rats of the 10,000-ppm group (Table 4). A large variation in urine iodide levels in some groups was attributed to one or two rats having high values, but all values measured were within an acceptable range per the laboratory’s experience. Levels of T₄ increased in PFBI-exposed rats, but levels of TSH and T₃ in PFBI-exposed rats were not statistically significantly different from control values (Table 5). The increase in serum T₄ was approximately threefold greater in male rats of the 1000- and 10,000-ppm groups compared to control males. In female rats of the 1000- and 10,000-ppm groups, the increase in serum T₄ was approximately twofold greater than control values.

Mean absolute organ weights were similar between control and PFBI-exposed rats, except for the 17% increase in liver weights of the 10,000-ppm female rats compared to liver weights of control females (data not shown). There were no treatment-related findings during gross necropsy (data not shown). The only treatment-related microscopic finding (data not shown) was hypertrophy/hyperplasia of goblet cells in the respiratory mucosa of the nasal septum (anterior region) in male and female rats of the 10,000-ppm PFBI group. The severity of this lesion was graded as minimal in all cases.

Bacterial Mutation Assay

In the preliminary toxicity test, PFBI was not toxic towards any tester strain, thus 5000 μg/plate was chosen as the highest dose level for the mutation test. No substantial increases in revertant colony numbers of any of the bacterial strains were observed following PFBI treatment at any dose level, in the absence or presence of S-9 (Table 6). The concurrent positive control compounds demonstrated the sensitivity of the assay and the metabolizing activity of the S-9 preparations (Table 6).

Chromosomal Aberration Assay

In the toxicity assessment, PFBI was highly toxic at concentrations ≥625 μg/ml in the absence of S-9. Dose levels of 39 to 200 μg/ml were selected for metaphase analysis in which 39 μg/ml was the highest nontoxic concentration. In the presence of S-9, PFBI was highly toxic at 313 μg/ml. Dose levels of 78 to 263 μg/ml were selected for metaphase analysis in experiments using S-9. Table 7 shows the results of metaphase analysis. No statistically significant increases were observed in the proportion of aberrant cells treated with PFBI compared to the solvent control cultures in the absence or presence of S-9. Positive-control compounds caused large statistically significant increases in the proportion of aberrant cells, demonstrating the efficacy of the S-9 fraction and the sensitivity of the test system.

DISCUSSION

The results of these studies indicate a low order of acute toxicity, as defined by EPA’s Toxicity Categories (EPA Health Effects Test Guidelines OPPTS 870.1000 Acute Toxicity Testing—Background) and the Department of Transportation’s toxicity categories for assigning hazardous materials to hazard zones and packing groups (CFR, Title 49—Transportation, Part 173). However, for chemicals that illicit cardiac sensitization, the results of the dog cardiac sensitization (to epinephrine) test become, in general, the most critical endpoint to consider for assessing acute health hazard. For PFBI, the LOAEL for cardiac sensitization was 6200 ppm and the NOAEL was 3900 ppm. Uncertainty factors (e.g., species extrapolation and sensitive populations) are not generally applied on results from the dog cardiac sensitization test because of the conservative nature of the test by design (Snyder, Bakshi, and Wagner 1997). Thus, the NOAEL value of 3900 ppm may be considered a justifiable acute exposure limit concentration for PFBI. The genotoxicity results observed following PFBI treatment indicated an absence of mutagenicity and clastogenicity. These results are only part of a battery of tests performed to evaluate a chemical’s potential for tumorigenicity. Therefore, though inconclusive, these results provide confidence that PFBI is not tumorigenic by direct acting genotoxic mechanisms.

Results of the 4-week subchronic study indicated PFBI has a low order of systemic toxicity, because concentrations as high as 10,000 ppm caused no tissue histopathologic effects, except minimal hypertrophy/hyperplasia in the upper respiratory tract. This effect was considered a nonspecific irritant effect, in that numerous chemicals produce similar results in rats following repeated inhalation exposure at high concentrations. An increase in serum triglycerides in rats exposed to 10,000 ppm PFBI (Table 4) suggests an interaction of PFBI on the triglyceride cycle and potential lipotoxicity or hepatotoxicity. However, other parameters measured in the 4-week study that are also indicators of liver toxicity, such as serum alanine aminotransferase (ALT), serum aspartate aminotransferase (AST), and liver histopathology, were not altered following PFBI exposure. Absolute and relative (to body weight and to brain weight) liver weights were mildly increased in female rats of the 10,000-ppm group, but not in male rats. The increase in serum triglycerides in male rats of the 1000-ppm group was not observed in female rats exposed to the same concentration of PFBI. Serum ALT, AST, liver weight, and liver histopathology were normal in rats exposed to 1000-ppm PFBI. Further investigation is needed to explain the increase in serum triglycerides caused by PFBI exposure.

A specific effect of PFBI is likely to be on the thyroid, because the thyroid is sensitive to compounds that interfere with iodine absorption, distribution, metabolism, and elimination. In the current 4-week study, serum T₄ increased in PFBI-exposed rats, but levels of TSH and T₃ were unchanged. Microscopically, the thyroids appeared normal in PFBI-treated rats. There is considerable scientific debate on interpreting the biological impact of changes in circulating levels of TSH, T₄, and T₃ and, further-more, extrapolating thyroid hormone results in animal studies to adverse effects in humans. This debate has been especially active for the chemical perchlorate, an inhibitor of iodine uptake. It is interesting to note that an Expert Review Panel of the Perchlorate State of the Science Symposium 2003 (University of Nebraska Medical Center 2003) considered

. . . developmental deficits or delays, and goiter and other effects of frank hypothyroid condition to be adverse effects. Subnormal concentrations of circulating thyroxine (T₄) and triiodothyronine (T₃) or supernormal concentrations of circulating thyrotropin (TSH) are considered to be adaptive. Iodide uptake inhibition and increased perchlorate excretion may be considered pre-adaptive.

At this time, the authors’ preliminary conclusion is that the observed increase in T₄ in PFBI-exposed rats is considered to be adaptive and not adverse, but that additional toxicology studies (e.g., 90-day, reproductive, etc.) need to be performed to provide a more definitive conclusion. Thus, the 4-week LOAEL for PFBI is 10,000 ppm, and the NOAEL is 1000 ppm.

There are limited toxicity data on perfluoroiodocarbons, because they are not produced as commercial products. One example where there are published toxicity data for a fluoroiodocarbon is trifluoroiodomethane (CF₃I) (Dodd et al. 1997a, 1997b, 1998, 1999), a replacement candidate for CF₃Br (Halon 1301). Unlike PFBI, CF₃I has a boiling point of –22.5°C and exists as a vapor at room temperature. Table 8 compares results of toxicity studies on PFBI reported here with results of toxicity studies reported by other investigators using CF₃I. In rats, CF₃I was less toxic than PFBI following single 4-h exposures, but was comparable with PFBI in producing cardiac sensitization in dogs. The criteria for LOAEL and NOAEL in the cardiac sensitization test were the same for both chemicals, and the tests were run in the same laboratory. Both CF₃I and PFBI were negative in mammalian cell genotoxicity screening assays, but CF₃I was positive in the Ames assay whereas PFBI was negative. One notable difference in methodology in the genotoxicity studies is that CF₃I was administered as a vapor, whereas PFBI was administered as a liquid. In the 2-week inhalation study with CF₃I, four groups of five male rats each were exposed 2 h/day, 5 days/week to 0, 30,000, 60,000, or 120,000 ppm (Dodd et al. 1997a). No deaths were observed, though lethargy and slight incoordination were noted in rats of the 60,000- and 120,000-ppm groups at the conclusion of each daily exposure. Mean body weight gains were depressed in rats of the 60,000- and 120,000-ppm groups. Serum thyroglobulin and reverse T₃ were increased at all CF₃I exposure levels. At necropsy, no gross lesions or differences in absolute or relative organ weights were noted. Histopathologic examination of the thyroid and parathyroid glands indicated no morphological abnormalities in the CF₃I-exposed rats. A LOAEL of 60,000 ppm was selected by the authors on the basis of clinical signs and depressed weight gains. The increases in serum thyroglobulin and reverse T₃ were not considered adverse effects, thus 30,000 ppm was selected by the authors as a NOAEL. When compared with the LOAEL and NOAEL of the 4-week inhalation study on PFBI reported here, the values are higher for CF₃I (Table 8). However, the CF₃I study exposed rats only 2 h/day for 14 days, whereas the PFBI study exposed rats 6 h/day for 20 days. Subsequently, a 13-week inhalation study (Dodd et al. 1997a) and a reproductive inhalation toxicity screen (Dodd et al. 1999) were conducted with CF₃I at concentrations ranging from 2000 to 80,000 ppm. Results indicated that the thyroid was the most sensitive organ (gland) of adverse effects following exposure, and that CF₃I was not a reproductive toxicant. Of interest, the EPA requested a health hazard assessment of the CF₃I toxicity database (Clewell and Lawrence 1999) for the purpose of establishing occupational exposure limits in conjunction with EPA’s SNAP program (Skaggs and Rubenstein 1999). For acute exposure, a ceiling of 2,000 ppm CF₃I was proposed based on the cardiac sensitization potential of CF₃I. For repeated (occupational) exposure, an 8-h time weighted average of 150 ppm CF₃I was proposed on the basis of potential systemic toxicity effects including thyroid hormone effects.

In conclusion, the results of these studies indicate a low order of general toxicity and an absence of genotoxicity following PFBI exposure. In general, the toxicity profile of PFBI appears to be similar to that of CF₃I.