Toxicology of chlorofluorocarbon replacements

Thyroid homeostasis in B6C3F1 mice upon sub-chronic exposure to trifluoroiodomethane (CF3I)

Trifluoroiodomethane (CF₃I) is a fire suppressant gas with potential for use in low global-warming refrigerant blends. Data from studies in rats suggest that the most sensitive health effect of CF₃I is thyroid hormone perturbation, but the rat is a particularly sensitive species for disruption of thyroid homeostasis. Mice appear to be less sensitive than rats but still a conservative model with respect to humans. The purpose of this study was to test tolerance and thyroid response to CF₃I in B6C3F1 male mice. Male mice were exposed to CF₃I for 6 h per day, for 28 days, via whole body exposure at concentrations of 2500, 5000 and 10,000 ppm. A 16-day recovery period was included to evaluate reversibility. No adverse clinical signs were observed throughout the study, and body weights were unaffected by exposure. CF₃I exposure had no effect on thyroid histology. An increase in relative thyroid weight was observed at 10,000 ppm on day 28 but not in a separate group of animals evaluated on day 29, and thyroid weight was not different from controls at 44 days. Slight and sporadic changes in serum triiodothyronine, thyroxine, and thyroid-stimulating hormone were observed but did not follow a consistent pattern with respect to timing, dose, or direction. Overall, exposure at up to 10,000 ppm (1.0%) of CF₃I gas for 28 days produced no overt general toxicity and only transient, recoverable effects on thyroid weight and hormones at certain concentrations. On the basis of the effect of CF₃I exposure on the thyroid, including evaluation of thyroid histopathology, the no observed adverse effect level for this study is 10,000 ppm. Considering the apparently greater toxicity reported in prior studies in male rats, our data suggest a species difference between rats and mice in terms of susceptibility to CF₃I-induced thyroid hormone perturbation.

The development of environmentally acceptable fluorocarbons

Chlorofluorocarbons (CFCs) were introduced in the 1930s as the safe replacements for the toxic and flammable refrigerants being used at that time. Subsequently, hydrochlorofluorocarbons (HCFCs) were also developed. In addition to refrigerant applications, they were used as foam blowing agents, as solvents and as propellants for many aerosols. In the 1970s and 1980s, concern developed about their environmental impact, specifically on stratospheric ozone depletion. Industry began to consider acceptable replacements. In 1987, many of the governments of the world came together and drafted the Montreal Protocol, calling upon Industry to initially phase out production of the CFCs and later HCFCs. Within 4 months of the signing of the Montreal Protocol, the 15 global major producers joined together to form the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS), which sponsored research into environmental effects and the Program for Alternative Fluorocarbons toxicity Testing, PAFT), which examined the toxicology of potential replacements for the CFCs and HCFCs. Nine replacements were identified by companies and, through this international cooperation; toxicology programs were designed, conducted, and evaluated without duplication of effort and testing; consequently these new products were introduced within less than 10 years. Indeed the Montreal Protocol has been recognized as the most appropriate international treaty to phase-down HFCs. In 2016 the Kigali Amendment to the Montreal Protocol set out a phase-down schedule for the consumption and production of HFCs. In order to reduce the consumption and emissions of high GWP HFCs. Recently lower GWP HFCs and very low GWP HFOs (hydrofluoroolefins and HCFOs (hydrochlorofluoroolefins) have been introduced into a range of applications. Summaries of the toxicology profiles of some of the original CFCs and HCFCs, the replacements and the new post-PAFT replacements are described. The chemicals in this review include CFC-11, CFC-12, CFC-113, CFC-114, HCFC 22, HCFC-123, HCFC-124, HCFC-141b, HCFC-142b, HCF-32, HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-245ea, HFC-245fa, HFO-1234yf, HFO-1234ze, and HCFO-1233zd.

Inhalation Toxicity and Genotoxicity of Hydrofluorocarbon (HFC)-236fa and HFC-236ea

The acute, subchronic, and developmental and genetic toxicity of hydrofluorocarbon (HFC)-236fa and HFC-236ea were evaluated to assist in establishing proper handling guidance. In acute inhalation studies, rats were exposed whole body for 4 hours to various concentrations of each isomer. Based on the lack of mortality, the approximate lethal concentration for HFC-236ea for male rats was > 85,000 ppm. For HFC-236fa, the LC50 for males and females (combined) was > 457,000 ppm. Narcotic-like effects, e.g., prostration, incoordination, and reduced motor activity, were observed only during exposure to either isomer, but were not evident after termination of exposure. In cardiac sensitization studies, HFC-236ea induced cardiac sensitization at ≥ 35,000 ppm, with fatal responses occurring at 50,000 ppm and greater. For HFC-236fa, a cardiac sensitization response was observed at 150,000 ppm and greater but not at 100,000 ppm. A fatal cardiac sensitization response was observed in one dog exposed to 150,000 ppm HFC-236fa. In 90-day subchronic inhalation studies, male and female rats were exposed whole body to HFC-236ea at concentrations of 0, 5000, 20,000, or 50,000 ppm for 6 hours/day, 5 days/week. Similarly, male and female rats were exposed whole body to HFC-236fa at concentrations of 0, 5000, 20,000, or 50,000 ppm for 6 hours/day, 5 days/week. During exposure, narcotic-like effect (reduced acoustic startle response) was observed at 50,000 ppm with both isomers, although there appeared to be an adaptive response to this effect as the study progressed. With HFC-236ea, dilatation of the seminiferous tubules, without effects on germ or Sertoli cells, was observed only in rats at 50,000 ppm. No other effects on in-life measures or on clinical or anatomic pathology, including histopathology, were observed for either isomer. In rat developmental toxicity studies, no evidence of embryotoxicity or teratogenicity was observed with either isomer exposed up to 50,000 ppm during gestational days 7 to 16. Also, no developmental toxicity was observed in rabbits exposed to HFC-236fa at concentrations of up to 50,000 ppm during gestational days 7 to 19. Neither of the HFC-236 isomers was mutagenic in the Ames reverse mutation assay or clastogenic in the chromosomal aberration assay with human lymphocytes. No increase in chromosomal aberrations was observed in in vivo micronucleus studies with either isomer.

Ecotoxicology of organofluorous compounds

Organofluorous compounds have been developed for myriad purposes in a variety of fields, including manufacturing, industry, agriculture, and medicine. The widespread use and application of these compounds has led to increasing concern about their potential ecological toxicity, particularly because of the stability of the C-F bond, which can result in chemical persistence in the environment. This chapter reviews the chemical properties and ecotoxicology of four groups of organofluorous compounds: fluorinated refrigerants and propellants, per- and polyfluorinated compounds (PFCs), fluorinated pesticides, and fluoroquinolone antibiotics. These groups vary in their environmental fate and partitioning, but each raises concern in terms of ecological risk on both the regional and global scale, particularly those compounds with long environmental half-lives. Further research on the occurrence and toxicities of many of these compounds is needed for a more comprehensive understanding of their ecological effects.

Generation of a novel fluorescent product, monochlorofluorescein from dichlorofluorescin by photo-irradiation†

Dichlorofluorescin (DCFH), a widely used fluorescent probe for reactive oxygen species (ROS) was decomposed completely and generated two distinct fluorescent products by photo-irradiation at 254 nm for 30 min. In the previous study, we had shown that one was dichlorofluorescein (DCF), a well known oxidized product of DCFH. In this study we investigated the other product and identified it as monochlorofluorescein (MCF) by 1H-NMR and fast atom bombardment/mass spectrum (FAB/MS) analyses. MCF was generated by photo-irradiation, but not by ROS. On the other hand, DCF was produced by both photo-irradiation and ROS. MCF showed similar fluorescent emission spectrum to DCF, however, its fluorescence intensity was more than that of DCF. The kinetic study suggested that MCF was not generated from DCF but from monochlorofluorescin, which might be generated from DCFH by photo-irradiation.

Uncontrolled occupational exposure to 1,1-dichloro-1-Fluoroethane (HCFC-141b) is associated with acute pulmonary toxicity

BACKGROUND

The toxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b), a hydrochlorofluorocarbon (HCFC), is low according to animal studies. However, pulmonary manifestations associated with acute HCFC exposure by inhalation have not been reported as yet in man. We evaluated the pulmonary effects of HCFC-141b inhalation, caused by an accident, in previously healthy individuals.

METHODS

The subjects in this study were 15 workers in whom unpleasant symptoms developed after inhaling HCFC-141b at work. Clinical manifestations, radiologic findings, and changes in pulmonary function and airway hyperresponsiveness (AHR) over time were assessed, and BAL fluid analyses findings for four subjects were compared with those of four healthy volunteers (control subjects).

RESULTS

(1) Cough, shortness of breath, and malaise developed in most patients, but only two patients complained of a sore throat. (2) A high-resolution CT scan of the chest revealed bilateral diffuse ground-glass opacities that were predominant in upper lung zones. (3) The mean (+/- SD) FVC was 71.4 +/- 18.86% predicted, and the mean FEV(1)/FVC ratio was 92.9 +/- 4.25%. Eleven patients (73%) showed restrictive ventilatory impairments during the initial tests. FVC gradually improved, and the FEV(1)/FVC ratio gradually decreased with time. (4) AHR was observed in four subjects during the initial tests. (5) BAL fluid samples revealed significantly higher neutrophil counts than those in control subjects.

CONCLUSIONS

Overexposure to HCFC-141b was associated with parenchymal lung injury that was characterized by ground-glass opacities, elevated BAL neutrophil counts, and restrictive ventilatory impairment. Restrictive impairments improved with time after exposure.

Non-positive autoimmune responses against CYP2E1 in refrigeration mechanics exposed to halogenated hydrocarbons

The aim of the study was to determine if occupational exposure to hydrofluorocarbons (HFC) and hydrochlorofluorocarbons (HCFC) generates autoimmune responses against CYP2E1. HFCs and HCFCs have replaced the chlorofluorocarbons (CFC) in e.g. refrigeration installations and air-conditioning systems. During the substitution period, refrigeration mechanics reported symptoms like asthma, influenza-like reactions, and joint troubles. These symptoms resemble those of chronic inflammatory diseases with an autoimmune component. Since exposure to structurally similar chemicals, e.g. halothane, has previously been associated with autoimmune responses and diseases, autoimmunity among the refrigeration mechanics might hypothetically explain the reported inflammatory symptoms. Serum from 44 Swedish men, occupationally exposed to halogenated hydrocarbons, was screened for antibodies against CYP2E1 with enzyme-linked immunosorbent assay. Thirty of the workers had asthma, joint problems or influenza-like symptoms whereas 14 of them had no such symptoms. They were all selected from a cohort of 280 refrigeration mechanics. Unexposed, healthy, Swedish men (n=35) constituted control group. The study was approved by the Ethics Committee at Karolinska Institutet. No increase in autoantibodies against CYP2E1 was detected among the occupationally exposed workers as compared to the unexposed controls. Further, there was no difference in antibody titer between the exposed workers with symptoms and the exposed, asymtomatic workers or the unexposed controls. The present study does not completely exclude a connection between exposure and effect but makes the relation less likely at these exposure levels.

Toxicokinetics of 1,1,1,2-tetrafluoroethane (HFC-134a) in male volunteers after experimental exposure

The aim of this study was to determine the uptake and disposition of inhaled 1,1,1,2-tetrafluoroethane (HFC-134a) in humans. Ten male volunteers were exposed to 500 ppm HFC-134a (2 h, 50 W exercise). The HFC-134a levels were monitored in blood, exhaled air and urine up to 19 h post-exposure. The concentration in blood increased rapidly, reaching a plateau of 9.4+/-1.9 microM (mean+/-S.D.) within 30 min, followed by a fast post-exposure decrease. HFC-134a in expired air decreased rapidly as well and in parallel with that in blood. The post-exposure urinary excretion was 0.002% of the inhaled amount, and the half-time was 58 min (pooled data). A physiologically based toxicokinetic (PBTK) model was developed for further analysis. Experimental and simulated time courses in blood and exhaled air agreed well in all 10 subjects. Further, the late decay in blood was consistent with a wash-out of HFC-134a from fat tissues, with a half-time of 114+/-21 min. The simulated relative uptake during exposure was 3.7+/-0.5%. No remarkable findings were observed in the electrocardiographic recordings. Fibrinogen in plasma increased 1 day after exposure, whereas no effects on C-reactive protein, serum amyloid A protein, D-dimer or uric acid were seen. Further studies are needed to investigate the possible inflammatory response.

An overview of environmental hazards and exposure risk of hydrofluorocarbons (HFCs)

Hydrofluorocarbons (HFCs) are being used as replacements for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) that cause significantly stratospheric ozone depletion and global warming. HFCs under commercial uses as cleaning solvents in the electronic components, blowing agent in the foamed plastics, refrigerant in the air conditioning units and refrigerators, fire suppression agent in the fire protection, propellant in the metered dose inhalers (MDIs), and dry etching agent in the semiconductor manufacturing. Among these HFCs, 1,1,1,2-tetrafluoroethane (HFC-134a) is the most widely used one. From the environmental, ecological, and health points of view, it is urgent to mitigate and control the emissions of these HFCs from a diversity of commercial applications and industrial processes. This article aims to introduce these HFCs in commercial uses and environmental hazards (i.e., global warming, photochemical potential, flammability safety, environmental partition and ecotoxicity). Further, the updated data on the human toxicity, occupational exposure and health risk of these HFCs (esp., HFC-134a) are addressed in this review paper.

Medical aerosol propellant interference with infrared anaesthetic gas monitors

BACKGROUND

1,1,1,2 Tetrafluoroethane is a hydrofluoroalkane (HFA) that is replacing chlorofluorocarbons (CFC) as a medical aerosol propellant in an attempt to reduce damage to the ozone layer. This study compared the effects of HFA- and CFC-based inhalers on four anaesthetic gas monitoring systems.

METHODS

The HFA- and CFC-based inhalers were activated in close proximity to the sample line of two Datex Ohmeda, an Agilent and a Siemens infrared anaesthetic agent monitoring systems. The effects were recorded on each system for five common anaesthetic agents.

RESULTS

The HFA inhaler caused either maximal false positive readings (with the exception of desflurane) or transient measurement failure on all systems. The Datex Ohmeda AS/3 system misidentified the HFA inhaler as carbon dioxide at low concentration (2 +/- 0 mm Hg). The CFC-based inhaler caused a minor false-positive reading (0.4 +/- 0%) for halothane only on the Datex Ohmeda AS/3 system only and was misidentified as carbon dioxide at 33.3 (sd 2.1) mm x Hg and 22.4 (8.9) mm x Hg by the Agilent and Siemens systems.

CONCLUSIONS

The HFA inhaler adversely affected all equipment tested. The infrared spectra of HFA and the common anaesthetic gases have considerable overlap at the 8-12 microm range that is not shared by the CFCs. The differences in spectral overlap explain the different effects of the HFA and CFC propellants. Anaesthetic gas concentration data may be erroneous using the HFA-based inhalers.

Selective inactivation of rat and bovine olfactory cytochrome P450 by three haloethanes

The effects of halothane, 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-1-fluoroethane (HCFC-141b) on the P450 system in olfactory and hepatic microsomes of bovine and rat have been investigated. In the in vitro experiments, all three compounds decreased olfactory CYP-dependent activities in microsomes from both species, especially under anaerobic conditions, halothane showing the greatest effect. Hepatic activities were not affected. A selective olfactory CYP depletion was also observed in vivo after treatment with halothane, but not with HCFC-123 or HCFC-141b. A loss of olfactory ethoxycoumarin-O-deethylase activity was also found both in vitro and in vivo experiments, suggesting that a CYP2A isoform may be the main target of inactivation. The present results therefore suggest that CYP2A, the major isoform expressed in the olfactory tissue of mammals, may be particularly prone to catalyze the reductive metabolism of halothane both in anaerobic and aerobic conditions.

Bioactivation and toxicity in vitro of HCFC-123 and HCFC-141b: role of cytochrome P450

The bioactivation and cytotoxicity in vitro of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-1-fluoroethane (HCFC-141b), two replacements for some ozone-depleting chlorofluorocarbons (CFC), were investigated in rat liver microsomes and isolated rat hepatocytes. Both compounds were activated by cytochrome P450 to reactive metabolites, as indicated by: (i) the depletion of exogenous and cellular glutathione, (ii) the increased LDH release from hepatocytes, (iii) the loss of microsomal P450 content and activities, and (iv) the formation of free radical species observed in the presence of the two compounds. Moreover, the formation of two stable metabolites and an increased production of conjugated dienes, a marker of lipid peroxidation, were observed for both HCFC-123 and HCFC-141b. The biotransformation of both compounds by pyridine- and phenobarbital-induced rat liver microsomes and the inhibition of LDH release by 4-methylpyrazole and troleandomycin indicate that P450 2E1, 2B and, possibly, also 3A are the isoforms involved in the bioactivation and toxicity of HCFC-123 and HCFC-141b in the rat.

Neoantigen formation and clastogenic action of HCFC-123 and perchloroethylene in human MCL-5 cells

In this study, the metabolic activation of 2,2-dichloro-1,1,1-trifluoroethane (hydrochlorofluorocarbons-123, HCFC-123), halothane or 1,1-dichloro-1-fluoroethane (HCFC-141b) was compared to that of perchloroethylene, using lymphoblastoma derived cell lines expressing human CYP1A1, CYP1A2, CYP2E1, CYP2A6 and CYP3A4 (MCL-5 cells). A dose dependent increase in micronucleus formation was detected over a nominal concentration range of 0.05-2 mM for HCFC-123 and halothane, but this was not seen with HCFC-141b. No dose response for HCFC-123 was seen in a control cHo1 cell line not expressing this cytochrome P450's. Cell lines expressing individual human cytochrome P-450 (CYP) forms were also used to define the enzymes responsible for the clastogenic events and to investigate the formation of immunoreactive protein by microsomal fractions. It was shown that CYP2E1 or CYP2B6 catalysed the clastogenic response, but CYP2D6, CYP3A4, CYP1A2 or CYP1A1 all appeared to be inactive. The formation of neoantigenic trifluoroacetylated protein adducts by microsomal mixtures incubated with HCFC-123 and NADPH was catalysed primarily by CYP2E1 and to a lesser extent by CYP2C19, whereas, only trace levels of immunoreactive protein were seen with microsomes expressing CYP2B6 or CYP2C8. With perchloroethylene as a substrate, the extent of activation was low in comparison with HCFC-123, as judged by the absence of micronuclei formation in the MCL-5 cell line and the weak immunoreactivity of proteins following Western blotting. CYP1A2, CYP2B6 and CYP2C8 appeared to be responsible for perchloroethylene immunoreactivity and in contrast to the findings with the HCFC's, no activation of perchloroethylene by CYP2E1 could be detected. These results show that even though both saturated and unsaturated halocarbons can result in neoantigen formation, there is a marked difference in the specificity of the CYP enzymes involved in their metabolic activation.

Bioactivation to free radicals and cytotoxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b)

1. The in vitro bioactivation by rat liver microsomes and the cytotoxicity in rat hepatocytes of 1,1-dichloro-1-fluoroethane (HCFC-141b), a replacement for some ozone depleting chlorofluorocarbons (CFC), have been investigated. 2. Anaerobic incubations of liver microsomes from pyridine-induced rats with HCFC-141b in the presence of the spin-trapping agent N-t-butyl-alpha-phenylnitrone (PBN) resulted in the formation of a typical ESR radical signal. 3. In the presence of HCFC-141b, a dose-dependent formation of conjugated dienes was observed that was partially inhibited by PBN, glutathione (GSH) and vitamin C. Moreover, HCFC-141b increased the release of lactate dehydrogenase (LDH) and the depletion of cellular glutathione in isolated rat hepatocytes under both normoxic and hypoxic conditions. 4. HCFC-141b-dependent cytotoxicity was completely prevented by PBN under both conditions and it was partially prevented under normoxic conditions by the broad-spectrum P450 inhibitor metyrapone, the P4502E1 specific inhibitor 4-methylpyrazole and the P4503A-specific inhibitor troleandomycin. Interestingly, HCFC-141b-dependent glutathione depletion was not prevented by PBN, metyrapone, 4-methylpyrazole or troleandomycin, whereas two glutathione depletors, 2,6-dimethyl-2,5-heptadien-4-one (phorone) and diethylmaleate, partially prevented LDH release. 5. The present results indicate that HCFC-141b is reductively metabolized in vitro to free radical intermediates by P450, in particular by the CYP2E1 and, to a lower extent, CYP3A isoforms, leading to peroxidative membrane damage and glutathione-independent cytotoxicity.

Epidemic of liver disease caused by hydrochlorofluorocarbons used as ozone-sparing substitutes of chlorofluorocarbons

BACKGROUND

Hydrochlorofluorocarbons (HCFCs) are used increasingly in industry as substitutes for ozone-depleting chlorofluorocarbons (CFCs). Limited studies in animals indicate potential hepatotoxicity of some of these compounds. We investigated an epidemic of liver disease in nine industrial workers who had had repeated accidental exposure to a mixture of 1,1-dichloro-2,2,2-trifluoroethane (HCFC 123) and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC 124). All nine exposed workers were affected to various degrees. Both compounds are metabolised in the same way as 1-bromo-1-chloro-2,2,2-trifluoroethane (halothane) to form reactive trifluoroacetyl halide intermediates, which have been implicated in the hepatotoxicity of halothane. We aimed to test whether HCFCs 123 and 124 can result in serious liver disease.

METHODS

For one severely affected worker liver biopsy and immunohistochemical stainings for the presence of trifluoroacetyl protein adducts were done. The serum of six affected workers and five controls was tested for autoantibodies that react with human liver cytochrome-P450 2E1 (P450 2E1) and P58 protein disulphide isomerase isoform (P58).

FINDINGS

The liver biopsy sample showed hepatocellular necrosis which was prominent in perivenular zone three and extended focally from portal tracts to portal tracts and centrilobular areas (bridging necrosis). Trifluoroacetyl-adducted proteins were detected in surviving hepatocytes. Autoantibodies against P450 2E1 or P58, previously associated with halothane hepatitis, were detected in the serum of five affected workers.

INTERPRETATION

Repeated exposure of human beings to HCFCs 123 and 124 can result in serious liver injury in a large proportion of the exposed population. Although the exact mechanism of hepatotoxicity of these agents is not known, the results suggest that trifluoroacetyl-altered liver proteins are involved. In view of the potentially widespread use of these compounds, there is an urgent need to develop safer alternatives.