Evaluation of the genotoxicity potential and chronic inhalation toxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b)

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.

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.

The genotoxicity of ambient outdoor air, a review: Salmonella mutagenicity

Mutagens in urban air pollution come from anthropogenic sources (especially combustion sources) and are products of airborne chemical reactions. Bacterial mutation tests have been used for large, multi-site, and/or time series studies, for bioassay-directed fractionation studies, for identifying the presence of specific classes of mutagens, and for doing site- or source-comparisons for relative levels of airborne mutagens. Early research recognized that although carcinogenic PAHs were present in air samples they could not account for the majority of the mutagenic activity detected. The mutagenicity of airborne particulate organics is due to at least 500 identified compounds from varying chemical classes. Bioassay-directed fractionation studies for identifying toxicants are difficult to compare because they do not identify all of the mutagens present, and both the analytical and bioassay protocols vary from study to study. However, these studies show that the majority of mutagenicity is usually associated with moderately polar/highly polar classes of compounds that tend to contain nitroaromatic compounds, aromatic amines, and aromatic ketones. Smog chamber studies have shown that mutagenic aliphatic and aromatic nitrogen-containing compounds are produced in the atmosphere when organic compounds (even non-mutagenic compounds) are exposed to nitrogen oxides and sunlight. Reactions that occur in the atmosphere, therefore, can have a profound effect on the genotoxic burden of ambient air. This review illustrates that the mutagenesis protocol and tester strains should be selected based on the design and purpose of the study and that the correlation with animal cancer bioassay results depends upon chemical class. Future emphasis needs to be placed on volatile and semi-volatile genotoxicants, and on multi-national studies that identify, quantify, and apportion mutagenicity. Initial efforts at replacing the Salmonella assay for ambient air studies with some emerging technology should be initiated.

Inhalation toxicity and genotoxicity of hydrochlorofluorocarbon (HCFC)-225ca and HCFC-225cb

The acute, subchronic and genetic toxicity of the hydrochlorofluorocarbons HCFC-225ca and HCFC-225cb were evaluated to assist in establishing proper handling guides. In acute inhalation studies, rats were exposed for 4 h to various concentrations of each isomer. Based on the mortality incidence, the LC50 value for HCFC-225cb for males and females (combined) was 36800 ppm. For HCFC-225ca, the LC50 for males and females (combined) was 37300 ppm. Narcotic-like effects, e.g. prostration, incoordination and reduced motor activity, were observed during exposure to either isomer, but these signs were not evident 15 min after termination of exposure. Histopathological examination of the liver revealed an increase in mitotic figures with vacuolation of hepatocytes and fluid-filled, congested hepatic sinusoids. In cardiac sensitization studies, HCFC-225cb induced a cardiac sensitization response at 20000 ppm, with one fatal response, whereas a blend of the two isomers (45% HCFC-225ca/55% HCFC-225cb) produced a cardiac sensitization response at 15000 ppm. In 4-week subchronic inhalation studies, male and female rats were whole-body exposed to HCFC-225cb at concentrations of 0, 1000, 5000 or 15000 ppm for 6 h a day, 5 days per week. Similarly, male and female rats were whole-body exposed to HCFC-225ca concentrations of 0, 50, 500 or 5000 ppm for 6 h a day, 5 days per week. During exposure, narcotic-like and irritant effects were observed. A dose-related decrease in cholesterol and triglycerides was observed in the treated rats, with males being affected more than females. Increases in liver weight were observed in most male and female rats exposed to either isomer. The increase in liver weight was consistent in male rats with microscopic evidence of hepatocyte hypertrophy. Although liver weight was increased in female rats, no hepatocyte enlargement was observed in treated female rats. Increases in cytochrome P-450 and beta-oxidation activities were also observed in male and female rats exposed to either isomer. Neither of the HCFC-225 isomers was mutagenic in the Ames reverse mutation assay, or clastogenic in the chromosomal aberration assay with Chinese hamster lung cells. Also, neither isomer induced unscheduled DNA synthesis in liver cells. However, both isomers were clastogenic in the chromosomal aberration assay with human lymphocytes in the absence of S-9. No increases in aberrant cells were observed in activated cells exposed to either isomer.

Rodent Leydig cell tumorigenesis: a review of the physiology, pathology, mechanisms, and relevance to humans

Leydig cells (LCs) are the cells of the testis that have as their primary function the production of testosterone. LCs are a common target of compounds tested in rodent carcinogenicity bioassays. The number of reviews on Leydig cell tumors (LCTs) has increased in recent years because of its common occurrence in rodent bioassays and the importance in assessing the relevance of this tumor type to humans. To date, there have been no comprehensive reviews to identify all the compounds that have been shown to induce LCTs in rodents or has any review systematically evaluated the epidemiology data to determine whether humans were at increased risk for developing LCTs from exposure to these agents. This review attempts to fill these deficiencies in the literature by comparing the cytology and ontogeny of the LC, as well as the endocrine and paracrine regulation of both normal and tumorigenic LCs. In addition, the pathology of LCTs in rodents and humans is compared, compounds that induce LC hyperplasia or tumors are enumerated, and the human relevance of chemical-induced LCTs is discussed. There are plausible mechanisms for the chemical induction of LCTs, as typified by agonists of estrogen, gonadotropin releasing hormone (GnRH), and dopamine receptors, androgen receptor antagonists, and inhibitors of 5alpha-reductase, testosterone biosynthesis, and aromatase. Most of these ultimately involve elevation in serum luteinizing hormone (LH) and/or LC responsiveness to LH as proximate mediators. It is expected that further work will uncover additional mechanisms by which LCTs may arise, especially the role of growth factors in modulating LC tumorigenesis. Regarding human relevance, the pathways for regulation of the hypothalamo-pituitary-testis (HPT) axis of rats and humans are similar, such that compounds that either decrease testosterone or estradiol levels or their recognition will increase LH levels. Hence, compounds that induce LCTs in rats by disruption of the HPT axis pose a risk to human health, except for possibly two classes of compounds (GnRH and dopamine agonists). Because GnRH and prolactin receptors are either not expressed or are expressed at very low levels in the testes in humans, the induction of LCTs in rats by GnRH and dopamine agonists would appear not to be relevant to humans; however, the potential relevance to humans of the remaining five pathways of LCT induction cannot be ruled out. Therefore, the central issue becomes what is the relative sensitivity between rat and human LCs in their response to increased LH levels; specifically, is the proliferative stimulus initiated by increased levels of LH attenuated, similar, or enhanced in human vs. rat LCs? There are several lines of evidence that suggest that human LCs are quantitatively less sensitive than rats in their proliferative response to LH, and hence in their sensitivity to chemically induced LCTs. This evidence includes the following: (1) the human incidence of LCTs is much lower than in rodents even when corrected for detection bias; (2) several comparative differences exist between rat and human LCs that may contribute, at least in part, to the greater susceptibility of the rat to both spontaneous and xenobiotic-induced LCTs; (3) endocrine disease states in man (such as androgen-insensitivity syndrome and familial male precocious puberty) underscore the marked comparative differences that exist between rats and man in the responsiveness of their LC's to proliferative stimuli; and (4) several human epidemiology studies are available on a number of compounds that induce LCTs in rats (1,3-butadiene, cadmium, ethanol, lactose, lead, nicotine) that demonstrate no association between human exposure to these compounds and induction of LC hyperplasia or adenomas. (ABSTRACT TRUNCATED)

Acute and subchronic toxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b)

The acute and subchronic toxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b), a CFC alternative, was evaluated in several acute and subchronic studies to assist in establishing proper handling guides. Data from acute toxicity studies in rats and rabbits demonstrated that HCFC-141b has very low acute toxicity. HCFC-141b was not a skin irritant, but was a mild eye irritant, in rabbits and was not a skin sensitizer in guinea pigs. Skin application of HCFC-141b to rabbits at 2000 mg/kg body weight produced no adverse effects. Oral administration at 5000 mg/kg body weight did not cause any deaths or clinical signs of toxicity in rats. The 4-hr LC50 for HCFC-141b was about 62,000 ppm in rats. Repeated exposures of rats for 6 hr/day, 5 days/wk for up to 90 days at concentrations of 2000, 8000 or 20,000 ppm did not result in significant adverse effects. Minor, but dose-dependent, reductions in body weight were observed in male and female rats during the 90-day study. Decreased responsiveness was also observed in rats but only at 20,000 ppm. An increase in serum cholesterol or triglycerides was observed in male and female rats at 20,000 ppm, and in males at 8000 ppm. No specific organ pathology was noted in these subchronic inhalation studies. The no-observable-adverse-effect level (NOAEL) from these studies was 8000 ppm. Results from other studies demonstrate that HCFC-141b was not neurotoxic in rats. As with trichlorofluoroethane (CFC-11), a cardiac sensitization response to an intravenous epinephrine challenge occurred in dogs with HCFC-141b at 5000 ppm and higher concentrations in experimental screening studies.