Approaches to evaluating the toxicity and carcinogenicity of man-made fibers: summary of a workshop held November 11-13, 1991, Durham, North Carolina.

The Workshop on Approaches to Evaluating the Toxicity and Carcinogenicity of Man-Made Fibers (MMF) was held in Durham, North Carolina, on November 11-13, 1991. The goal of the workshop was to reach a consensus, or to determine the extent to which a consensus existed, in two areas. Participants were asked to identify scientifically sound approaches for evaluating the toxicity and carcinogenicity of man-made fibers based on today's science and to determine research appropriate for study during the next 5 years that can provide an improved scientific basis for future revisions of approaches used to evaluate man-made fiber toxicity and carcinogenicity. During the first day, a series of "state of knowledge" presentations were made to provide all participants with a common data base from which to interact and discuss scientific issues. The workshop participants were assigned to one of four discussion groups, which met separately in three half-day sessions following the first day of presentations. All groups discussed the same topics: exposure assessment, hazard identification, and dose-response information needed to integrate to characterize risk in the first session; approaches to obtaining the needed information in the second session; and recommended approaches and guidelines for evaluating the toxicity and carcinogenicity of MMF and research needs in the third session. The workshop participants reconvened as a whole after each discussion session, and one member from each group reported the group's conclusions. A closure period was also included at the end of the workshop for review and discussion of items that had been considered during the workshop. The primary conclusions reached were the following: -All fiber types capable of depositing in the thorax are not alike in their pathogenic potential. -Only fiber samples with dimensions similar to those to which humans can inhale should be tested. -A complete characterization (i.e., dimensions, fiber number, mass, and aerodynamic diameter) of the fiber aerosol and retained dose is essential. -Appropriate aerosol generation methods must be used for inhalation studies in order to preserve fiber lengths. -A tiered approach to toxicity evaluation is recommended that includes: 1. In vitro screening for durability, surface properties, cytotoxicity, and similar properties, etc; 2. Short-term inhalation or other in vivo studies; 3. That chronic inhalation studies are the "gold standard" (i.e., provide most appropriate data for risk characterization). -The rat is the most appropriate species for inhalation studies. -In chronic inhalation studies, animals should be retained to at least 20% survival after 2-year exposure. -Serial lung burden analyses are an essential component of inhalation studies and are essential for understanding exposure-dose-response relationships. -Studies oriented to understanding mechanisms of toxicity and carcinogenicity are important adjuncts to traditional toxicity studies. -Histopathological analyses of tissues of the respiratory tract represent primary endpoints for evaluating effects of inhaled fibers. Major effects include pulmonary fibrosis, lung tumors, and mesotheliomas. Experimental tissues should be archived for future studies; wherever possible, handling and preservation of tissues should be done in a way that maximizes their future use in mechanistic studies. -Potential human exposures throughout the entire life-cycle of the fiber must be considered and fibrous material for toxicologic studies prepared accordingly. -Intracavity studies are inappropriate for risk characterization but can play a useful screening role in assessing fiber toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Meeting new challenges in industrial toxicology.

A major challenge facing toxicologists is the development of improved human risk assessment methods based on understanding the mechanisms of chemical carcinogenesis in animal and human cells. Such methods will enable us to close the gap between experimental toxicity data and their relevance to human health. We have used 1,3-butadiene (BD), a potent mouse carcinogen but weak oncogen in the rat, as a model compound to determine if genetic toxicity results from animal and human cells can aid in extrapolating animal toxicity data to man. Sister chromatid exchange and micronucleus induction data for BD parallel the chemical's carcinogenicity in the mouse and rat. Effort is underway to determine BD's genotoxic effects in human cells in vitro and to compare these effects in corresponding cultured rodent cells. This approach will help identify which species is a better predictor of the human response. If the BD research proves useful in assessing its hazard to man, similar methods can be extended to other major chemicals.

Pulmonary response to impaired lung clearance in rats following excessive TiO2 dust deposition.

Rats were exposed to TiO2 by the inhalation route at concentrations of 0, 10, 50, or 250 mg/m3 for 6 hr/day, 5 days/week for 2 years. Lung weights of rats at 10 mg/m3 were within normal limits after 2 years exposure. Lung weights increased significantly after 6 months at 50 mg/m3 and after 3 months at 250 mg/m3. After 2 years exposure, TiO2 retention in dried lung was 3.1% (26.5 mg per lung) at 10 mg/m3, 16.9% (124 mg per lung) at 50 mg/m3, and 28% (665 mg per lung) at 250 mg/m3. Lung clearance mechanisms appeared to be overloaded at 250 mg/m3. Dust particles were retained in the lung in a dose-related fashion, but there was no significant difference in lung clearance rate between 10 and 50 mg/m3. Lung response at 10 mg/m3 satisfied the biological criteria for a "nuisance dust," while adverse effects resulting from gradually accumulated particles (8.1%, 67.7 mg per lung) were found after 1 year of exposure to 50 mg/m3. An early pulmonary response indicating an overloaded lung clearance mechanism was manifested by massive accumulation of dust-laden macrophages (dust cells), foamy dust cells, free particles, or cellular debris derived from disintegrated foamy dust cells in the alveoli adjacent to the alveolar ducts. Alveolar proteinosis also appeared to be an important marker of an overloaded lung clearance mechanism and was observed at 50 and 250 mg/m3 after 1 year of exposure. Cholesterol granulomas were developed with degenerative foamy dust cells at 50 and 250 mg/m3 after 1 year of exposure. After 2 years exposure at 250 mg/m3, bronchioalveolar adenomas occurred in the alveoli showing type II pneumocyte hyperplasia, while cystic keratinizing squamous carcinomas were developed from squamous metaplasia of alveoli showing bronchiolarization in the alveolar duct region. Since the lung tumors were a unique type of experimentally induced tumors under exaggerated exposure conditions and have not usually been seen in man or animals, their relevance to man is questionable.

Transmigration of titanium dioxide (TiO2) particles in rats after inhalation exposure.

Titanium dioxide (TiO2) has been used extensively in the manufacturing of white pigment and has generally been regarded as a nuisance dust in animals and man. After inhalation exposure, little is known about transmigration routes and potential toxic effects of translocated particles in other organs. In order to answer these questions, rats were exposed to TiO2 by inhalation exposure at concentrations of 0, 10, 50, and 250 mg/m3 for 2 years. A few free particles were retained in the nasal and tracheobronchial epithelium without any cellular damage, but aggregates of dust-laden macrophages (dust cells) were found in the lymphoid tissue of the submucosa. Inhaled particles were mostly engulfed by alveolar macrophages and confined sharply to the alveolar duct region at 10 and 50 mg/m3, while dust cells were scattered throughout alveoli at 250 mg/m3. A fraction of the inhaled particles was retained in the membranous pneumocytes and interstitial macrophages. A dense accumulation of dust cells was found in the perivascular and peribronchial lymphoid tissue. Some dust cells entered peribronchial lymphatics or pulmonary blood vessels and the general circulation. Dust cells in the hyperplastic peribronchial lymphoid tissue were exposed directly in the luminal surface of the airways and were subsequently eliminated via airways. Massive dust deposition was observed in the tracheobronchial lymph nodes. Dust transmigration was markedly reduced in the cervical lymph nodes, and only a trace amount of dust particles was found in the mesenteric lymph nodes. Some dust cells entered either blood or lymphatic vessels in the lymph nodes and then migrated into the general circulation. The incidence of extrapulmonary dust deposition in the liver or spleen was increased in a dose-related fashion similar to the lung dust burden. Since there was no tissue response to translocated particles in the lymph nodes, spleen, or liver, potential adverse health effects appear to be negligible.

Pulmonary response of rats exposed to titanium dioxide (TiO2) by inhalation for two years.

Rats were exposed to TiO2 by inhalation exposure to concentrations of 0, 10, 50, and 250 mg/m3 for 6 hr/day, 5 days/week for 2 years. There were no abnormal clinical signs, body weight changes, or excess mortality in any exposed group. Exposed groups showed slight increases in the incidence of pneumonia, tracheitis, and rhinitis with squamous metaplasia in the anterior nasal cavity. The pulmonary response at 10 mg/m3 satisfied the biological criteria for a "nuisance dust." The lung reaction was characterized by dust-laden macrophage (dust cell) infiltration in the alveolar ducts and adjoining alveoli with hyperplasia of Type II pneumocytes. Rats at 50 and 250 mg/m3 exposure concentrations revealed a dose-dependent dust cell accumulation, a foamy macrophage response, Type II pneumocyte hyperplasia, alveolar proteinosis, alveolar bronchiolarization, cholesterol granulomas, focal pleurisy, and dust deposition in the tracheobronchial lymph nodes. Minute collagenized fibrosis occurred in the alveolar walls enclosing large dust cell aggregates. The pulmonary lesions with massive dust accumulation appeared to be the result of an overwhelmed lung clearance mechanism at 250 mg/m3 exposure. Bronchioloalveolar adenomas and cystic keratinizing squamous cell carcinomas occurred at 250 mg/m3 exposure, while no compound-related lung tumors were found in rats exposed to either 10 or 50 mg/m3. In addition to excessive dust loading in the lungs of rats exposed chronically at 250 mg/m3, the lung tumors were different from common human lung cancers in terms of tumor type, anatomic location, tumorigenesis, and were devoid of tumor metastasis. Therefore, the biological relevance of these lung tumors and other pulmonary lesions for man is negligible.

Cardiac arrhythmias and blood levels associated with inhalation of Halon 1301.

In this study we determined airborne concentrations of Halon 1301 (CBrF3) and the associated blood levels which produce cardiac arrhythmias in dogs. Beagle dogs were exposed by inhalation to Halon 1301 concentrations ranging from 5 to 20% and, after five minutes of exposure, were given epinephrine by intravenous injection (8--10 micrograms/kg). Electrocardiograms were recorded. Serious cardiac arrhythmias were produced with concentrations of 7.5% or greater. A second group of dogs with cannulas surgically implanted in the common carotid artery and external jugular vein were exposed to 5%, 7.5% and 10% Halon 1301 for 60 minutes. The blood concentration of Halon 1301 increased rapidly during the first five minutes of exposure, plateaued within twenty minutes, and declined rapidly after exposure. The mean blood concentrations at equilibrium were directly proportional to airborne concentrations: at a concentration of 5% in air -- arterial 19.2 micrograms/mL, venous 14.6 micrograms/mL; at 7.5% in air -- arterial 30.6 micrograms/mL, venous 28.4 micrograms/mL; and at 10% in air -- arterial 402 micrograms/mL, venous 32.1 microgram/mL. Since there was no rapid increase in blood fluorocarbon concentration after the first five minutes of exposure, it does not seem likely that risk of cardiac sensitization would increase with increased length of exposure to a given concentration.

Urinary bladder tumors in dogs from 4,4'-methylene-bis (2-chloroaniline) (MOCA).

Six female beagle dogs were given a daily dose of 100 mg MOCA, by capsule, 3 days per week for the first 6 weeks and then 5 days per week continuously for periods up to 9.0 years. The dose varied from 8 to 15 mg/kg body weight/day among the dogs. Six female beagle dogs were kept as untreated controls. The test was terminated after 9.0 years of treatment. The average plasma glutamic-pyruvic transaminase activity of the dogs fed MOCA was higher than that of the controls during the first and last two years on test. During the eighth and ninth years the urine sediment from MOCA dogs contained excessive numbers of erythrocytes, leukocytes, and epithelial cells. Some epithelial cells contained abnormalities that suggested neoplasia in the genitourinary tract. One MOCA dog, sacrificed after 8.3 years on test was found to have a papillary transitional cell carcinoma of the urinary bladder. Of four MOCA dogs sacrificed after 9.0 years on test, three were found to have papillary transitional cell carcinomas of the urinary bladder and one had a combined transitional cell carcinoma and adenocarcinoma of the urethra. The urethral tumor had metastasized to the liver, but the papillary transitional cell carcinomas found in the other four dogs did not invade the muscle layers of the bladder wall and did not metastasize. Since no urinary bladder tumors were found in the six control dogs, MOCA was considered to be carcinogenic for the urinary bladder of dogs under the conditions employed (p less than 0.025, Fisher's Exact Test, one tail). Three of five MOCA dogs contained hyperplastic nodules in the liver with no such nodules in six control dogs (p greater than 0.05, Fisher's Exact Test, one tail). This was considered to be suggestive of an effect of MOCA treatment.

Toxic gases from fires.

The major lethal factors in uncontrolled fires are toxic gases, heat, and oxygen deficiency. The predominant toxic gas is carbon monoxide, which is readily generated from the combusion of wood and other cellulosic materials. Increasing use of a variety of synthetic polymers has stimulated interest in screening tests to evaluated the toxicity of polymeric materials when thermally decomposed. As yet, this country lacks a standardized fire toxicity test protocol.

Liver and urinary bladder tumors in dogs from 3,3'-dichlorobenzidine.

Six female beagle dogs were given, by capsule, a daily oral dose of 100 mg of 3,3'-dichlorobenzidine (DCB), 3 times per week for 6 weeks, then 5 times per week continuously for periods up to 7.1 years. The DCB test was terminated after 7.1 years. Six untreated female beagle dogs served as controls for several tests and were sacrificed after 8.3 to 9.0 years on test. All 6 DCB dogs had an elevated plasma glutamic-pyruvic transaminase activity during the first 3 years on test; two dogs showed persistent elevation throughout the test. One DCB dog, sacrificed in extremis after 3.5 years on test, had no tumors. Another DCB dog, sacrificed in extremis after 6.6 years on test, developed an undifferentiated carcinoma of the liver with metastases to many organs; this dog also had a papillary transitional cell carcinoma of the urinary bladder. Of the 4 remaining DCB dogs sacrificed after 7.1 years on test, 3 developed hepatocellular carcinomas and all 4 had papillary transitional cell carcinomas of the urinary bladder. No liver or urinary bladder tumors were found in the 6 control dogs. DCB was found to be carcinogenic for the liver and urinary bladder in dogs under the conditions employed (p less than .025, Fisher's Exact Test, one tail).

Liver and lung tumors in dogs from 4,4'-methylene-bis(2-methylaniline).

Six female beagle dogs were given, by capsule, a daily dose of 100 mg 4,4'-methylene-bis(2-methylaniline) (MeMDA), 3 times per week for 6 weeks, then 5 times per week for 5 weeks, at which time the dose was reduced to 50 mg 5 times per week, continuously for periods up to 7.0 years. Six female beagle dogs were kept as untreated controls for several studies and were sacrificed after 8.3 to 9 years test. MeMDA dogs developed renal atrophy with an elevated blood urea nitrogen during an approximate six-month period prior to death or being sacrificed in extremis. As three of three MeMDA dogs that survived for 5.2 years to 7.0 years developed hepatocellular carcinomas and two of the three dogs also developed primary lung tumors, with no liver or lung tumor in six control dogs, MeMDA was considered to be carcinogenic for the dog (liver tumors: p less than .05; lung tumors: p less than 10; Fisher's Exact Test, one tail).

The effect of myocardial infarction on the cardiac sensitization potential of certain halocarbons.

We have previously shown that many halocarbons and hydrocarbons are capable of producing cardiac sensitization. Briefly, the test method involved exposure of healthy, unanesthetized, beagle dogs to various inspired levels of sensitizing agent, followed by an intravenous dose (8 mug/kg) of epinephrine. Along, this epinephrine dose produces only mild ECG alterations, but, at threshold levels of a sensitizing agent, may induce a serious cardiac arrhythmia and sometimes death. Using the same test protocol, dogs with experimentally-induced myocardial infarctions were used to determine whether this type of heart condition might significantly lower the threshold for cardiac sensitization. Test results on three halocarbons showed no greater potential for cardiac sensitization among dogs having recovered from myocardial infarction as compared to normal, healthy animals.