Time course of pulmonary response of rats to inhalation of crystalline silica: histological results and biochemical indices of damage, lipidosis, and fibrosis.

Previous studies have determined that alpha-quartz (crystalline silica) can cause pulmonary inflammation, damage, and fibrosis. However, the temporal relationship between silica inhalation and pulmonary inflammation, damage, and fibrosis has not been fully examined. To address this gap in our knowledge of silica-induced pulmonary fibrosis, a chronic inhalation study using rats was designed. Specifically, rats were exposed to a silica aerosol (15 mg/m3 silica, 6 h/d, 5 d/wk, 116 d), and measurements of pulmonary inflammation, damage, and fibrosis were monitored throughout the study. We report (1) data demonstrating that the silica aerosol generation and exposure system produced a consistent silica aerosol of respirable size particles; (2) the time course of silica deposition in the lung; (3) calculations that demonstrate that the rats were not in pulmonary overload; (4) histopathological data demonstrating time-dependent enhancement of silica-induced alveolitis, epithelial hypertrophy and hyperplasia, alveolar lipoproteinosis, and pulmonary fibrosis in the absence of overload; and (5) biochemical data documenting the development of lipidosis, lung damage, and fibrosis.

Augmentation of pulmonary reactions to quartz inhalation by trace amounts of iron-containing particles.

Fracturing quartz produces silica-based radicals on the fracture planes and generates hydroxyl radicals (.OH) in aqueous media. .OH production has been shown to be directly associated with quartz-induced cell damage and phagocyte activation in vitro. This .OH production in vitro is inhibited by desferrioxamine mesylate, an Fe chelator, indicating involvement of a Fenton-like reaction. Our objective was to determine if Fe contamination increased the ability of inhaled quartz to cause inflammation and lung injury. Male Fischer 344 rats were exposed 5 hr/day for 10 days to filtered air, 20 mg/m3 freshly milled quartz (57 ppm Fe), or 20 mg/m3 freshly milled quartz contaminated with Fe (430 ppm Fe). High Fe contamination of quartz produced approximately 57% more reactive species in water than quartz with low Fe contamination. Compared to inhalation of quartz with low Fe contamination, high Fe contamination of quartz resulted in increases in the following responses: leukocyte recruitment (537%), lavageable red blood cells (157%), macrophage production of oxygen radicals measured by electron spin resonance or chemiluminescence (32 or 90%, respectively), nitric oxide production by macrophages (71%), and lipid peroxidation of lung tissue (38%). These results suggest that inhalation of freshly fractured quartz contaminated with trace levels of Fe may be more pathogenic than inhalation of quartz alone.

Monitoring of aromatic amine exposures in workers at a chemical plant with a known bladder cancer excess.

BACKGROUND: In April 1991, an excess of bladder cancer cases among workers employed at a chemical manufacturing facility in Niagara Falls, NY, was reported. This excess was primarily confined to 708 workers who had ever been employed in the rubber chemicals manufacturing area of the plant, where the aromatic amines aniline and o-toluidine have historically been used. PURPOSE: An environmental and biological monitoring survey was conducted to evaluate current exposures to aniline and o-toluidine in the rubber chemicals department. METHODS: Personal air sampling for aniline and o-toluidine was conducted with the use of a modified Occupational Safety and Health Administration (OSHA) 73 method. Urine samples were collected before and after work (i.e., pre-shift and post-shift, respectively) and stored at -70 degrees C. Base hydrolysis was used to convert acetanilide and N-acetyl-o-toluidine, metabolites of aniline and o-toluidine present in the urine, to the parent compounds. The parent compounds were extracted from the alkaline urine into butyl chloride and then back-extracted from the butyl chloride into aqueous hydrochloric acid. An aliquot of each acidic extract was subjected to ion-interaction reversed-phase liquid chromatography with coulometric electrochemical detection. Hemoglobin (Hb) was extracted from blood and stored at -70 degrees C. For the measurement of adducts of aniline, o-toluidine, and 4-aminobiphenyl (4-ABP), precipitated Hb was dissolved in 0.1 M sodium hydroxide in the presence of recovery standards, and the hydrolysate was extracted with hexane, derivatized with pentafluoropropionic anhydride, and analyzed by gas chromatography-mass spectrometry with negative chemical ionization. RESULTS: A total of 73 workers, including 46 of 64 exposed workers who were employed in the rubber chemicals department and had the potential for exposure to aniline and o-toluidine and 27 of 52 unexposed workers employed in other departments where aniline and o-toluidine were not used or produced, had data available for both aniline and o-toluidine and Hb adducts; 28 of the workers in the former group also had personal air-sampling data. Personal air sample measurements showed that airborne concentrations of aniline and o-toluidine were well within the limits allowed in the workplace by OSHA. Urinary aniline and o-toluidine levels, however, were substantially higher among exposed workers than among unexposed control subjects. The most striking differential was for post-shift urinary o-toluidine levels, which averaged (+/- standard deviation) 2.8 micrograms/L (+/- 1.4 micrograms/L) in unexposed subjects and 98.7 micrograms/L (+/- 119.4 micrograms/L) in exposed subjects (P = .0001). Average aniline-Hb and o-toluidine-Hb adduct levels were also significantly higher (P = .0001) among exposed workers than among unexposed control subjects. Average levels of adducts to 4-ABP, a potential contaminant of process chemicals, were not significantly different (P = .48), although three exposed workers had 4-ABP levels above the range in unexposed workers. CONCLUSIONS: The adduct data suggest that, among current workers, o-toluidine exposure substantially exceeds aniline exposure and that 4-ABP exposure, if it occurs at all, is not widespread. These data support the conclusion that occupational exposure to o-toluidine is the most likely causal agent of the bladder cancer excess observed among workers in the rubber chemicals department of the plant under study, although exposures to aniline and 4-ABP cannot be ruled out.

Particle activity and in vivo pulmonary response to freshly milled and aged alpha-quartz.

This study examined the possibility of freshly fractured alpha-quartz being more toxic and inflammatory in vivo than aged quartz of the same composition and particle size. Fresh quartz was generated by a jet mill, and used immediately, while aged dust was stored for two months before use. Both the production of hydrogen peroxide and hydroxyl radicals and the analysis of surface radicals verified the enhanced surface activity of fresh quartz. Male Fischer 344 rats were exposed to fresh or aged alpha-quartz by inhalation (20 mg center dot m-3, 5 h per day, 5 d per week, for 2 weeks) and their pulmonary responses were determined 1--3 d postexposure. Exposure to aged quartz resulted in an increase in cytotoxic and inflammatory parameters. In comparison, the inhalation of freshly cleaved quartz resulted in dramatically greater increases in all of the pulmonary responses. This finding suggests that exposure to freshly machined quartz may result in a greater risk of pulmonary disease.

Biological monitoring for occupational exposures to o-toluidine and aniline.

Epidemiological evidence that occupational exposure to o-toluidine and aniline is associated with an increased risk of bladder cancer led to efforts to identify biomarkers of workplace exposures to these aromatic amines. For the determination of o-toluidine and aniline in worker urine specimens, a method using high performance liquid chromatography (HPLC) followed by electrochemical detection was developed. The limits of detection were 0.6 microgram/l and 1.4 micrograms/l for o-toluidine and aniline, respectively. Recovery of o-toluidine and aniline from spiked urine averaged 86% and 93%, respectively, over a range of 4-100 micrograms/l. Reproducibility in the range 2-100 micrograms/l for analyses of split field samples was 13% (average RSD) for o-toluidine and 16% (average RSD) for aniline. Application of this method to pre- and post-shift samples collected from potentially exposed and unexposed workers indicated elevated concentrations of o-toluidine and aniline in urine from exposed workers. To develop methods for biomarkers of internal dose, o-toluidine binding to the blood proteins hemoglobin and albumin was investigated utilizing in-vivo (rodent) and in-vitro (hemoglobin and albumin) studies. Base-hydrolyzable protein adducts were analyzed by HPLC (fluorescence) and/or GC/electron capture (EC). The methods were compared for sample preparation requirements, selectivity and sensitivity. While the GC/EC method was more sensitive than HPLC, the presence of interfering peaks limited the utility of this approach. Results from these studies suggested that the HPLC method could be useful for determination of o-toluidine exposures in individuals acutely or chronically exposed to high levels.