[Acute silicosis. Clinical, radiologic, functional, and cytologic characteristics of the broncho-alveolar fluids. Observations of 6 cases]

We describe six cases of acute silicosis which were characterised by an intense exposure to pure silica; there was a rapid onset with diffuse abnormalities on the radiological image and severe respiratory abnormalities. The duration of occupational exposure to silica was four to eighteen years. Three patients presented with a cough associated with disabling dyspnoea (stage III and IV). The physical examination showed finger clubbing in three patients and rales and crepitations on auscultation in two patients. There was general debility in four of the cases with weight loss. The chest x-ray showed a rapid progress with confluence of the diffuse nodular opacities. Respiratory function tests showed a restrictive ventilatory defect (mean +/- standard error of mean: TLC 67 +/- 5%, Vital Capacity +/- 7%, FEV1 63.5 +/- 6%) and alteration in the transfer factor for carbon monoxide (DLCO: 49.5 +/- 5%). The initial broncho-alveolar lavage showed a lymphocytosis (23.6 +/- 4.2%) associated with an alveolar neutrophilia (7 +/- 2.5%). A lung biopsy was carried out in three patients and a transbronchial biopsy in one patient confirming the diagnosis of silicosis in three cases and of silicoproteinosis in one case. After a period of eighteen months to 14 years, four patients died either due to cardiopulmonary complications of their disease (two cases) or to intercurrent disorders (two cases). The last two patients are currently stable.

An overview of the role of mineral solubility in silicosis and asbestosis

Asbestosis and silicosis are fibrotic diseases initiated by the inhalation of silica-containing dusts, asbestos and quartz. There are various approaches for explaining the causes of these diseases. At present, our knowledge on the matter indicates that silicic acid dissolved from these minerals, contact between macrophages and minerals, highly reactive and oxidative species formed on the mineral surface, and lysosomal enzymes released upon engulfment of particulate mineral of appropriate size all contribute to various extents to the initiation of fibrosis. Among these mineral solubility seems to have a substantial contribution as a causative factor.

Reactive oxygen species and silica-induced carcinogenesis

Although silica has recently been designated as a carcinogen, its mechanism of carcinogenesis is not fully understood. Recent studies suggest that free-radical reactions may play an important role in the initiation and progression of cancer. This article summarizes literature on the generation of reactive oxygen species (ROS) directly from silica and from silica-stimulated cells. It also summarizes information concerning the role of ROS in silica-induced DNA damage as well as in silica-induced cell proliferation, including the effects of silica on the activation of nuclear transcription factors, induction of growth factors and oncogene expression, redox regulation of the p53 tumor suppressor gene, induction of apoptosis, and division of damaged cells. Understanding the role of ROS in silica-mediated reactions may help develop therapeutic agents to block silica-induced free radical reactions and thus prevent or attenuate silica-induced carcinogenesis.

Tentative explanatory variable of lung dust concentration in gold miners exposed to crystalline silica

INTRODUCTION

The first objective of the study was to investigate the relationships between quantitative lung mineral dust burdens, dust exposure history, and pathological fibrosis grading in silicotic workers. The second objective was to evaluate the association between particle size parameters, concentration of retained silica particles and the severity of the silicosis. Sixty-seven paraffin-embedded lung tissue samples of silicotic patients were analyzed. The cases of silicosis included 39 non-lung cancer patients and 28 patients with lung cancer. All of the cases were gold miners in the Province of Ontario, Canada.

MATERIAL AND METHODS

Particles, both angular and fibrous, were extracted from lung parenchyma by a bleach digestion method, mounted on copper microscopic grids by a carbon replica technique, and analyzed by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Quartz concentration was also determined by X-ray diffraction (XRD) on a silver membrane filter after the extraction from the lung parenchyma.

RESULTS

Total particles, silica, clay, and quartz also increase in concentration with increased age at death, although the trends are not statistically significant. Quartz concentration has a statistically significant correlation with the silicosis severity score (r = +0.45, p < 0.001), with the geometric mean concentration increasing from 2.24 micrograms/mg in the group having silicosis severity score less than 1 to 4.80 micrograms/mg in group with highest score. Quartz concentration is the only significant explanatory variable of the silicosis severity with a regression coefficient of +0.41 (p < 0.001).

CONCLUSION

Among several dust exposure variables extracted from the work history of the miners, the calendar year of first exposure was the primary significant determinant of lung retained total particles, silica, and clay minerals, except for quartz. A statistically significant linear relationship between lung quartz concentration and silicosis severity in the gold miners was observed (p < 0.001). Among the several types of lung particles detected, quartz was the only significant determinant of the silicosis severity in the gold miners in this study and vice versa, although it explained only 20% of the variation in the severity. This study suggested no significant linear relationship between the duration of dust exposure and the lung burden of any particle types in the gold miners.

Effects of silica exposure on substance P immunoreactivity and preprotachykinin mRNA expression in trigeminal sensory neurons in Fischer 344 rats

Trigeminal sensory neurons innervate the nasal cavity and may release substance P (SP) upon exposure to inhaled irritants. The purpose of this study was to determine if silica dust, an occupational irritant causing inflammation, activates sensory neurons supplying the nasal cavity. Male Fischer 344 rats were placed in inhalation chambers and exposed daily to 2 mg/m3 of fresh silica (average diameter 1 microm) for 6 mo. Following exposure, the trigeminal ganglia (TG) were removed and prepared for SP immunocytochemistry and for preprotachykinin (PPT) autoradiographic in situ hybridization. The SP-like immunofluorescence in TG neurons was subjectively categorized as high, moderate, or low (background) intensity. In situ hybridization autoradiographs were quantified on the basis of grain density using digital imaging analysis. The SP immunoreactivity and PPT mRNA expression in the TG neurons were significantly increased after silica inhalation. The proportion of highly positive SP-immunoreactive neurons shifted from 1.30 +/- 0.58% in controls to 11.30 +/- 1.15% after silica treatment. The neurons exhibiting high grain density for PPT mRNA increased from 1.50 +/- 0.87% in controls to 11.67 +/- 0.58% in the silica group. Thus, inhalation of silica causes upper airway irritation resulting in increased levels of immunoreactive neuronal SP and PPT mRNA. These findings suggest that silica activates sensory pathways that may be involved in nasal inflammation.

Silica, compensated silicosis, and lung cancer in Western Australian goldminers

OBJECTIVES

Silica has recently been reclassified as carcinogenic to humans based largely on the observed increase in rates of lung cancer in subjects with silicosis. Other recent reviews have arrived at different conclusions as to whether silicosis or silica itself is carcinogenic. This study aims to examine exposure-response relations between exposure to silica and subsequent silicosis and lung cancer in a cohort of goldminers.

METHODS

2,297 goldminers from Kalgoorlie in Western Australia were examined in 1961, 1974, and 1975. Data were collected on respiratory symptoms, smoking habits, and employment history. Subjects were followed up to the end of 1993. Survival analyses for lung cancer mortality and incidence of compensated silicosis were performed with age and year matched conditional logistic regression analyses.

RESULTS

89% of the cohort were traced to the end of 1993. 84% of the men had smoked at some time and 66% were current smokers. 1386 deaths occurred during the follow up period, 138 from lung cancer, and 631 subjects were compensated for silicosis. A strong effect of smoking on mortality from lung cancer, and a smaller effect on the incidence of compensated silicosis was found. There was a strong effect of duration and intensity of exposure on the incidence of silicosis. The risk of mortality from lung cancer increased after compensation for silicosis. Of all direct measures of exposure to silica, only log cumulative exposure was significantly related to incidence of lung cancer, but this effect disappeared once the onset of silicosis was taken into account.

CONCLUSIONS

The incidence of silicosis was clearly related to exposure to silica and the onset of silicosis conferred a significant increase in risk for subsequent lung cancer, but there was no evidence that exposure to silica caused lung cancer in the absence of silicosis.

[Cutaneous sarcoidosis secondary to inhalation of wall insulating material particles]

BACKGROUND

Sarcoidosis is a systemic disease defined by multiple granulomas. We report a case of sarcoidosis which occur concomitantly or secondary to foreign body granuloma of the lung.

CASE REPORT

A 50-year-old women presented with Lofgren syndrome, subcutaneous granulomatous nodular lesions on the arms and legs. Computed tomography revealed a foreign body granuloma of the lung centered on particles of mural isolation material that the patient had inhaled accidentally. Analysis of the foreign body particles showed non crystalline silica, calcite monohydrate and phenol resin.

DISCUSSION

Recent studies support the hypothesis that sarcoidosis is an antigen-driven disease involving pulmonary T-cell activation. The antigen-mediated reaction may be caused by infectious agents, particularly mycobacteria, occupational and environmental agents (beryllium) or as in our observation following inhalation of mural isolation material particles.

Obliterative central bronchitis due to mineral dust in patients with pneumoconiosis

OBJECTIVE

We studied at autopsy a distinctive obliterative bronchitis in three persons with pneumoconiosis and hilar node fibrosis.

METHODS

Lungs were evaluated macroscopically, microscopically, and with energy-dispersive spectroscopy.

RESULTS

Chest roentgenogram demonstrated right middle lobe syndrome in one patient; bronchostenosis was seen at bronchoscopy in another. The stenotic sites were in perihilar bronchi and showed an upper lobe predominance. Fibrosis with silicotic nodules involved the bronchus, peribronchial tissue, and adjacent lymph nodes. Simple coalworkers' pneumoconiosis was observed in two patients; the third had complicated, mixed dust fibrosis.

CONCLUSION

Obliterative bronchitis represents an unusual fibrotic response to free crystalline silica. The process may occur simultaneously in the adjacent lymph node and the bronchial wall; however, it need not be associated with complicated pneumoconiosis. Clinically, obliterative bronchitis may masquerade as bronchogenic carcinoma.

The reawakening of national concern about silicosis

From West Texas to West Virginia, from California to New York, in industries from oil refining to coal mining and work settings from foundries to shipyards, the United States is experiencing an epidemic of silicosis, a preventable disease. Silica sand has been linked to cancer, and the International Agency for Research on Cancer has named silica as a probable human carcinogen. This article analyzes the reawakening of national concern about silicosis and the social, economic, and epidemiologic factors that have led scientists, policy makers, industrial hygienist, and labor and industry representatives to reassess the danger that silica sand poses to the health of an estimated two million workers in this country.

Toxicity and occupational health hazards of coal fly ash (CFA). A review of data and comparison to coal mine dust

Coal fly ashes (CFA) are complex particles of a variable composition, which is mainly dependent on the combustion process, the source of coal and the precipitation technique. Toxic constituents in these particles are considered to be metals, polycyclic aromatic hydrocarbons and silica. The purpose of this review was to study the in vitro and in vivo data on coal fly ash and relate the studied endpoints to the role of (crystalline) silica, considering its recent classification as a human carcinogen. For most of the effects coal mine dust was chosen as a reference, since it contains up to 10% of crystalline silica (alpha-quartz) and is well studied both in vivo and in vitro. Most studies on fly ash toxicity were not designed to elucidate the effect of its silica-content nor did they include coal mine dust as a reference. Taking this into account, both in vitro and in vivo experimental studies show lower toxicity, inflammatory potential and fibrogenicity of CFA compared to silica and coal mine dust. Although in vitro and in vivo studies suggest genotoxic effects of fly ash, the data are limited and do not clarify the role of silica. Epidemiological studies in fly ash exposed working populations have found no evidence for effects commonly seen in coal workers (pneumoconiosis, emphysema) with the exception of airway obstruction at high exposure. In conclusion, the available data suggest that the hazard of coal fly ash is not to be assessed by merely adding the hazards of individual components. A closer investigation of 'matrix' effects on silica's toxicity in general seems an obligatory step in future risk assessment on fly ashes and other particles that incorporate silica as a component.

Silica-induced pleural disease: an unusual case mimicking malignant mesothelioma

A 57-year-old man with a history of exposure to silica for 32 years presented with pleural thickening of the lower lobe of the left lung and a chronic right-sided pleural effusion without any radiographic evidence of parenchymal nodules in either lung. Light microscopic examination of a left visceral pleural biopsy specimen revealed markedly thickened pleura with fibrosis and macrophages containing birefringent silica and silicates. Occasional rounded intrapleural silicotic nodules were present. The underlying lung tissue did not show fibrosis or silicotic nodules. An energy-dispersive x-ray analysis confirmed the presence of silica. In the absence of lung involvement, this case represents a very unusual pathologic reaction caused by silica and silicates and adds to the clinical differential diagnosis of chronic pleuritis and malignant mesothelioma.

[The role of free radicals in the etiopathogenesis of systemic sclerosis]

This article reviews the current concept in the ethiology and pathogenesis of systemic sclerosis. It is suggested that free radicals play a crucial role in pathomechanisms of scleroderma. In addition, the influence of some environmental agents (silica, bleomycin, alcohol, toxic oil) on free radical production and subsequent induction of scleroderma or scleroderma-like syndrome is also described.

A battle for compensation for Welsh coal miners: JS Haldane v "Sericite" Jones, 1932-1934

Toward the end of the 1920s, technical advances in mining led to an increase in airborne burdens of dust in the South Wales coal mines. This coincided with a dramatic increase in the incidence of disability and death from respiratory disease among the miners. For their condition to be compensable, claimants were required to have worked with rock containing more than 50% 'free silica.' Dr W.R. Jones, a mining geologist, was asked to help obtain compensation for those claimants who could not satisfy the 'free silica' condition. He was unable to identify high-silica rocks where none had been said to exist. He did however, successfully argue the brief against the eminent Professor J.S. Haldane (who was the dominant authority, having had lengthy experience in the field of health and mining), for the fibrous form of sericite being commonly the important agent responsible for pneumoconiosis. As a consequence, the category of miner eligible for compensation was broadened. Evidence was gathered worldwide that supported the hypothesis that silicates and not just crystalline silica could cause pneumoconiosis. Despite the suspicions raised about the special power of mineral fibers during this public debate, some 40 years were to elapse before potential health hazards from fibers other than asbestos were to be taken seriously and investigated.

Occupational asthma in a cheese packer

Occupational asthma is an increasingly common clinical problem. A worker who develops asthma for the first time when starting work in a new environment may be straightforward to diagnose. However, when asthma occurs after a latent period following initial exposure, or when a pre-existing asthmatic develops work-related symptoms, the occupational link may be less easy to appreciate. This case report concerns a cheese factory worker with pre-existing asthma who experienced severe symptoms when a new process was introduced for drying grated cheese and was able to return to work only after the process was modified. The drying agent responsible has not been previously reported as a cause of asthma.

Investigation of silicone oil and fumed silica in an adjuvant animal model

Human adjuvant disease is the label given to a syndrome that resembles a connective tissue disease such as scleroderma and that has been hypothesized to follow augmentation mammoplasty with silicone gel implants or silicone with adulerants. To date, there is no proof that pure silicone is the cause of these symptoms. The cases presented in the literature suggest a comparison to the events seen in the rat adjuvant arthritis model. Male Lew/SsN rats (n = 65) were used. To evaluate both the adjuvant and antigenic properties of the gel implant, variations of the standard Freund's complete adjuvant inoculum were prepared. Tested were the abilities of low molecular weight silicone to act as an adjuvant and for fumed silica to act as an antigen by modifying a rat adjuvant arthritis model to include silicone and fumed silica. On day 0, 0.25 ml of each inoculum was injected intradermally into the plantar aspect of the hindfoot of each rat. The foot diameter was recorded at each time period, compared with the contralateral hindfoot, and normalized to controls at regular time periods over the course of 120 days. Silicone oil did not act as an adjuvant. Furthermore, fumed silica alone did not act as an antigen; however, it is capable of eliciting a reaction that is both delayed and uncharacteristic of the rat adjuvant arthritis model. These results indicate that "human adjuvant disease" may be inappropriate and misleading.

Electron microscopic microanalysis of bronchoalveolar lavage: a way to identify exposure to silica and silicate dust

OBJECTIVES

The diagnostic implications of finding non-fibrous inorganic particles in bronchoalveolar lavage (BAL) fluid has not been fully assessed. The aim of this study has been to measure the silica and non-fibrous silicates in BAL fluid from populations with different exposures to inorganic dust, and to find whether such measurement is useful for diagnostic purposes.

MATERIALS AND METHODS

BAL samples from 19 subjects with only environmental exposure to inorganic dust (group A, mean (SD) age 50.7 (15.2)), 23 subjects with normal chest x ray films exposed to silica or silicates at work (group B, mean (SD) age 52.0 (12.4)), and 15 subjects with a previous diagnosis of silicosis (group C, mean (SD) age 68.0 (6.5)) were studied. Absolute and relative cell counts were found, and the samples were prepared for microanalysis by electron microscopy (EM). Firstly, semiquantitative x ray microanalysis was performed to find the level of silicon (Si) (peak/background Si) and this was followed by microanalysis of individual particles by EM. Variables related to the level of Si detected were assessed with multivariate analysis.

RESULTS

Detected levels were higher in group B (2.09, 95% confidence interval (95% CI) 1.56 to 2.82) and C (1.50, 95% CI 1.07 to 2.12) than in group A (0.87, 95% CI 0.66 to 1.16) (P < 0.05, Dunett t test). A first multivariate analysis showed that exposure to silica or silicates was the only determinant of the level of Si expressed as log peak/background Si, when adjusted for age, sex, smoking habit, and cell count. A second multivariate analysis with microanalysis of individual particles as an independent variable showed the silica count to be the main predictor of detected concentration of Si. Silica and non-aluminium silicates together explain 55.5% (R2) of the variation in detected levels of Si.

CONCLUSIONS

Detected levels of Si in BAL fluid depend on silica count and are higher in subjects with exposure to inorganic dust at work, but will not discriminate between exposed subjects with and without silicosis. Because semiquantitative x ray microanalysis does not accurately define exposure to non-silica inorganic particles, this measurement must be followed by EM microanalysis of individual particles in most cases, especially when exposure to silicates or metal dust is suspected.

Soil derived dust as a source of silica: aerosol properties, emissions, deposition, and transport

Quartz is an abundant mineral in wind generated dust throughout the United States. Of the 18.9 million tons of particles smaller than 10 microns (PM10) dust emitted into the atmosphere by the wind, a significant fraction is silica. Transport of some of this silica to populated areas is possible.

Noncancer inhalation toxicology of crystalline silica: exposure-response assessment

Silicosis from inhalation of silica has long been recognized as an occupational hazard. Concern has arisen regarding the potential risk of silicosis from ambient silica (primarily quartz dust). This presentation reviews available data regarding ambient silica levels and estimates of the risk of silicosis at low exposure levels as they relate to the current U.S. Environmental Protection Agency National Ambient Air Quality Standards (NAAQS) for particulate matter. Current data indicate that for individuals not compromised by other respiratory ailments and for ambient environments expected to sustain 10% or less silica fraction in particulate matter with a mean aerodynamic diameter of < or = 10 microns (PM10), maintenance of the 50 micrograms/m3 annual NAAQS for PM10 is adequate to protect against fibrotic effects from ambient silica exposures. Issues such as the large divergence of risk estimates within the occupational setting (particularly at high cumulative exposures) and factors to consider for extrapolating risk in an occupational setting to risk from ambient exposure are discussed.

Criteria for conducting quantitative risk assessments for silica

Should quantitative risk assessment using epidemiologic data be performed for a substance such as silica dust? The criteria for conducting this step have been described by Hertz-Picciotto (1995) for individual epidemiology studies, and this paper applies the criteria to a body of cancer epidemiology research, indicating what the evidence is lacking. Discussion focuses on the cancer risk assessment calculations currently in the literature, the need for more research, and the relevance to decision making.