Analysis of lung asbestos content

Asbestos and disease - a public health success story?

OBJECTIVE

This paper discusses the failure and success of society to decrease the adverse health effects of asbestos exposure on workers' health in relation to scientific knowledge.

METHODS

The findings are based on a narrative literature review.

RESULTS

Early warnings of the adverse health effects of workplace exposure to asbestos were published already in the 1930s. Serious health effects, such as malignancies and fibrosis due to occupational asbestos exposure, were highlighted in major medical journals and textbooks in late 1960s. New technologies could detect also asbestos fibers in the lung of non-occupational exposed persons in the 1970s. The first bans for using asbestos came in the early 1970s, and more general bans by authorities came in the 1980s and continue until today.

CONCLUSIONS

The rather late recognition of adverse effects of asbestos exposure in the general population and measures to decrease the exposure through more general bans came rather late. However, the very strong measures such as general bans in many countries have been a success. A Swedish study showed that the general ban and other measures have decreased the risk of malignancies due to occupational exposure. The effect of the bans on adverse effects in the general population has yet to be studied. Analysis of fibers in the lungs of persons born after the bans could be an efficient method.

Integration of inflammation, fibrosis, and cancer induced by carbon nanotubes

Carbon nanotubes (CNTs) are nanomaterials with unique physicochemical properties that are targets of great interest for industrial and commercial applications. Notwithstanding, some characteristics of CNTs are associated with adverse outcomes from exposure to pathogenic particulates, raising concerns over health risks in exposed workers and consumers. Indeed, certain forms of CNTs induce a range of harmful effects in laboratory animals, among which inflammation, fibrosis, and cancer are consistently observed for some CNTs. Inflammation, fibrosis, and malignancy are complex pathological processes that, in summation, underlie a major portion of human disease. Moreover, the functional interrelationship among them in disease pathogenesis has been increasingly recognized. The CNT-induced adverse effects resemble certain human disease conditions, such as pneumoconiosis, idiopathic pulmonary fibrosis (IPF), and mesothelioma, to some extent. Progress has been made in understanding CNT-induced pathologic conditions in recent years, demonstrating a close interconnection among inflammation, fibrosis, and cancer. Mechanistically, a number of mediators, signaling pathways, and cellular processes are identified as major mechanisms that underlie the interplay among inflammation, fibrosis, and malignancy, and serve as pathogenic bases for these disease conditions in CNT-exposed animals. These studies indicate that CNT-induced pathological effects, in particular, inflammation, fibrosis, and cancer, are mechanistically, and in some cases, causatively, interrelated. These findings generate new insights into CNT adverse effects and pathogenesis and provide new targets for exposure monitoring and drug development against inflammation, fibrosis, and cancer caused by inhaled nanomaterials.

Mesothelioma: cases associated with non-occupational and low dose exposures

OBJECTIVES

To estimate the importance of low dose exposure to asbestos on the risk of mesothelioma.

METHODS

A review of the literature.

RESULTS AND CONCLUSIONS

There is no evidence of a threshold level below which there is no risk of mesothelioma. Low level exposure more often than not contains peak concentrations which can be very high for short periods. There might exist a background level of mesothelioma occurring in the absence of exposure ot asbestos, but there is no proof of this and this "natural level" is probably much lower than the 1-2/million/year which has been often cited.

Mineral fibre analysis and routes of exposure to asbestos in the development of mesothelioma in an English region

OBJECTIVES

To compare the concentrations of inorganic fibres in the lungs in cases of mesothelioma and controls: to determine whether concentrations of retained asbestos fibres differ with the different exposures identified from interview; and to investigate the existence of a cut off point in concentrations of asbestos fibres that indicates occupational exposure.

METHODS

Case-control study; 147 confirmed cases of mesothelioma and 122 controls identified from deaths occurring in four districts of Yorkshire between 1979 and 1991. Surviving relatives were interviewed to determine lifetime exposure history to asbestos. Mineral fibre analysis was carried out on lung tissue from postmortem examinations.

RESULTS

Odds on high concentrations of retained asbestos fibres were greater in cases than controls. After excluding subjects with occupational and paraoccupational exposure, the odds on high concentrations were still greater in cases than controls, but only significantly so for amphiboles. There was only a weak relation between probability of occupational exposure to asbestos and concentrations of retained asbestos fibres, and no significant difference in fibre concentrations was found between subjects who had been exposed to asbestos through different routes: these comparisons were only based on small groups. There was considerable overlap in concentrations of retained asbestos fibres between cases and controls with and without histories of occupational exposure.

CONCLUSIONS

The study has confirmed previous results of higher concentrations of asbestos fibres in cases than controls, and has shown that this is still found in subjects with little evidence of occupational and para-occupational exposure. The overlap in concentrations of retained asbestos for different groups of subjects did not suggest a clear cut of value.

Asbestos lung burden and asbestosis after occupational and environmental exposure in an asbestos cement manufacturing area: a necropsy study

OBJECTIVE

The largest Italian asbestos cement factory had been active in Casale Monferrato until 1986: in previous studies a substantial increase in the incidence of pleural mesothelioma was found among residents without occupational exposure to asbestos. To estimate exposure to asbestos in the population, this study evaluated the presence of histological asbestosis and the lung burden of asbestos fibres (AFs) and asbestos bodies (ABs).

METHODS

The study comprises the consecutive series of necropsies performed at the Hospital of Casale Monferrato between 1985 and 1988. A sample of lung parenchima was collected and stored for 48 out of 55 necropsies. The AF concentration was measured with a TEM electron microscope with x ray mineralogical analysis. The ABs were counted and fibrosis evaluated by optical microscopy. The nearest relative of each subject was interviewed on occupational and residential history. Mineralogical and histological analyses and interviews were conducted in 1993-4.

RESULTS

Statistical analyses included 41 subjects with AF, AB count, and interview. Subjects without occupational exposure who ever lived in Casale Monferrato had an average concentration of 1500 AB/g dried weight (gdw); Seven of 18 presented with asbestosis or small airway lung disease (SAL). G2 asbestosis was diagnosed in two women with no occupational asbestos exposure. One of them had been teaching at a school close to the factory for 12 years. Ten subjects had experienced occupational asbestos exposure, seven in asbestos cement production: mean concentrations were 1.032 x 10(6) AF/gdw and 96,280 AB/gdw. Eight of the 10 had asbestosis or SAL.

CONCLUSION

The high concentration of ABs and the new finding of environmental asbestosis confirm that high asbestos concentration was common in the proximity of the factory. Subjects not occupationally exposed and ever living in Casale Monferrato tended to have higher AB concentration than subjects never living in the town (difference not significant). The concentrations of ABs and AFs were higher than those found in other studies on nonoccupationally exposed subjects.

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.

Risk assessment of oxidant gases and particulate air pollutants: uncertainties and research needs

The assessment of risks to human health associated with exposure to oxidant air pollutants has not received adequate attention despite the recognized public health threat posed by the ubiquitous presence of these compounds in the environment. In this article, research needs and uncertainties at each of the steps in the risk assessment of oxidant air pollutants are identified: hazard identification, dose-response assessment, exposure assessment, and risk characterization. Many of these limitations and uncertainties arise at the interface between the laboratory and the regulatory arenas. Therefore, as a case study, relevant methodologic problems associated with the application of experimental findings to the risk assessment of respirable dusts are also discussed. These issues include the extrapolation of animal data to the human case and extrapolation from high-dose to environmentally relevant, low-level exposures.

Epidemiological significance of mineral fiber persistence in human lung tissue

For the experimentalist, mineral fiber persistence may provide clues to disease mechanisms, for the epidemiologist, to the measurement of exposure. Qualitatively, this can be valuable when unsuspected exposures have been demonstrated as, for example, MMMF workers exposed to amosite or chrysotile workers to tremolite. Quantitatively, the potential of lung burden analyses to assess lifetime mineral fiber exposure has yet to be achieved with confidence. The difficulties are 2-fold, the first related to sampling and the second to the dynamics of biopersistence. Until some noninvasive method is found to identify and quantify numerically inorganic fibers in human tissue during life, epidemiological studies must depend on lung samples obtained at autopsy or thoracic surgery. This source is inevitably subject to seriously large and indefinable bias of various kinds. Of equal importance is the present uncertain state of knowledge concerning factors that determine what is present in the lung at any time. These determinants clearly include the dimensional features of airborne environmental particulates and characteristics that affect their durability in tissue.