Technique dependent variations in asbestos burden as illustrated in a case of nonoccupational exposed mesothelioma

Measurements of asbestos burden in tissues

Asbestos inhaled into the lung is recognized as a potential causal agent for the development of diseases in man. The diseases induced by asbestos include lung cancer, fibrosis of the lung (asbestosis), and extrapulmonary tumors including mesothelioma (a tumor of the serosal membrane), as well as fibrosis and other changes in the pleura linings. The cause of these diseases can often be more specifically linked to asbestos exposure once tissue burden of asbestos is established. The asbestos burden in tissue can be defined as the number of asbestos bodies and/or the numbers and types of asbestos fibers found in the tissue. In either of these cases the quality of information is directly dependent on the preparative techniques and instrumentation used in the analysis. The present article will discuss the significance of findings of tissue burden based on both these variables.

Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability

BACKGROUND

Chrysotile asbestos has found multiple applications in the production of friction products. At one point it comprised 40-50% of the composition of brake linings thus generating the potential for the development of asbestos related diseases in millions of workers involved in vehicle repairs. While some attention has been given to the health status of workers involved in the handling of worn components, little has been given to the potential for exposure during the handling and fitting of new (unused) components as replacement parts.

METHODS

Unused brake linings or brake shoes with attached linings from four different sources were gently rinsed with prefiltered water that was then collected on filters for analysis by Analytical Transmission Electron Microscope.

RESULTS

Large numbers of chrysotile asbestos containing structures, the majority of respirable size, were present in each sample.

CONCLUSIONS

We conclude that any manipulation of new asbestos containing brake components would be expected to yield free dust containing chrysotile asbestos of respirable size. That the vast majority of these fibers and particulates would not be counted as regulated fibers rendering assessment of potential exposures in the work place, based on data of Permissible Exposure Limits or Regulated Fibers, questionable.

Quality control analysis of the potential for asbestos contamination during tissue processing in pathology laboratories

CONTEXT

Various quality assurance procedures are applied in pathology and analytical microscopy laboratories to ensure accurate results.

OBJECTIVE

To assess the potential of cross-contamination of tissue with asbestos fibers and asbestos bodies during the fixation and washing process.

DESIGN

Lung tissue from 10 patients with potential asbestos-related disease was evaluated. Samples of fixative, water, and lung tissue from each case were evaluated by light and analytical transmission electron microscopy for asbestos bodies and uncoated asbestos fibers.

RESULTS

The lung samples tested contained a range of asbestos bodies and uncoated asbestos fibers. One wash water sample contained one asbestos body. No asbestos bodies or uncoated asbestos fibers were found in any other water or fixative samples.

CONCLUSIONS

The absence of uncoated asbestos fibers in wash water or fixative samples argues that the fixation process stabilizes asbestos fibers within tissue and the protocol used in this pathology laboratory protects against cross-contamination of tissue. The finding of one asbestos body in one water sample further supports the efficiency of the protective controls used in the testing methods, since this asbestos body was in the external solution that was being discarded before tissue sampling occurred.

Asbestos fiber length as related to potential pathogenicity: a critical review

BACKGROUND

Asbestos inhalation is recognized as an exposure that increases the risk for the development of lung disease. It is unique among dusts in that it is both a carcinogen and capable of inducing extrapulmonary responses such as pleural thickening and fibrosis as well as malignancy. One feature of asbestos suggested as crucial in its pathological activity is its fibrous morphology. Long fibers that have been inhaled are cleared less readily and are thus more persistent in the body. Furthermore certain experimental models link fiber length to levels of risks for development of certain diseases. The present review will survey the data on this subject.

METHODS

The review considers experimental models that have been used to assess the response to various lengths of fibers in animal models in addition to data obtained from studies of human materials. The review also emphasizes the importance in defining the method by which a sample is categorized.

RESULTS

Data are offered which support the potential for longer fibers as well as shorter fibers to contribute to pathological responses.

CONCLUSIONS

The data presented argue that asbestos fibers of all lengths induce pathological responses and that caution should be exerted when attempting to exclude any population of inhaled fibers, based on their length, from being contributors to the potential for development of asbestos-related diseases.

Quantitative analysis of asbestos burden in women with mesothelioma

BACKGROUND

Lung tissue from 15 women who died from mesothelioma was evaluated for tissue burden of ferruginous bodies and uncoated asbestos fibers. The group contained individuals who had occupational exposure to asbestos and others had family members whose work history included vocations where contact with asbestos containing materials occurred.

METHODS

Tissue samples from tumor free lung were digested and filtered and then investigated for ferruginous bodies by light microscopy and asbestos and non-asbestos fibers by analytical transmission electron microscopy (ATEM). Size and type of fibers were also analyzed.

RESULTS

Asbestos bodies were found in 13 of the 15 samples and asbestos fibers were found in all cases. The most commonly found uncoated asbestos fiber in these individuals was amosite whereas tremolite was the second most commonly found form. The asbestos fiber burden in these females was often of mixed types.

CONCLUSIONS

The asbestos body and fiber burden in these cases show variation in tissue burden. Some cases in this study had appreciable burden, which was attributed to secondhand exposure from occupationally exposed family members. Mesothelioma can occur also in individuals with comparatively low tissue burdens of asbestos.

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.

Analysis of asbestos fiber burden in lung tissue from mesothelioma patients

Mesothelioma is a rare neoplasm that occurs most frequently in individuals with previous asbestos exposure. Differences for risk of development of asbestos-related mesothelioma and lung cancer have been attributed to the various types of asbestos, as well as to the dimension of the inhaled fibers. In the present study, 55 individuals with the pathological diagnosis of mesothelioma were evaluated as to ferruginous body and fiber content in lung tissue. The procedures used in the analysis included tissue digestion and analysis of the collected material for ferruginous bodies by light microscopy and for uncoated fibers by analytical transmission electron microscopy. Forty-six of the samples had ferruginous body concentrations of over 1000/per gram dry weight of lung tissue. The majority of the cores of these ferruginous bodies were amosite. Likewise, the most common uncoated asbestos fiber in the tissue was amosite. Only a small percentage of each type of asbestos would have been visible by light microscopy or even potentially by electron microscopy if the magnification was not sufficient to detect those with thin (< 0.2 micron) diameters. The consistent finding in most of the cases was a considerable presence of asbestos, often of mixed types.