Identification of Asbestos
Over the years much data have been accumulated about asbestos, which suggests that amphibole asbestos and its nonasbestos analogues possess very different biologic potential.
Davis et al demonstrated that although asbestiform tremolite was extremely carcinogenic when
injected into peritoneal cavities of rats, nonasbestiform tremolite samples had little or no carcinogenic potential. Therefore, it is important to distinguish between asbestiform and nonasbestiform amphiboles and types of fibers in bulk, air, and tissue samples.
There are some problems related to the mineralogic techniques necessary to prepare and characterize samples. The designation of the shape and size of fibrous materials can be relatively easily revealed by optical examination. Optics became the technique of choice to investigate the occurrence of inorganic fibrous airborne particulates at occupational sites, in schools, or any buildings, and even outdoors where filters could be set up to obtain a representative aliquot of the air.
However, the light (optical) microscope does not have enough spatial resolution and so is not sufficient on its own for positive identification of minerals. It is difficult to identify some fibers such as chrysotile in the tissue samples under the optical microscope because of the small fiber sizes. Since the small fiber size of chrysotile in the tissue samples preclude the use of optical microscopes, morphologic, chemical, and structural identifications are done by combinations of methods in order to makeunambiguous mineral identifications.
The crystal chemical range of potentially hazardous inorganic and mineral species should be accurately identified. Morphologic identifications can be performed by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Chemical information is most commonly obtained by energy dispersive spectroscopy (EDS) or wavelength dispersive spectroscopy (WDS), which is an integral part of SEM or TEM.
A relative error percentage for EDS is about 10% and for WDS is about 1%. Therefore, EDS provides only semiquantitative information, but WDS provides more quantitative information on chemical composition of the sample.
Crystal structures can be determined by electron diffraction (ED) on samples. Powder x-ray diffraction (XRD) is a powerful technique providing that enough material is available, but not for a mineral present at low percentage in tissue and air samples. Certain regulations may require specific species of amphiboles; thus, quantitative chemical data may be necessary.
For example, substitution solid solution series of amphiboles, such as a tremolite and an actinolite, must be identified. The SEM studies combined with EDS may not be conclusive because of the lack of information on the mineral structure. It is also very difficult to observe chrysotile through the electron microscope because of its beam sensitivity.
Analysts tend to measure fibers that are more stable under beam conditions. Lung burden studies indicate that chrysotile is often inhaled as a shorter fiber than amphiboles. Therefore, in a tissue with both amphibole and chrysotile, it is possible to make a misjudgment unless the fibers are identified individually.
Over the years much data have been accumulated about asbestos, which suggests that amphibole asbestos and its nonasbestos analogues possess very different biologic potential.
Davis et al demonstrated that although asbestiform tremolite was extremely carcinogenic when
injected into peritoneal cavities of rats, nonasbestiform tremolite samples had little or no carcinogenic potential. Therefore, it is important to distinguish between asbestiform and nonasbestiform amphiboles and types of fibers in bulk, air, and tissue samples.
There are some problems related to the mineralogic techniques necessary to prepare and characterize samples. The designation of the shape and size of fibrous materials can be relatively easily revealed by optical examination. Optics became the technique of choice to investigate the occurrence of inorganic fibrous airborne particulates at occupational sites, in schools, or any buildings, and even outdoors where filters could be set up to obtain a representative aliquot of the air.
However, the light (optical) microscope does not have enough spatial resolution and so is not sufficient on its own for positive identification of minerals. It is difficult to identify some fibers such as chrysotile in the tissue samples under the optical microscope because of the small fiber sizes. Since the small fiber size of chrysotile in the tissue samples preclude the use of optical microscopes, morphologic, chemical, and structural identifications are done by combinations of methods in order to makeunambiguous mineral identifications.
The crystal chemical range of potentially hazardous inorganic and mineral species should be accurately identified. Morphologic identifications can be performed by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Chemical information is most commonly obtained by energy dispersive spectroscopy (EDS) or wavelength dispersive spectroscopy (WDS), which is an integral part of SEM or TEM.
A relative error percentage for EDS is about 10% and for WDS is about 1%. Therefore, EDS provides only semiquantitative information, but WDS provides more quantitative information on chemical composition of the sample.
Crystal structures can be determined by electron diffraction (ED) on samples. Powder x-ray diffraction (XRD) is a powerful technique providing that enough material is available, but not for a mineral present at low percentage in tissue and air samples. Certain regulations may require specific species of amphiboles; thus, quantitative chemical data may be necessary.
For example, substitution solid solution series of amphiboles, such as a tremolite and an actinolite, must be identified. The SEM studies combined with EDS may not be conclusive because of the lack of information on the mineral structure. It is also very difficult to observe chrysotile through the electron microscope because of its beam sensitivity.
Analysts tend to measure fibers that are more stable under beam conditions. Lung burden studies indicate that chrysotile is often inhaled as a shorter fiber than amphiboles. Therefore, in a tissue with both amphibole and chrysotile, it is possible to make a misjudgment unless the fibers are identified individually.
The levels of sensitivity using the high-resolution techniques now available mandate that we follow up the reactions delineated as interference of inorganic materials in the biologic environment. The information on the inorganic fibrous particulates can be matched with the equally high-resolution techniques applied to analyses of tissues, with data gathered at the cellular and molecular levels.
The advances in techniques increase the possibilities that we can test hypotheses and, it is hoped, gain greater understanding from the anatomic to the genetic of the reactions that lead to induction of disease. Coordinating ultramicroscopic levels with the health and mineralogic investigations for a particular geographic area should enable us to refine the possibilities. The exchange of information among the several disciplines is needed to advance our knowledge.
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