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|Asbestos analysis is conceptually simple. The objective, in most environmental analyses, is to determine the number of asbestos fibers per unit area or volume in a sample. The sample may be a consumer product, an ambient air sample, or a water sample. This determination is complicated by several factors: (1) sample collection and preparation, (2) counting techniques, and (3) operational definitions of asbestos in use. Three different definitions have been used in the study of environmental samples and are summarized in Table 1. The analytical procedure and detail required in the analysis vary with the definition of asbestos. Accordingly, this may be the only type of environmental analysis where the definition of a substance dictates the choice of analytical methods, and the rigor demanded of the analysis. Lead, arsenic, or beryllium are sub- stances having a constant definition and the method of analysis chosen depends on the concentration and precision required. However, the meaning of the term asbestos fiber is dependent on the eye of the beholder. Macroscopically, asbestos has certain physical properties that make it highly useful. Rockforming minerals do not display similar characteristics. Now, the question arises as to how three definitions of asbestos came into being. This is a result of two factors: (1) the definition of asbestos on any scale intrinsically involves the morphology or shape of the material, and (2) the advent of the transmission electron microscope permits detection of asbestos fibers and other mineral fragments in a size range where the physical properties of asbestos such as tensile strength, flexibility, or thermal resistance are difficult, if not impossible, to measure. There is a good deal of controversy about which definition is most appropriate for regulatory purposes because of a lack of appropriate health effects data (Cooper, 1978). Most differences of opinion center on the questions surrounding the following: 11 Morphology-Is a 3:l aspect ratio an appropriate medical or physical lower limit for the definition of an asbestos fiber? 2) Length-Are asbestos fibers shorter than some arbitrary length (5 pm) as hazardous as longer fibers? 3) Mineralogy-Is the mineralogical distinction between asbestos and nonasbestos minerals medically significant? While these questions are directly resolvable only with the biological and health effects data, ultimately such data reflects the ability of analytical procedures to fully characterize the materials used in health effects studies on animal models, and to monitor the exposure to particulates with different physical attributes in the workplace or community (Cooper, 1978). The following sections outline the analytical problems involved in distinguishing the asbestos and nonasbestos varieties of the same mineral; the analytical procedures available for identifying asbestos and measuring its concentration in environmental samples; the ability of these methods to distinguish asbestos fibers from nonasbestos particles; and their precision and reproducibility. Finally, we suggest some future directions in terms of definition and procedure that would greatly improve the quality of such analyses. ASBESTOS VS. NONASBESTOS Asbestos that is mined commercially belongs to two mineral families; amphibole and serpentine (Zoltai, 1978, Wylie, and Steel, 1978). The|