Asbestos occurrence

Each asbestos occurrence is unique, and some variations of morphology, composition, and physical properties are expected from sample to sample, not only from one geographic source to another, but within a particular mine. 

The replacement of asbestos fibers by other fibrous materials has raised similar health issues in relation to substitute materials. However, since lung cancer has a latency period of approximately 25 years, and since the fiber exposure levels in contemporary industries is far lower than those which prevailed half a century ago, the epidemiological data on most substitutes is insufficient. A possible exception is slag fibers for which several studies on worker populations are available over extended periods (44) some results show a substantial increase in lung cancer occurrence. Consequentiy, the toxicity of asbestos substitute fibers remains a subject of active investigation. 

Total frequencies of environmental illness are difficult to measure. When causes can be identified, however, scientists observe that frequencies of occurrence of a particular illness vary directly with the severity and extent of exposure. Particularly frequent in the workplace are skin lesions from many different causes and pulmonary diseases related to the inhalation of various dusts, such as coal dust (black lung), cotton dust (brown lung), asbestos fibers (asbestosis), and silica dust (silicosis). Environmental agents can also cause biological effects without overt clinical illness (for example, chromosome damage from irradiation). 

The data in the references provided for each entry in the Appendices are extremely variable. Except for those of the asbestos minerals, the general descriptions of most minerals give little more than cursory mention of their occurrence as fibers. A journal citation indicates some information on composition, crystal structure, size, morphological characteristics, and other... 

The individual cylindrical chrysotile fibrils undoubtedly contribute to the occurrence of this mineral species in fibrous form and may account for some of the flexibility and enhanced tensile strength of chrysotile fibers. Aveston (1969, p. 632) commented that asbestos was inferior [in tensile strength]... 

Occurrences in the United States were known as early as 1698 with numerous finds along Brandywine Creek in Pennsylvania (Frondel, 1988). The celebrated purse made from asbestos that Benjamin Franklin took to London in 1724, and which now resides in the British Museum of Natural History, may have been made of long-fiber asbestos from Newbury, Massachusetts. As a journeyman printer, Franklin made paper from asbestos, as did many Europeans. It was also used in making lamp wicks and cloth. Commercial mining in the United States took place some time after the first discovery of asbestos on Staten Island, New York, in 1818. (Asbestos continued to be mined at the site until 1876.) By 1825 more than seventy localities were known to produce asbestos in the United States (Robinson, 1825). However, as early as 1804 Jameson had recorded the mineralogy of the species and listed the numerous university, societal, and private mineral collections containing specimens of asbestos from U.S. localities and asbestos products of local manufacture. 

The fibrous forms of amphiboles, and serpentines, in addition to occurring in aggregates amenable to mining, are widespread as minor constiments of many rocks. The fibers are also widely distributed throughout the soils and waters of the world. These occurrences, together with the many long-term uses for asbestos society has devised, ensure that the ubiquitous presence of asbestos in our environment. 

Ross, M. (1981). The geologic occurrences and health hazards of amphibole and serpentine asbestos, pp. 279-324. In Veblen, D. R., ed. Amphiboles Petrology and Experimental Phase Relations. Reviews in Mineralogy, 9B. Min. Soc. America, Washington, DC. 

Hillerdal, G. (1980). Pleural plaques occurrence, exposure to asbestos and clinical implications. Acta Universitatis Upsceliensis 363 1-277. 

Overview of Health Effects. Studies in humans and animals indicate that inhalation of asbestos fibers may lead to fibrotic lung disease (asbestosis), pleural plaques and thickening, and cancer of the lung, the pleura, and the peritoneum. It may also increase the risk of cancer at other sites, but the evidence is not strong. Significant effects on other tissues have not been detected. A number of researchers have found that the occurrence of asbestosis and lung cancer correlates with cumulative exposure (that is, the product of concentration [PCM fibers/mL] multiplied by years of exposure). Therefore, human exposures are expressed below as PCM f-yr/mL. Animal data are provided in terms of exposure level (PCM f/mL) and duration, and the cumulative exposure can be found simply by calculating the product. However, due to differences in clearance rates and lifespan as well as other differences, cumulative doses in animals are not expected to be directly comparable to cumulative doses in humans. Studies that provide reliable dose-... 

M.B. Schenker of Institute of Toxicology, University of California Davis in Davis, California is leading a multidisciplinary study supported by National Cancer Institute (NCI). This study will examine whether environmental asbestos deposits in California are associated with increased rates of mesothelioma. The study will address geological occurrence of asbestos and potential human exposure based on population patterns and known occupational exposure, and epidemiological characteristics of the disease in the state. The project will plan a case-control study to rigorously test the hypothesis that mesothelioma in California is independently associated with environmental asbestos exposure. 

Dodoli D, Del Nevo M, Fiumalbi C, et al. 1992. Enviromnental household exposures to asbestos and occurrence of pleural mesothelioma. Am J Ind Med 21 681-687. 

Selikoff IJ. 1965. The occurrence of pleural calcification among asbestos insulation workers. Ann NY Acad Sci 132 351-367. 

Physical and Chemical Properties, Occurrence, and Detection Tremolite Asbestos... 

Occurrence in Chiysotile Amphibole asbestos, identified as tremolite asbestos or actinolite asbestos, has been reported to be a minor contaminant in some deposits of chrysotile in Quebec. Part of the evidence that tremolite asbestos exists in certain chrysotile deposits mined in Quebec comes from observations of higher concentrations of tremolite asbestos fibers than chrysotile fibers in autopsied lung tissues of certain miners and millers who were chronically exposed to chrysotile ores (see Case 1994 for review). Inhaled tremolite asbestos fibers are more persistent in lungs than inhaled chrysotile fibers. 

As discussed in the Occurrence ofTremolite Asbestos section, small amounts of amphibole asbestos fibers have been identified in some samples of vermiculite-containing consumer garden products from the United States (EPA 2000). EPA (2000) concluded that consumers may face only a minimal health risk from occasionally using vermiculite products at home, and can reduce any risk by limiting the production of dusts when using the products. 

Churchill RK, Higgins CT, Hill RL. 2001. A pilot project to map areas likely to contain natural occurrences of asbestos - El Dorado County, California. Poster presentation. 2001 Asbestos Health Effects Conference. Sponsored by U.S. Environmental Protection Agency. May 24-25, 2001. San Francisco, CA. 

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