Asbestos, health effects

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. 

After the mid-1970s, the downsizing of North American vehicles and the introduction of front wheel drive vehicles brought about the widespread usage of a new class of friction materials (4) called semimetallics, also called semimets and carbon—metaUics. Because of the allegedly adverse health effects associated with asbestos [1332-21 -4] (qv) fibers, a second new class of friction materials called nonasbestos organics (NAOs) came about (5). Such materials are called either asbestos-free or nonasbestos friction materials (2). 

In Chapter 2 we introduce some basic concepts from mineralogy and materials sicence before describing several mineral and synthetic fibrous inorganic materials. In Chapter 3 we outline the physiology of the human lung, cellular biology and the diseases associated with asbestos exposure—the pertinent information for discussions of the health effects of asbestos and other inorganic fibers. 

Because of the international sources of asbestos minerals, the variety of manufacture and use of asbestos and asbestos products, notably as insulation and in cement pipe, coupled with the publicity given to their potential health effects, there is probably not a single country in the world that has not become attuned, in the last ten years, to the hazards of asbestos exposure. The epidemiological data collected on disease related to asbestos exposure, es-... 

Asbestos is a fibrous inorganic material. It is mined and exploited because of its unique chemical and physical properties, in part the result of its distinctive fibrous form. The hazards, as we understand them, are also attributed to this fibrous character, but asbestos represents only a fraction of the many inorganic fibers now in use. Furthermore, although it is a readily recognizable form, fiber has no precise scientific or technical definition. Thus, to address the health effects of asbestos, federal government (OSHA—Oc-... 

Asbestos is an airborne contaminant (Section 3.3.2), a hazardous solid waste (Section 3.5), and also a waterborne contaminant, regulated by many states. The health effect of asbestos in water, however, is not totally known. 

Adverse health effects have not been reported for workers exposed to magnesite containing no asbestos and <1% crystalline silica. No cases of human systemic magnesium intoxication from inhalation of magnesite have been reported. 

Recent reports show unexpected information on the role of free radicals in the health effects of nanotubes currently employed in many industries.31 Unlike asbestos and most toxic particles, nanotubes do not release but blunt free radicals, which are considered one of the features imparting toxicity to particulates. Multi-wall carbon nanotubes (MWCN) in aqueous suspension do not generate oxygen or carbon centered free radicals detectable with the spintrapping technique. Conversely, when in contact with an external source of hydroxyl (HO) or superoxide radicals (CL h MWCN exhibit a remarkable radical scavenging capacity (Figure 3). It is therefore possible that the inflammatory reaction reported in vivo should be ascribed to MWCN features other than particle derived free radical generation. 

Asbestos can arise from natural sources and from asbestos cement pipe. Exposure to asbestos fibres through drinking-water is not considered to cause health effects in humans also, the analysis is difficult and expensive. 

Chapter 3 Health Effects Specific health effects of asbestos are reported by type of health effect (death, systemic, immunologic, reproductive), by route of exposure, and by length of exposure (acute, intermediate, and chronic). In addition, both human and animal studies are reported in this section. NOTE Not all health effects reported in this section are necessarily observed in the clinical setting. Please refer to the Public Health Statement to identify general health effects observed following exposure. 

No MRLs were derived for oral exposure to asbestos for any duration. No studies were located regarding noncancer health effects in humans orally exposed to asbestos fibers, although asbestos cement pipes have been used in some community water systems for many years. Because ingested asbestos fibers are poorly... 

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-... 

McDonald and McDonald 1980 Voisin et al. 1994). As with other asbestos-related respiratory health effects, asbestos-induced mesothelioma appears to have a long latent period of development. For example, Anderson et al. (1976) described two cases of women who presumably experienced household contact with asbestos as children, when their fathers worked with asbestos, and developed clinically detected pleural mesothelioma more than 30 years later. In a review of 1,105 cases of malignant mesotheliomas associated with occupational exposure to asbestos, Lanphear and Buncher (1992) reported that 99% had a latent period >15 years, and calculated a median latent period of 32 years. 

Overview of Oral Health Effects. Studies in humans and animals indicate that ingestion of asbestos causes little or no risk of noncarcinogenic injury. However, there is some evidence that acute oral exposure may induce precursor lesions of colon cancer, and that chronic oral exposure may lead to an increased incidence risk of gastrointestinal tumors. Studies that provide quantitative data on the effects of ingested asbestos are summarized in Table 3-3 and Figure 3-3, and the data are discussed below. 

No studies were located regarding the following health effects in humans or animals after dermal exposure to asbestos ... 

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