Amosite exposures

The risk of gastrointestinal cancer from exposure to amosite asbestos has been suggested, but the reported studies are inconsistent (Peto et al., 1977 Selikoff et al., 1979 Morgan et al., 1985). Other cancers ascribed to asbestos exposure (ovarian, alimentary tract, for example) have low incidence (low SMRs), inconclusive evidence in establishing cause and effect. The amphibole materials, with their characteristic cleavage into sharp, finely divided particles and their low solubility (relative to chrysotile), are cited by many investigators as the bad actors in disease induction. 

While lung cancer and mesothelioma are generally associated with chronic exposure to asbestos, there are several studies that indicate that short-term exposures are also of concern. For example, it has been noted that workers exposed to asbestos for only 1-12 months had an increased risk of developing lung cancer a number of years later. In animals, mesotheliomas developed in two rats exposed to high concentrations of amosite or crocidolite for only 1 day. These data are not extensive enough to define the dose- or time-dependency of health risks from short-term exposure to asbestos, but the data do indicate that short-term exposures should not be disregarded. 

Using a predictive model developed from mesothelioma data from studies of asbestos insulation workers (Peto et al. 1982), asbestos textile workers (Peto 1980), amosite factory workers (Seidman 1984), and asbestos-cement workers (Finkelstein 1983), EPA (1986a) estimated that continuous lifetime exposure to air containing 0.0001 f/mL of asbestos would result in about 2-3 cases of mesothelioma per 100,000 persons. The corresponding cumulative lifetime exposures associated with excess risks of 10 " -10 are shown in Figure 3-1. Cumulative exposure levels of 0.031, 0.0031, 0.00031, and 0.000031 f-yr/mL represent excess mesothelioma risks of 10" , 10 , 10, and 10 ", respectively. Appendix D provides further details on the derivation of these risk estimates. Currently (in 2001), EPA is in the process of reviewing their cancer risk estimates for asbestos fibers. 

Animal studies also indicate that inhalation exposure to asbestos produces mesotheliomas. Mesotheliomas have been observed in rats exposed to chrysotile, amosite, anthophyllite, crocidolite, or tremolite at concentrations ranging from 350 to 1,600 f/mL for 1-2 years (Davis and Jones 1988 Davis et al. 1985 Wagner et al. 1974, 1980a) and in baboons exposed to either 1,110-1,220 f/mL for 4 years (Goldstein and Coetzee 1990) or 1,100-1,200 17mL for up to 898 days (Webster et al. 1993). Incidences of mesothelioma ranged from 0.7 % to 42% in these studies. 

No studies were located regarding death in humans or animals after acute or intermediate oral exposure to asbestos. Feeding studies in rats and hamsters indicate that ingestion of high amounts (1% in the diet, equivalent to doses of 500-800 mg/kg/day) of chrysotile, amosite, crocidolite, or tremolite does not cause premature lethality, even when exposure occurs for a lifetime (NTP 1983, 1985, 1988, 1990a, 1990b, 1990c). 

Churg A, Stevens B. 1993. Absence of amosite asbestos in airway mucosa of non-smoking long term workers with occupational exposure to asbestos. Br J Ind Med 50(4) 355-359. 

Dodson RE, Ford JO. 1991. Tissue reaction following a second exposure to amosite asbestos. Cytobios 68 53-62. 

Ehrlich R, Lilis R, Chan E, et al. 1992. Long term radiological effects of short term exposure to amosite asbestos among factory workers. Br J Ind Med 49 268-275. 

Jones AD, McMillan CH, Johnston AM, et al. 1988a. Pulmonary clearance of UICC amosite fibres inhaled by rats during chronic exposure at low concentration. Br J Ind Med 45 300-304. 

McCoimell EE, Rutter HA, Ulland BM, et al. 1983a. Chronic effects of dietary exposure to amosite asbestos and tremolite in F344 rats. Environ Health Perspect 53 27-44. 

McDonald AD, Fry JS, Woolley AJ, et al. 1982. Dust exposure and mortality in an American factory using chrysotile, amosite, and crocidolite in mainly textile manufacture. Br J Ind Med 39 368-374. 

Nolan RP, Langer AM, Wilson R. 1999. A risk assessment for exposure to grunerite asbestos (amosite) in an iron ore mine. Proc Natl Acad Sci USA 96 3412-3419. 

Seidman H, Selikoff IJ, Gelb SK. 1986. Mortality experience of amosite asbestos factory workers Dose-response relationships 5 to 40 years after onset of short-term work exposure. Am J Ind Med 10 479-514. 

Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) recognize six asbestos minerals chrysotile, a serpentine mineral and five amphibole minerals, actinolite asbestos, tremolite asbestos, anthophyllite asbestos, crocidolite asbestos, and amosite asbestos. Nonasbestiform amphibole minerals are not included in U.S. health regulations regarding asbestos because there is insufficient evidence that they will produce adverse health effects of the same type and severity produced by chronic exposure to asbestos. 

In animals, mesothelioma developed in two rats exposed to high concentrations of amosite or crocido-lite for only 1 day. These data are not extensive enough to define the dose-response but data indicate that short-term exposures should not be regarded. 

Another problem with inhalation studies conducted with rats is a lack of sensitivity for detecting the induction of fiber-inducted neoplasms, particularly mesotheliomas. Rats develop a low incidence of such tumors following exposure to amosite or crocidolite, which are known to cause tumors in humans. 

Asbestos is the name given to a group of naturally occurring silicates, chrysotile, amosite, and crocidolite, and the asbestiform types of tremolite, actinolite, and antho-phylite. Exposure to asbestos is a well-documented cause of pulmonary and pleural fibrosis, iung cancer, and mesothelioma, illnesses that may appear many years after exposure. 

The association between exposure to asbestos dust and the development of lung carcinoma and diffuse mesotheliomata of the pleura and peritoneum has been well documented (Selikoff and Lee 1978). Both crocidolite and amosite were capable of augmenting the oncogenic effect of benzo[a]-pyrene. This putative synergistic effect was evident when fibres and chemicals were added to cultures of murine fibroblast cultures as simple mixtures and when benzo[a]pyrene was adsorbed to the surface of the fibres (Brown et al. 1983). 

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