Asbestos deposits

The term alumen plumosum has had a long association with asbestos. Alumen (= alum) is a general term for naturally occurring hydrous alkali aluminum sulfates. These are efflorescent mineral materials of fibrous, feathery appearance. Confusion with the more durable silicate composition asbestos was not settled until 1741, by Tourneforte following a visit to asbestos deposits in Asia Minor. 

Soil may be contaminated with asbestos by the weathering of natural asbestos deposits, or by land-based disposal of waste asbestos materials. While disposal of waste asbestos to landfills was a common practice in the past, current regulations restrict this practice (see Chapters 5 and 8). 

The concentration of asbestos fibers in water (expressed as million TEM fibers per liter, MFL) varies widely. Concentrations in most areas are <1 MFL (EPA 1979b), but values of 1-100 MFL and occasionally higher have been detected in areas contaminated by erosion from natural asbestos deposits (EPA 1976 Kanarek et al. 1980) or from mining operations (Sigurdson et al. 1981). 

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. 

Finkelstein MM, Duffesne A. 1999. Inferences on the kinetics of asbestos deposition and clearance among chrysotile miners and millers. Am J Ind Med 35 401-412. 

The Fibrous Minerals. The fibrous minerals contain very long silicate ions in the form of tetrahedra condensed into a chain, as shown in Figure 31-6. These crystals can be cleaved readily in directions parallel to the silicate chains, but not in the directions which cut the chains. Accordingly crystals of these minerals show the extraordinary property of being easily unravelled into fibers. The principal minerals of this sort, tremolite, C.a.jMg..Si 022(0H)2, and chrysotile, Mg6Si40u(0H)p/H20, are called asbestos. Deposits of these minerals are found, especially in South Africa, in layers several inches thick. These minerals are shredded into fibers, which are then spun or felted into asbestos yarn, fabric, and board for use for thermal insulation and as si heat-resistant structural material. 

Ca. 98% of the worldwide production of asbestos (3.110 t/a in 1993, see Table 5.2-4) is chry.sotile. The most important deposits are in Canada and the former States of the USSR with the largest amphibole asbestos deposit being in South Africa. The worldwide reserves have been estimated to be 100 to 150 lO t/a and should at current consumption levels (2 I O t/a in 1997) last for 50 to 75 years. The asbestos content of the stone from economically workable deposits is ca. 4 to 10% (Quebec, Urals), the minimum level for economic workability being ca. 3%. 

Asbestos induces NF-kB and AP-1 transcription-factor activation, possibly through ROS-mediated hpid peroxidation and arachidonic acid metabolism. In macrophages, asbestos caused increased release of arachidonic acid and the formation of prostaglandins E2 and F2a In alveolar macrophages, asbestos induced the releases of arachidonic acid metabolites as early as 1 h post-in vitro exposure. Persistent release of arachidonic acid metabolites at sites of asbestos deposition are implicated in the constitutive activation of NF-kB. ... 

If it is assumed that both the deposition of fibers on the filter and the selection of fields for counting are random, then there will be a variability in the results that can be described by a Poisson distribution. For fiber counts of 50 this leads to 95% confidence intervals in the results of + 15 (30%) and a coefficient of variation of 15%, although for smaller fiber counts the variability will be much larger. In addition to this variability there is an unavoidable degree of nonuniformity of the asbestos deposit on the filter. There is also subjective variation between microscopists in interpretation of fiber structures and in their ability to detect and identify fibers. Overall counting performances caimot then be expected to produce a coefficient of variation better than 25% for counts of 50 fibers. 

FIGURE 2.6. Marsh cell. A vertical section B plan, sectional diagram C original cathode with asbestos paper diaphragm D asbestos deposited cathode finger. The symbols are the same as in Fig. 2.4. 

Steel, E. and Wylie, A., Riordan, P.H. (Ed.), Mineral-ogical Characteristics of Asbestos, Geology of Asbestos Deposits, pp. 93- 101,SME-AIME, 1981. 

---