Asbestiform Fibers Nonoccupational Health Risks (1984) / Chapter Skim
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3 Assessing Nonoccupational Exposures to Asbestiform Fibers
3 Assessing Nonoccupational Exposures to Asbestiform Fibers
Pages 48-81
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From page 48... ...
Information on past exposures serves as a guide for interpreting observed health impacts in epidemiological research and as a basis for estimating cumulative exposures. Information on current and projected future exposures provides information useful in making decisions about regulating exposure levels.
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From page 49... ...
o UJ m Cot tr: in 9 1° 0 8 ~7 UJ m 5 U' ~4 20 2 _~ O\ 1 · 1 · I ~ 0 10 20 30 40 50 60 70 so 90 loo PE RCENT OF POPU LATION EXPOSED TO CONCENTRATIONS AT OR ABOVE THE INDICATED LEVEL FIGURE 3-1. Distribut ion of exposures to asbestos in ambient air of urban areas.
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From page 50... ...
natural weathering mining and mi 11 ing manufacturing processes transportation storage use industrial discharges waste disposal - environmental transport · How many people are exposed by various routes and under various conditions? - single routes of exposure - multiple routes and types of exposure, e.g., oral and respiratory, occupational and consumer In general, these questions are not easily answered, and fibrous materials such as asbestos pose some special difficulties.
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From page 51... ...
This model is useful for making rough exposure estimates when few or no measurements exist. It incorporates a scheme representing commercial and environmental flows of fibers, including such factors as natural occurrence, imports and exports, disposal, ambient concentrations, and biodisposition.
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From page 52... ...
In addition to exposures from natural sources, humans are exposed during such activities as mining, milling, manufacturing, use, and disposal of fiber-containing products. Because the committee was asked to study nonoccupational exposures, this report is focussed on environmental discharges or releases, rather than on exposures in the workplace.
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From page 54... ...
54 o V V D e ~ Cal 0 ~.
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From page 55... ...
Because the heaviest exposures to asbestos occur in the workplace, they have received the most attention. There has been particular interest in exposures associated with the following activities: · asbestos mining and milling · asbestos product manufacturing · shipyard activities · installation and removal of insulation in buildings · brake lining manufacturing and replacement However, these occupational exposures are not of concern in this study except as they provide reference points and influence total exposure in conjunction with nonoccupational exposures.
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From page 56... ...
S Consumption of Asbestos Fibers in Secondary Produc t ~ during 1982a Consumpt ion Chrysot i le Secondary Product (thousand of metric tons)
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From page 57... ...
Leineweber, Manville Total 1,445 Corp., personal co~nmunicat ion, 1983 Estimated Annual Produc t ion ~ thousands of metric tons ~ Mineral wool 200 J
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From page 58... ...
as well as in drinking water as a result of migration from asbestos-cement pipe (American Water Works Association, 1974~. Because both natural and waste asbestos can also reach drinking water through contamination of its source, drinking water is usually classified as an exposure from the general environment.
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From page 59... ...
Nonoccupational exposures attributable to the use of manufactured products have often been assumed to be relatively low, because almost all these products contain asbestos in a binding matrix, such as cement, plastic, rubber, or resin. However, exposures can occur if fibers are liberated from these matrices through such occurrences as traffic on asbestos flooring, wear of brake finings, 1 and abrasion or leaching from pipe or paper.
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From page 60... ...
Only the finer fibers remain suspended in ambient air for long times. Therefore, general environmental exposures to asbestos entail a larger proportion of fine fibers than do occupational or community exposures.
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From page 61... ...
When interpreting health effects information obtained from occupa~cional studies, it may be necessary to convert nonoccupational exposures to equivalent occupational dose expressed in (fibers/cm3~yr. To do so, the number of lifetime fibers is divided by the volume of air inhaled at
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From page 62... ...
Virtually none of the population would experience lifetime exposures as high as 109 fibers. Most community exposures might average about 108 LM lifetime fibers for perhaps 15 million people, a figure consistent with the distribut ion of ambient air exposures (Suta and Levine, 1979~.
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From page 63... ...
Thus, although some uses of manufactured products may result in people being exposed to relatively high fiber concentrations, use of manufactured products probably does not contribute greatly to the lifetime exposure of the average urban dweller. Exposures to asbestos in drinking water may have an impact on human health.
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From page 64... ...
me discharges from mines and mills, which consist of fibers and bundles larger than those from other sources, are presumably deposited relatively close to their sources and do not contribute as much to general ambient concentrat ions. If all discharges into water were confined to rivers, the average concentration would simply be the quotient of the discharge rate and the aggregate river flow rate, or approximately 0.02 to 0.05 ~Ig/lieer.
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From page 65... ...
For example, no details of living, ~hopping, and working patterns were inc luded in estimates of exposures to airborne concentrations and no firm relationships were established between the content of water supplies, the content of delivered tap water, and the actual populations consuming them. The inevitable conclusion is that errors in estimating the lifetime fiber exposures for the various exposed populations could be very large.
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From page 66... ...
Occupational and related exposures increased rapidly after about 1940 and then decreased in the 1960s after risk factors associated with such exposures became known. Regulatory standards and a dec tine in the demand for asbestos products have led to lower occupational exposures and possibly to a reduction in community and general environmental exposures.
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From page 67... ...
FIGURE 3-3. Estimated lifetime exposures and numbers of people in various groups potentially exposed to asbestos.
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From page 68... ...
If one accepts the estimates, the following conclusion can be drawn from this chart: assuming total population exposures and risks are the criteria governing the level of concern, then some of the nonoccupational exposure classes may rival some occupational exposures in overall population risk. For most of the populations noted in the figure, however, it would be very difficult to detect health effects attributable to ambient concentrations of asbestos because of the small relative excesses expected (Marsh, 1983; National Research Council, 1983 )
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From page 69... ...
Attapulgite consists principally of short asbestiform fibers of the mineral palygorskite (Hugging et al., 1962; Zoltai and Stout, 1984~. As with ocher minerals, some material will exhibit ashestiform properties to a greater degree than will other material.
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From page 70... ...
Because attapulgite is mined and processed in a region of relatively low population density, population exposures from these operations should be relatively low. Some uses, such as in pet waste absorbents, fertilizers, and pesticides, could release substantial amounts of attapulgite into the air.
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From page 71... ...
e ., rock wool and ~ lag wool) , and ceramic fibers.
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From page 72... ...
For example, the few measurements that have been made indicate that few fibers escape into the air during air filtration applications; otherwise, the utility of the filters would be compromised. 7 Occupational exposures to fibrous glass have tended to be considerably lower than those to asbestos, mainly because of innate processing differences (JRB Associates, Inc., 1981)
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From page 73... ...
Total mineral wool production in the United States is estimated to be approximately 200, 000 metric tons. ~ Because of the generally less elaborate processes for manufacturing these two types of mineral wool, their diameter distribution tends to be broader than that of fibrous glass, and the product contains relatively large amounts of "shot" or residual unfiberized droplets of the molten material (Pundsack, 1976~.
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From page 74... ...
The target range of diameters is 2 to 3.5 ~m, but the diameters can range from less than 1 Am to 12 ~m. Fiber lengths are often several centimeters, but many fibers a few micrometers in length are also produced (JRB Associates, Inc., 1981~.10 In general, occupational exposures to ceramic fibers seem to fall within the same range as those for mineral wools, i.e., usually well under ~ fiber/cm3, but they occasionally exceed that figure (Esmen et al., 1979; Fowler, 1980; Health and Safety Commission, 1979~.
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From page 75... ...
reported that only about 250 metric tons of high-modulus (i.e., with the high-strength properties most like an asbestiform f iber) carbon fibers were produced in the limited
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From page 76... ...
As examples of commercial fibers, the committee assessed exposure to chrysotile, crocidolite, and other asbestos fibers; attapulgite; fibrous glass, mineral wool, and ceramic fibers; and carbon fibers. Fibrous erionite was chosen as an example of a noncommercial, naturally produced ant distributed asbestiform fiber.
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From page 77... ...
Exceptions are some types of ceramic fibers, Which are near the upper limit of the Despicable range, and the fine grades of fibrous glass. With the possible exception of carbon fibers, most synthetic fiber products include some fibers of respirable size.
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From page 78... ...
1980. Industrial Hygiene Survey of Occupational Exposures to Mineral Wool.
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From page 79... ...
insulation. Presented at the Biological Effects of Man-Made Mineral Fibres, Occupational Health Conference, Copenhagen, April 20-22.
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From page 80... ...
Presented at the Bin logical Effects of Man-Hade Mineral Fibres, Occupational Health Conference, Copenhagen, April 20-22. World Health Organization.
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From page 81... ...
U.S. Occupational Safety and Health Administration, 1983.
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