United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EP A/600/8-91/037
September 1991
&EPA
Health Assessment
Document for
Vermiculite
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EPA/600/8-91/037
SEPTEMBER 1991
HEALTH ASSESSMENT DOCUMENT
FOR VERMICULITE
ENVIRONMENTAL CRITERIA AND ASSESSMENT OFFICE
OFFICE OF HEALTH AND ENVIRONMENTAL ASSESSMENT
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
Printed on Recycled Paper
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DISCLAIMER
This document has been reviewed in accordance with U.S. Environmental Protection
Agency policy and approved for publication. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
11
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CONTENTS
TABLES
AUTHORS, CONTRIBUTORS, AND REVIEWERS
PREFACE
1. SUMMARY .......
2. BACKGROUND INFORMATION
2.1 PHYSICAL AND CHEMICAL PROPERTIES ......
2.2 PRODUCTION AND INDUSTRIAL USE
2.3 SOURCES OF EMISSIONS
2.4 EXPOSURE
2.5 AMBIENT LEVELS
2.6 ENVIRONMENTAL FATE
2.7 ANALYTICAL METHODS
3. TOXICOLOGY
3.1 RETENTION, BIODISPOSITION, AND CLEARANCE
3.2 ANIMAL TOXICITY
3.3 EFFECTS ON HUMANS
3.3.1 Cross-Sectional Studies, Clinical
Evaluations, and Case Reports . .
3.3.2 Retrospective, Prospective, and
Historical Prospective Studies
4. REFERENCES
v
vii
1-1
2-1
2-1
2-2
2-2
2-3
2-8
2-8
2-9
3-1
3-1
3-2
3-3
3-3
3-5
4-1
111
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TABLES
2-1 Occupational Exposure to Airborne Concentrations
of Asbestos in Vermiculite Processing Plants
2-2 Summary of Occupational and Nonoccupational
Inhalation Exposure to Asbestos in Vermiculite
Page"
2-6
2-7
IV
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
This document was prepared by Dynamac Corporation under Contract No. 68-03-4140,
to the Environmental Criteria and Assessment Office, Research Triangle Park, NC; Dennis J.
Kotchmar, M.D., Project Manager.
The following Dynamac Corporation personnel were involved in the preparation of this
document: Nicolas P. Hajjar, Ph.D. (Project Manager/Principal Author); Barrett N.
Fountos, Claire Kruger-McDermott, Ph.D., Patricia Turck, Mary E. Cerny, Dawn Webb,
Brion Cook, Nancy McCarroll, William,McLellan, Ph.D., Christian Alexander, John Bruno,
Ph.D., Edward Flynn, Charles Rothwell, Ph.D., Janice Runge, and Sharon Segal, Ph.D.
(Authors); Karen Swetlow (Technical Editor); Sanjivani Diwan, Ph.D., and Gloria Fine
(Information Specialists).
The following scientists reviewed an earlier draft of this document and submitted
comments:
Dr. K.P. Lee
Haskell Laboratory for
Toxicology and Industrial Medicine
E.I. du Pont de Nemours and Company
Newark, DE
Dr. Friedrich Pott
Medical Institute for Environmental
Hygiene
Dusseldorf University
Dusseldorf, Federal Republic of
Germany
Dr. J.C. Wagner
MRC External Staff
Team on Occupational Lung
Diseases
Llandough Hospital
Penarth, Glamorgan, England
Dr. Jon Konjen
Medical and Scientific Committee
Thermal Insulation Manufacturers
Association
Stamford, CT
Dr. A. Morgan
United Kingdom Atomic Energy
Authority
Environmental and Medical
Sciences Division
Oxfordshire, United Kingdom
Dr. Lorenzo Simonato
Unit of Analytical Epidemiology
International Agency for Research
on Cancer
Lyon, France
Dr. Janet Hughes
Department of Biostatistics and
"-" Epidemiology
Tulane Medical Center
New Orleans, LA
Dr. William J. Nicholson
Department of Community Medicine
Mount Sinai School of Medicine
New York, NY
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Dr. Gary M. Marsh
Department of Biostatistics
University of Pittsburg
Pittsburg, PA
Dr. Aparna Koppikar
U.S. Environmental Protection Agency
Human Health Assessment Group
Washington, DC
Mr. Steven Bayard
U.S. Environmental Protection Agency
Human Health Assessment Group
Washington, DC
Dr. Karen Milne
U.S. Environmental Protection Agency
Office of Toxic Substances
Washington, DC
Mr. John Cherrie
Institute of Occupational Medicine
Edinburg, Scotland
Norman Kowal
U.S. Environmental Protection Agency
Environmental Criteria and Assessment
Office
Cincinnati, OH
William Pepelko
U.S. Environmental Protection Agency
Human Health Assessment Group
Washington, DC
Charles Ris
U.S. Environmental Protection Agency
Human Health Assessment Group
Washington, DC
Dr. William H. Maxwell
U.S. Environmental Protection Agency
Office of Air Quality Planning and
Standards
Research Triangle Park, NC
Dr. David Coffin
U.S. Environmental Protection Agency
Health Effects Research Laboratory
Research Triangle Park, NC
Dr. Vanessa T. Vu
U.S. Environmental Protection Agency
Health and Environmental Review
Division
Office of Toxic Substances
Washington, DC
Anne Sergeant
U.S. Environmental Protection Agency
Office of Health and Environmental
Assessment
Washington, DC
Shelia Rosenthal
U.S. Environmental Protection Agency
Human Health Assessment Group
Washington, DC
Bob Sonawane
U.S. Environmental Protection Agency
Human Health Assessment Group
Washington, DC
VI
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PREFACE
This health assessment on vermiculite was prepared for the Office of Health and
Environmental Assessment to serve as a source document for EPA use. In the development
of the assessment document, the scientific literature has been inventoried, key studies have
been evaluated, and summary/conclusions have been prepared so that the chemical's toxicity
and related characteristics are qualitatively identified. Observed effect levels and other
measures of dose-response relationships are discussed, where appropriate, so that the nature
of the adverse health responses is placed in perspective with observed environmental levels.
The relevant literature for this document has been reviewed through early 1991.
Any information regarding sources, emissions, ambient air concentrations, and public
exposure has been included only to give the reader a preliminary indication of the potential
presence of this substance in the ambient air. While the available information is presented as
accurately as possible, it is acknowledged to be limited and dependent in many instances on
assumption rather than specific data. This information is not intended, and, therefore, should
not be used, as an exposure assessment by which to estimate risk to public health.
Vll
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1. SUMMARY
Concern surrounding the adverse health effects of asbestos on the general population
simulated interest in the potential health effects of other related minerals and man-made
fibers. One of these is vefmiculite, a nonfibrous silicate mineral with multiple consumer uses
that has been shown to contain .various concentrations of asbestiform fibers. The health
effects of verrniculite are discussed in this document.
Vermiculite (CAS No. 1318-00-9) is a micaceous hydrate of magnesium-iron-
aluminum silicates. Vermiculite crystals are composed of two silicate layers connected by a
hydrous layer. The chemical composition of vermiculite is
(Mg,Fe,Al)3(Al,Si)4O10(OH)2»4H2O. It is unique among minerals in its ability to exfoliate
or expand up to 20 times its original size at high temperatures. It has high-cation-exchange
capacity and a very low thermal conductivity. About 275,000 metric tons were produced in
the United States in 1988. Most of the vermiculite mined and beneficiated is exfoliated and
used in construction aggregates, insulation, and agricultural applications.
It has been estimated that approximately 802 x 103 kg of vermiculite were released into
the air, 89,900 X 103 kg were released into water, and 2.490 x 103 kg were released as
solid waste in 1979 based on a production volume of 1 million tons (1.2 x 109 kg).
Exposure to vermiculite occurs mainly via the inhalation route; ingestion and dermal
absorption are not significant routes of exposure. However, exposure to asbestos in the
occupational environment or from ambient air near point sources is of concern. Prior to
1973, occupational exposures to asbestos fibers ranged from 0.049 fibers/cm3 to
1.511 fibers/cm3 for an 8-h, time-weighted average (TWA) for workers in a vermiculite-
processing company. Miners' exposure to tremolite from a vermiculite mine in Montana
ranged from the highest dust concentrations of 101.5 to 124.9 fibers/cm3 prior to 1970 to a
low of 22.1 to 27.1 fibers/cm3 after 1970. At a mining and milling operation in Montana,
prior to 1964, exposure estimates for various jobs ranged from 13 to 182 fibers/cm3.
Exposure estimates decreased greatly and were < 1.0 fiber/cm3 in most areas from 1977 to
1982. Based on samples taken by the company in 1984, the average 8-h TWA exposure was
0.1 fibers/cm3. The National Occupational Hazard Survey (1976) reports that 104,456
1-1
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workers were potentially exposed to vermiculite from 1972 to 1974, whereas the National
Occupational Exposure Survey (1984) estimated that 4,293 workers, including 365 females,
were exposed to vermiculite in 1980.
Nonoccupational exposure to vermiculite is high. In 1979, approximately 13 million
persons were estimated to have been exposed to vermiculite near exfoliation plants in the
United States. In addition, about 106 million persons were exposed to consumer products
containing vermiculite.
Ambient levels of asbestos fibers in the vicinity of vermiculite mines and mills have
been reported to range from 0.5 fibers/cm3 (4.5 km from a mine) to 0.02 fibers/cm3 (50 m
from a mine).
Vermiculite is not expected to undergo chemical transformation when released into the
environment. Analytical procedures used to identify vermiculite are the membrane filter,
analysis of samples by polarized light microscopy with dispersion staining, phase-contrast
light microscopy, scanning electron microscopy using energy dispersive x-ray analysis and
transmission electron microscopy, optical microscopy, and x-ray diffraction.
No information is available on the retention, biodisposition, or clearance of vermiculite
following oral administration or inhalation exposure. However, several studies of miners and
millers suggest that vermiculite may be inhaled, deposited, and retained in the lungs. No
information was found on the acute, subchronic, or chronic toxicity of vermiculite. Female
Sprague-Dawley rats injected intrapleurally with 25 mg of vermiculite developed granulomas
in the lungs and viscera. However, no tumors were observed after 104 weeks. Genotoxicity
and cytotoxicity studies were not found in the available literature. Similarly, teratogenicity
and reproductive effects studies were not found.
An association between previous vermiculite exposure and parenchyma! and pleura!
radiographic abnormalities has been found in three cross-sectional morbidity studies of miners
and millers. Although these changes did not correlate with pulmonary function tests, they did
correlate with age and fiber-years. However, the vermiculite contained fibrous tremolite—
actinolite. A historical prospective mortality study of one of the mining and milling facilities
indicated a significant twofold excess in mortality for lung cancer and nonmalignant
respiratory disease (NMRD), especially in the highest exposure category and among those
cases with a latency period of greater than or equal to 20 years.
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Similar results were observed in another historical prospective mortality study of the
same mine and mill. It was concluded that the workers in this facility had a serious hazard
from lung cancer, pneumoconiosis, and mesothelioma. However, the presence of tremolite-
actinolite asbestos precludes concluding that there is a direct relationship between exposure to
vermiculite and lung cancer or NMRD.
Consequently, the weight of evidence from data for human health effects and animal
toxicity is inadequate to characterize the carcinogenic potential of vermiculite. Similarly,
human health effects and animal toxicity data are inadequate to characterize noncarcinogenic
effects associated with vermiculite exposure.
However, the weight of evidence for asbestos-contaminated vermiculite is sufficient to
show a causal relationship for increased lung cancer in miners and millers.
1-3
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2. BACKGROUND INFORMATION
2.1 PHYSICAL AND CHEMICAL PROPERTIES
Vermiculite (CAS No. 1318-00-9) is a micaceous hydrate of magnesium-iron -
aluminum silicates. The chemical composition of vermiculite varies, but an acceptable
general formula is (Mg,Fe,Al)3(Al,Si)4O10(OH)2*4H2O (Bates and Jackson, 1980).
Vermiculite crystals can be colorless, pale brown, or brownish-green depending upon the
•metallic base, and are composed of two silicate layers connected by a hydrous layer. The
thickness of the unit cell in fully hydrated materials is about 14 A (Gruner, 1934).
Vermiculite is composed of monoclinic, plate-like crystals that exhibit perfect (001) basal
cleavage. '
Vermiculite has a specific gravity of 2.6 g/cm3, a melting point of 1,315 °C, and a
significant capacity for reversible cation exchange. All of the major commercial deposits
occur in ultramafic and mafic host rocks. The material that is mined is mixed-layer
vermiculite—biotite and vermiculite—phlogopite (silicate materials). Other minerals
commonly present in the deposits include quartz, feldspar, apatite, corundum, chlorite,
asbestos, talc, and clays. The main commercial mining deposits of vermiculite are located in
Montana, Virginia, and South Carolina, as well as hi South Africa (Dixon et al., 1985).
Vermiculite is a soft mineral and has the unique ability to exfoliate or expand up to
20 times its original size with the application of flash heat between 400 and 1,100 °C
(Lockey, 1981; Meisinger, 1985; Moatamed et al., 1986). Exfoliation can also be achieved
by chemical processes such as soaking in hydrogen peroxide, weak acids, and other
electrolytes. Expanded vermiculite is lightweight, noncombustible, and chemically inert with
a high surface area and ion-exchange capacity (Moatamed et al., 1986).
Crude vermiculite has a loose bulk density of 640 to 1000 kg/m3, whereas exfoliated
vermiculite expands to a bulk density of 56 to 192 kg/m3. It also has a very low thermal
Conductivity and a relatively narrow range of cation-exchange capacity, primarily associated
with magnesium.
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2.2 PRODUCTION AND INDUSTRIAL USE
Vermiculite has been mined in the United States since 1929. The amount of vermiculite
produced in the United States in 1988 was 275,000 metric tons (Potter, 1990). The largest
domestic producer is W.R. Grace and Co., with mines in Libby, MT, and Enoree, SC.
Exfoliated vermiculite is produced by W.R. Grace and Co. at 29 plants in 24 states (of a total
of 43 plants in 29 states). Vermiculite is also mined and processed by Patterson Vermiculite
Co. near Enoree, SC, and by Virginia Vermiculite, Ltd., in Louisa County, VA (Meisinger,
1985).
Vermiculite's capacity for reversible cation exchange permits its use as a fertilizer and
soil additive, and its low thermal conductivity permits wide usage as a heat-resistant insulator
(Dixon et al., 1985; JRB, 1982). Vermiculite is also used as an inert carrier for pesticides
and herbicides and as an absorptive material in the water purification and chemical industries
(Moatamed et al., 1986).
The largest portion of exfoliated vermiculite is used in construction aggregates (51%),
followed by insulation (26%), agriculture (22%), and other end uses (1%). Vermiculite is
sold in five grades (Dixon et al., 1985).
2.3 SOURCES OF EMISSIONS
Emissions of vermiculite are associated with mining, milling, and exfoliation processes;
transportation; and its use in secondary productions. These emissions can also involve the
release of asbestos or asbestiform fibers, which are readily transported through the
atmosphere (Dixon et al., 1985). Estimates of the amounts of vermiculite released into the
environment during mining, processing, transport, and use have been reported by JRB (1982,
as cited in Dixon et al., 1985). Based on a production volume of 1 million tons (1.2 x
109 kg) of vermiculite ore mined and beneficiated in 1979 to produce 314 x 106 kg of crude
vermiculite, approximately 802 x 103 kg were released into the air, 89,900 x 103 kg were
released into water, and 2,490 x 103 kg were released as solid waste. The water releases
were disposed of in settling ponds, and the water was recycled. Releases into air resulted
from fugitive releases from dust-control equipment, whereas particulates collected in the dust
control system constituted the solid wastes that were disposed of in landfills. For estimates
2-2
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of releases during exfoliation, JRB (1982, as cited in Dixon et al., 1985) assumed that dust-
control equipment was 98% efficient. Releases during transport are negligible, whereas the
largest release is during direct application of vermiculite, as a component of agricultural
products such as fertilizers and soil conditioners, to soil.
2.4 EXPOSURE
Exposure to vermiculite occurs mainly via inhalation; ingestion and dermal absorption
are insignificant routes of exposure. Wastewater from vermiculite mining, milling, and
exfoliation is generally sent to settling ponds and the supernatant is recycled, thus no
discharge of asbestos-laden vermiculite to the environment is expected. Because of this,
ingestion via this route either as a potable water source or through entry into the food chain is
not expected to be significant. Dermal contact would not be expected to result in exposure
since the fibers would probably not penetrate intact skin surfaces. Exposure to asbestos- or
asbestiform fiber-contaminated vermiculite occurs in the occupational environment or from
ambient air near point sources and is consequently of concern.
Several studies have been conducted to determine occupational exposure to vermiculite.
Lockey et al. (1984) assessed the respiratory status of workers exposed to tremolite-
contaminated vermiculite in an Ohio processing company. A total of 512 employees
participated in the study. Exposure estimates were divided into low, medium, and high
exposure departments. The low exposure department consisted of the chemical process,
research, and front office areas; the medium exposure department consisted of the central
maintenance, packaging, and warehouse areas; and the high exposure department consisted of
the expanding, maintenance, and plant areas. Due to tremolite contamination, optical fiber
counts of tremolite were performed. Particles with a length greater than 5 /mi, a diameter
less than 3 /«n, and an aspect ratio of 3:1 or greater were counted as fibers. Prior to 1973,
exposures were generally higher. In Group I (low), the 8-h, TWA exposure was estimated at
0.049 fibers/cm3. The Group 2 (medium) TWA exposure estimates ranged from 0.110 to
0.415 fibers/cm3, whereas the Group 3 (high) TWA exposure estimates ranged from 1.264 to
1.511 fibers/cm3. In 1974, improved environmental controls were implemented and the
TWA exposure estimates decreased in Groups 2 and 3. Group 2 estimates ranged from 0.031
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to 0.131 fibers/cm3, whereas those for Group 3 ranged from 0.212 to 0.375 fibers/cm3. The
work areas with highest airborne fiber exposure were the vermiculite expander's area and the
vermiculite railroad car and truck unloading areas.
Miners' exposure to vermiculite in a Montana mine was studied by McDonald et al.
(1986). Concern for the health of the miners stemmed from the fact that the ore body is
contaminated with fibrous amphibole deposits in the tremolite series. Tremolite exposures
were measured by standard optical microscopy. Due to the short-term personal samples, the
authors stated that the exposure estimates probably reflect ambient concentrations rather than
TWA exposures. The highest dust concentrations (101.5 to 124.9 fibers/cm3) occurred in the
dry mill prior to 1970. The concentrations then dropped significantly (22.1 to
27.1 fibers/cm3) after the installation of a major piece of ventilation equipment. For the
period 1960 through 1970, exposure estimates in the mine pit, skip boot, river station,
hauling, and testing areas were 2.3 to 12.5, 2.0 to 68.8, 4.7 to 12.0, 5.4 to 24.0, and 1.0 to
2.9 fibers/cm3, respectively. For the period 1970 through 1980, exposures for all areas
ranged from 0.2 to 1.5 fibers/cm3.
Exposure to tremolite—actinolite—contaminated vermiculite at a mining and milling
operation in Libby, MT, was studied by Amandus et al. (1987a). The site was divided into
25 location-operations, and sampling information from the period before 1950 through 1982
was collected and analyzed. Fibers counted were >5 urn in length and >0.45 /an in width.
Prior to 1964 the greatest exposure came from dry mill jobs, and estimates for working
areas, sweepers, skipping, and the quality control laboratory were 168, 182, 88, and
13 fibers/cm3, respectively. From 1964 to 1977, exposure estimates decreased greatly. For
the same operations, they were 33, 36, 17, and 3 fibers/cm3, respectively. Prior to 1971,
exposure estimates for mining jobs including drilling and nondrilling operations were 9 to
23 and <2 fibers/cm3, respectively. At the river loading station, exposure estimates prior to
1971 for ore loading at the river office, the conveyor tunnel, the river dock, and the river
station bin area ranged from 5 to 82, 10 to 11, 112 to 113, 5 to 117, and 20 to
21 fibers/cm3, respectively. Exposure estimates for all operations decreased annually from
1972 to 1976 and leveled off in 1982. Exposures in most areas during 1977 through 1982
were < 1.0 fibers/cm3 and ranged from 0.6 to 1.0 fibers/cm3 in the mill. Estimates for an
8-h TWA fiber exposure from 1981 through 1982 ranged from 0.6 to 0.8 fibers/cm3 for mine
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and mill jobs. However, based on samples taken by the company in 1984, the average TWA
exposure was 0.1 fibers/cm3. ,
Due to the presence of asbestos as a contaminant in vermiculite, Dixon et al. (1985)
conducted a study to determine airborne concentrations of asbestos in processing plants.
Sampling was conducted in 1980 at the W.R. Grace mine and milling facility near Libby,
MX, from October 21 through October 26, and at both the Grace and Patterson mine and
processing facilities near Enoree, SC, from November 3 through November 6. Both air
samples and bulk samples were collected at each location. The sampling methods employed
attempted to capture particles during various stages of production. The possibility existed
that during exfoliation asbestos fibers trapped between vermiculite plates could be released;
therefore, samples were analyzed as they were received using an exfoliation process that
allowed the samples to retain the asbestos to determine if additional fibers were shed.
Laboratory analysis suggested that a higher quantity of asbestiform fibers existed in smaller-
size grades of vermiculite than in larger-size grades. Multiple grades of bulk samples, which
were mined from the Grace facility at Libby and observed under transmission electron
microscopy (TEM), consisted of the amphibole group minerals anthophyllite and actinolite-
tremolite and contained a range of 1 to 1,800 X 106 fibers/kg. Corresponding concentration
ranges were from 1 to 41,000 ppm (Dixon et al., 1985). Exposure to asbestos was higher in
miners and millers of vermiculite than in exfoliaters (Table 2-1).
The National Institute for Occupational Safety and Health has conducted two workplace
exposure surveys. The National Occupational Hazard Survey (NOHS), conducted from 1972
to 1974, estimated the number of workers potentially exposed to chemical agents in the
workplace in 1970 (NOHS, 1976). These estimates were derived from observations of the
actual use of the agent, the use of trade name products known to contain the agent, and the
use of generic products suspected of containing the agent. NOHS estimated that 104,456
people were potentially exposed .to vermiculite: 4% were exposed to the actual product, 21%
were exposed to trade name products, and 75% were exposed to generic products suspected .
of containing vermiculite. ;
The National Occupational Exposure Survey (NOES), conducted from 1980 to 1983,
estimated the number of workers potentially exposed to chemical agents in the workplace in
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TABLE 2-1. OCCUPATIONAL EXPOSURE TO AIRBORNE CONCENTRATIONS
OF ASBESTOS IN VERMICULITE PROCESSING PLANTS
Population
Miners and millers of vermiculite
Grace mine and mill at Libby
Grace mine at Enoree
Grace mine at Enoree
Exfoliators of vermiculite
Grace facility at Enoree
^atterson facility (beneficiation,
exfoliation at J3noree)
Asbestos Fiber
Concentration"
(fibers/cm3)
0.03
<0.01
1.7
0.8
6.4
0.11
0.15
0.15
<0.01
0.03
0.14
0.08
0.08
0.02
0.16
0.05
Comments
Front loader, mine
Pit haul driver, mine
Mine analyst, mine
Bottom operator, mill
No. 2 operator, mill
Operator mine
Shuttle truck between
plants
Truck driver
Dragline operator -
Mill monitor
Mill lab technician
Bagger (Grade 4)
Bagger (Grade 3)
Payload operator
Plant foreman
Bagger/forklift operator
"Concentrations are an average of values determined by two independent laboratories, Ontario Research
Foundation and ITT Research Institute.
Source: Dixon et al. (1985).
1980 (NOES, 1984). Unlike NOHS, the NOES estimates were based only on observations
by the surveyor of the actual use of the agent. The NOES estimated that 4,293 workers,
including 365 females, were potentially exposed to vermiculite in the workplace in 1980.
Consumers can potentially be exposed to vermiculite due to its various uses; however,
no data are available to estimate vermiculite levels. Table 2-2 lists the ranges of asbestos
concentrations to which consumers may be exposed as a result of asbestos-contaminated
vermiculite use.
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TABLE 2-2. SUMMARY OF OCCUPATIONAL AND NONOCCUPATIONAL
INHALATION EXPOSURE TO ASBESTOS IN VERMICULITE
Population
Occupational
Miners and millers
Exfoliators
Users of exfoliated
vermiculite
Aggregates and
insulation producers
Transporation
Truck
Rail
Warehouse
Consumers
Attic insulators
Garden fertilizers
Lawn
Number
of Persons
Exposed
250
1,694-1,979
1,694-1,979
298
129
108
Unknown
188,000
32,000,000
74,400,000
Asbestos Exposure Level"
fibers/cm3 /tg/m3
NDb-9.7
ND-0.38
ND-0.38
6,800
XO.01-0.3
Unknown —
0
:>"
6,800
20
4.4
Duration
(hours)
43.0
41.5
41.5
36.9
39.9
39.9
— ^ 39-9
8
1
4,
Disposal
Food
Drinking water
Unknown
Unknown
Unknown
Ambient air
Near mills
Near exfoliation plants
Ambient water
4,600
13,147,496
ND-0.5
Unknown
5.0 X10-5
2.5X102
168
168
Ambient land
Unknown
"Data expressed either by fiber count or by weight.
bND = None detected.
Source: Dixon et al. (1985).
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2.5 AMBIENT LEVELS
There was limited information on the ambient levels of vermiculite. Ambient levels of
fibers (vermiculite contaminated with asbestos) in the vicinity of mines and mills were
reported by MDRI (1982, as cited in Dixon et al., 1985). A maximum of 0.5 fibers/cm3 was
recorded in Libby about 4.5 km downwind from the mine, 0.03 fibers/cm3 was recorded at
the W.R. Grace mine in Enoree, 0.05 fibers/cm3 was reported 100 m downwind of the mill,
and 0.02 fibers/cm3 was reported within 50 m of the Patterson site in Enoree.
2.6 ENVIRONMENTAL FATE
Vermiculite is a naturally-occurring clay mineral, formed through weathering of primary
aluminosilicate minerals such as biotite, feldspar, and hornblende. In the environment, it
eventually decomposes into simpler clay minerals. In general, a clay crystal lattice is
comprised of sheets of silica tetrahedra or alumina octahedra. This sheet structure results in
negatively charged particles with extremely high surface areas (750-800 m2/g for vermiculite)
that have an affinity for water and cations.
Vermiculite's crystal unit is comprised of an octahedral layer sandwiched between two
tetrahedral layers. Magnesium may substitute for some aluminum in the octahedral layers,
aluminum replaces much of the silicon in the tetrahedral layers, and water molecules hold
crystals together. When other water molecules are attracted to the spaces between crystals,
the lattice expands somewhat. The magnesium-aluminum and aluminum-silicon substitutions
also leave vermiculite with a very high net negative charge, so it has the highest cation
exchange capacity (CEC) of any clay—about 150 milliequivalents (meq) per 100 g of material
(other clays range from about 15 to 100 meq/100 g) (Brady, 1984). This high CEC gives
vermiculite the ability to adsorb a variety of cations (including plant nutrients) and some
organic compounds.
Thus, while vermiculite is not in itself highly reactive, its high surface area and sorptive
capacity strongly influence the behavior of other materials in soil. The only important
physicochemical factors influencing the transport of vermiculite are density and particle size
and shape (Dixon et al., 1985). Because vermiculite occurs in nature in the smallest soil
particle size fraction (less than 0.002 mm), it is very easily transported by wind and water.
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Properties such as melting and boiling point, solubility, vapor pressure, and octanol/water
partition coefficient do not significantly affect its transport.
2.7 ANALYTICAL METHODS
The analysis of samples of vermiculite is dependent upon the sampling technique,
sample preparation, and the resolution capabilities of the instrumentation.
Current sampling techniques have been changed or modified from earlier methods due
to limitations of these methods. In several studies, the early sampling method employed was
the midget impinger method. Although an acceptable method at the time, the impinger
technique tends to underestimate fiber exposure in tremolite-contaminated vermiculite. Later
sampling was done by the membrane filter to give a more complete estimate of exposure
(Amandus et.al., 1987a; Dixon et al., 1985; McDonald et al., 1986). Lockey et al. (1984)
also employed a modified version of the industrial breathing zone method that enables the
sampler to estimate exposure by job area.
Airborne samples of vermiculite are usually analyzed first by polarized-light microscopy
with dispersion staining to identify contaminants. A major limitation of this method is that
only massive amphibole fragments can be seen (Lockey et al., 1984; Moatamed et al., 1986).
Amandus et al. (1987a) and Dixon et al. (1985) subjected tremolite-contaminated vermiculite
dust to phase-contrast light microscopy, which allowed sizing of the tremolite fibers
according to length, width, and aspect ratio. After this initial analysis, airborne samples of
vermiculite can be subjected to a variety of analytical methods depending upon the
information sought. Scanning electron microscopy (SEM) using energy dispersive x-ray
analysis and TEM using selected area electron diffraction allows elemental chemical analysis
and an estimate of the abundance of vermiculite present in the sample (Lockey et al., 1984;
McDonald et al., 1986; Moatamed et al., 1986). An analytical technique employed by
Moatamed et al. (1986) subjected expanded and unexpanded forms of vermiculite to SEM for
comparative identification of fibers as small as 0.01 jam in diameter. Wada and
Kamitakahara (1991) investigated lattice dynamics of vermiculite by inelastic neutron
scattering and Raman scattering.
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Bulk analysis of vermiculite samples was performed by Amandus et al. (1987a) and
Dixon et al. (1985). Amandus et al. (1987a) subjected bulk samples of vermiculite to
polarized-light microscopy to locate fibrous material and to determine physical characteristics.
Further analysis by scanning transmission electron microscopy with an energy dispersive
x-ray spectrometer determined the fibrous mineral content for classification. Dixon et al.
(1985) analyzed bulk samples of vermiculite by electron microscopy to determine fibrous
mineral content. Optical microscopy and x-ray diffraction techniques were then employed to
determine fiber classification. The additional step of subjecting exfoliated vermiculite to
TEM allowed the authors to determine if any fibers were "trapped" in exfoliated vermiculite.
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3. TOXICOLOGY
3.1 RETENTION, BIODISPOSITION, AND CLEARANCE
There was no information in the available literature on the retention, biodisposition, or
clearance of vermiculite. In general, inhaled particles may enter the body either by inhalation
or by ingestion. Most ingested particles apparently pass through the gastrointestinal tract
without being absorbed.
A number of mechanisms influence the deposition of both nonfibrous and fibrous
particles in the respiratory tract. For example, deposition in the nasal passages occurs mainly
by inertia! impaction due to the high velocity of the air stream. Impaction is also an
important factor in the larger conducting airways but, as the flow rate diminishes and the
airway caliber reduces, gravitational settling assumes greater significance. The development
of secondary flows at airway bifurcations enhances the deposition of both nonfibrous
(Schlesinger et al., 1977) and fibrous particles (Morgan et al., 1977; Brody et al., 1982) at
these sites. For particles that are small enough to reach the alveolar region of the lung,
diffusion becomes an important factor in determining deposition. With fibrous particles,
other mechanisms such as interception and electrostatic attraction assume importance.
When nonfibrous compact particles are inhaled, most of those having a diameter greater
than about 5 urn are trapped in the nasal passages (Walton, 1982, as cited in National
Research Council, 1984); however, the aerodynamic behavior of fibers differs from that of
nonfibrous particles. Fibers with a given diameter will behave aerodynamically in a similar
manner to spherical particles with a significantly larger diameter (Gross, 1981; Timbrell
et al., 1970). The equivalent aerodynamic diameter of a particle (Dae) is defined as "the
diameter of a unit-density sphere with the same falling speed as the particle".
Particles and fibers deposited in the nasal passages and in the conducting airways of the
lung are rapidly cleared by mucociliary action, but the fate of those deposited in the alveolar
region depends primarily upon their solubility and length. For insoluble particles or fibers,
such as amphibole asbestos and possibly vermiculite, clearance depends upon their transport
to the ciliated airways for all practical purposes. It appears that this process is mediated by
alveolar macrophages and that clearance decreases with increasing fiber length. (Timbrell,
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1982). Indeed, it appears that fibers with length exceeding a critical value (about 15 jam)
cannot be mobilized by macrophages and remain in the lung indefinitely unless removed by
other mechanisms such as coughing. Short fibers may also be transported within
macrophages to the regional lymph nodes. Epithelial cells are also reported to take up
asbestos fibers (Pinkerton et al., 1983), and fibers may be translocated between epithelial
cells to the interstitium and pleura (National Research Council, 1984).
Studies of miners and millers exposed to vermiculite contaminated with tremplite
suggest that vermiculite may be inhaled, deposited, and retained by the lungs (Amandus
et al., 1987b; Lockey et al., 1984). In one study, the estimated cumulative exposure to
contaminated vermiculite fibers (particles with a length >5 /an and a diameter <3 /mi, and
an aspect ratio J>3:1) of a group of 512 workers (480 males, 32 females) was 0.01 to
39 fibers/cm3/year (Lockey et al., 1984). Pleuritic chest pain occurred in 4.4% (22) of the
exposed population and was correlated (0.05 > p < 0.01) with cumulative fiber
concentration. The authors suggested that these effects, which were not considered severe,
were indicative of a low cumulative fiber exposure. A series of similar studies by Amandus
and coworkers (1987a,b) support Lockey's findings.
3.2 ANIMAL TOXICITY
No information on the acute, subchronic, or chronic toxicity of vermiculite was found
in the available literature. Similarly, there was no information on developmental or
reproductive effects, genotoxicity, or in vitro cytotoxicity of vermiculite.
Results from one study indicate that vermiculite is not carcinogenic following
intrapleural administration. Hunter and Thomson (1973) tested the carcinogenicity of
vermiculite after intrapleural injection of 25 mg in 0.2 cm3 saline into a group of 21-day-old
female Sprague-Dawley rats. The vermiculite sample consisted of amorphous particles and
had a particle size 93% <5 /tm and 37% <2 jam. The animals receiving vermiculite
developed granulomas in the lung and viscera, but no tumors developed after 104 weeks.
A comparable dose of chrysotile asbestos produced mesotheliomas in 48% of the rats.
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3.3 EFFECTS ON HUMANS
This chapter presents a critical review and analysis of the carcinogenic and
noncarcinogenic effects in humans following exposure to vermiculite. 'cross-sectional
studies, clinical evaluations, and case reports are discussed, followed by reviews of
retrospective and historical prospective studies.
3.3.1 Cross-Sectional Studies, Clinical Evaluations, and Case Reports
Results of three studies indicated an association between past fiber exposure and
parenchyma! and pleura! radiographic abnormalities but no correlation with pulmonary
function tests. The effect of smoking and the presence of tremolite-actinolite fibers
confounded the findings of increased pleura! disease.
In a review of nonasbestos fibrous materials, Lockey (1981) concluded that vermiculite
itself did not produce adverse health effects, but noted that vermiculite ore may contain
asbestos fibers. In a later study by Lockey et al. (1984), workers exposed to vermiculite
contaminated with fibrous tremolite were examined. A total of 530 employees, in a plant
processing vermiculite ore to its expanded form were studied. Industrial hygiene sampling of
airborne fibers was initiated in 1972, 15 years after the plant had begun using vermiculite.
Particles with a length >5 /mi, a diameter <3 #m, and an aspect ratio of 3:1 or greater
were counted as fibers. A high-exposure group was identified and compared with the
chemical processing facility where exposure was low. The highest cumulative fiber exposure
for an employee was 39 fibers/cm3-year; only 9.6% had an exposure greater than
o - • • .
10 fibers/cm-year, and 10.7% had been employed 20 years or more since initial exposure.
A cluster of 12 cases of pleura! effusions was identified in the high-exposure group of
194 workers. Radiographic changes correlated with exposure when age-matched groups and
groups with comparable smoking habits were compared. The prevalence of pleuritic changes
was significantly related to fiber exposure, but no correlation was found between fiber
exposure and various pulmonary function tests.
McDonald et al. (1986) obtained chest radiographs from three groups of workers from a
vermiculite mine in Montana. The first group consisted of 164 men and women employed by
the company on July 1, 1983. The second group consisted of 80 men who had been hired
before January 1, 1963, and had been employed for at least one year. The third group
3-3
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comprised 47 men without known exposure to dust who were not selected or matched with
the mine workers but were used only to control the reading process. A logistic regression
analysis showed that there was an effect of cumulative exposure, age, and smoking on the
prevalence of small opacities (p ^0.02). Pleura! thickening on the chest wall was affected by
age and cumulative exposure (p <0.02) but not by smoking. There were several potential
problems in this study. First, exposure estimates were approximate, particularly for those
employed before 1972. Second, the radiographic techniques and radiographic readings were
major sources of variation. Third, the sample size was small. At present exposure levels,
which were reported to average 0.1 fibers/cm3, no excess of radiological change was detected
after a working life of 40 years. The authors suggested that by retirement age, the increase
in prevalence of small parenchyma! opacities.(>1/10) was between 5 and 10% per
100 fibers/cm3»years.
Amandus et al. (1987b) conducted a cross-sectional morbidity study of 191 men
employed for at least five years between 1975 and 1982 at a vermiculite ore mine and mill
near Libby, MT. Radiographic examinations had been administered by a local hospital to all
active workers in 1959 and annually since 1964. Questionnaires on smoking habits and
respiratory symptoms had been administered by the company to most active workers
employed after 1975. Chest radiographs were available for 184 workers, and questionnaires
about smoking and respiratory symptoms were available for 121 workers. Radiographic
findings were independently interpreted by three readers blinded to other data. The
radiographic readings indicated that the prevalence of small opacities was 10%, any pleural
change was 15%, pleural calcification was 4%, and pleural thickening on the wall was 13%.
Fiber exposure, as measured by fiber-years, was significantly related to small opacities, any
pleural change, and pleural thickening on the wall (p <0.05). The prevalence of small
opacities was related to age and fiber-years but not significantly related to smoking. The
confounding effect of smoking could not be accurately assessed, however, due to the small
number of nonsmokers (25 overall).
Hesse! and Sluis-Cremer (1989) studied 172 workers mining and processing South
African vermiculite, which appears to contain some asbestos but at a low level by comparison
with that in Libby, MT. The cohort of all black workers underwent x-ray examination and
lung function testing and completed a respiratory symptom questionnaire. The vermiculite
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workers were compared with other workers involved in the mining or refining of copper.
Only two of the vermiculite workers showed evidence of small opacities of I/O or more
(according to the ILO 1980 classification), lung function was comparable with the other
groups of workers, and there was no excess of respiratory symptoms among the vermiculite
workers. The authors concluded that workers exposed to vermiculite that is minimally
contaminated with asbestos are probably not at risk for pneumoconiosis, lung function
impairment, or respiratory symptoms. The study suffers from limitations: (1) Dust exposure
data are very sketchy, (2) a mortality study would be impractical due to the limited death
registration for rural blacks, and (3) the sample size was small enough that only large effects
of vermiculite exposure would have been detected.. As such, the findings from this study
cannot exclude the risk of mesothelioma caused by amphibole contamination of the
vermiculite.
3.3.2 Retrospective, Prospective, and Historical Prospective Studies
Amandus and Wheeler (1987) conducted a historical prospective mortality study of
575 men hired prior to 1970 and employed at least one year at the vermiculite ore mine and
mill near Libby, MT. Vital status was ascertained for 569 of the 575 cohort members (99%)
as of December 31, 1981. Death certificates were obtained for all but two of the decedents
(1.2%) and coded according to the 8th Revision of the ICD. Expected deaths were calculated
from the U.S. white male death rates. Individual cumulative fiber exposure estimates (fiber-
years) for the cohort were computed for 25 "location-operations" (LOs) for the years after
1968 by using an arithmetic average of fiber concentrations (fibers per centimeter cubed) and
for the years before 1968 by using an arithmetic mean of dust concentrations (mppcf).
Vermiculite ore was found to be contaminated with fibrous tremolite-actinolite (Amandus
etaL, 1987a).
The results of the mortality analysis indicated a significantly increased risk of mortality
for lung cancer (20 observed, 9.0 expected, standardized mortality ratio (SMR) = 223.2,
p <0.01) and NMRD (20 observed, 8.2 expected, SMR = 243.0, p <0.05). An analysis
by exposure, measured as fiber-years (f-y), showed a significant increase hi mortality in the
highest exposure category (>399 f-y) for both lung cancer (10 observed, 1.7 expected,
SMR = 575.5, p <0.01) and NMRD (7 observed, 1.8 expected; SMR = 400.7, p <0.01).
3-5
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Mortality from NMRD was also significantly elevated in the lowest exposure category
(<150 f-y) (8 observed, 3.6 expected, SMR = 220.0, p <0.05). Mortality from lung
cancer and NMRD was further evaluated by f-y and years of latency. No clear pattern
emerged with respect to latency for lung cancer, although the significant increases occurred in
the highest f-y exposure category (>399) at < 10 years latency (2 observed, 0.2 expected,
SMR = 1,370.2, p <0.05) and >20 years latency (7 observed, 1.0 expected, SMR = 671.3,
p <0.01). No exposure-response association was found for NMRD; significant effects
occurred after 10 to 19 years of latency for 100 to 399 f-y (3 observed, 0.6 expected,
SMR = 459.9, p <0.05) and >399 f-y (4 observed, 0.5 expected, SMR = 774.5,
p <0.01). At >20 years, only the lowest exposure category (<50 f-y) was significant
(7 observed, 2.1 expected, SMR = 327.8, p <0.05). There was insufficient power to detect
significant increases in risk at other exposure and latency periods. In addition to small cohort
size and insufficient power to detect lung cancer and NMRD among the whole cohort, a
confounding variable in this study was the effect of smoking. The proportion of current and
former smokers among 161 vermiculite workers was found to be 15.5% higher than that
among U.S. white males in 1975.
McDonald et al. (1986) conducted an independent historical prospective mortality study
of the same vermiculite ore mine and mill studied by Amandus and Wheeler (1987) and
obtained similar results. The cohort consisted of 406 men hired prior to 1963 who were*
employed for at least one year. Compared to the cohort studied by Amandus and Wheeler
(1987), this study had a smaller cohort (406 vs. 575 men), whose members were hired earlier
(1963 vs. 1970), and a longer followup (July 1, 1983 vs. December 31, 1981). In both
studies, cohort members were employed at least one year and death certificates were coded
by the same nosologist. In addition to U.S. white male death rates, McDonald et al. (1986)
used Montana males as a further comparison for deaths from respiratory cancer. By the end
of the followup period, July 1, 1983, 226 (55.y%) of the 406 workers were alive;
165 (40.6%) had died; and 15 (3.7%) were lost to followup. Death certificates were
obtained for all but two (98.7%) of the decedents. Prior to 1965, investigators assumed
mean dust concentrations of 101.5 fibers/cm3. Between 1970 and 1974, mean dust
concentrations measured through personal and area sampling were found to be
22.1 fibers/cm3. The current mean dust concentration is 0.1 fibers/cm3.
3-6
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Compared to U.S. white males, the cohort experienced excess mortality from all causes
(165 observed, 141.0 expected, SMR = 117, p <0.05), respiratory cancer (23 observed,
9.39 expected, SMR = 245, p < 0.001), NMRD (21 observed, 8.24 expected, SMR = 255,
p <0.001), arid accidents (SMR •= 214, p <0.005). Compared to Montana males, who had
lower expected deaths from respiratory cancer than U.S. white males, the SMR for
respiratory cancer was slightly higher (303). Four deaths were from malignant
mesothelioma.
In addition, McDonald et al. (1986) conducted a nested case-control analysis of
exposure-response of 23 respiratory cancer deaths. Controls for each respiratory cancer case
were selected from men who survived beyond the age of death of the case and who worked
within three years of the case. For each control, exposure accrued until the age of death of ir
the matching case. This nested case-control analysis resulted in a statistically significant
linear relationship between relative risk for respiratory cancer and cumulative exposure, and
was most pronounced 20 or more years after first employment (chi square = 7.04,
p <0.01).
The investigators concluded that the cohort was small but was sufficient to show that
workers in the mining facility experienced a serous hazard from lung cancer,
pneumoconiosis, and mesotheliomas. They attributed those diseases to tremolite
contamination of vermiculite ore and the dusty conditions prior to 1974. As in the study of
Amandus and Wheeler (1987), the presence of tremolite prevents any conclusions as to the
role of vermiculite in causing lung cancer.
McDonald et al. (1988) studied a small cohort of 194 men with low exposure to fibrous
tremolite (mean 0.75 f/ml«y) in the mining and milling of vermiculite in the Enoree region of
South Carolina. The cohort experienced 51 deaths, 15 years or more from first employment.
The SMR taH causes) was 117, reflecting excess deaths from circulatory disease. There were
four deaths from lung cancer and 3.31 expected (SMR 121, 95% CI 0.33 to 3.09). Three of
the four deaths were in the lowest exposure category (< 1 f/ml-y); no deaths were attributed
to mesothelioma or pneumoconiosis. A radiographic survey of 86 current and recent South
Carolina employees found four with small parenchyma! opacities (> 1/0) and seven with
pleural thickening. These proportions were not higher than in a nonexposed group.
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Examination of sputum from 76 current employees showed that only two specimens contained
typical ferruginous bodies, confirming low cumulative fiber exposure.
The American Thoracic Society (ATS, Weill et al., 1990) discusses the health effects of
tremolite and reviews the studies of vermiculite health effects. The ATS notes that the South
Carolina study does not add information because a detectible increase in lung cancer risk
would not have been expected because of the low exposure levels and the small size of the
cohort. They additionally state that the observation for the Montana cohort of a dose-
response relationship for lung cancer risk is important evidence of tremolite asbestos as a
carcinogen in vermiculite mining, but note that, because this is based on only one cohort and
because no other data on other relatively large populations of vermiculite miners are
available, appropriate caution in interpreting nonreplicated epidemiological study results is
warranted.
In regards to tremolite asbestos, the ATS (Weill et al., 1990) concludes the following
after a review of other tremolite studies beyond those of contaminated vermiculite.
1. Unquestioned health effects of tremolite asbestos have been demonstrated in
both humans and animals. These effects are identical to those produced by
*
other forms of asbestos.
2. There may be important physicochemical distinctions between asbestosform and
non-asbestosform tremolite dust particles. However, there appears to be
considerable controversy in applying these mineralogic definitions to specific
samples of minerals, particularly individual particles viewed microscopically after
collection by air sampling or found in human lungs or when used experimentally.
3. At present, the prudent public health policy course is to regard appropriately sized
tremolite "fibers", in sufficient exposure dose (concentration and duration), as
capable of .producing the recognized asbestos-related diseases, and they^should be
regulated accordingly.
la summary, after examining the above studies and reviews, the weight of evidence for
a causal relationship between exposure to vermiculite and lung cancer or NMRD is
inadequate because vermiculite ore was found to be contaminated with asbestos. However,
mere is sufficient evidence for asbestos-contaminated vermiculite.
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»
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J. D. (1983) Characterization of three types of chrysotile asbestos after aerosolization. Environ. Res.
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the human tracheobronchial tree. J. Aerosol Sci. 8: 429-445.
Tirabrell, V. (1982) Deposition and retention of fibres in the human lung. Ann. Occup. Hyg. 26: 347-369.
Timbrell, V.; Bevan, N. E.; Davies, A. S.; Munday, D. E. (1970) Hollow casts of lungs for experimental
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Wada, N.; Kamitakahara, W. A. (1991) Inelastic neutron- and Raman-scattering studies of muscovite and
vermiculite layered silicates. Phys. Rev. Sect. B: Condens. Matter 43: 2391-2397.
Walton, W. H. (1982) The nature, hazards and assessment of occupational exposure to airborne asbestos dust:
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Weill, H.; Abraham, J. L.; Balmes, J. R.; Case, B.; Churg, A. M.; Hughes, J.; Schenker, M.; Sebastien, P.
(1990) Health effects of tremolite. Am. Rev. Respir. Dis. 142: 1453-1458.
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