Asbestos Fibers and Other Elongate Mineral Particles: State of the ...

A limitation of the epidemiological studies of
RTV talc workers is the lack of an exposure-response
analysis based on direct measurements
of airborne EMP concentrations. Most of the
studies used tenure as a surrogate for exposure,
and the exposure metric used in the Honda et
al. [2002] study was respirable dust, which may
not be correlated with exposure to EMPs. Relationships
between health outcomes and exposure
to an agent of interest can be attenuated
when a nonspecific exposure indicator is used
as a surrogate for exposure to the agent of interest
[Blair et al. 2007; Friesen et al. 2007]. Thus,
when the exposure index used to assess the effect
of EMPs is based on a surrogate measure,
such as respirable dust, rather than on specific
measurement of EMP concentrations, the
lack of an exposure-response relationship between
the exposure index and the health outcome
might not accurately reflect the true risk,
particularly where the composition of a mixed
dust exposure varies by work area.
Finally, a cohort study of Vermont talc miners
and millers has some relevance for interpreting
the findings from the studies of New York talc
workers [Selevan et al. 1979]. Airborne dust
samples and talc bulk samples from all locations
in the mines and mill studied were analyzed
by X-ray diffraction or analytical EM, which
showed the talcs to be similar in composition;
no asbestos was detected in any of the samples.
To determine potential differences between the
talcs mined and milled by a company no longer
in operation, seven samples of talcs were
obtained and also analyzed by X-ray diffraction
or analytical EM. These samples were reported
to be free of asbestos contamination and
the mineral composition was within the range
of samples from then-producing operations.
The one remaining company, no longer operating
at that time, had been located in the same
geographic area as two of the then-producing
NIOSH CIB 62 • Asbestos
companies. The talc in one of the closed mines
was reported to have had “cobblestones” of serpentine
rock that were highly tremolitic. In the
mining of this talc, these cobblestones were reported
to have been avoided and/or discarded.
Therefore, miners may have been exposed
to tremolite, but it is unlikely that the millers
from this company were exposed [Selevan
1979]. Van Gosen [2004] described the talc deposits
in this area as “associated spatially with
serpentinite masses that in some areas host
well-developed chrysotile asbestos [Bain 1942;
Cady et al. 1963]. The alteration zone locally
contains actinolite, tremolite, anthophyllite,
and (or) cummingtonite, as described by Cady
et al. [1963]. Zodac [1940] described ‘radiating
masses of fibrous actinolite, which often have
to be handled carefully as the needlelike crystals
may penetrate fingers, are common on the
dumps’ in a talc quarry near Chester, Vermont.
The amphiboles present were not identified as
asbestiform.
A statistically significant excess of NMRD
mortality was observed among the millers
(SMR = 4.1; 95% CI = 1.6–8.4), but not among
the miners (SMR = 1.6; 95% CI = 0.20–9.6), in
this study [Selevan 1979]. In contrast, respiratory
cancer mortality was found to be significantly
elevated among the miners (SMR = 4.3;
95% CI = 1.4–10), but not among the millers
(SMR = 1.0; 95% CI = 0.12–4.0). The authors
suggested that their respiratory cancer findings
might be due to non-talc exposures, such as radon
progeny, because exposures to talc dust
were higher among millers than miners. The
pattern of excess respiratory cancer observed
in this study is similar to that reported in studies
of RTV miners and millers. It has been noted
[Lamm and Starr 1988] that this provides
evidence against the hypothesis that the lung
cancer excess among RTV miners is caused
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