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

estricted to smokers than among all study
subjects. However, it is no surprise that an association
was observed between smoking and
lung cancer, and the fact that the negative (inverse)
exposure-response trend was stronger
among smokers does not explain why the cohort
as a whole experienced much higher lung
cancer rates than expected.
Only two cases of pleural mesothelioma have
been reported in the cohort studies of RTV
miners and millers [Honda et al. 2002], and
those authors reported that it was unclear
whether these cases are attributable to exposure
to talc at the RTV mine and mills. One of the
individuals had worked for only a short time in
a job with minimal talc exposure, had previously
worked for many years in the construction of
a talc mine, and had subsequently worked on
repairing oil heating systems. The other case
developed only 15 years after first exposure to
RTV talc, although mesothelioma has more
typically been observed to develop after much
longer times from first exposure. NIOSH has
recently received unpublished reports of additional
cases of pleural mesothelioma among
workers at RTV or its predecessor, International
Talc [Abrams 2010; Maimon 2010], and
a report of at least one worker using products
from the mine who may also have died from
mesothelioma [Satterley 2010]. NIOSH has also
received unpublished observations concerning
findings from chest radiographs RTV has obtained
on its workers semiannually since 1985.
Although pleural plaques were more frequently
observed, the program has identified only one
worker with irregular parenchymal opacities
consistent with asbestosis-like disease, results
that a consulting pulmonologist “did not find
… to be consistent with that of a workforce exposed
to asbestos” [Kelse et al. 2008].
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Van Gosen [2007] has reported that fibrous
varieties of talc, tremolite, and anthophyllite
occur in the tremolite-talc deposits of the
Governeur talc mining district of upstate New
York. It has been debated whether the fibrous
amphiboles in those talc ores meet the criteria
of asbestos, with the debate centered on the
complex and unusual transitional fibers composed
partly of talc and partly of anthophyllite.
NIOSH [1980] and others [Van Gosen 2006;
Webber 2004] have reported that dust from the
RTV mine, which is in the Governeur talc mining
district, contains asbestos. In an industrial
hygiene assessment conducted at RTV mines
by NIOSH [1980], X-ray diffraction and petrographic
microscopic analyses of talc product
samples found them to contain 4.5%–15%
anthophyllite (some of which was categorized
as asbestos). In contrast, Kelse [2005] reported
the percentage by weight of talc from the
RTV mine in upstate New York as 1%–5%
nonasbestiform anthophyllite. In airborne samples
collected by NIOSH at the mine and mill
and analyzed by TEM, 65% of the EMPs that
were longer than 5 µm were anthophyllite and
7% were tremolite, and much of the tremolite
was from a nonfibrous habit [NIOSH 1980].
Kelse [2005] reported that up to 1.8% was from
an asbestiform habit, though the asbestiform
component was reported not to be asbestos.
Serpentine and amphibole minerals typically
develop through the alteration of other minerals.
Consequently, they may exist as partially
altered minerals having variations in elemental
compositions. Minerals undergoing this alteration
are often called “transitional minerals.”
Thus the elemental composition of individual
mineral particles can vary within a mineral deposit
containing transitional minerals, which
could account for differences in the reported
composition of talc from the RTV mine.
NIOSH CIB 62 • Asbestos