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

not demonstrate any clear health risks associated
with exposure to the nonasbestiform EMPs covered
by the NIOSH “airborne asbestos fiber” definition.
Whether or not to include EMPs from nonasbesti
form analogs of the asbestos minerals
in federal regulatory asbestos policies has been
the subject of long-standing debate. The exposure-related
toxicity and health effects associated
with the various morphologies (e.g., acicular,
prismatic) of the nonasbestiform analogs of
the asbestos minerals continue to be a central
point in the debate. In 1986, OSHA revised its
asbestos standard and included nonasbestiform
anthophyllite, tremolite, and actinolite (ATA)
as covered minerals within the scope of the revised
standard [OSHA 1986]. OSHA’s decision
to include nonasbestiform ATA proved controversial.
In a 1990 proposal to reverse this revision,
OSHA [1990] noted that there were “a
number of studies which raise serious questions
about the potential health hazard from occupational
exposure to nonasbestiform tremolite,
anthophyllite and actinolite,” but that the “current
evidence is not sufficiently adequate for OSHA to
conclude that these mineral types pose a health
risk similar in magnitude or type to asbestos.”
In the preamble to the final rule removing
nonasbestiform ATA from its asbestos standard,
OSHA [1992] stated that:
20
…various uncertainties in the data** and
a body of data showing no carcinogenic effect,
do not allow the Agency to perform
qualitative or quantitative risk assessments
concerning occupational exposures. Further,
the subpopulations of nonasbestiform
** OSHA was referring to the scientific data on which
NIOSH based its own carcinogenic health effect recommendation
to OSHA.
ATA which, based on mechanistic and toxicological
data, may be associated with a
carcinogenic effect, do not appear to present
an occupational risk. Their presence in
the workplace is not apparent from the record
evidence.
In its 2005 proposed rule for asbestos, MSHA
stated that substantive changes to its asbestos
definition were beyond the scope of the proposed
rule and chose to retain its definition of
asbestos, which “does not include nonfibrous
or nonasbestiform minerals” [MSHA 2005].
These decisions are reflected in MSHA’s final
rule published in 2008 [MSHA 2008]. In formal
comments during the rulemaking process,
NIOSH agreed with MSHA’s decision not
to modify its asbestos definition in the current
rulemaking, stating that “NIOSH is presently
re-evaluating its definition of asbestos and
nonasbestiform minerals, and will work with
other agencies to assure consistency to the extent
possible” [NIOSH 2005]. In the interim,
the following subsections provide more detail
on the three elements comprising NIOSH’s rationale
for recommending in 1990 that nonasbestiform
analogs of the asbestos minerals be
encompassed by the REL.
2.7.1.1.1 Epidemiological Studies
The first element of NIOSH’s rationale for recommending
in 1990 that nonasbestiform analogs
of the asbestos minerals be encompassed
by the REL related to evidence from epidemiological
studies.
A number of epidemiological studies have been
conducted to evaluate the health risk to workers
reported to be exposed to EMPs. Epidemiological
studies have been conducted in the
Governeur talc district of upstate New York in
NIOSH CIB 62 • Asbestos