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

are made available to the research community
for testing and standardization. This will allow
minerals with matching properties (e.g., morphology,
dimension) to be chosen for study. To
accomplish this research, exhaustive characterization
of the samples, including contaminants,
is necessary. Detailed characterizations of minerals
should include their ability to affect biological
activities and properties such as (1) purity,
(2) particle morphology (range of dimensions
and sizes), (3) surface area, (4) surface chemistry,
and (5) surface reactivity. The particle characteristics
identified by Hochella [1993] should
be considered for particle characterization. The
use of these samples in research would facilitate
meaningful comparisons and reduce uncertainties
in the interpretation of results between and
among studies.
Care must be taken to ensure that a sufficient
amount of the studied material is available, not
only for current studies, but also as reference material
for possible future studies. The repository
should accept and store samples from researchers
conducting EMP studies so that further testing
and characterizations can be performed. The
information developed from all of these efforts
should be entered into a database, which can
serve as a tool for selection of minerals for testing
and validation of toxicological tests, as well
as to assist in identification of worker populations
for possible epidemiological studies.
The development of a comprehensive, publicly
available information system incorporating all
studies of the toxicity, exposures, and health
effects of asbestos and related minerals could
help enhance the development of the research
programs, avoid duplication of effort, and enhance
interpretation of the data generated. The
system should include all pertinent information
about methods, doses or exposures, minerals,
particle characteristics, and other topics.
NIOSH CIB 62 • Asbestos
3.4 Develop a Broader
Understanding of the
Important Determinants of
Toxicity for Asbestos Fibers
and Other EMPs
To address this objective, one of the first steps
will be to identify the range of minerals and mineral
habits needed to systematically address the
mineral characteristics that may determine particle
toxicity. Care must be taken to ensure that
mineralogical issues in a study are adequately addressed.
Information on both crystalline lattice
structure and composition is needed to define a
mineral species, because information on either
alone is insufficient to describe the properties of
a mineral. For example, nonasbestiform riebeckite
and asbestiform riebeckite (crocidolite) share
the same elemental composition but have different
expressions of their crystalline lattices. EMPs
from nonasbestiform riebeckite are not flexible.
Crocidolite fibers generally have chain-width defects,
which explain their flexibility. These chainwidth
defects also affect diffusion of cations and
dissolution properties, both of which can explain
greater release of iron into surrounding fluid by
crocidolite than by nonasbestiform riebeckite
[Guthrie 1997].
In addition to elemental content and crystalline
habit, the particle characteristics identified
by Hochella [1993] should be considered
for particle characterization. For example, the
current paradigm for fiber pathogenicity does
not discriminate between different compositions
of biopersistent fibers, except insofar as
composition determines biopersistence. Two
biopersistent fiber types, erionite [Wagner et
al. 1985] and silicon carbide [Davis et al. 1996],
show a special proclivity to cause mesothelioma,
for reasons that are not easily explained by
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