ABSTRACT
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There is a wide spectrum of different approaches to the testing of particles that range from long-
term inhalation studies, with the final endpoint of cancer, to short-term tests in vitro determining the
ability of the particle to modulate cellular functions. The value of each of these tests in predicting
pathogenicity varies; but in general, there is a playoff between the extended timescale and high cost
of long-term pathogenicity experiments in animals which can be used in risk assessment and the
short timescale and relative inexpensiveness of in vitro data, which can, at best, be used in hazard
assessment. If epidemiological or clinical data were available on the pathogenic outcome of
exposure to a novel particle, then this would form the basis of a rational test strategy. However,
in the absence of such information, a strategy based on knowledge of structure, chemistry, and
shape of the particle could allow benchmarking to similar particles of known pathogenicity in order
to decide on the most appropriate endpoint.
