The evaluations for both crystallin

The evaluations for both crystalline and amorphous silica pertain to inhalationresulting from workplace exposures. Lung cancer was the primary focus. The W orkingGroup' s evaluation of the epidemiological evidence for potential causal relationsbetween silica and cancer risk was focused principally on findings from studies that were1east like1y to have been distorted by confounding and selection biases. Among thesestudies, those that addressed exposure-response associations were especially influentialin the Working Group's deliberations.Crystallne silicaPossible differences in carcinogenic potential among polymorphs of crystalline silicawere considered. Sorne studies were of populations exposed principally to quartz. ln onlyone study (that of United States diatomaceous earth workers) was the exposure predominantlycristobalite. Studies of mixed environments (i.e. ceramics, pottery, refractorybrick) cou Id not delineate exposures specifically to quartz or cristobalite. Although therewere sorne indications that cancer risks varied by type of industry and process in amanner suggestive of polymorph-specific hazards, the Working Group cou Id only reacha single eva1uation for quartz and cristobalite. Nonetheless, the W orking Group did notea reasonab1e degree of consistency across studies of workers exposed to one or bothpolymorphs.

The evaluations for both crystalline and amorphous silica pertain to inhalation
resulting from workplace exposures. Lung. Cancer was the primary focus. The W orking
Group 's evaluation of the epidemiological evidence for potential causal relations
between. Silica and cancer risk was focused principally on findings from studies that were
.1east like1y to have been distorted by confounding and selection biases. Among these
studies those that, addressed exposure-response. Associations were especially influential
in the Working Group 's deliberations.

Crystallne silica Possible differences in. Carcinogenic potential among polymorphs of crystalline silica
were considered. Sorne studies were of populations exposed. Principally to quartz.Ln only
one study (that of United States diatomaceous earth workers) was the exposure predominantly
cristobalite. Studies. Of mixed environments (i.e. Ceramics pottery, refractory
brick), cou Id not delineate exposures specifically to quartz or. Cristobalite. Although there
were sorne indications that cancer risks varied by type of industry and process in a
.Manner suggestive of, polymorph-specific hazards the Working Group cou Id only reach
a single eva1uation for quartz and. Cristobalite. Nonetheless the W, orking Group did note
a reasonab1e degree of consistency across studies of workers exposed. To one or both
polymorphs.