Inhaled amorphous silica particulates: what do we know about their toxicological profiles?

The International Agency for Research on Cancer (IARC) recently published a monograph on the evaluation of carcinogenic risks to humans of exposure to crystalline and amorphous silica particles. The IARC Working Group concluded that crystalline silica, in the form of quartz or cristobalite, from occupational sources posed a carcinogenic risk to humans (Category 1). IARC also determined that amorphous silica particles were not classifiable as to its carcinogenicity to humans (Category 3). With regard to amorphous silica, the evaluation was based primarily on the lack of toxicological and epidemiological data for these materials and this was noted in the IARC document. This manuscript is designed to provide a brief summary of the limited inhalation toxicity database related to amorphous silica particulates and to cite a few studies wherein the pulmonary toxicological effects of inhaled crystalline and amorphous silica particles were compared.