GENERAL REMARKS ON THE SUBSTANCES eONSIDERED

This sixty-eighth volume of IARC Monographs considers certain forms of crystalIine and amorphous silica, some silicates (palygorskite, also called attapulgite; sepiolite; wollastonite; and some natura1 and synthetic zeolites, exc1uding erionite), coa1 dust and para-aramid fibrils. Some of these agents are fibrous in nature (palygorskite, sepiolite, wollastonite and sorne natural zeolites, as well as para-aramid fibrils). With the exception of coal dust, zeolites (other than erionite) and para-aramid fibrils, these agents were evaluated by previous IARC working groups in 1986 (IARC, 1987a,b) (see Table 1). Since these previous eva1uations, new data have become available, and the Preamble to the ¡ARC Monographs has been modified (Vainio et al., 1992) to permit