Silica (crystalline, respirable) - OEHHA

FINAL February 2005
X. Appendix
Particulate Levels of Interest for Exposure to Respirable Crystalline Silica Isomorphs
150 µg/m 3 Federal 24 hour PM10 standard
65 µg/m 3 Federal 24 hour PM2.5 standard
50 µg/m 3 California 24 hour PM10 standard
50 µg/m 3 Federal PM10 annual standard (chronic exposure)
50 µg/m 3 8 hour TLV for quartz, cristobalite, and tridymite for workers (ACGIH Method)
50 µg/m 3 estimated workplace LOAEL for silicosis from studies by Theriault et al. (“)
20 µg/m 3 CA annual PM10 standard (chronic exposure) (arithmetic mean)
15 µg/m 3 Federal annual PM2.5 standard (chronic exposure)
12 µg/m 3 CA annual PM2.5 standard (chronic exposure) (arithmetic mean)
12 µg/m 3 current silica TLV adjusted to equivalent continuous exposure
(50 µg/m 3 x 8 h/24 h x 5 d/7d) (ACGIH)
10 µg/m 3 TLV for silica proposed by Greaves (2000) (ACGIH)
8 µg/m 3 current silica TLV further adjusted by 46/70 years occupational exposure
(ACGIH)
8 µg/m 3 estimated high-end ambient crystalline silica level in US (USEPA, 1996) (PM10)
6.7 µg/m 3 lower bound on 1% risk of silicosis estimated by USEPA (1996) (PM10)
5 µg/m 3 TLV for silica proposed by Chen et al. (2001) (ACGIH)
5 µg/m 3 “acceptable” ambient level for silica (10% of PM10) (USEPA, 1996)
5 µg/m 3 RfC for diesel exhaust particulate, a respirable PM (PM2.5)
3 µg/m 3 estimated average ambient exposure to crystalline silica (USEPA, 1996) (PM10)
3 µg/m 3 draft silica chronic REL proposed by OEHHA (ACGIH)
2.3 µg/m 3 (1.17-3.46; n=12)* silica level during 1989 in Santa Maria, CA (urban site) (PM10)
0.6 µg/m 3 (0-1.44; n=16)* silica level during 1989 in Santa Ynez, CA (rural site) (“)
0.2 µg/m 3 (0-1.15; n=18)* silica level during 1989 in Buellton, CA (remote background)(“)
* mean, range, and number of crystalline silica measurements (Mukherji et al., 1993)
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