Table 3 Average measured total cerium and titanium retained lung burdens (n = 4) and estimated elimination half-time
Exposure group | Exposure time and concentration | Av. measured Ce lung burden ± sd (µg) | CeO2 half-time (days) | Av. measured Ti lung burden ± sd (µg) | TiO2 half-time (days) | ||||
|---|---|---|---|---|---|---|---|---|---|
| Â | 18Â h | 7 days | 14 days | Â | 18Â h | 7 days | 14 days | Â | |
Control, single | 6 h on 1 day to clean air | 0.01 ± 0.00 | 0.01 ± 0.001 | 0.01 ± 0.003 | n.a. | 0.27 ± 0.08 | 0.22 ± 0.01 | 0.25 ± 0.03 | n.a. |
Low, single | 30 min on 1 day to 20 mg/m3 | 13 ± 1.7 | 12 ± 1.3 | 10 ± 0.9 | 40 | 9.4 ± 1.7 | 7.3 ± 1.1 | 6.1 ± 1.1 | 18 |
Mid, single | 2 h on 1 day to 20 mg/m3 | 49 ± 4.1 | 48 ± 8.5 | 48 ± 6.9 | n.d. | 29 ± 3.0 | 23 ± 2.8 | 19 ± 5.1 | 20 |
High, single | 6 h on 1 day to 20 mg/m3 | 145 ± 12 | 144 ± 7.5 | 143 ± 10 | n.d. | 91 ± 11 | 84 ± 5.0 | 68 ± 9.5 | 31 |
| Â | 18Â h | 30 days | 60 days | Â | 18Â h | 30 days | 60 days | Â | |
Control, single | 6 h on 1 day to clean air | 0.01 ± 0.001 | 0.01 ± 0.001 | 0.01 ± 0.004 | n.a. | 0.24 ± 0.01 | 0.34 ± 0.07 | 1.21 ± 0.19 | n.a. |
Low, repeated | 30 min on 2 × 5 days to 5 mg/m3 | 26 ± 3.3 | 17 ± 2.6 | 13 ± 2.2 | 58 | 22 ± 2.1 | 10 ± 0.74 | 4.5 ± 0.76 | 25 |
Mid, repeated | 2 h on 2 × 5 days to 5 mg/m3 | 110 ± 5.1 | 92 ± 8.4 | 70 ± 11 | 99 | 82 ± 4.3 | 41 ± 5.7 | 11 ± 2.0 | 20 |
High, repeated | 6 h on 2 × 5 days to 5 mg/m3 | 351 ± 15 | 269 ± 32 | 239 ± 27 | 134 | 241 ± 30 | 120 ± 18 | 50 ± 12 | 26 |