Table 1.
Intracage ammonia levels (in ppm; mean ± 1 SD)
| Housing group | Ammonia level over entire 28 d | Ammonia level on day 12 | Ammonia level on day 18 | Day on which ammonia level (in parentheses) exceeded TWA |
| 1 male mouse | <10 | <10 ± 0 | <10 ± 0 | Never |
| 1 female mouse | <10 | <10 ± 0 | 12.3 ± 8.0 | Never |
| 3 male mice | 19 | <10 ± 0 | 22.8 ± 26.4 | day 21 (39) |
| 3 female mice | 29 | 13 ± 9.6 | 72 ± 124.4 | day 17 (30) |
| 5 male mice | 95 | 119 ± 144a | 137.3 ± 82 | day 9 (58) |
| 5 female mice | 32 | 9.5 ± 1.1 | 10.3 ± 2.95 | day 12 (27) |
| Breeder pair | 63 | 51.4 ± 72.4 | 98 ± 115.9 | day 9 (26) |
TWA, 8-h time-weighted threshold limit value for human exposure (that is, 25 ppm).
a
Ammonia level was significantly (P ≤ 0.05) greater than that of all other groups.