Table 9.
Rodent Studies Evaluating SCEs Following Exposure to Styrene or Styrene Oxide
| Species/gender | Route | Doses and duration | Sampling times | Methods | Results | Comments | Reference |
|---|---|---|---|---|---|---|---|
| Styrene | |||||||
| Mouse C57B1/6/male | i.p. | 50, 100, 250, 500, 750, and 1,000 mg/kg. Single injection. | 24 hr after BUdRa implant and styrene injection. | Bone marrow. Implanted BUdR tablet, i.p. injection of styrene 30 min after tablet implant. Three to four animals per group, except in the top two dose groups where death resulted in two and one animal scored; 30 sec division cells scored. | SCEs/cell Negative control: 4.3 ± 0.70. Solvent control: 3.9 ± 0.68. Authors report a statistically significant increase in SCEs; however, the highest frequency was seen at the 500 mg/kg level (6.0 ± 0.97) and declined at the higher doses. Replicative index was not impacted in the animals that survived (and were scored). |
Number of animals per group is below the OECD recommended (five), particularly in the top dose groups. i.p. is no longer considered a relevant route of exposure. | Sharief et al. (1986) |
| Mouse BDF1/male | Inhalation, head only | 565 ± 18.5 ppm; 6 hr/day for 4 days. | Next day following last exposure. | Bone marrow and liver cells (from hepatectomized animals). BUdR on last day of styrene exposure. 4 controls and 4 treated (with and without hepatectomy). 30 cells scored. | The treated animals had a much higher (and statistically significant) SCE frequency than the controls. SCEs/cell in bone marrow: Controls: mean 3.0 ± 1.9 (hepatectomized) and 3.3 ± 1.9 (non‐hepatectomized). Treated: 11.9 ± 3.4 (hepatectomized) and 11.0 ± 4.0 (non‐hepatectomized). Liver: control mean 3.8 ± 2.0 and treated 12.2 ± 3.7. | Only a single dose. The number of animals per group is below the OECD recommended 5. The liver SCE is not a standard method. Small number of cells scored. The large difference between the controls and treated is difficult to dismiss based on study deficiencies. However. It would not be appropriate to call the response positive based on a single dose. | Conner et al., 1979 |
| Mouse BDF1/male | Inhalation, head only | 104, 387, 591, and 922 ppm, 6 hr/day for 4 days and 922 ppm, 6 hr/day for 1 or 2 days. | Next day following last exposure. | Bone marrow, alveolar macrophages. Two sets of animals (one hepatectomized and one not). Regenerating liver in hepatectomized animals. BUdR injection immediately after last treatment. Fifteen animals in the controls. The treated groups ranged from three to four animals. The number of second division cells scored ranged from 23–62. | The authors report exposure related increases in SCEs. The low dose groups (for all three cell types) were not different than controls. The other dose groups were significantly higher than the controls, with the exception that the single day exposure (top dose) was not different than the controls. The controls ranged from 2.9 to 3.5 SCEs/cell. The highest response was seen in the top dose/4‐day treatment where the SCEs/cell ranged from 8.0 to 11.0 SCEs/cell. | The number of animals in treated groups is below the OECD recommended (five). The liver SCE is not a standard method. The large difference between the controls and top dose treated is difficult to dismiss based on study deficiencies. It is noted that earlier study by Conner et al. (1979) used a single dose of 565 ppm. The SCE/cell values observed in that study were similar to the values obtained in this study at the 922 ppm dose. This highlights the variability between the two studies. | Conner et al. (1980) |
| Mouse LACA Swiss/male | i.p. | 75, 150, 300, and 450 mg/kg. Single injection. | 24 hr postinjection. | Five animals per group (one died in the top dose group). Splenocytes isolated and cultured for 40 hr. Twenty metaphases scored. Replicative index determined. | A statistically significant increase at the top dose. SCEs/chromosome: control (0.23 ± 0.02), 450 mg/kg (0.27 ± 0.02). This dose was lethal in 1 of 5 animals. | Insufficient number of cells scored. i.p. is no longer considered a relevant route of exposure. Top dose was too toxic. | Simula and Priestly (1992) |
| Rat Porton/male | i.p. | 375, 750, 1,500, and 3,000 mg/kg. Single injection. | 48 hr postinjection. | Five animals per group (four died in the top dose group). Splenocytes isolated and cultured for 62 hr. Twenty metaphases scored. Replicative index determined. | A statistically significant increase in the top three doses (however, the top dose lost four animals). SCEs/chromosome: control (0.21 ± 0.01), 1,500 mg/kg (0.45 ± 0.04). | Insufficient number of cells scored. i.p. is no longer considered a relevant route of exposure. Top dose was too toxic (and above the 2,000 mg/kg top dose recommended in the OECD CA and MN TGs). | Simula and Priestly (1992) |
| Mouse B6C3F1/female | Inhalation, whole body | 125, 250, and 500 ppm, 6 hr/day for 14 days. | One day after last exposure. | Mononuclear leucocytes from blood or spleen from six animals were cultured with BUdR. Lung cells isolated and cultured and BUdR added (from eight animals). Peripheral blood lymphocytes cultured with BUdR. Where possible 50 s division metaphases scored. For the peripheral blood, 25 sec division metaphase scored (where possible). | The authors reported the SCE response in the splenic lymphocytes, peripheral blood lymphocytes, and lung cells to be positive. Spleen: Controls varied from 9.8 to 10.9 SCEs/cell and the top dose group varied from 12.4 to 13.3 SCEs/cell (with one animal having too few cells to score). Peripheral blood: Controls varied from 9.6 to 10.1 SCEs/cell and the top dose group varied from 10.9 to 12.1 SCEs/cell. There were fewer than six animals evaluated in each group for peripheral blood. Lung: Controls varied from 8.0 to 11 SCEs/cell and the top dose group varied from 10.3 to 12.7 SCEs/cell. | Overall a positive response. It should be noted that the lung cell SCE is not a standardly conducted method. There were fewer than five animals in each group for the peripheral blood SCE analysis. | Kligerman et al. (1992, 1993) |
| Rats Fischer 344/female | Inhalation, whole body | 125, 250, and 500 ppm, 6 hr/day for 14 days. | One day after last exposure. | Peripheral blood lymphocytes with BUdR. Five animals per group; 50 sec division metaphases scored. | Authors report a statistically significant positive response. Control: 11.3 ± 0.7 SCEs/cell. Top dose: 14.3 ± 2.1 SCEs/cell. | A positive response. | Kligerman et al. (1993) |
| Rats Fischer 344/male | Inhalation, whole body | 150, 500, and 1,000 ppm, 6 hr/day, 5 days/week for 4 weeks. | 1, 2, 3, and 4 weeks and 4 weeks after last exposure. | Peripheral blood lymphocytes. Cultured with BUdR added 24 hr after culture initiation. Cells harvested 68 hr after culture initiation. A minimum of 25 sec division cells scored. Four to six animals per group. Positive control: ethylene oxide. | No increase in the treated vs. controls. The control means ranged from 5.36–6.6 SCEs/cell. The treated means ranged from 5.02–6.8 SCEs/cell. | Small number of cells scored. Some groups may have had less than five animals (number unclear). Overall a negative response, but not definitive. | Preston and Abernethy (1993) |
| Styrene Oxide | |||||||
| Chinese hamster/male | Inhalation, whole body and i.p. | 25, 50, 75, and 100 ppm. Nine hours (6 hr Day 1 and 3 hr Day 2) and 21 hr (6 hr daily for 3 days and 3 hr Day 4) (except for the top dose only 9 hr exposure; the animals showed signs of poisoning). The low dose also used for a 3‐week exposure (6 hr daily, 5 days/week). Single dose of 500 mg/kg (i.p.). | After last exposure for the inhalation and for i.p. 7 hr after injection. | 2–3 animals in each treatment group; 6 animals in the i.p. group. 13 animals in the negative control. 4 animals in the olive oil (vehicle control). Bone marrow cells, labeled with BUdR in vitro. Number of cells scored varied from 10–104 in the SO treated animals. MMS used as a positive control. | Negative control: 7.9 SCEs/cell. The SO treated animals varied from 6.4–7.8 SCEs/cell. The 500 mg/kg i.p. treated animals were 9.4 SCEs/cell, which was statistically different than the control. The MMS positive control: 17.5 SCEs/cell. | Insufficient number of animals in each dose group. Insufficient number of cells scored. The top doses used, particularly for i.p. were clearly too toxic. i.p. is no longer considered a relevant route of exposure. | Norppa et al. (1979) |
| Mouse | Inhalation | 50 and 70 ppm, 5 h. | Unclear. | Bone marrow, alveolar macrophages and regenerating liver cells. Three animals in the control and 50 ppm groups and one to two animals in the 70 ppm group. Twenty cells scored. | The authors report this a preliminary experiment; with a slight increase in SCEs in the alveolar macrophages and regenerating liver cells at 50 ppm but not 70 ppm. However, the top group had only one to two animals and there was a “dramatic reduction in total as well as second division metaphase yields.” | Uninterpretable. Methods are not detailed. Only two doses the top dose being very toxic. Too few cells scored. | Conner et al. (1982) |
| Mouse CD1/male | i.p. | 100 mg/kg, single injection. Both S and R enantiomers. | 24 hr after injection. | Bone marrow. Four animals per group; 30 s division cells scored. Positive control DMBA.b | The R enantiomer was negative (control: 3.55 ± 0.48 and treated: 3.61 ± 0.25 SCEs/cell). The S enantiomer was statistically different (control: 3.55 ± 0.48 and treated 5.06 ± 0.49 SCEs/cell). | A single dose. Insufficient number of cells scored. Four animals per group. i.p. is no longer considered a relevant route of exposure. | Sinsheimer et al. (1993) |
a
BUdR, bromodeoxyuridine.
b
DMBA, 2,4‐dimethoxybenzaldehyde.