Table 7.

Summary of Studies Evaluating Styrene/SO in the in vitro MN Assay

Cell line	Methods	Results	Comments	Reference
Styrene
No identified data
Styrene Oxide
V79 cells	Only a single concentration (0.75 mM). Three harvest times, 25, 40, and 50 hr. Both a cloning efficiency and a mitotic index.	The number of MN appears to be substantially higher in the single treated culture than in the control culture.	Not OECD TG487 compliant. Although the number of MN in this culture appears to be substantially higher than the number of MN in the control culture, the lack of an appropriate cytotoxicity measure and the fact that only one concentration is presented make the study uninterpretable.	Turchi et al. (1981)
Whole blood cultures from two male and two female donors	Cytokinesis‐block method. Cells were exposed to 10, 20, 50, 100, and 200 μM SO. Scoring for the presence of MN was accomplished using 1,000 binucleated cells per individual per test concentration. Cytotoxicity was assessed using CBPI (an OECD TG487 compliant method for cytotoxicity using lymphocytes).	All of the cultures were within the acceptable cytotoxicity range. The background frequency varied from 3 to 18 MN/1,000 cells and in all cases a clear induction of MN was observed in the cultures treated with SO.	OECD TG487 reasonably compliant (number of cells scored less than the current recommendation). Positive.	Laffon et al. (2001)
Whole blood cultures from 20 individuals	Whole blood cultures were exposed to SO (0.1, 0.2, or 0.3 mM), and 1,000 cells were scored for the presence of MN.	No difference in the MN frequency controls and treated.	Not OECD TG487 compliant. Because there was no measure of cytotoxicity the results are uninterpretable.	Godderis et al. (2006)
Whole blood cultures (from health male or female nonsmokers)	500, 600, and 750 μM SO exposure. Cytokinesis‐block method. The study was designed to compare the addition of CytoB 2 hr after the initiation of exposure to whole blood cultures and at the start of exposure 1,000 cells scored per culture. The nucleus division index (i.e., the replicative index) was used as measure of cytotoxicity.	Data presented graphically. Clearly positive when tested using the standard in vitro assay.	OECD TG487 compliant. Positive.	Speit et al. (2012)