Genetic toxicity evaluation of octamethylcyclotetrasiloxane

Octamethylcyclotetrasiloxane (OMCTS; CAS No. 556-67-2) was evaluated in a g enetic toxicity battery. In preincubation tests with Salmonella typhimurium strains TA98, TA100, TA1535, TA1537, and TA1538, no mutagenicity was detec ted (maximum dose = 5 mg/plate) with or without S9 in two independent trial s. Treatment of cultured Chinese hamster ovary (CHO) cells was limited by c ytotoxicity at OMCTS concentrations greater than 0.003 mg/mL without S9 and 0.03 mg/ml with S9. CHO cells treated with up to 0.003 mg/ml without S9 an d 0.03 mg/ml with S9 showed no significant dose-related increases in chromo somal aberration frequencies. No significant dose-related increases in sist er chromatid exchanges (SCEs) occurred in OMCTS-treated CHO cells (maximum OMCTS concentration = 0.003 mg/ml without S9; 0.03 mg/mL with S9). Therefor e, OMCTS was concluded to be negative in the SCE essay. In a screen for in vivo clastogenic potential, Sprague-Dawley rats received 700 ppm OMCTS by w hole-body vapor inhalation 6 hr dairy for 5 days. A negative control group received filtered air on the same schedule. A positive control group was ex posed to filtered air on the same schedule and received cyclophosphamide 2 4 hr before termination. The OMCTS-treated animals were terminated 6 and 24 hr after the final exposure. Positive and negative control animals were te rminated 24 hr after the last exposure. No significant, treatment-related i ncreases in chromosomal aberrations were detected. The results of these stu dies indicate that OMCTS does not possess significant in vitro genotoxic po tential. No adverse genetic findings were seen in the in vivo screen for ch romosome aberrations. Environ. (C) 2000 Wiley-Liss, Inc.