Methyltrimethoxysilane (MTMS).

Methyltrimethoxysilane (MTMS) has been used as a coupling agent in thermoplastics and thermosetting resins, a cross-linker in silicone sealants, a water repellent component, and in silicone hard-coats for plastics. Acute studies in experimental animals showed a low order of toxicity for MTMS via oral, dermal, and inhalation routes. MTMS was slightly irritating to both eyes and skin in rabbits. A weight of evidence assessment supports that MTMS is not a dermal sensitizer. Available in vitro and in vivo assays indicated MTMS has a low potential for genotoxicity. MTMS did not produce any changes in either reproductive or developmental parameters. Short-term, repeated inhalation in rats produced treatment-related observations in the urinary bladder and kidney. In a 90-day inhalation study in rats, MTMS was associated with production of urinary bladder epithelial hyperplasia, calculi formation, and moderate kidney dilation with hyperplasia of the pelvic epithelium and granulomatous inflammation. However, an expert panel review concluded that changes in the bladder and kidney were adaptive responses to physical or chemical irritation. The NOAEL of 100 ppm (557 mg/m³) from the 90-day inhalation study was considered the point of departure for the health-based WEEL derivation. After adjusting to account for duration of exposure and interindividual variability, the resulting 8-h TWA WEEL value of 10 ppm (55 mg/m³) is fully expected to provide a significant margin of safety against potential adverse health effects in workers.