1,1,1,3,3,3-Hexamethyldisilazane (HMDZ) is used industrially to treat the surface of silica, as an intermediate adhesion promoter or silylating agent in the semiconductor industry, as a chemical modifier of inorganic fillers, and as a water scavenger silicone sealant. In animal studies, HMDZ is considered to be slightly to at most moderately toxic following acute administration via oral, dermal, and inhalation routes of exposure. HMDZ is neither an eye irritant nor was it dermally irritating under semiocclusive conditions; however, it caused dermal necrosis in two studies under occlusive conditions. HDMZ is not genotoxic or mutagenic in in vitro assays and was not reproductively or developmentally toxic in an inhalation screening study in rats. Short-term and subacute, high-dose inhalation exposure to HMDZ produced respiratory tract irritation, reduced feed consumption, changes in clinical chemistry parameters, and reversible central nervous system depression in rats. In a 90-day inhalation exposure study in rats, HMDZ exposure-related effects were observed in the kidneys of male rats but were determined to be alpha-2µ-nephropathy, thus, not relevant to humans. Based on the results of the 90-day (subchronic) inhalation study, 75 ppm was determined to be the no-observed adverse effect level (NOAEL) and was selected as the point of departure for the derivation of the 8-h time-weighted average (TWA), health-based workplace environmental exposure level (WEEL) value. This subchronic inhalation NOAEL was adjusted to account for duration of exposure, interindividual variability, and intraindividual variability. The resulting 8-h TWA WEEL value of 10 ppm is fully expected to provide a significant margin of safety against any potential adverse health effects in workers following long-term inhalation exposure to HMDZ vapor. A 15-min short-term exposure limit of 50 ppm was also established to protect workers from reversible effects produced by acute, high-dose inhalation of HMDZ vapor. A skin notation (Skin) is warranted because of the potential for the dermal route to significantly contribute to the overall exposure to HMDZ.
Short-term, high-dose administration of corticosterone by injection facilitates trace eyeblink conditioning in young male rats