Abstract
Methoxyisopropanol and Methoxyisopropyl Acetate, commonly known as propylene glycol monomethyl ether (PGME) and propylene glycol monomethyl ether acetate (PGMEA), respectively, have fragrance, solvent, and viscosity-decreasing functions in cosmetics, although only Methoxyisopropanol is in current use at concentrations ranging from 4% to 35%. Methoxyisopropanol is easily absorbed into the bloodstream upon inhalation or ingestion. The acetate ester is readily metabolized to Methoxyisopropanol in the body, which is excreted unchanged in the expired breath or in the urine as free or conjugated Methoxyisopropanol, or as the primary metabolite propylene glycol. In acute oral toxicity studies, the LD50 values of Methoxyisopropanol were 4.6 to 9.2g/kg in rats, with similar low acute toxicity in other animal species. Inhalation exposures of rats, mice, and rabbits to 3000 ppm Methoxyisopropanol for 6 h per day for 9 days to 13 weeks produced increased relative liver weights, signs of central nervous system (CNS) depression, and in some cases, elevated serum alkaline phosphatase, alanine aminotransferase, or hepatocellular hypertrophy, but the kidneys were unaffected. The no observed adverse effect level (NOAEL) for 13-week inhalation exposures to Methoxyisopropanol was 1000 ppm in rats and rabbits. In a 90-day dermal exposure study using rabbits, 10 ml/kg undiluted Methoxyisopropanol produced narcosis and increased kidney weights and the NOAEL was 7.0 ml/kg. Chronic (2-year) daily inhalation exposures of rats and mice to 3000 ppm Methoxyisopropanol produced signs of liver toxicity (rats and mice) and some evidence of renal toxicity in rats. The only observation at 1000 ppm was dark foci of the liver in male rats. For female rats and male and female mice, the NOAEL of this chronic inhalation study was 1000 ppm Methoxyisopropanol. Methoxyisopropanol and Methoxyisopropyl Acetate were found to be nonirritating to slightly irritating and non-sensitizing in rabbit and guinea pig skin. Repeated applications of undiluted Methoxyisopropanol to the eyes of rabbits produced transient slight to moderate irritation. Pregnant rats exposed to 200 or 600 ppm Methoxyisopropanol by inhalation on gestation days 6 to 17 had no effects on maternal health or normal fetal development. Adult male rats exposed to these concentrations had no effects on the reproductive organs. Pregnant rats and rabbits exposed to 500 to 3000 ppm Methoxy-isopropanol by inhalation during gestation had no significant embryotoxic or fetotoxic effects, althougth CNS depression and reduced body weight gain were observed in the 3000 ppm group. In a two-generation inhalation study using rats, continuous inhalation of 3000 ppm Methoxyisopropanol produced CNS depression, prolonged estrous cycles, reduced fertility indices, reduced pup weights and pup survival, and delayed sexual development, with a NOAEL for reproductive and developmental effects of 1000 ppm. In a continuous breeding protocol using mice, 2.0% Methoxyiso-propanol in drinking water produced reduced growth, reduced relative epididymis weight, reduced relative prostate weight, and increased liver weight (females only) in offspring, with a NOAEL at a 1% concentration. Exposure of mice or rats to 300 ppm to 3000 ppm Methoxyisopropanol by inhalation produced no signs of carcinogenicity. Methoxyisopropanol was negative for mutagenicity or genetic toxicity in the bacterial reverse mutation assay (≤5000 g/plate), the unscheduled DNA synthesis (UDS) assay (≤0.1 M), V79 Chinese hamster lung assay (>100 mM), and in the Siberian hamster embryo assay (concentrations not reported). In other assays, 100 mM Methoxyisopropanol increased sister chromatid exchanges in V79 cells. In human inhalation exposure studies of 1 to 7 h duration, 50 to 75 ppm Methoxyisopropanol vapor had an objectionable odor; 150 ppm was slightly irritating to the eyes and throat; 250 ppm produced eye irritation, lacrimation, blinking, rhinorrhea, and headache; 300 ppm was mildly irritating to the eyes, nose, and throat; 750 ppm was extremely irritating; and 2050 ppm produced extreme discomfort with severe lacrimation, blepharospasm, and painful breathing. None of the concentrations tested impaired motor coordination or performance on neurological tests. The irritating effects subsided within 15 min to 24 h of removal from the inhalation chamber. The National Institute of Occupational Safety and Health (NIOSH) recommended an 8-h time-weighted average for occupational exposure of 100 ppm. A margin of safety of 500 was determined, based on a calculated exposure from the normal use of nail polish remover products (100% absorption) and the NOAEL for reproductive toxicity. The absorption of Methoxyisopropanol through the nail is likely to be low, suggesting this margin of safety is conservative. Because Methoxy-isopropanol is volatile, exposure by inhalation is possible, but the odor becomes objectionable at 50 to 75 ppm in air. The Cosmetic Ingredient Review (CIR) Expert Panel concluded that Methoxy-isopropanol and Methoxyisopropyl Acetate are safe for use in nail care products in the practices of use and concentration as described in this safety assessment.