for rats, 88 ppm for guinea pigs, 37 ppm for rabbits and 36 ppm for mice. In dogs acute lethality by inhalation is also noted, although no LC50 has been determined. Oral administration of MeAN has been tested on rats, mice and gerbils, showing a LD50 of 200 mg/kg for rats, 17 mg/kg for mice and 4 mg/kg for gerbils. Skin administration on rabbits causes death at a LC50 of 268 mg/kg. The NOAEL and LOAEL values for rats are determined at 50 mg/kg for NOAEL and 100 mg/kg for LOAEL. This is based on another sign of methacrylonitrile poisoning; urine retention, with 58% of rats showing bladder distention at an administered dose of 100 mg/kg. Reproductive toxicity was tested in rats, but different outcomes have been reported. Willhite et al. suggest a LOAEL for reproductive effects of 50 mg/kg, while a report by the National Research Council claims no significant reproductive effects have been found. Lastly, carcinogenic, mutagenic and genotoxic effects have been tested but unlike acrylonitrile, methacrylonitrile does not show signs of any such effects. References Monomers Nitriles