U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

January 2001


Field studies were conducted in California to assess efficacy of chlorophacinone-treated steam-rolled oats for controlling rangeland rodents. An objective of these studies was to assess the potential hazards of chlorophacinone residues in rangeland rodent carcasses and livers to mammalian and avian scavengers, especially raptors. Belding's ground squirrels, valley pocket gophers and Microtus spp. carcasses collected during the efficacy studies were analyzed for chlorophacinone residues. The method limit of detection (MLOD) for liver and carcass tissue samples averaged 0.036 μg/g and 0.034 μg/g, respectively. Chlorophacinone residues in Belding's ground squirrel (n=62) liver and carcass tissue ranged from Microtus sp. (n=3) tissue ranged from 0.26 to 4.1 μg/g, respectively. Risk assessment indicated acute risk for mammalian scavengers and negligible to minimal risk for avian scavengers consuming rangeland rodents exposed to chlorophacinone baits.