1. Food Safety Department, The National Food Centre, Teagasc, Dunsinea, Castleknock, Dublin 15, Ireland, NRA Laboratoire de Pharmacologie-Toxicologie, 180 Chemin de Tournefeuille, BP3, 31931, Toulouse, France, and Foodborne Contaminants Research Unit, Western Regional Research Center, USDA Agricultural Research Service, 800 Buchanan Street, Albany, California 94710