Great blue heron (Ardea herodias) eggs and prey items were collected from six colonies on the Columbia and Willamette rivers and Puget Sound during 1994-95. Contaminant concentrations, reproductive success, and biomagnification factors (BMFs) were determined and effects of residue levels were measured by H4IIE rat hepatoma and ethoxyresorufin-O-dealkylase (EROD) bioassays....