Threshold Theory and argues that it has been misapplied to environmental regulation. He discusses toxicology, epidemiology, and the scientific principles he believes should guide public policy. John Dale Dunn has been an emergency physician for more than fifty years and an attorney (inactive) for forty years, admitted to the bars of Nebraska, Louisiana and Texas by examination. For more than thirty years, Dunn has been a student of environmental science, environmental laws, toxicology, epidemiology, and radiation biophysics.