1.  The exact toxic component of gliadin has not been identified and the pathogenetic mechanism of coeliac disease remains uncertain.

2.  The EPA panel and Ms. Browner said they do not want MTBE replaced by toxic components.

3.  Hundreds of researchers from Vietnam, the United States and other nations attended the conference to share information on the defoliant and its highly toxic component, dioxin.

4.  The specifications by the Environmental Protection Agency are aimed at reducing exhaust pollution from sulfur, benzene and other toxic components in gasoline.