Michigan's Kalamazoo River is polluted by polychlorinated biphenyls (PCBs), highly toxic chemicals banned in the 1970s.

CNN: Pregnant women should follow guidelines on eating fish

Bush announced his support for a global treaty which calls for the elimination of a dozen highly toxic chemicals.

CNN: Sci-Tech - Bush aides defend environmental record

One contentious moment was when Jackson and the EPA told BP to stop using highly toxic chemicals in the Gulf to disperse the oil.

CNN: EPA's Jackson haunted by oil spill unknowns

Campaigners worry that incinerators produce dioxins (a highly toxic family of chemicals that can cause cancer and birth defects) and tiny particles of soot (also carcinogenic).

ECONOMIST: Tough landfill targets prompt a return to flaming rubbish