Polychlorinated biphenyls (PCBs) were first synthesized in 1881, and commercial production in the United States began in 1929. PCBs were used in the electrical industry, as well as surface coatings and plasticizers in sealants, caulking, rubber, paints and asphalt. By 1972, scientific evidence showed that PCBs were an environmental and human health hazard and, in 1977, the manufacturing and non-electrical use of PCBs was banned. PCBs are a chemical that gained a lot of attention when scientific evidence began to suggest that it was an extremely dangerous substance.
Helicobacter pylori (H. pylori) are a type of intestinal bacteria that cause the majority of ulcers in the stomach and duodenum. They thrive in highly acidic environments and have a unique way of adapting to the harsh environment of the stomach. H. pylori have been classified as low-potential carcinogens (cancer-causing substances) by the World Health Organization.