DDTs and PCBs are both organochlorines (also known as chlorinated hydrocarbons), toxic chemicals that are slow to break down in the environment. The chemicals can accumulate in plants and animals and move through the foodweb to become more concentrated in higher predators.Human health problems associated with increased exposure to DDTs and PCBs include cancer and liver disease. Most of the DDTs and PCBs contaminating the marine environment near Los Angeles came from companies that dumped their waste products into the regional sewer system many years ago. The wastewater was discharged into the ocean through outfalls offshore of White Point, on the Los Angeles County coast.

"DDTs" refers to a mixture of six similar chemicals. DDT (dichloro-diphenyl-trichloroethane) was once one of the most widely used pesticides in the world, and one of the largest DDT factories was located in Torrance, CA. During production, the factory released hundreds of tons of DDT waste products into the Los Angeles County Sanitation District's sewer system. Because of the environmental damage, the U.S. Environmental Protection Agency (U.S. EPA) banned the use of DDTs in 1972.

PCBs (polychlorinated biphenyls) are a group of 209 related oil-like chemicals first manufactured in 1929. These chemicals, found to be good insulators and stable when exposed to heat and pressure, were used for a variety of industrial purposes including making paint, use as transformer coolants, and in hydraulic fluids. The U.S. EPA began the phase-out of PCB production and use in 1976.