DDT is a banned pesticide, and PCBs are toxic chemical compounds.
The contaminants are too deep for human contact, but they are a risk to people who eat fish from the area.
The contamination occurred from the 1950s until the early 1970s. The chemicals flowed through Los Angeles County's sanitation system and collected along nine miles of seafloor off the Palos Verdes Peninsula.
AP contributed to this report.