USC scientists said levels of copper, cadmium, lead and other metals in Southern California's coastal waters have declined over the past 40 years since the 1972 passage of the Clean Water Act.
The improvement in coastal water quality can be attributed to sewage treatment regulations that were part of the act, researchers said.
"We can see that if we remove the contaminants from wastewater, eventually the ocean responds and cleans itself. The system is resilient to some extent," Sergio Sanudo-Wilhelmy, a USC professor of biological and Earth sciences, said.
The USC researchers compared water samples from roughly 30 locations along the Southern California coast to samples taken in the exact same locations in 1976 by two researchers from the University of California, Santa Cruz, Kenneth Bruland and Robert Franks.
"We wanted to assume that the Clean Water Act was working, but we needed good data to allow us to compare water conditions 'before and after,'" Sanudo-Wilhelmy said in a USC release Friday.
"Fortunately for us, we have the data generated by Bruland and Franks. That gave us a rare opportunity to see the impact of cleaning our sewage and see the effect on the coastal ocean."