More than 30 years after the dumping of DDT off the Palos Verdes peninsula was halted, seals and sea lions are still bearing the burden. A new study shows they carry large amounts of DDT in their blubber, as well as significant levels of another class of chemicals called PCBs.

In the first study to show long-term contamination levels for marine mammals off the Southern California coast, biologists at California State University, Long Beach, analyzed tissue samples from harbor seals, sea lions and elephant seals collected over 13 years.

The results were especially strong for California sea lions, said Gwen Goodmanlowe, who conducted the study with marine biology masters-degree student Mary Blasius. (California sea lion shown at right.)

“Even though the levels in the sediments are decreasing slowly, which is good for California sea lions, we still saw really high levels,” said Goodmanlowe, a marine biologist and full-time lecturer at the university.

Both chemicals, now banned, were dumped from a Los Angeles County sewer outfall pipe from the 1940s to 1972. They linger in sediments because they don’t dissolve in water, accumulating first in marine worms and other small animals, then working their way up the food chain as each successive predator consumes the chemicals in the bodies of their prey.

The chemicals become highly concentrated in the bodies of top predators, such as seals and sea lions.

Other studies have revealed significant amounts of both DDT and PCBs, once used in electrical transformers, in fish off Southern California, such as bottom-dwelling white croaker. 

The researchers collected tissue samples preserved at the Fort MacArthur Marine Mammal Center in San Pedro and at the Pacific Marine Mammal Center in Lagnua Beach from 145 animals that stranded themselves on beaches, then died, from 1994 to 2006.

The researchers found high levels of the two chemicals in all three species studied, though elephant seals had lower levels than the seals and sea lions.

Still, the results suggest that elephant seal pups and sub-adults are feeding more than previously thought off Southern California, even though they normally range farther north. (Harbor seal shown at left.)

The fact that DDT levels were higher than PCB levels was significant, showing the animals are feeding in a DDT “hot spot.” In most animals, PCB levels are higher.

Most of the California sea lion samples came from females and pups because males rarely become stranded. Females had 93 percent lower levels of the two chemicals than males, and 81 percent lower levels than pups and juveniles.

That’s what the scientists expected to see. Females transfer most of their contaminants to their offspring through the placenta and, later, through milk, as their blubber is depleted. Then, they gradually build it back up.

While the study suggests some dropoff in chemical levels in these mammals over time, it still reveals an ocean ecosystem stressed by toxic contamination, she said.

“We all live here,” Goodmanlowe said. “What is going on here is going to affect humans as well, whether or not we’re eating the fish they’re eating. We’re all interrelated.”

The study was published recently in the Marine Pollution Bulletin.

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