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Researchers Find High Levels of Contamination in Marine Mammals

Published: December 15, 2008

From the late 1940s through the early 1970s, Southern California manufacturing firms dumped large quantities of waste laden with the pesticide DDT and the chemical PCB into the Los Angeles County sewer system that ended up in a massive sediment deposit at the end of sewer outfall pipes located off the Palos Verdes Peninsula’s White’s Point.

According to the U.S. Environmental Protection Agency, more than 9 million cubic meters of sediment contaminated with about 110 tons of DDT and 11 tons of PCB spread across more than 40 square kilometers. Because both of these compounds are lipophilic (are absorbed easily in fats), they don’t dissolve in water, and therefore have remained concentrated in the area.

Certain local fish, particularly the bottom-dwelling white croaker, are known to be contaminated. However, contamination in pinnipeds including California sea lions, Pacific harbor seals and northern elephant seals living or feeding in the Southern California Bight—the Pacific Ocean near-shore area between Point Conception and the Mexico border—had not been studied, so CSULB marine biology master’s student Mary Blasius and full-time lecturer Gwen Goodmanlowe recently published a research article in the journal Marine Pollution Bulletin demonstrating that these animals continue to be contaminated.

“Because pinnipeds have such a large blubber layer and because these contaminants are lipophilic, you would expect these animals to have very high levels,” Goodmanlowe said. The contaminants move up the marine food chain, starting with worms and other invertebrates that live in the sediment, moving to fish and finally, to top-level carnivores like marine mammals.

They obtained samples of blubber from the Fort MacArthur Marine Mammal Center in San Pedro and the Pacific Marine Mammal Center in Laguna Beach from 145 animals that had stranded on local beaches and subsequently died at the centers. Since the centers preserve tissue from dead animals, they were able to obtain samples covering a 13-year time period, from 1994 to 2006.

“We wanted to study the three species of pinnipeds that commonly occur in Southern California, which are the California sea lion, northern elephant seal and the Pacific harbor seal. We thought that there might be a difference in the amount of contaminants they have in their blubber depending on how much time they spend in the Southern California Bight,” Goodmanlowe said. “Northern elephant seals are not known to spend much time in the bight; although they spend time out at Catalina, their southernmost breeding area on the coast is San Simeon. Juveniles, however, are known to feed in the Southern California Bight. Harbor seals are the most resident of the three species and are very strongly tied to where they are born. California sea lions are a mix because the males go farther north to feed while the females stay fairly close to their breeding grounds.”

“We expected to see differences in contaminant levels overall, based on the species’ different residency patterns,” she continued. “Another issue is that all three species forage on different species of prey, which would also be expected to affect the levels of contaminants found in both the prey and the pinnipeds. For instance, the northern elephant seals’ main prey are squid and octopus, which are much lower in fat than some of the fatty fish like herring and anchovies that harbor seals and sea lions feed on.”

They also wanted to look at age differences among the animals. “Because these contaminants are lipophilic, they are readily absorbed into the mother’s milk, and the mother can pass those contaminants to her offspring. So, we wanted to compare young pinnipeds to adult pinnipeds, and also compare males vs. females, since females can offload their contaminants to their young and males cannot. Finally, we wanted to examine contaminant levels over time since dumping of these contaminants ended in 1972,” Goodmanlowe said.

However, because of various animal populations and characteristics, they weren’t able to study all of those factors for each species. “For example, we had a very low sample size of harbor seals, mainly because they don’t strand as often as the other two species for a variety of reasons, including population size (32,000 in southern California vs. 300,000 for California sea lions) and foraging habits.” She said that most of the elephant seal samples were from pups that were more likely to become stranded than adults. Their largest samples came from California sea lions of all ages.

“We found some interesting things,” Goodmanlowe said. “We found that DDT was still very high in all three species, especially California sea lions, even though the dumping of contaminants ended over 30 years ago. PCB levels were also high, but DDT was much higher than PCBs. This indicates that these pinnipeds are feeding in the Southern California Bight because in most other studies, PCBs are usually higher than DDT in the blubber. That’s because PCBs are more ubiquitous in the environment, so if the animal is not located near a DDT hotspot, their levels of DDT will be lower than their levels of PCBs.

“We found that for California sea lions, the females had about 93 percent lower levels of DDT and PCB than males and 81 percent lower levels than pups and juveniles. The levels of both contaminants increased with age and then decreased again with older females, which is exactly what we expected because females are offloading these lipophilic contaminants to their offspring. They can get rid of these contaminants if they lose their blubber layer, so fasting is one way to get rid of the contaminants. Pups are extremely fat when they are weaned, probably with high levels of contaminants from their mother’s milk and placental transfer during gestation. Then in the time period that it takes for them to learn how to feed, they lose their blubber layer and the contaminants within it. So, the mom offloads the contaminants to the pups, who then lose it when they’re learning how to feed. Then they build it up again throughout their lifespan, losing a little bit every time they fast.”

Adult males had the highest levels and females had the lowest levels, she said. “That had been shown in other species but it had never shown in California sea lions.”

California sea lions and Pacific harbor seals had higher levels of DDT and PCBs compared to northern elephant seals. Among sea lions, “The pups and females are more resident. We didn’t have many adult male sea lion samples because they’re very large and don’t strand on beaches as often. The more resident species of sea lion females and pups and the harbor seals did not differ in their amounts of contaminants, but both had higher levels than the elephant seal. However, the elephant seal had higher levels than previously found, which is interesting because this shows that the pups and sub-adults are probably feeding in the Southern California Bight more often than was previously thought.”

Finally, over the 13 years examined, contaminant levels decreased among sea lions, although levels remained higher than animals previously studied from other California waters. Because domoic acid causes many strandings of California sea lions in the Southern California Bight, Goodmanlowe would like to continue this study and investigate the possible causal relationship between high levels of these contaminants and of domoic acid.