November 6, 1995 Contact: Robert Irion (408/459-2495)
DDT CONTAMINATION IN SEA LIONS PLUMMETS A HUNDREDFOLD IN TWENTY YEARS
FOR IMMEDIATE RELEASE
SANTA CRUZ, CA--Amid concerns about the lingering effects of DDT along California's coast comes this bit of good news: Sea lions carried about one hundred times less of the toxic substance in their fat a few years ago than they did two decades earlier.
The average level of DDT and its major breakdown product, DDE, was 5.2 parts per million in sea-lion blubber collected between 1988 and 1992. In contrast, blubber analyzed in 1970 contained an average of 760 parts per million--an incredible quarter-pound of DDT in each animal's body. Although DDT and DDE levels have dropped in other animal populations over the same period, the decline in California sea lions is the most precipitous yet seen. Researchers at the University of California, Santa Cruz, conducted both studies.
The scientists say there is a direct link between this dramatic change and the cessation of DDT dumping off southern California. The Montrose Chemical Corporation, at the time the world's largest manufacturer of DDT, flushed thousands of tons of DDT waste into the ocean between 1949 and 1970. The waste polluted a huge gyre of water near the Channel Islands, tainting much of the breeding habitat for California sea lions.
Since then, the population of the species has more than doubled, although factors other than lower DDT levels may have helped them thrive. But even with this heartening progress, researchers warn that the remaining amounts of DDT-related chemicals still may inflict subtle harm on sea lions and other marine mammals.
"The levels of DDT we measured in sea lions in 1970 were extraordinarily high, essentially pharmacological doses," says UCSC marine biologist Burney Le Boeuf. "Clearly the situation along the coast has improved vastly since then. But I don't think we can say that these substances no longer pose a problem for marine mammals, because we don't know about possible long-term effects."
A team from UCSC's Institute of Marine Sciences published the follow-up study in the November 1995 issue of Marine Pollution Bulletin. First author is Patricia Lieberg-Clark, who started the project as an undergraduate at UCSC and now works at BioSystems Analysis in Santa Cruz. Coauthors are staff research associates Corinne Bacon of UCSC and Stephanie Burns, now at UC Davis; researcher Walter Jarman; and Le Boeuf, a research professor of biology.
Sea lions and other animals at the top of the coastal food chain, such as falcons, pelicans, and eagles, bear the brunt of environmental pollutants. DDE, PCBs, and other compounds become more concentrated as they pass from lower to higher animals, finally lodging in the brains and fatty tissues of birds and marine mammals. DDE is most notorious for thinning the eggshells of birds of prey, which nearly wiped out the state's peregrine falcons. Bald eagles brought to the Channel Islands since 1980 still cannot hatch their eggs, because DDE from the Montrose Chemical Corporation bleeds out of nearby ocean sediments.
When Le Boeuf and former UCSC marine biologist Michael Bonnell conducted their 1970 study, California sea lions faced major reproductive problems. Various surveys found that nearly half of the pups in each breeding season died after premature births. Suspecting that DDT was the culprit, the researchers collected tissue samples from animals--both from southern California and from Ano Nuevo, north of Santa Cruz--that had died naturally or been shot by others. Their stark results on DDT residues in 25 sea lions appeared in Nature in November 1971. Only in brown pelicans, the authors noted, had scientists observed such extreme levels.
For the follow-up study, Lieberg-Clark--who coordinated the Marine Mammal Stranding Network for Santa Cruz County--collected baseball-sized chunks of blubber from the carcasses of seven adult or subadult male sea lions that washed ashore near Ano Nuevo or in Monterey Bay. Under Jarman's direction, the team analyzed the DDT and DDE content of the blubber at the Trace Organics Laboratory at UCSC's Long Marine Lab. To compare the results with those from 1970, the team refigured Le Boeuf's data to include only the twelve adult or subadult males in his study.
Studies from other DDT hot spots around the globe have found tenfold drops in DDT residues in various animals since the early 1970s, the authors state. Declines in DDT levels in brown-pelican eggs are the only well-documented figures to approach the same hundredfold magnitude as the data from California sea lions.
Jarman extracts a lesson from the study--and words of caution. "The waste from just one industrial plant was enough to have a severe effect on an entire population of animals, because it was dumped directly into their habitat," he says. "But the DDT levels we found are not 'low,' they're just 'lower'--and they're still higher than in marine mammals in many other parts of the world."
Editor's notes: You may reach the coauthors as follows:
Patricia Lieberg-Clark: (408) 459-9132 or email@example.com
(focus: specifics of latest study) Walter Jarman: (408) 459-3769 or firstname.lastname@example.org
(focus: DDT and other contaminants in the environment) Burney Le Boeuf: (408) 459-2845 or email@example.com
(focus: biological questions, historical perspective on marine- mammal populations)
A photograph of California sea lions is available from the UCSC Public Information Office.
This release is also available on UC NewsWire, the University of California's electronic news service. To access by modem, dial (209) 244-6971.