DDT Still Packs Punch 25 Years Later : Pesticide Dumped at Sea Blamed in Island Birds’ Disappearance
Twenty-five years after 350 to 700 tons of DDT were dumped into the ocean about 15 miles off Los Angeles, the pesticide’s devastating impact is still being felt and may persist for decades.
Results of a new study of sediments found in two abandoned ocean dumps 10 miles from Santa Catalina Island show that DDT is not only still present in high concentrations, but that its presence is probably responsible for the disappearance of the bald eagle and peregrine falcon in the area.
“We can only conclude now that it was this dumping that wiped out these species throughout the Channel Islands,” said ecologist Robert W. Risebrough of the Center for Marine Studies at the University of California at Santa Cruz.
These first findings of the study, commissioned by the Los Angeles Regional Water Quality Control Board, were disclosed here Wednesday at the sixth annual International Ocean Disposal Symposium.
Risebrough also said an analysis of chemical “fingerprints” has led him to conclude that the DDT in question was dumped by the Montrose Chemical Co., which manufactured DDT in Torrance.
State records indicated that the firm dumped DDT in the ocean from 1947 to the early 1960s. Attempts Wednesday to reach the company for comment were unsuccessful.
“For a number of years, we thought this problem was over. But over the past several years, some unexpectedly high levels of DDT compounds began to show up in Los Angeles area (fish) and we began to wonder if perhaps the environmental levels of these compounds were not declining as fast as we might have expected,” Risebrough said.
After it became widely known a year ago that bottom fish, including the white croaker, had high levels of DDT, the state Department of Health Services posted warnings against eating the fish. The warnings are still in effect.
“The whole system has been contaminated. There are still some high levels in dolphins’ blubber and some of the seals,” Risebrough said.
DDT concentrations just a year ago in dolphins found in Santa Monica Bay have been as high as 2,500 parts per million (ppm), compared to the federal Food and Drug Administration’s maximum recommended level for eating fish of 5 ppm.
Last year, the water quality board commissioned a series of studies of ocean contamination off Southern California, including the two former dump sites.
“We didn’t know whether we would be able to see any continuing effect from the dumping. Now I think we have,” Risebrough said.
The study is still continuing. However, the early results indicate that significant levels of DDT are persisting on the 2,900-foot deep ocean floor 25 years after the dumping was halted. From there, the chemical, originally in barrels, was gradually cycled through the food chain.