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Is Long Banned DDT Still Threatening Endangered Birds?

(Beyond Pesticides, September 18, 2013) DDT, a pesticide banned in 1972, is behind the mystery surrounding the reproductive problems of dozens of endangered condors. This is according to a peer-reviewed paper written by 10 condor experts, including biologists from the Los Angeles and Santa Barbara zoos and the U.S. Fish and Wildlife Service. The researchers, who spent six years studying the reproductive problems, including eggshell thinning, in California condors have “established a strong link” to DDT in the birds’ food source.

Condors are large scavenger birds with wingspans up to 10 feet and were reintroduced to California’s coast in 1997 after a century-long population decline. However, in 2006 biologists began observing thinning shells in many condor nests. Over the next six years, scientists observed condors feeding on dozens of sea lions, and found that in Big Sur, California, condor populations had low hatching success — just 20-40 percent. In contrast, 70-80 percent of southern California condors in the Tejon area had hatched successfully over the same time. The southern California condors are inland, and sea lions are not a food source.

According to the study published in the journal, The Condor, the outer crystalline layer of shells was absent or greatly reduced, similar to thin-shelled condor eggs laid in southern California in the 1960s. The researchers found that the rate of hatchling loss increased significantly with decreasing shell thickness, which can also lead to increased bacterial infections in the eggs. One shell found crushed in a nest was 54 percent thinner than normal. Biologists familiar with the ravages of DDT in bird populations suspect DDT as the cause.

The scientists theorize that the major source of food for these birds, sea lions, have been accumulating DDT in their fat during their lifetimes, as they migrate to the central coast from southern California, where the Montrose Chemical Corp., which manufactured technical grade of DDT from 1947 until 1982, routinely dumped DDT along the coast for decades until the 1970s. The Montrose plant and the ocean off Palos Verdes where it dumped DDT are now listed as U.S. Environmental Protection Agency (EPA) “Superfund” sites.

DDT is an organochlorine pesticide that was banned in the U.S. in 1972 due to its persistent and highly toxic nature. DDT was widely used to control mosquitoes for malaria abatement, and in agriculture. Despite the fact that DDT was banned in the U.S. 40 years ago, concentrations of this toxic chemical’s major metabolite, DDE, have remained alarmingly high in many ecosystems, including surface waters, the Arctic, and even U.S. national parks. This is because DDT/DDE are persistent organic pollutants (POPs). POPs are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, are capable of long-range transport, bioaccumulate in human and animal tissue, and biomagnify in food chains. The science shows DDT was responsible for the deaths of millions of bald eagles and other bird species along the California coast, and that the pesticide bioaccumulates in the tissues of animals throughout the food chain. In the early 1970s, exceptionally high concentrations of several DDT metabolites, principally DDE, were recorded in the blubber and tissues of California sea lions in both southern and central California. One 2005 study also found elevated concentrations of DDT in fish samples taken in National Parks. In addition, a surge of additional problems with the lingering effects of DDT have risen in recent years, particularly with its buildup in waterways. It has currently been identified as a threat to the Columbia River, as well as to the Arctic.

Organochlorines like DDT have also been linked to a number of adverse effects to human health, including birth defects,  breast cancer and autism. DDT has also been linked to Vitamin D deficiency, non-Hodgkin’s Lymphoma, and diabetes. Exposure to DDT can occur by eating contaminated fish. The California’s Office of Environmental Health Hazard Assessment (OEHHA) has issued fish advisories that recommend limited or no consumption of fish from certain waterways in California. Last year, after years of limited success with clean-up, the EPA launched a three-year plan to pinpoint the cause of continuously high DDT levels in the San Francisco Bay, and engage the surrounding community in cleanup and education efforts.

The authors of the study state that DDT/DDE from wastes of a DDT factory discharged into the Southern California Bight have been linked to extensive eggshell thinning and reproductive failures of fish-eating and raptorial birds.  “A vast majority of California sea lions have spent at least a portion of their lives in the waters of southern California, which is the most DDT-contaminated coastal environment in the world,” said Kelly Sorenson, executive director of Ventana Wildlife Society and a co-author of the new study. “Northward movements of sea lions provide a pathway of DDT to condors in central California.”

Early critics of the study say it only looks closely at one potential cause of reproductive problems (DDT), and fails to properly evaluate the potential effects of other contaminants and factors that may be involved. But the authors are hopeful that the DDT problem would fade over time. “Like bald eagles and other bird species previously affected by DDT, the thickness of condor eggshells should recover as contamination declines in the coastal environment,” said co-author Robert Risebrough, executive director, Bodega Bay Institute, and expert on the effects of DDT on birds.

Source and photo courtesy: CBS News

All unattributed positions and opinions in this piece are those of Beyond Pesticides.




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