Banned Contaminants Still Threaten Endangered California Condors | Information Center
Researchers from SDSU and the San Diego Zoo Wildlife Alliance have found high levels of toxic compounds in coastal condors and the marine mammals they consume.
Contaminants banned decades ago are still threatening critically endangered California condors, a new study has found. Condors may be at increased risk for reproductive harm because they consume dead marine mammals along the California coast.
The research, led by scientists from San Diego State University (SDSU) and the San Diego Zoo Wildlife Alliance (SDZWA), in collaboration with the Centro de Investigación Científica y de Educación Superior de Ensenada and the National Oceanographic and Atmospheric Administration, found that marine mammals stranded on the California coast harbor relatively high levels of halogenated organic contaminants (HOCs). Researchers have detected more than 400 contaminants in samples taken from stranded marine mammals that California condors may be feeding on.
On the California coast, marine mammals had about seven times more DDT and 3.5 times more PCBs than their counterparts in Baja California, Mexico. Other less studied compounds have also been detected. A group of these compounds have been estimated to be 148 times more abundant in marine mammals in California than in those in Baja California.
“This kind of broad contaminant survey shows us that condors and marine mammals have a host of contaminants that have never really been examined before, especially in detail,” the corresponding author explained. Nathan Dodder, an analytical chemist and researcher at the SDSU School of Public Health and the SDSU Research Foundation. “The off-target contaminant analysis we used not only identifies known legacy contaminants, but has the added benefit of identifying new contaminants, in addition to known but less-reviewed contaminants that are not routinely screened.”
An average of 32 contaminants were detected in blood samples from coastal condors, compared to just eight from inland condors. DDT and PCBs are estimated to be seven times and 40 times more abundant, respectively, in coastal condors than in inland condors. The contaminant TCPM was abundant in coastal condors, but completely absent in inland condors. Another related contaminant, TCPMOH, was about 56 times more abundant in coastal condors than in inland condors.
“TCPM and TCPMOH are associated with DDT, but understudied in terms of abundance in marine fauna and toxicity,” said the study co-author. Eunha Ho, a professor in the SDSU School of Public Health. “This is the first research to find these compounds in California condors.”
Even though HOCs were banned decades ago, they are highly resilient to environmental degradation and continue to accumulate in marine food webs, with the potential to physiologically harm marine life. Many of these compounds, such as DDT and PCBs, are endocrine disruptors, and there is evidence that coastal condors experience eggshell thinning associated with exposure to HOCs in recovered marine mammal carcasses.
“Marine mammals in the Gulf of California probably have less DDT and other halogenated compounds because there has been no historical release or spillage off the coast like we see in southern California,” added the co-author. daisy stack, a research specialist at the SDSU Research Foundation. “Our study highlights the value of the Baja California site because it provides this habitat where food may not contain as many contaminants.”
California condors were nearly extinct a few decades ago and their population has slowly recovered through extensive breeding and reintroduction efforts. Lead poisoning remains the leading cause of death for condors in the California interior due to ingestion of fragments from land animals shot with lead ammunition. Coastal habitats likely have a lower risk of lead exposure due to the availability of marine mammal carcasses for condors, making coastal sites advantageous for condor reintroduction. But ancient contaminants found in marine mammal carcasses may pose a renewed threat to rare birds.
“The goal of the recovery program is to have condors throughout their historic range, which begins in the Pacific Northwest and ends in Baja California,” the co-author said. Ignacio (Nacho) Vilchis, associate director of recovery ecology at SDZWA. “Each site will have its advantages and disadvantages. One of the advantages of the Baja site is the availability of a food source that is not as contaminated as in California.
In addition to less exposure to HOCs in Baja, no condors have died there from lead poisoning in the past five years, compared to 19 condors in California. The research, funded by NOAA, the California Sea Grant and the San Diego Zoo Wildlife Alliance, highlights the value of Baja California, Mexico as a condor reintroduction site.
“These results can help inform management of the Baja herd as it continues to grow,” noted the co-author. Christopher Tubbs, Associate Director of Reproductive Sciences at SDZWA. “Some of the contaminants in the marine mammal samples we collected are ‘unknown’ in terms of structure and potential to disrupt hormone function. This study focused exclusively on one hormonal pathway, estrogen, but many of the contaminants identified are well known to interfere with multiple hormonal pathways. These deserve further study.
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