Conservationists find high DDT and PCB contamination risk for critically endangered California coastal condors

A new study has found contaminants that were banned decades ago are still imperiling critically endangered California condors. The condors may be at increased risk for reproductive impairment because they consume dead marine mammals along the California coast.

The research, led by San Diego State University (SDSU) and San Diego Zoo Wildlife Alliance (SDZWA) scientists, in collaboration with 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 detected more than 400 contaminants in samples taken from stranded marine mammals that California condors may feed on.

On the California coast, the marine mammals had an estimated seven times more DDT and 3.5 times more PCBs than their counterparts in Baja California, Mexico. Other lesser-studied compounds were also detected. One group of these compounds was estimated to be 148 times more abundant in California marine mammals compared to those in Baja California. 

The study, published May 17 in the journal Environmental Science & Technology, also reveals that coastal condors have more contaminants in their blood than inland condors, which lack a marine mammal diet. 

“This kind of broad survey of contaminants shows us that the condors and the marine mammals have a multitude of contaminants that have never really been examined before, especially in detail,” explained corresponding author Nathan Dodder, Ph.D., analytical chemist and research scientist in the School of Public Health at SDSU and the SDSU Research Foundation. “The non-targeted contaminant analysis we used not only identifies known legacy contaminants, but has the added advantage of identifying novel contaminants, in addition to known but less-examined contaminants that are not routinely screened.”

An average of 32 contaminants were detected in the coastal condor blood samples, compared to only eight in the inland condors. DDT and PCBs were estimated to be seven times and 40 times more abundant, respectively, in coastal condors than 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 inland condors. 

“TCPM and TCPMOH are associated with DDT, but understudied in terms of their abundance in marine wildlife and toxicity,” said study co-author Eunha Hoh, Ph.D., professor in SDSU’s School of Public Health. “This is the first research to find these compounds in the California condors.”

Even though HOCs were banned decades ago, they are highly resistant 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-disrupting chemicals, and there is evidence that coastal condors are experiencing eggshell thinning associated with exposure to HOCs in scavenged marine mammal carcasses.

“The marine mammals in the Gulf of California presumably have less DDT and other halogenated compounds because there wasn't a historic discharge or dumping off of the coast like we see in Southern California,” added co-author Margaret Stack, research specialist at the SDSU Research Foundation. “Our study highlights the value of the Baja California site because it provides this habitat where the food may not have as many contaminants in it.”

California condors were nearly extinct a few decades ago and their population has been slowly recovering thanks to extensive breeding and reintroduction efforts. Lead poisoning remains the primary cause of death for inland California condors due to ingesting fragments from land animals shot with lead ammunition. Coastal habitats likely present lower risk of exposure to lead because of the availability of marine mammal carcasses for condors to eat, making coastal sites advantageous for condor reintroduction. But old contaminants found in the marine mammal carcasses may pose a renewed threat to the rare birds. 

“The goal of the recovery program is to have condors throughout their historical range, which starts in the Pacific Northwest and ends in Baja California,” said co-author Ignacio (Nacho) Vilchis, Ph.D., associate director of recovery ecology at SDZWA. “Every site is going to have its pros and cons. One of the pros to the Baja site is the availability of a food source that is not as contaminated as it is in California.” 

In addition to less exposure to HOCs in Baja, no condors there have died from lead poisoning in the last five years, compared to 19 condors in California. The research, funded by NOAA, California Sea Grant and San Diego Zoo Wildlife Alliance, highlights the value of Baja California, Mexico as a reintroduction site for condors.

“These findings can help inform management of the Baja flock as it continues to grow,” noted co-author Christopher Tubbs, Ph.D., associate director of reproductive sciences at SDZWA. “Some of the contaminants present in marine mammal samples that we collected are ‘unknown’ in terms of their structure and potential to disrupt hormone function. This study exclusively looked at one hormone pathway, estrogen, but many of the contaminants identified are well known to interfere with multiple hormone pathways. These warrant further study.”

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About San Diego State University 

San Diego State University is a major public research institution that provides transformative experiences for its more than 36,000 students. SDSU offers bachelor’s degrees in 96 areas, master’s degrees in 84 fields and doctorates in 23 areas, with additional certificates and programs at regional microsites. SDSU ranks as the number 1 California State University in federal research support, as one of the top public research universities in California. In addition to academic offerings at SDSU, SDSU Imperial Valley and SDSU Georgia, SDSU Global Campus offers online training, certificates and degrees in areas of study designed to meet the needs of students everywhere. Students participate in transformational research, international experiences, sustainability and entrepreneurship initiatives, internships and mentoring, and a broad range of student life and leadership opportunities. SDSU is committed to inclusive excellence and is known for its efforts in advancing diversity and inclusion. SDSU is nationally recognized for its study abroad initiatives, veterans’ programs and support of LGBTQA+ students, as well as its powerhouse Division I Athletics Program. About 50% of SDSU’s undergraduate and graduate students are students of color. The university resides on Kumeyaay land and was most recently recognized as an Asian American Native American Pacific Islander-Serving Institution (AANAPISI). SDSU is also a long-standing Hispanic-Serving Institution (HSI). The university’s rich campus life and location offers opportunities for students to lead and engage with the creative and performing arts, career and internship opportunities with SDSU’s more than 491,000 living alumni, and the vibrant cultural life of the greater San Diego and U.S.- Mexico region.

About San Diego Zoo Wildlife Alliance 

San Diego Zoo Wildlife Alliance is a nonprofit international conservation leader, committed to inspiring a passion for nature and creating a world where all life thrives. The Alliance empowers people from around the globe to support their mission to conserve wildlife through innovation and partnerships. San Diego Zoo Wildlife Alliance supports cutting-edge conservation and brings the stories of their work back to the San Diego Zoo and San Diego Zoo Safari Park—giving millions of guests, in person and virtually, the opportunity to experience conservation in action. The work of San Diego Zoo Wildlife Alliance extends from San Diego to strategic and regional conservation “hubs” across the globe, where their strengths—including the renowned Wildlife Biodiversity Bank—are able to effectively align with hundreds of regional partners to improve outcomes for wildlife in more coordinated efforts. By leveraging these tools in wildlife care and conservation science, and through collaboration with hundreds of partners, San Diego Zoo Wildlife Alliance has reintroduced more than 44 endangered species to native habitats. Each year, San Diego Zoo Wildlife Alliance’s work reaches over 1 billion people in 150 countries via news media, social media, their websites, educational resources and San Diego Zoo Wildlife Explorers television programming, which is in children’s hospitals in 13 countries. Success is made possible by the support of members, donors and guests to the San Diego Zoo and San Diego Zoo Safari Park, who are Wildlife Allies committed to ensuring all life thrives.