Johnson co-authors study finding high concentrations of DDT-related chemicals in California condors
Jade Johnson is part of a research team that has found new and mysterious DDT chemicals accumulating in coastal California condors. The Los Angeles Times reports the team has “identified more than 40 DDT-related compounds — along with a number of unknown chemicals — that have been circulating through the marine ecosystem and accumulating in this iconic bird at the very top of the food chain.”
The study, published in May 2022 in the American Chemical Society journal Environmental Science and Technology, found that coastal condors had seven times more of the DDT-related chemicals than inland condors. They found this is due to the consumption of scavenged marine mammals in Southern California, which also had seven times more contamination than marine mammals in the Gulf of California in Mexico. These findings are important factors to consider when choosing condor reintroduction locations.
Christopher Tubbs, a co-author and reproductive sciences expert at the San Diego Zoo Wildlife Alliance, told the LA Times, “this DDT story, and contaminants interfering with reproduction, is what we call a sublethal exposure. They don’t kill a bird outright, but they could interfere with estrogen receptors or any other endocrine pathway.”
Jade assisted Margaret Stack, first author, in pooling and preparing the condor plasma samples for the non targeted analysis (NTA) based on comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC/TOF-MS). This analytical method allows for detection and identification of both known and unrecognized contaminants, some of which are not routinely monitored in condors but may have potential toxic effects.
“It was interesting to see how NTA was used to allow for a comprehensive halogenated organic contaminant (HOC) profile comparison across the condors and marine mammals,” Jade shared. “Despite over 400 unique HOCs identified, DDT and its metabolites still emerged as the most abundant and largest known threat to coastal CA condors.”
The LA Times story connected this research to “DDT’s toxic — and insidious — legacy in California,” including that “the nation’s largest manufacturer of this pesticide once dumped its waste into the deep ocean,”resulting in “as many as half a million barrels could still be underwater today.” Nathan Dodder, co-author and environmental analytical chemist at SDSU, added, "the sewage outfall off Palos Verdes is the major known source of DDT to the marine environment. The contribution of offshore dumping is currently uncertain until further assessments take place."
“If the California condor is accumulating such high amounts of DDT, that means that every link of the coastal food chain — including people — is also exposed,” the newspaper continued.
Assessing Marine Endocrine-Disrupting Chemicals in the Critically Endangered California Condor: Implications for Reintroduction to Coastal Environments. Margaret E. Stack, Jennifer M. Cossaboon, Christopher W. Tubbs, L. Ignacio Vilchis, Rachel G. Felton, Jade L. Johnson, Kerri Danil, Gisela Heckel, Eunha Hoh, and Nathan G. Dodder. Environmental Science & Technology Article. May 17, 2022. https://doi.org/10.1021/acs.est.1c07302