Research Highlight: The Dolphin Sentinels

Eight dolphins have given Scripps Institution of Oceanography at UC San Diego researchers and their collaborators a new catalog of information about chemicals in the marine food web—and a few surprises along the way.

The researchers analyzed chemicals in the blubber of Bottlenose Dolphins that died of natural causes over a 15-year period and washed ashore on beaches in Southern California, a region known for historical wastewater and storm water discharge loads and historical contamination from DDT (dichlorodiphenyltrichloroethane, a banned, once commonly used pesticide) and PCBs (polychlorinated biphenyls, banned chemicals previously used in a variety of industrial and commercial applications). As dolphins are at the apex of the marine food web, the new information provides insight into how chemicals are accumulated from the prey fish they ingest, including species that also end up on our dinner tables.

More than 300 chemicals emerged in the new catalog-like resource. Some were clearly linked to human-produced sources, including 29 chemicals related to the pesticide DDT and another 17 polybrominated diphenyl ethers (PBDEs), chemicals that until recently were manufactured and broadly used as flame retardants in the textile and electronics industries.

But the researchers also found a surprisingly significant portion of previously undetected and potentially toxic compounds.

“Ninety-four of the 327 unique chemicals in the new library at this point are unknown,” said Nellie Shaul, a Scripps graduate student and lead author of the study. “That was significant and surprising because it tells us that not only are these chemicals currently not on our monitoring radar, there is a lot of stuff out there that we really need to learn more about.”

Shaul noted that dolphins can be considered sentinel species, akin to canaries in a coal mine, for human health since they are mammals that sit at the top of the food web and can give us information about the seafood we consume.

“These dolphins are giving us a better idea of what chemicals are out there, and they are showing us what’s inside some of our own food sources,” said Lihini Aluwihare, a Scripps chemical oceanographer and coauthor of the new study. “By adding information about new contaminants of concern, we can enable a better understanding of which contaminants are cycling out there and new knowledge about how anthropogenic compounds might make it into the environment and how they are distributed.”

Working with collaborators at the Southern California Coastal Water Research Project, San Diego State University, and NOAA’s Southwest Fisheries Science Center, the Scripps researchers employed a new technique for detecting chemicals and possible toxic contaminants in the marine environment.

When tracking harmful chemicals, the U.S. Environmental Protection Agency and regional agencies investigate specific chemical targets such as DDT and PCBs. The new study flipped that approach and instead employed a novel “non-targeted” method that cast a wide view to see what types of chemicals emerge in the marine environment. The new technique used cutting-edge analytical tools to separate and analyze the suite of chemical compounds.

“This non-targeted approach is allowing us to see everything out there and possibly show us potential new targets to monitor and learn something new about how contaminants are being modified in the environment,” said Aluwihare. “The huge new data set provides a starting point to evaluate our monitoring efforts and perhaps start to construct new studies on toxicity.”

The paper, published in the journal Environmental Science and Technology, is a product of the new Scripps Center for Oceans and Human Health (COHH), a program focused on tracking natural chemicals off California known as halogenated organic compounds, or HOCs, which resemble human-manufactured chemicals.

“We know many of these compounds are made by humans and they are going through the food web and accumulating. It really does powerfully demonstrate how connected we are to our environment,” said Aluwihare.

“We feel gratified to see this work in print,” said Keith Maruya, a study coauthor and principal scientist at the Southern California Coastal Water Research Project. “In addition to the detailed cataloging effort, the study helps provide critical information on the utilization of habitat by sentinel marine mammal species, such as the dolphins that frequent our coastline and that are the subject of long-term research by our NOAA collaborators.”

The study was funded by the National Science Foundation, the National Institute of Environmental Health Sciences through the Oceans and Human Health Program, the California State University Program for Education and Research in Biotechnology, California Sea Grant, and the member agencies of the Southern California Coastal Water Research Project Authority.

In addition to Shaul, Aluwihare, and Maruya, coauthors include Nathan Dodder of the Southern California Coastal Water Research Project Authority; Susan Mackintosh and Eunha Hoh of San Diego State University; and Susan Chivers, Kerri Danil, and David Weller, of NOAA’s Southwest Fisheries Science Center.

-- Mario C. Aguilera

Related Image Gallery: Dolphin Chemicals