Sperm whales throughout the Pacific Ocean carry evidence within their bodies of exposure to multiple man-made pollutants, according to a new Environmental Health Perspectives study.
In a surprising finding, researchers found that whales living near the Galapagos Islands appear to have higher levels of pollutants than those in other areas of the Pacific. The Galapagos Islands are a UNESCO-protected site and had been considered pristine.
The pollutants include the pesticide DDT, polycyclic aromatic hydrocarbons (PAH's, which can also have natural sources, such as volcanoes), hexachlorobenzene, and 30 types of polychlorinated biphenyls (PCB's).
"Ingestion is the main route of exposure for whales, via contaminants present in their diet," study co-author Celine Godard-Codding said, adding that absorption through skin, such as after an oil spill, is another significant route of exposure.
She and her colleagues biopsied skin and blubber from 234 male and female sperm whales in five locations across the Pacific: the Gulf of California, Mexico; the Galapagos Islands, Ecuador; Pacific waters between the Galapagos Islands and Kiribati (Pacific Crossing); Kiribati; and Papua New Guinea.
The scientists analyzed the tissue samples for expression of CYP1A1, an enzyme that metabolizes certain aromatic hydrocarbons. According to the researchers, the more a whale has been exposed to the pollutants mentioned in the study, the more it will express this enzyme.
CYP1A1 presence was highest in whales from the Galapagos Islands, second highest in those from the Gulf of California, and lowest in whales from waters farthest from the continents (Kiribati and Pacific Crossing.)
"We were surprised by the highest levels of the CYP1A1 biomarker seen in the Galapagos," Godard-Codding told Discovery News. "Whether this actually reflects higher levels of pollutants in the Galapagos waters, or in the food chain in these waters, remains unknown."
She explained that the studied pollutants "are mainly man-made" and "end up in the oceans upon release into the environment."
"The oceans are considered the final sink for most persistent environmental contaminants," she said. "It's a global pollution issue with pollutants potentially distributed worldwide by atmospheric or oceanic currents."
Godard-Codding and her team were not able to do a detailed study on the health of the biopsied whales, since the whales were in the wild. Prior research on laboratory animals, including captive aquatic carnivorous mammals, has shown that the pollutants "can cause deleterious effects," she said.
For years, scientists have suspected that sperm whales are likely to accumulate fat-soluble pollutants because the whales are massive -- weighing up to 50 tons -- and can live up to 70 years. This makes them potentially more susceptible to chronic toxic exposure.
Given the present findings, it's now thought that sperm whales may be important sentinels of ocean health, revealing what organic pollutants persist in the marine environment. They may also provide information on specific regions of the Pacific, especially because females and juveniles tend to stay within a 621-mile range.
Sierra Rayne of the University of Victoria and colleagues conducted earlier research on free-ranging orcas, also known as killer whales, and found evidence that they too retain pollutants. In this case, chemical markers for flame retardant compounds were detected in killer whale blubber biopsy samples.