Are industrial chemicals killing rare whales and familiar dolphins?

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  • Dozens of whales and dolphins that stranded on the U.S. Atlantic coast contained high levels of pollutants and heavy metals in their fat and liver tissue, according to a new study.
  • For the first time, scientists have detected the widely used antibiotic Triclosan and the popular herbicide Atrazine in rare species that spend their lives hundreds of kilometers offshore.
  • Although the results suggest that these toxins may contribute to the disappearance of marine mammals, more research is needed to determine the direct cause and effect.

Marine mammals washed up on beaches in the southeastern United States have died with high levels of pollutants stored in their organs and fat, researchers recently reported in Frontiers in marine sciences.

“Marine mammals are like a litmus test for the ecosystem,” said senior author Annie Page-Karjian, clinical veterinarian at the Harbor Branch Oceanographic Institute, Florida Atlantic University. “Looking at them and the toxins to which they are exposed gives us insight into what is happening in the marine environment. “

The Atlantic spotted dolphins (Stenella frontalis) in this study died with a long list of conditions, including myocardial fibrosis, hepatitis, and atrophy of the pancreas and thyroid gland. Photo credit: Sheilapic76 / creative commons

Thousands of chemicals from households, farms and factories quietly enter the ocean every day. Some easily absorb on pieces of another common pollutant: plastic. When mistaken for food by small animals like plankton and anchovies, plastic enters the food chain, along with the chemicals it absorbs.

While the amount of toxins ingested by an anchovy is tiny, most marine mammals are top predators, eating hundreds of fish, squid, or krill every day. Through a process called bioaccumulation, small amounts of ingested toxins concentrate in carnivores over time, compromising their immune systems and bodily functions.

Researchers collected autopsy data from 83 stranded toothed whales and dolphins in Florida and North Carolina between 2012 and 2018. They examined 46 bottlenose dolphins (Tursiops truncatus), 21 pygmy sperm whales (Kogia Breviceps), and a small number of animals of nine other species.

The team looked at liver and fat samples for heavy metals like mercury, lead, and arsenic. They also researched triclosan, an antibiotic used in dozens of household products; Atrazine, a herbicide used on corn and sugarcane fields; and a handful of plasticizing chemicals like BPA and NPE, found in countless products, from food containers to clothing.

The study looked at three melon-headed whales (Peponocephala electra), a common offshore species, which contained high levels of selenium and mercury and traces of BPA and NPE in their tissues.  Photo credit: Laura Morse, NOAA / NMFS / PIFSC
The study included three melon-headed whales (Peponocephala electra), a common offshore species, which contained high levels of selenium and mercury and traces of BPA and NPE in their tissues. Photo credit: Laura Morse, NOAA / NMFS / PIFSC

“We have found some of the highest levels of mercury ever reported in any living thing anywhere, ever,” Page-Karjian told Mongabay. Two bottlenose dolphins stranded in Waves, North Carolina, and North Palm Beach, Florida, had more than 1,400 micrograms of mercury per gram of tissue (1,400 parts per million) in their livers. Only 10 parts per million of mercury can cause neurological damage in human fetuses.

Besides the toxins in their tissues, each animal suffered from a number of physical illnesses, including kidney deterioration, thyroid tumors, and chronic liver disease. “Many of these [ailments] can be caused by stranding or shock, but they can also be caused by exposure to toxins, ”Page-Karjian said.

Veterinarians traditionally record pathological data during autopsies, but they usually do not test for toxins. The authors believe it is useful to consider both. Even though the toxins are not the direct cause of death, Page-Karjian explained, they “could have resulted in the death of the animal.”

However, it is difficult to prove that the pollutants killed the animals, said Kathleen Colegrove, clinical professor of zoological pathology at the University of Illinois. “The authors did a great job in really trying not to take that leap,” she told Mongabay.

Nine of the 15 pygmy sperm whales (Kogia breviceps) autopsied for the study were emaciated at death, none considered to be in
Nine of the 15 pygmy sperm whales (Kogia breviceps) autopsied for the study were emaciated at death, none considered to be in “robust” condition. Photo credit: Inwater Research Group

A species included in the six-year project, the Gervais’ beaked whale (Mesoplodon europaeus), is so elusive that only a few people have ever seen them alive. “[This study] had three species of beaked whales, which is amazing because these animals rarely run aground, ”said Colegrove, who was not involved in the study.

Many offshore species like the Gervais’ beaked whale spend their lives thousands of miles from shore, feeding thousands of feet underwater. And yet, evidence shows they contain life-threatening levels of industrial chemicals, suggesting that the dangers of ocean pollution go deeper than we thought.

The study is an effective first step towards expanding our understanding of chemical contamination in offshore species, Colegrove said. She added that the report “will set up future studies to look more precisely” at how pollution affects some of the ocean’s least studied mammals.

Quote:

Page-Karjian A, Lo CF, Ritchie B, Harms AA, Rotstein DS, Han S, Hassan SM, Lehner AF, Buchweitz JP, Thayer VG, Sullivan JM, Christiansen EF, Perrault JR. Anthropogenic contaminants and histopathologic findings in beached cetaceans in the southeastern United States, 2012-2018. Before Mar Sci. 2020. https://doi.org/10.3389/fmars.2020.00630 (https://www.frontiersin.org/article/10.3389/fmars.2020.00630)

Hansen Cypress (@pollenplancton, cypresswritesscience.com) is a graduate student in the Science Communication program at the University of California, Santa Cruz. Other Mongabay stories produced by UCSC students can be found here.

Animals, Environment, Green, Mammals, Marine mammals, Microplastics, Oceans, Plastic, Pollution, UCSC, Water pollution, Fauna


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