Blue Whale Earwax Reveals Pollution Accumulated Over a Lifetime

Earwax collected from a beached whale shows that the creature ingested a host of toxins, such as DDT and mercury, throughout its life

Blue whale earplugs can reveal some of these aquatic giants’ life events.
Blue whale earplugs can reveal some of these aquatic giants’ life events. Photo by Flickr user Mike Baird

If you think extracting globs of earwax from your own ear is gross, imagine handling a nearly foot-long, inch-thick tube of whale earwax.

To protect delicate eardrums, around 8 to 10 baleen whale species have ear canals that are naturally sealed off from the external environment. Over the years, earwax begins to build in the narrow tubes. Whales don’t hear like humans–fat deposits in their jaw funnel low-frequency sound vibrations toward their eardrum, so the wax does not get in the way of their hearing.

By the end of a blue whale’s life, the wax forms a solid, permanent tube of what researchers refer to as an earplug in the animal’s ear canal. While most people would likely consider the prospect of handling this stuff rather off-putting, for scientists the earwax provides “unprecedented lifetime profile” of the animal, according to a new paper published in Proceedings of the National Academy of Sciences.

Like tree rings, layers found within whale earplugs are already used to help researchers estimate an animal’s age. In this new study, scientists guessed that the wax may have more secrets to tell.

Traces of events recorded from birth to death may leave their mark in the whale’s ear wax, they figured. Chemical pollutants, for example, are a problem for ocean creatures, included endangered blue whales. Many of these contaminants build up in whales’ fatty tissues, but fat offers no clues as to when a whale might have been exposed to those chemicals. Perhaps the earplug would.

The 12-year-old blue whale
The 12-year-old blue whale used in this study washed ashore in California after being killed by a ship strike. Photo by Michelle Berman- Kowalewskic, Santa Barbara Museum of Natural History

However, testing this hypothesis requires invasively getting at that golden substance–a difficult task while the whale is alive. But in 2007, a 12-year-old, 70-foot long blue whale washed ashore near Santa Barbara, dead from a ship strike. The recovered 10-inch long earplug sat in a freezer for a couple years, until the team sampled it. They also took samples of its blubber to compare it with the wax and get chemical profiles of these two lipid-rich materials’.

Earwax is continuously deposited throughout the whale’s lifetime, but forms alternating light and dark layers on approximately 6 month intervals. The light corresponds to periods in the whale’s lifecycle when it’s feeding, while the dark represents times of fasting and migration. The team performed numerous chemical analyses to produce a profile of the whale’s life, told at a 6-month resolution.

Within the wax, they found markers of the stress hormone cortisol, growth-inducing testosterone, contaminants such as pesticides and flame retardants, and mercury. Much like humans, this particular whale’s stress levels increased as it got older, effectively doubling over its lifetime. Testosterone peaked when the whale was about 10 years old–the height of puberty for male blue whales.

The contaminants tell an interesting story. From the whale’s birth until about 12 months old, anthropogenic chemicals such as dichlorodiphenyltrichloroethanes (better known as DDT), chlordanes, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers appeared in his earwax. About 20 percent of the the whale’s total organic contaminants turned up during this first year, indicating that although the whale’s mom likely did a good job nursing her son, she also inadvertently transferred toxins to her baby during gestation and through her milk.

After the whale was weaned, the bulk of pollutants that built up in the whale’s body likely came from krill, it’s main food source. Blue whales can consume up to one ton of the little shrimp-like crustaceans each day, so small contaminants present in the tiny creatures can accumulate over time in the whale’s body. The contaminants also work their way into bodily secretions such as earwax.

Mercury, which gets into earwax the same way as the other pollutants, peaked in two separate events much later in life, first when the whale was about five years old and then again at about ten years old.

Both the organic pollutants and the mercury continued to accumulate throughout the whale’s lifetime, meaning that the older the whale became, the more pollutants built up in its ears. About 90 percent of these contaminants also turned up in the blubber, confirming that both blubber and earwax can be used as markers of exposure, but that earwax provides a method of tracking when exposure occurred.

The extracted whale earplug
The extracted whale earplug (B); a cross-section of the earplug (C); and a cross-section of the earplug magnified 20x to show the different waxy layers. Photo from Trumble et. al., PNAS

“DDT was banned 30 years before this animal was born, but it was still exposed to DDT over its entire lifetime,” study author Sascha Usenko of Baylor University pointed out in an interview. “It was exposed to both historical and current chemicals, like brominated flame retardants.”

Pollutants like DDT and mercury are known to cause a host of problems for animals, including developmental disorders and thyroid issues. While these findings don’t bode well for the health of the ocean’s creatures–especially endangered ones like the blue whale–the researchers are excited about using the chronically archived wad of wax to better understand the extent to which humans are tampering with marine fauna’s health. It also provides marine biologists with a new tool for studying of whale life events. “For a majority of the species on the planet, lifetime profiles such as these are simply unattainable,” the researchers write.

The team hints at the wax’s research possibilities. For example, they noticed that stress hormones began to rage after the whale went through testosterone-triggered puberty, indicating the big guy may have been flustered over competition and pressure to win a lady friend. On the other hand, some of the whale’s ever-growing stress may be due to accumulating pollutants, though this study only scratches the surface of that question. Large pulses of pollutants, like the mercury seen in this whale, may indicate that the animal came near a polluted shore (the coast of California in this case, perhaps) or was exposed to a major contamination event.

“To be able to scientifically measure chemicals that are not as persistent, such as hormones that degrade in the body, is outstanding,” Usenko said. “We can ask questions like ‘Do contaminants have impacts on changes in stress?’ and maybe do a better job at addressing those questions.”

Examining old museum specimens’ ear wax from the 1950s and onwards, the team thinks, may reveal significant changes to the ocean and its creatures’ health over the years. Additionally, the researchers have confirmed the method works on grey whales, and they suspect it should also apply to other species of baleen whales. “This innovative tool increases the feasibility of accurately assessing anthropogenic impact on everything from an individual organism to marine ecosystems,” they write.

The earplug is no doubt only beginning to reveal its secrets. In the meantime, whale researchers may celebrate over less of a need to handle whale blubber, poop and blood–up until now the conventional means of studying whale health, and probably even more unpleasant than handling a giant tube of years-old wax, even though the earplug does reportedly have a pungent fishy smell. “It’s not something you want to get on your clothes, it sticks around with you for a while,” Usenko said.

Get the latest Science stories in your inbox.