Unprecedented chemical profiles found in whale earwax

Professors Stephen Trumble and Sascha Usenko, of Baylor University, have developed a new method to determine the lifetime chemical profiles of blue whales. As revealed in the journal Proceedings of the National Academy of Sciences, the scientists found the answer in the whales’ earwax plugs.

The researchers discovered that both man-made and endogenous chemicals had been recorded and archived in whale earwax, having extracted the stress hormone cortisol, testosterone, organic contaminants such as pesticides and flame retardants, and mercury. While scientists have previously found similar results in whale blubber, that method only provides information over short, finite periods of time and can be cost-prohibitive and difficult to obtain.

The whale earplug from a blue whale that was used in the study.

“Blubber just tells us that the organism was exposed to those specific contaminants, but it actually doesn’t convey when the exposure occurred,” said Usenko.

Earwax, on the other hand, has been successfully used as an ageing tool, similar to tree rings, “and as you go deeper into the earwax, the farther back in time you go”, Usenko said. By going back in time, he said, “we can not only see what chemicals the animals were exposed to, but actually when that exposure took place”.

By analysing these contaminants, the researchers can assess the human impact on individual whales, multiple generations and marine ecosystems, answering a “100-year-old question”, according to Usenko. He said they can conduct the same assessments on earplugs archived decades ago “and examine critical issues such as the effects of pollution, use of sonar in the oceans and the introduction of specific chemicals and pesticides in the environment over long periods of time”.

The earplugs can further provide time-specific biological information about the whales. Trumble explained that hormones such as oestrogen and progesterone, found in the archived earplugs of female whales, “will show markers of development, sexual maturity, birth events, pregnancies, and this will give far greater resolution than ... anything else thus far”.

“Our research was able to improve upon estimates of sexual maturity for blue whales,” he continued. “Previous estimates provided a 10-year range of maturity, and we have been able to pinpoint exactly when the whale in the study hit sexual maturity.”

All this information was previously unattainable and is described as Usenko as “exceptionally valuable”. Trumble added that this has “never been done before”, as “whales are free-ranging animals, and you can’t get these types of profiles or information on free-ranging animals in any part of the world”.

The researchers concluded that the use of the earplugs “will allow for a more comprehensive examination of stress, development and contaminant exposure, as well as improve the assessment of contaminant use/emission, environmental noise, ship traffic and climate change on these important marine sentinels”.

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