Earwax reveals whale’s pollutant exposure

Studying a 10-inch-long piece of earwax might not sound like the most pleasant research experience. But scientists have discovered that a whale’s earplug is a treasure trove of information about the animal’s stress level and exposure to pesticides and mercury.

In some baleen whales, plugs of wax, fat, and keratin build up in their ear canals starting at birth. Researchers have used these earplugs to help determine the whale’s age, “in a manner that is similar to counting growth rings in trees,” the study authors write in Proceedings of the National Academy of Sciences. They wondered if the wax also could provide a record of the chemicals the animal produced or was exposed to over its lifetime.

To find out, the team analyzed an earplug from a 12-year-old blue whale that was killed by a ship collision off the coast of California. The researchers measured cortisol, a stress hormone, and found that average levels doubled during the whale’s life. They detected pollutants such as pesticides, as well as two spikes in mercury levels around five and 10 years of age.

The authors don’t know what caused the whale’s increased stress, but they speculate that anything from migration to noise could have contributed. The timing of the pollutant peaks suggests that pesticides may have been transferred to the whale from its mother. Roberta Kwok | 16 September 2013

Source: Trumble, S.J. et al. 2013. Blue whale earplug reveals lifetime contaminant exposure and hormone profiles. Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1311418110.

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