Earwax is not, by any stretch of the imagination, an appealing topic. But an “earplug” 25.4 centimeters in length from a young blue whale turns out to be a time capsule with valuable information about the real effect of chemicals, pesticides and other pollutants on wildlife and the environment.
As scientists from Baylor University write in the Proceedings of the National Academy of Sciences, “obtaining lifetime chemical profiles (i.e., from birth to death) is extremely rare and difficult for most of Earth’s animals.” A whale’s earwax can provide just such information.
Environmental scientist Sascha Usenko and colleagues were able to extract the earplug from a blue whale (Balaenoptera musculus) who had been killed after colliding with a ship off the coast of Santa Barbara, California, in 2007. His age was estimated to be twelve years. Blue whales can live to be 90 to 100 years ago, so the whale was quite young and just around the age to reach sexual maturity.
A whale’s earwax is a “fat-rich deposit that stores the same chemical data as blubber,” says Nature.com. It is laid down in layers of light and dark bands, each of which can be roughly correlated with a six-month period; it remains in the animal’s auditory canal through their life and stays intact even after their death.
In addition, earwax can provide a sense of the time when a whale was exposed to various chemicals just as the rings of a tree provide information about drought and other environmental conditions. In contrast, blubber, which scientists have long used to trace levels of chemical contaminants in whales, does not indicate when a whale might have been exposed to such substances, or for how long.
Five discoveries the scientists made from analyzing the blue whale’s earplug:
1. The whale had come into contact with 16 persistent organic pollutants, including pesticides and flame retardants, during his short life.
2. At least some of these contaminants were transferred to the whale from his mother while he was in her womb and while nursing, as the scientists found that his exposure to pesticides was the greatest in his first year of life.
3. Mercury was found at higher levels in the whale’s earwax twice, when he was about five and ten years old. This suggests that he encountered this chemical, which can cause brain damage in whales as well as in humans, from somewhere in the environment rather than via his mother.
As these levels peaked when the whale was about ten years old and reaching sexual maturity, scientists say that stress from sexual competition could be the reason. But weaning or another natural event could also be the cause, as could human activities including noise pollution from sonar, which other research has shown can drive blue whales away from their feed grounds and lead to them starving to death.
5. The presence of flame retardants, which were outlawed in 2005, reveals how pollutants can linger for years (50 in the case of these chemicals) in the environment, with adverse effects both for whales and, indeed, for their unborn young.
More study is needed to figure out baseline stress levels in blue whales and to get a betterpicture of the extent to which human activity is adversely affecting them.
Usenko and his team (featured in the video above) now hope to analyze some of the 1,000 or more whale earwax specimens in museums around the world, noting that “if we can look at individuals that lived in an environment without some of the stresses we see now, then we could tease out the causes of the cortisol increase.” Study co-author Stephen Trumble of Baylor University also points out that studying earplugs from the 1960s and “from a whale that is 30-40 years old will provide a look into what the world’s oceans were like pre-WWII etc.”
Only some 5,000-12,000 blue whales survive today, the result of extensive hunting in previous centuries. Fishing nets, environmental noise and cargo ships also pose serious threats to their survival. The Baylor University scientists’ study shows that pollutants can harm whales even when they are in the womb. The fact that these substances leave traces in a whale’s ear suggests the extent to which they’ve penetrated deep inside an animal’s body.
Photo from flickkerphotos