Blue Whale Earwax Offers a Surprisingly Good Record of Pollution

Humans have steadily pumped the oceans full of pollution, and bioaccumulation of chemicals is a problem that threatens the health of marine systems—as well as the viability of all the tasty fish we eat. But when chemicals diffuse through water, how exactly can we study how chemicals have accumlated over time? New research uses a surprisingly novel bio-barometer: whale earwax.

New research in PNAS shows how the wax earplug of a male blue whale could be used to construct "birth to death" profiles of both contaminants and hormones. Even more astoundingly, the profiles were constructed with a resolution of six months. That's an impressively detailed records of minute chemical changes, and it's all preserved in earwax.

The study relies on samples of wax collected from a single dead blue whale by researchers at the Santa Barbara Museum of Natural History. According to NPR, the scientists collected the wax from the endangered whale's skull. Whales produce wax in their auditory canals just like humans. Only in this case, the plug recovered by scientists is nearly a foot long.

"It's kind of got that icky look to it," co-author Sascha Usenko, an environmental scientist at Baylor University, told NPR. "It looks kind of like a candle that's been roughed up a bit. It looks waxy and has got fibers. But it's pretty rigid — a lot stronger and a lot more stable than one would think."

The plugs that build up have light and dark bands, called laminae, that are known to develop over certain periods of time. (The color difference is due to environmental differences between regions whales migrate between.) In the case of the blue whale, a new band is created every six months; the study whale had 24 laminae, putting its age at 12 years, give or take half a year. The natural comparison is to tree rings, and apparently using earwax to find the age of whales is pretty common—here's a paper describing the process for southern fin whales from 1972.

But no one had used the whales' wax as a record of environmental conditions until now. As the authors note in the paper, it's a big step forward because there's currently no method of charting the effects of pollution on whales over time—aside perhaps from sampling the same whale over and over, which isn't feasible:

Besides whaling activities, well-known anthropogenic activities including fishery entanglement, chemical use/emission, environmental noise, ship strikes, and climate change are impacting whales, with evidence found through morphological or epidemiological analysis as well as chemical profiles from tissue, fecal, and exhalation samples. However, we are currently unable to monitor and therefore assess the lifetime impacts of such anthropogenic pollution/activities on whales.

Because the study only involved one sample, the actual concentrations of contaminants and hormones found can't be compared to any other data. However, the whale's life history can be reconstructed. Hormonal profiles lended evidence about the whale's birth and maturation. Perhaps more fascinating is how temporal-spatial histories can be reconstructed.

As the authors write, "The mercury profile also highlights two pulse events ranging from 60 to 72 mo and from 120 to 126 mo. Because this blue whale appeared to routinely traverse the coast of California (ship strike near Santa Barbara, CA), we speculate that these pulse events may be associated with regional environmental and/or anthropogenic increases of mercury."

That means that comparing the date of a spike in chemical contamination to its known seasonal ranges can lend insight into where pollution is coming. In simple terms, a dead whale's earwax shows that when it was between five and six years old, it swam through waters with high concentrations of mercury, likely off the coast of Santa Barbara.

That's a surprisingly precise picture considering that no other method for measuring chemical load offers a built-in timeline. It's truly fascinating research, and offers a new tool for marine biologists looking to both understand whale development as well as better monitor the historical effects of pollution on marine systems.

@derektmead