Back in 2007, a blue whale was struck by a ship in the Pacific Ocean, and washed up on a California beach. Scientists collected and preserved bits of the dead whale, including its ear wax. Yes, whales have ear wax too, and it turns out it's a good indicator of which chemicals are polluting our oceans. NPR's Rhitu Chatterjee reports.

RHITU CHATTERJEE, BYLINE: How often do whales clean their ears? Never. So year after year the stuff builds up, layer upon layer. By the time this blue whale died, its ear wax was almost a foot long.

SASCHA USENKO: It's kind of got that icky look to it. It looks kind of like a long candle that's been roughed up a bit. It definitely looks waxy. It's pretty rigid.

CHATTERJEE: Sascha Usenko, of Baylor University, studied the ear wax. He says the column of wax has light and dark layers.

USENKO: Historically in the past, they've been used to estimate the age of the whale, very similar to counting tree rings.

CHATTERJEE: But age is not what Usenko was really after. He studies how organic pollutants like DDT and flame retardants are affecting whales. These pollutants get deposited in fatty tissues, like whale blubber. And scientists often analyze blubber to see what whales are ingesting. But, Usenko says, there's a limitation.

USENKO: I would only know that that organism, that animal, was exposed to those contaminants, but I wouldn't know when.

CHATTERJEE: This is why ear wax has the edge. Like blubber, it's made of fatty material that accumulates toxic chemicals. But each layer of wax corresponds to six months of the animal's life, so by working through a plug of wax, scientists can figure out when an animal was exposed to a chemical. In the case of this whale, Usenko found that it was exposed to organic pollutants throughout its lifetime. And, he says...

USENKO: A significant percentage of the exposure to contaminants occurred in the first early stages of the animal's life.

CHATTERJEE: When it was still nursing. In other words, the pollutants came from the mother through her milk. At that age, Usenko says, the animal would have been at its most vulnerable, but he can't say just from looking at the wax whether these chemicals are hurting the development of blue whales. After all, he only studied only one animal and the ear wax can't reveal whether the chemicals caused harm.

He's published his results in the latest "Proceedings of the National Academy of Sciences." But he needs more data, so he suggests scientists start collecting ear wax from beached whales the world over and mail it to him.

Rhitu Chatterjee, NPR News.

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