Elephant Seals Dive Deep with 'Smoker's Blood'

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Elephant seals have surprisingly high levels of naturally produced carbon monoxide — a noxious gas that is deadly at high concentrations — in their blood, a new study finds. In fact, the amount of carbon monoxide found in the blood of these large mammals is roughly the same as that in people who smoke 40 or more cigarettes each day, researchers say.

Carbon monoxide is an odorless and colorless gas that is naturally produced in small quantities in humans and animals. The scientists are unsure why elephant seals have such unexpectedly high levels of the gas in their blood, but the researchers suggest it could protect the animals from injury when they dive to extreme depths in search of food.

In humans and animals, carbon monoxide is a byproduct of the breakdown of hemoglobin, which carries oxygen in red blood cells throughout the body, said study leader Michael Tift, a comparative physiologist at the Scripps Institution of Oceanography at the University of California, San Diego. (Gallery: California's Deep-Diving Elephant Seals)

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Carbon monoxide binds to hemoglobin, effectively suffocating the protein and preventing it from transporting oxygen. In healthy adult humans, about 1 percent of hemoglobin is bound to carbon monoxide. But the amount of hemoglobin incapacitated by carbon monoxide can reach as high as 10 percent in elephant seals and chronic, heavy cigarette smokers (who are exposed to carbon monoxide from burning and inhaling tobacco), the researchers said.

"Elephant seals are known to have the highest blood volume of any mammal, so we knew there was the potential for producing a lot of carbon monoxide," Tift told Live Science. "When we looked into the levels of carbon monoxide in the blood, we suspected there could be a lot."

Yet, while elephant seals appear to have elevated levels of carbon monoxide in their bloodstreams, the concentration of the gas is not so high as to cause harm, the researchers said.

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"The levels in elephant seals are not high enough to inhibit oxygen transport or lead to carbon monoxide poisoning," Tift said.

Carbon monoxide's colorless and odorless properties have earned it a reputation as a "silent killer." When the gas invades up to 20 percent of hemoglobin stores, humans typically begin to suffer the effects of carbon monoxide poisoning — lightheadedness, headaches and other flu-like symptoms. The gas typically becomes deadly when it incapacitates more than 50 percent of hemoglobin stores, Tift said.