Out of all the attributes that separate humans from fish, the ability to breathe underwater is one that makes us land dwellers most envious. So it's hard not to get worked up over word this past week that a Korean design student may have come up with a blueprint for a wearable device that can extract sufficient air from seawater, enabling just about anyone to breathe like a fish.
It's a remarkable claim considering that no one has yet come up with anything resembling actual “artificial gills.” Codenamed "Triton," the mysterious concept comes in the form of a small mouthpiece, reminiscent of the "rebreather" James Bond uses in Thunderball (1965) and Die Another Day (2002). It is designed to mechanically capture the oxygen gas present in water and store it in a compressed air tank. As creator Jeabyun Yeon describes on his website, water is filtered using a pair of cylindrical shaped gills that house fine threads with "holes smaller than water molecules." A built-in micro compressor, powered by a quick-charging miniaturized battery, then condenses the oxygen, making it readily available as the wearer inhales.
Several skeptics have since chimed in, pointing to certain technological challenges that would ultimately render Yeon's idea, as it's detailed, anywhere from implausible to ridiculously far-fetched. To grasp why artificial gills have been nothing more than a pipe dream thus far, one must understand some of the intrinsic biological differences between man and finned sea creature. First, and most obvious, is that fish possess gills that have evolved to absorb oxygen while keeping out waste gases; human respiratory systems are equipped to tap into the oxygen in the air. Fish are also cold-blooded, meaning they require a lot less energy. This adaptation is essential as the concentration of dissolved oxygen in water is scarce, about 20 times less than what's found in the same volume of air.
The Blog ZidBits explains that artificial gills would need to be huge to provide an adequate amount of oxygen for humans:
This problem is amplified thanks to sea water only containing 7 ppm of oxygen. As a result of this low concentration, 1,000 tonnes of sea water holds only 14 lbs. of O2. Since an average diver needs 1 quart of oxygen per minute, you would need 51 gallons of sea water per minute to pass through the ‘gills’.
The blog DeepSeaNews critiqued Yeon's technology, estimating that, even at the low-end, such a system would need to pump and extract oxygen from around 24 gallons of water for every minute spent submerged. Moreover, inhaling pure oxygen filtered from water can be highly toxic. While 20 percent of air is made up of oxygen, scientists have discovered that breathing air comprised of 100 percent oxygen can cause symptoms such as blurred vision, seizures and convulsions due to fluid accumulating in the lungs.
That said, these challenges haven't thwarted others' attempts to ditch pressurized scuba tanks. Israeli inventor Alon Bodner has been developing a battery-powered prototype that uses a high-speed centrifuge to reduce the pressure of captured seawater, which causes oxygen to bubble up and escape into a separate chamber, much the same way carbon dioxide gases are released when opening a can of soda. The drawback is that the contraption, dubbed "LikeAFish," requires a high-capacity (and likely heavy) power source to function.
Another more exotic approach by scientists at Nottingham Trent University in England was inspired by the great diving beetle, an insect with anatomical features that allow it to survive underwater. Tiny hairs located on its abdomen work to trap a pocket of air between its respiratory opening and the surrounding water. This protective layer of air also acts as a filter, allowing oxygen gases locked up in the water to pass in and carbon dioxide to diffuse out. In one experiment, researchers were able to mimic this effect, to some degree, using a "super-water-repellant porous foam" material wrapped around an oxygen inhaling device.
But, any way you frame it, it looks like it will be a while before a human can be one with the fishes.