When oil tankers crash and inevitably spill oil into the open seas, a go-to clean-up method is corralling the rapidly spreading oil and burning it. But in some places, like the ice-strewn Arctic ocean, physically corralling that oil with boats and boons is practically impossible. Now, there's a better way to collect that leaked gunk—and the methods users, greener, more biodegradable chemicals, too.

To make corralling that oil easier, chemists developed a tool called an oil herder. Essentially, oil herders make oil clump together naturally when sprayed in the ocean around a spill. The problem is that these silicone-based herders will stay in the ocean more or less indefinitely. And although they're already being tested in open water, we have no idea what ecological toll they take.

"We've tested our chemical in room temperature, cold, ice, and hot water."

In a new study out today, a group of chemists at Tulane University and City College of New York just announced the development of the first class of "eco-friendly, biodegradable, and plant-based [oil] herders," says George John, a chemist at CUNY who's part of the research team. As John and his colleagues report in the journal Science Advances, the inexpensive new oil herder is chiefly made of plant-sourced phytol (a key component of chlorophyll), which already exists in great abundance in the natural marine environment thanks to organisms like green algae.

"We've tested our chemical in room temperature, cold, ice, and hot water, as well as different salinity levels of water. In every case our chemical works with exactly the same results and efficiency as do the silicon-based herders," John says. "Normally you need these herders to work and keep oil contracted for maybe 10 to 15 minutes before you can start a fire. Our chemical starts [biodegrading] in around a few hours, and completely [degrades] in maybe two weeks to a month."

Raising the tension

When oil spills into the sea, it floats to the top of the water and spreads... fast. That's because the surface tension of water is remarkably strong, much stronger than that of the floating oil, and the difference in tension causes the oil to be continually squeezed up across the top of the water until it's stretched extremely thin. That's a problem, according to John, because oil can only be burnt effectively when it's clumped together and at least 1/10 of an inch thick. Light oil naturally wants to spread much, much thinner than that.

Like soap, John's biodegradable chemicals break up and drop the surface tension dramatically, making the oil prefer to clump together rather than spread out. The chemical does this by forming a hyper-thin single-molecule layer, which, on a molecular level, looks a little bit like millions of pins poking out of the water. The sharp body of each pin is the plant-sourced phytol molecule, and the head is a simple sugar molecule or harmless amino acid. At no point does the oil herder attach to or alter the floating oil—it only reduces the surface tension of the water around it. After a few hours, the connection between the head and the body of the molecular pin will break down, causing both parts to dissolve into the ocean's water column.

Biodegradable, but better?

How much better for the environment are these new oil herders compared to the old ones? The short answer is: We actually have no idea. Gary Shigenaka, a biologist with the Emergency Response Division of the US's National Oceanic and Atmospheric Administration, says that despite new "interest in herders, especially for waters [like the Arctic] where floating ice may preclude the use of other more traditional mechanical cleanup methods. . . there are currently no herders approved by [the EPA] for use during oil spills." The upshot: No long-term (or even short-term) ecological studies have ever been done to see the ecological toll that herders can take.

"Our chemical starts biodegrading in around a few hours, and completely degrades in two weeks."

Until scientists compare the two chemicals, Shigenaka is cautious to say whether, even on principle, John's plant-based oil herder would be ecologically safer than a non-biodegradable option. "'Eco-friendly' and 'biodegradable' are rather tricky descriptors for any product," he says. "Some of the green cleaners that are based on pine or citrus oils, for example, can kill exposed marine organisms quite readily. . . when I lecture on toxicity for our Science of Oil Spills classes, I try to point out that nothing is really nontoxic, it all just comes down to dose," he says.

For the most part, John readily agrees with Shigenaka. "But keep in mind," John says, "Our motive was just to see if it would even be possible to use, simple, naturally occurring molecules to develop an [oil herder] that would work as well as what's already commercially available. We found that we could. What we hope for now is that our research will spark a new initiative to talk about these herders, to test them, and to design newer and even better ones."

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