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A ghost crab eats oil from the Gulf of Mexico spill, shown glowing yellow-orange under ultraviolet light, at Gulf Islands National Seashore near Pensacola (map), Florida.
Late last week coastal geologist Rip Kirby was on the seashore as part of an effort to detect oil by shining UV lights—widely used to spot blood at crime scenes—on Gulf beaches. The method, he hopes, will allow scientists and cleanup crews to tackle hard-to-spot oil, such as crude mixed with mud or light stains on sand, that's washed ashore from the sinking of the BP-leased Deepwater Horizon rig.
Under UV light, clean sand appears purple or black. Some minerals, such as calcium carbonate in seashells, glow blue, as does a shovel handle in the picture above.
Although hydrocarbons have long been known to fluoresce, or glow, under ultraviolet light, this may be the first time the technology has been used outside a lab to spot oil. "The use of UV light to identify [types of] oil is an industry-wide process," said Kirby, a graduate student at the University of South Florida. But "I've always seen it in a [lab] machine," he said.
"The first time I took the UV flashlight out on the beach to see if it would work, it was beyond my wildest dreams," Kirby said. "It was easy to see that there was oil on the beach ... the contamination was widespread."
At center, tar patties and tarballs—normally brown or black—near Pensacola Beach, Florida, glow orange-yellow under an ultraviolet spotlight.
Graduate student Kirby hopes that ultraviolet light can be used on beaches to guide oil-spill cleanup operations. The heavy-duty spotlight his team uses costs thousands of dollars, making it probably too expensive to supply to the tens of thousands of workers cleaning oil from Gulf beaches.
However, a U.S. $17 portable UV flashlight—like those used by bouncers to spot fake IDs—was also successful at spotting the oil. "You almost have to be right on top of the oil to see the orange fluorescence" with the inexpensive light, but it could suffice for beach cleanup work, Kirby said.
Under UV light, tar from the Gulf of Mexico oil spill lights up orange-yellow on the beaches of Gulf Islands National Seashore (picture) while clean sand glows purple in a long-exposure picture.
Before landing on the beach, the oil had become "weathered," made foamy and gooey by extended exposure to air and water.
One challenge of working with UV light—also a component of sunlight—is that it can damage eyesight.
"The damaging parts of sunlight aren't really the visible parts of the spectrum but the invisible ones," Kirby said. "That's why ophthalmologists say to wear UV-filtering sunglasses." Powerful UV spotlights such as the one being used in the above picture—which Kirby calls the "Klingon death ray"—are particularly dangerous, he said.
Boots worn by University of South Florida graduate student Katie Brusché are stained with yellow-brown tar from the Gulf oil spill, as seen under ultraviolet light in a long-exposure photograph. Under UV light, even lightly contaminated sand glows bright orange-yellow.
One challenge of cleaning up the oil is collateral contamination, including the transfer of oil via workers' boots, Kirby said.
"BP hasn't put cleaning stations at all the exits [to the beach], as required by federal law," he said. "People ... go back to the parking lot and scrape off [the oil]. Other people step in the brown gunky stuff," and the oil contamination spreads.
In a trench dug by a University of South Florida Coastal Research Lab team, layers of oil-stained sand light up orange under ultraviolet light. Clean sand appears violet.
According to graduate student Kirby, UV light could help cleanup crews pinpoint hard-to-see oil that might then be treated with oil-eating bacteria.
"You could drive up the beach and dig a trench"—like the one seen above—"and see if you get layers of orange sand, and spray [bacteria] there to eat the oil."
Some scientists, however, warn that encouraging bacterial growth could upset a beach's ecological balance.
Photographs by Chris Combs, National Geographic
Published July 8, 2010
Although hydrocarbons have long been known to fluoresce, or glow, under ultraviolet light, this may be the first time the technology has been used outside a lab to spot oil.