Scientists have found signs of an oil-and-dispersant mix under the shells of tiny blue crab larvae in the Gulf of Mexico, the first clear indication that the unprecedented use of dispersants in the BP oil spill has broken up the oil into toxic droplets so tiny that they can easily enter the foodchain.
Marine biologists started finding orange blobs under the translucent shells of crab larvae in May, and have continued to find them "in almost all" of the larvae they collect, all the way from Grand Isle, Louisiana, to Pensacola, Fla. -- more than 300 miles of coastline -- said Harriet Perry, a biologist with the University of Southern Mississippi's Gulf Coast Research Laboratory.
And now, a team of researchers from Tulane University using infrared spectrometry to determine the chemical makeup of the blobs has detected the signature for Corexit, the dispersant BP used so widely in the Deepwater Horizon
"It does appear that there is a Corexit sort of fingerprint in the blob samples that we ran," Erin Gray, a Tulane biologist, told the Huffington Post Thursday. Two independent tests are being run to confirm those findings, "so don't say that we're 100 percent sure yet," Gray said.
"The chemistry test is still not completely conclusive," said Tulane biology professor Caz Taylor, the team's leader. "But that seems the most likely thing."
With BP's well possibly capped for good, and the surface slick shrinking, some observers of the Gulf disaster are starting to let down their guard, with some journalists even asking: Where is the oil?
But the answer is clear: In part due to the1.8 million gallons of dispersant that BP used, a lot of the estimated 200 million or more gallons of oil that spewed out of the blown well remains under the surface of the Gulf in plumes of tiny toxic droplets. And it's short- and long-term effects could be profound.
BP sprayed dispersant onto the surface of the slick and into the jet of oil and gas as it erupted out of the wellhead a mile beneath the surface. As a result, less oil reached the surface and the Gulf's fragile coastline. But more remained under the surface.
Fish, shrimp and crab larvae, which float around in the open seas, are considered the most likely to die on account of exposure to the subsea oil plumes. There are fears, for instance, that an entire year's worth of bluefin tuna larvae may have perished.
But this latest discovery suggests that it's not just larvae at risk from the subsurface droplets. It's also the animals that feed on them.
"There are so many animals that eat those little larvae," said Robert J. Diaz, a marine scientist at the College of William and Mary.
Oil itself is of course toxic, especially over long exposure. But some scientists worry that the mixture of oil with dispersants will actually prove more toxic, in part because of the still not entirely understood ingredients of Corexit, and in part because of the reduction in droplet size.
"Corexit is in the water column, just as we thought, and it is entering the bodies of animals. And it's probably having a lethal impact there," said Susan Shaw, director of the Marine Environmental Research Institute. The dispersant, she said, is like " a delivery system" for the oil.
Although a large group of marine scientists meeting in late May reached a consensus that the application of dispersants was a legitimate element of the spill response, another group, organized by Shaw, more recently concluded "that Corexit dispersants, in combination with crude oil, pose grave health risks to marine life and human health and threaten to deplete critical niches in the Gulf food web that may never recover."
One particular concern: "The properties that facilitate the movement of dispersants through oil also make it easier for them to move through cell walls, skin barriers, and membranes that protect vital organs, underlying layers of skin, the surfaces of eyes, mouths, and other structures."
Perry told the Huffington Post that the small size of the droplets was clearly a factor in how the oil made its way under the crab larvae shells. Perry said the oil droplets in the water "are just the right size that probably in the process of swimming or respiring, they're brought into that cavity."
That would not happen if the droplets were larger, she said.
The oil droplet washes off when the larvae molt, she said -- but that's assuming they live that long. Larvae are a major food source for fish and other blue crabs -- "their siblings are their favorite meal," Perry explained. Fish are generally able to excrete ingested oil, but inverterbrates such as crabs don't have that ability.
Perry said the discovery of the oil and dispersant blobs is very troubling -- but not, she made clear, because it has any impact on the safety of seafood in the short run. "Unlike heavy metals that biomagnify as they go up the foodchain, oil doesn't seem to do that," she said. Rather, she said, "we're looking at long-term ecological effects of having this oil in contact with marine organisms."
Diaz, the marine scientist from William and Mary, spoke at a lunchtime briefing about dispersants on Capitol Hill on Thursday.
Dispersant, he explained, "doesn't make the oil go away, it just puts it from one part of the ecosystem into another."
In this case, he said, "the decision was to keep as much of the oil subsurface as possible." As a result, the immediate impact on coastal wildlife was mitigated. But the effects on ocean life, he said, are less clear -- in part because there's less known about ocean ecosystems than coastal ones.
"As we go further offshore, as the oil industry has gone offshore, we find that we know less," he said. "We haven't really been using oceanic species to assess the risks, and this is a key issue."
(Similar concerns have been expressed about the lack of important data that would allow scientists to accurately assess the effects of the spill on the Gulf's sea turtles, whose plight is emerging as particularly poignant.)
Diaz warned of the danger posed to bluefin tuna -- and also to "the signature resident species in the Gulf, the shrimp." He noted that all three species of Gulf shrimp spawn offshore before moving back into shallow estuaries.
Diaz also expressed concern that dispersed oil droplets could end up doing great damage to the Gulf's many undersea coral reefs. "If the droplets agglomerate with sediment," he said, "they could even settle to the bottom."
Nancy Kinner, co-director of the Coastal Response Center at the University of New Hampshire, said the use of dispersants in this spill raises many issues that scientists need to explore, starting with the effects of long-term exposure. She also noted that scientists have never studied the effects of dispersants when they're injected directly into the turbulence of the plume, as they were here, or at such depth, or at such low temperatures, or under such pressure.
She also said it will be essential for the federal government to accurately determine how much oil made it out of the blown well. A key data point for scientists is the ratio of dispersant to oil, she said, and "if you don't know the flow rate of the oil, you don't know what you dispersant to oil ratio is."
After a series of ludicrous estimates, the federal government settled last month on an official estimate of about 20,000 to 40,000 barrels a day, but BP is widely expected to contest that figure and some scientists think it is still a low-ball estimate.
There seems to be no doubt that history will record that the use of dispersants was good for BP, making it harder to tell how much oil was spilled, and reducing the short-term visible impact. But what's less clear is whether it will turn out to have been good for the Gulf.
Dan Froomkin is senior Washington correspondent for the Huffington Post. You can send him an e-mail, bookmark his page; subscribe to his RSS feed, follow him on Twitter, friend him on Facebook, and/or become a fan and get e-mail alerts when he writes.