The timing could not be worse for the bluefin tuna. The majestic, deepwater giant — threatened by overfishing — had just lost a bid for protection as an endangered species when oil started gushing into its spawning grounds in the Gulf of Mexico.
Now, a part of the emergency response to the oil — the large-scale use of dispersants — could further imperil the species by sinking the oil beneath the Gulf’s surface and into the zone where its eggs and larvae are floating, marine biologists say.
The chemical dispersants — a standard tool in the oil cleanup business — are being used by the Deepwater Horizon response team to break up the oil offshore in hopes of preventing thick crude from wrecking delicate marshlands, mangroves and pristine beaches.
The federal government — the National Oceanic and Atmospheric Administration, the Environmental Protection Agency, the U.S. Coast Guard and other agencies — has signed off on BP’s use dispersants as a necessary part of the company’s damage-control strategy in the wake of the April 20 accident aboard the Deepwater Horizon drilling rig.
But the chemicals, which are being used in unprecedented volumes and in previously untested ways, may come with a big tradeoff, scientists say. That’s because no one can accurately predict how large the impact will be on the mammals, fish and turtles that inhabit the open ocean.
“It’s a whole new ball game,” said Ted Van Vleet, a professor of chemical oceanography in the college of Marine Science at the University of South Florida. “People are totally unsure as to how it is going to affect the ecosystems."
Dispersants themselves are toxic. But a bigger concern in the scientific community is what happens in dispersing the oil, which is far more hazardous to living creatures.
Typically, dispersant is sprayed on the surface of the water, where the oil naturally comes to rest, and works a bit like a dishwashing detergent on grease. It breaks down the slick into millions of tiny oil droplets that then become suspended below the surface, normally in the top 30 to 50 feet of the ocean. There, over the course of weeks and months, oil-eating bacteria, sunlight and wave action help break the oil down into its chemical components, which are then diluted throughout the water.
But in the interim, the oil droplets drift in the upper layer of water, where many sea creatures live and reproduce.
“The fact that (dispersants) remove oil from the surface doesn’t mean it’s not toxic,” said Van Vleet. “It moves oil down into the water column, where other marine animals are exposed to it. ... It trades one ecosystem for another.”
In the Deepwater Horizon accident, the response team has used more than 670,000 gallons of chemical dispersants as of Friday — far surpassing any previous use in the United States. Most of it has been sprayed from airplanes, but the Deepwater Horizon response team also has applied at least 55,000 gallons in a completely untested way — injecting it at the well’s leaking riser, some 5,000 feet below the surface.
While the dispersant may result in fewer oily egrets in the marsh, the bluefin is one of the creatures that may suffer greatly instead. The oil spill area overlaps with only known spawning area for one of two remaining bluefin populations. This bluefin population spends about 10 months of the year in the cold waters of the north Atlantic and then swims thousands of miles to reach an area near the Deepwater Horizon well to disseminate sperm and eggs in the warm Gulf waters between April and June. The larvae float about 10 to 15 feet below the surface in early stages of growth. No one is certain whether the oil will destroy the eggs or kill the larvae, but scientists fear that could happen.
“It is a critical habitat … and this is the most delicate life stage,” said Barbara Block, a professor at Stanford University studies bluefin tagged with sophisticated tracking devices. “The biodiversity of bluefin is at stake right now. … If we lose the year (of new bluefin) it will have a very large impact on a population of bluefin that is on the edge of extinction.”
This is the spawning ground for many other species, including marlin, swordfish and yellowfin tuna, which arrive in the summer.
Some of the chemical components distributed throughout the water will remain toxic for decades, and it's not clear what the impact could be on future generations of bluefin or other creatures — sperm whales, Bryde’s whales, offshore dolphin populations and seabirds — that fish far from shore.
Monitoring the impact of oil and dispersant chemicals on open-sea fish and other creatures is difficult, experts say, because unlike shorebirds and oysters, they are hard to count.
“It’s hard to see them,” said Lee Crockett, director of U.S. Fisheries policy at the non-profit Pew Charitable Funds environmental group. “If they die, they are on the bottom of the ocean a mile down … For bluefin and marlins, it could be several years before you see what the impact was.”
Deep sea mystery and dead zones
One of the biggest unknowns is how the dispersants might affect the environment near the well head, a mile beneath the surface. BP and the EPA have said that initial monitoring of dispersants suggests the chemicals are helping to break up the crude.
But scientists say the monitoring plan has not been made available for outside review — raising a general complaint about a lack of transparency from the oil company and the government.
And some note that little is known about the deepwater ecosystem — or how the oil and dispersants will react under extremely high water pressure, very low temperatures, limited oxygen and virtually no light. Just getting good samples at this depth is a major challenge.
“There are a bunch of things in the deep sea that we don’t know very much about,” said Ed Overton, professor in the Marine Sciences Department at Louisiana State University. “What happens if those resources are damaged? How does that affect the ecology of the Gulf? It’s a crapshoot … an educated crapshoot.”
The conditions at the bottom of the Gulf also could affect the bacteria that help break down the oil near the surface, as they are less active in cold temperatures than in the warm surface waters, and they may be less abundant in the deep.
“We know that the surface material has been degrading,” says Ralph J. Portier, professor of environmental studies at LSU. “But what about the microbial population at depth?”
If the oil on the ocean floor is not degraded by bacteria, the danger is that it will remain toxic for much longer than it would near the surface — potentially lingering for years instead of weeks or months — during which time it could be carried to deep coral reefs that provide shelter and nurseries to many species of fish.
There is a debate about the extent to which the Deepwater Horizon oil has entered the Loop Current, a warm flow that moves water — and any contaminants in it — southeast out of the Gulf, through the Florida Straits and into the Atlantic Ocean — potentially threatening the Florida Keys and other sensitive coral reef areas.
The massive use of dispersants in addition to oil may also be further depleting the water of oxygen contributing to “dead zones.”
“All chemicals do this,” said Portier. “If we poured in 400,000 or 500,000 gallons of buttermilk, we’d have a problem with oxygen,” he said.
The other unknown
The dispersant itself, while not the main concern, also is under scrutiny.
BP has used hundreds of thousands of gallons of Corexit, which is produced by Nalco, a Naperville, Ill.-based company.
About a third of the product, which is EPA approved, is a soap-like surfactant that breaks up the oil, according to Van Vleet, the chemical oceanographer. The surfactant is not considered toxic, though some studies suggest it may corrode fish eggs, made up largely of lipids, much as it dissolves oil.
Another third is a petroleum-based “carrier” that facilitates spraying. This component is somewhat toxic to plants and animals — though far less so than crude oil.
The final third of the ingredients are not publicly disclosed because the information is considered proprietary.
Shifting with the tides
On May 15, after some initial testing, the EPA and the Coast Guard approved BP’s use of dispersants at the well head, saying they had collected preliminary data showing it was helping keep some of the oil from reaching the surface.
The same day, however, The New York Times reported that a group of scientists aboard the research vessel Pelican had identified massive plumes of subsea oil — some as big as 10 miles long and 3 miles wide. The article said that scientists on the ship speculated that heavy use of dispersants had contributed to creation of the plumes.
NOAA challenged the report the next day, saying the release of the Pelican team's data was premature, that the interpretation was misleading and that there was no information connecting subsurface layers of oil with the subsea dispersants.
“NOAA continues to work closely with EPA and the federal response team to monitor the presence of oil and the use of surface and sub-surface dispersants,” said NOAA Administrator Jane Lubchenko. “As we have emphasized, dispersants are not a silver bullet. They are used to move us towards the lesser of two environmental outcomes.”
But on Thursday, the EPA issued a statement saying it had ordered BP to begin using a “less toxic” alternative to Corexit within 24 hours, even though the latter product is on a list of EPA-approved dispersants. The directive came a month after the Deepwater accident and after some 600,000 gallons of Corexit dispersants had been applied.
“Because of its use in unprecedented volumes and because much is unknown about the underwater use of dispersants, EPA wants to ensure BP is using the least toxic product authorized for use,” the agency said. “We reserve the right to discontinue the use of this dispersant method if any negative impacts on the environment outweigh the benefits.”
This is just one area in which the Deepwater Horizon oil mess has taken responders into uncharted territory.
“The science hasn’t caught up with the situation,” said Overton, the marine scientist from LSU and a member of the scientific support team for NOAA.