MEXICO CITY — The Ixtoc 1 oil spill in Mexico's shallow Campeche Sound three decades ago serves as a distant mirror to today's BP deepwater blowout, and marine scientists are still pondering what they learned from its aftereffects.
In terms of blowouts, Ixtoc 1 was a monster — until the ongoing BP leak, the largest accidental spill in history. Some 3.3 million barrels of oil gushed over nearly 10 months, spreading an oil slick as far north as Texas, where gooey tar balls washed up on beaches.
Surprisingly, Mexican scientists say that Campeche Sound itself recovered rather quickly, and a sizable shrimp industry returned to normal within two years.
Luis A. Soto, a deep-sea biologist, had earned his doctorate from the University of Miami a year before the June 3, 1979, blowout of Ixtoc 1 in 160 feet of water in the Campeche Sound, the shallow, oil-rich continental shelf off the Yucatan Peninsula.
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Soto and other Mexican marine scientists feared the worst when they examined sea life in the sound once oil workers finally capped the blowout in March 1980.
"To be honest, because of our ignorance, we thought everything was going to die," Soto said.
The scientists didn't know what effects the warm temperatures of gulf waters, intense solar radiation, and other factors from the tropical ecosystem would have on the crude oil polluting the sound.
There were political implications as well; the spill pitted a furious shrimping industry, reliant on the nutrient-rich Campeche Sound, against a powerful state oil company betting its future in offshore drilling, particularly the continental shelf in the Gulf of Mexico it began developing in the late 1970s.
In the months after Ixtoc 1 was capped, scientists trawled the waters of the sound for signs of biological distress.
"I found shrimp with tumor formations in the tissue, and crabs without the pincers. These were very serious effects," Soto said.
Another Mexican marine biologist, Leonardo Lizarraga Partida, said the evaluation team began measuring oil content in the sediment, evaluating microorganisms in the water and checking on the biomass of shrimp species.
As the studies extended into a second year, scientists noticed how fast the marine environment recovered, helped by naturally occurring microbes that feasted on the oil and degraded it.
Perhaps due to those microbes, Tunnell found that aquatic life along the shoreline in Texas had returned to normal within three years — even as tar balls and tar mats remained along the beaches, sometimes covered by sand.
"We were really surprised," Lizarraga said. "After two years, the conditions were really almost normal."
The Gulf currents and conditions of the Ixtoc 1 spill helped. Unlike the BP blowout, which has spewed at least 5,000 barrels of oil a day, and perhaps many times that, at depths near 5,000 feet, the Ixtoc 1 oil gushed right to the surface, and currents slowly took the crude north as far as Texas, killing turtles, sea birds and other sea life.
"I measured 80 percent reduction in all combined species that were living in the intertidal zone," said Wes Tunnell, a marine biologist at the Harte Research Institute of Gulf of Mexico Studies at Texas A&M University in Corpus Christi.
While that was severe, Tunnell noted that natural oil that seeps from the seabed releases the equivalent of one to two supertankers of crude in the Gulf of Mexico each year.
"It's what I call a chronic spill," Tunnell said. "The good side of having all that seepage out there is that we've got a huge population of microbes, bacteria that feed on petroleum products in the water and on shore. So that helps the recovery time."
An expert on the biodegradation of petroleum, Rita R. Colwell, who holds posts both at the University of Maryland and Johns Hopkins University, said microorganisms are good at breaking down the short chain molecular compounds in crude.
"For the bacteria, they really chew it and release it as CO2," Colwell said. "The longer stuff that has long ring compounds, that's the stuff that remains."
A bloom in oil-consuming microorganisms turned out to be a boon to shrimp in the Campeche Sound, to the relief of the crews on the 650 shrimp boats that trawled in the sound back then.
"The shrimp fed on the bacteria. When you are making the chemical analysis of the shrimp, you obtain the fingerprint," Soto said, adding that petroleum compounds contain unique chemistry just as flora and fauna contain unique genes.
Just as a human body rallies its defenses to fight off invasive germs, Soto said, the microorganisms prevalent in warmer ocean waters help break down the crude.
"What we learned is that tropical environments have a better chance to recover equilibrium," Soto said, adding that he believes the Campeche Sound was largely back to normal "perhaps in a year and a half."
Crude oil does contain toxic compounds, known as polycyclic aromatic hydrocarbons, which aren't easily absorbed by bacteria. Scientists are still studying whether bacteria can be cultivated to break down them down.
"Fortunately, they don't bio-magnify in species as they go up the food chain. They seem to just get passed through and dropped out," Tunnell said.
Colwell, nonetheless, warned of eating shrimp harvested in the immediate area of an oil spill: "If you are eating shrimp during the current season or next season, I wouldn't recommend it."
Lizarraga, who works at the Center for Scientific Research and Higher Studies of Ensenada, on the Baja California peninsula, criticized the heavy use of chemical dispersants to break up the oil gushing from the BP spill into droplets, saying it isn't yet clear how the dispersants will affect the oil-degrading microorganisms.
In the Ixtoc 1 spill, "not so many dispersants were used," he said, allowing natural processes to take their course.
Some fundamental questions remain about the volumes of oil that microorganisms can break down in an oil spill. Tunnell said long-term comprehensive studies are rarely carried out after workers finish mopping up crude oil coating beaches.
"When its cleaned up, the studies stop," he said. "There's a lot that we don't have the real answers to."
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