That spectacular Ixtoc 1 oil well blowout, which spilled 140 million gallons of crude oil into the Gulf of Mexico, seems to have done relatively little environmental damage.
Released in a subtropical marine environment that hastened its degradation and blown out to sea by prevailing winds, the floating oil film broke into progressively smaller pieces and eventually dissipated. Less than 1 percent of it washed ashore, although the bit that did foul beaches was a major nuisance at the time.
These findings, reported recently in Nature, have emerged from an extensive study carried out by John S. Patton and Mark W. Rigler of the University of Georgia and Paul D. Boehm and David L. Fiest of Energy Resources Company in Cambridge, Mass.
Ixtoc 1 was finally capped in March 1980. It had leaked oil for nine months, creating a spill over twice as great as the 66 million gallons released in the breakup of the tanker Amoco Cadiz off Brittany in March 1978. Unlike the tanker , which spilled its oil within a short time period onto a coast where it caused something like $1.5 billion damage, the Ixtoc well leaked oil slowly, and this was carried mainly out to sea.
The four scientists found that the mass of floating oil broke into pancakes about three inches across that were covered with a mustard-yellow skin. They contain an oily substance which the researchers call "mousse" because it resembles the chocolate dessert of that name.
This mousse tends to remain chemically similar to the original oil. However, weathering causes flakes to spall off the pancakes. These change composition and may contain embedded particles, including microscopic plants and animals. Some flakes accumulate enough debris to sink to the bottom. Others, floating on the surface, could dissolve and eventually evaporate or may form tar balls, according to Patton. Flaking also enhances microbial colonization and breakdown of the oil residue.
All told, the scientists report that the oil persists longer as pancakes than as flakes. On the other hand, flaking tends to break down the pancakes.
The oil film seems to have broken up more because of weathering than because of microbial attack, which had been thought to be a major factor in disrupting previous slicks. Once microbes begin working on the flakes, however, they can help break them down.
As Patton notes, oil is not all bad in the marine environment. "Oil spills are carbon sources," he explains. "Crude oil has many of the elements necessary for life. Thus, much of a spill will eventually pass through the food chain and will 'burn' to carbon dioxide and disappear." But he adds that "the small amount which remains as refractory tar balls will undoubtedly persist in the environment."
These findings do not imply that oil spills can be shrugged off as harmless. But they do suggest that fears of mass ive damage raised by the Ixtoc incident were premature.