WASHINGTON - A surprisingly small number of scientists have studied the impacts of the oil spill resulting from the 1979 blowout at the Ixtoc I oil rig in the Gulf of Mexico. Wes Tunnell, who first studied the spill's effects in July and August of 1980 and has returned many times since, is one of the few exceptions.

A surprisingly small number of scientists have studied the impacts of the oil spill resulting from the 1979 blowout at the Ixtoc I oil rig in the Gulf of Mexico. (photo: Ixtoc I oil well blowout after the platform Sedco 135 burns and sinks/NOAA) Days after speaking to IPS in June, he flew back to Veracruz to see what remnants, if any, are still present from the disaster - the largest accidental oil spill in history before the spill resulting from the Apr. 20 blowout at the Deepwater Horizon rig eclipsed that record this summer.

"We're going to do a really good search to see if there's any [oil remnants] left or if they're all gone, just to fill in the story," Tunnel, a biologist at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University in Corpus Christi, said in June.

Later that week, he was snorkelling in Enmedio reef, north of Veracruz, where he has watched the tar mats that settled there in 1979 slowly degrade over the decades.

"So I pretty well knew where the [tar] was," he told IPS in a phone interview. "Instead of being a foot thick like it was back in 1979, though, it was about two inches thick."

But when he picked up a piece in shallow water and broke it open, he could still see the shininess inside and the smell of petroleum. "It kind of surprised me. It's kind of inert on the outer edge but you can still see or smell the petroleum on the inside," Tunnell said.

On his next trip, in July, Tunnell went to mangrove forests along the western Yucatan - the first time he or anyone has studied the spill's effects there since there were no roads leading to the area when the Ixtoc spill occurred, he says.

There, he found a landscape not unlike that near where the brunt of the Deepwater Horizon spill's impact is likely to be felt. "All that open marsh just faces the open Gulf of Mexico, so it's kind of the tropical counterpart of the eastern side of the Mississippi Delta," Tunnell says.

After some searching, his team again found tar, about three-quarters of an inch thick, that when cut open unlocked the shininess and smell of petroleum.

What effects might these crusted-over oil remnants be having? Tunnell thinks there is no impact once several inches of shell and sand build up on the tar found in the reefs. And in the mangroves, he even observed roots "going down through where the tar was."

But the picture may be a bit more complicated for the mangrove habitat. He describes open areas in the vegetation - an anomaly in the normally dense thicket of branches and roots.

He and his team went into one of those open areas and found something that looked like peat, "but you wouldn't typically find that in a mangrove swamp, so I think it was probably degraded oil," he says. Upon further searching, they found another three-quarters-of-an-inch-thick band of tar.

Without further sampling, though, it is impossible to say whether that tar is left over from Ixtoc or another, smaller, more recent spill.

Some of the other evidence of impacts Tunnel's team encountered are as compelling as they are anecdotal.

The researchers did not see any mangrove oysters in the areas they visited, for instance, and several fishermen said the oysters had died following Ixtoc and never came back. One old fisherman, however, said he knew where some were.

"While he ate them, they tasted fine, but afterwards, a burp would have a taste or smell of oil," Tunnell said, though he notes that thirty-year old oil would not be that aromatic and that the taste must come from a more recent spill.

Their last stop was the shore south of Campeche. There, they found small patches of tar along the rocky shore, about three feet above the water line. In the town of Champoton, a 78-year-old spear fisher told them how he used to catch plenty of grouper and snapper in the days before Ixtoc. Even though only a small amount of oil reached that area in 1979, his mask and body would get covered in a film of oil. The spear fisher found that dead fish were washing ashore and stopped fishing.

But Tunnell cautions that there is wide variation in the stories fisher-folk tell along the coast from Veracruz to Campeche. "Some of them said it didn't affect them in any way, some said it took 2 years for the fish to come back, some said it took four to five years. One guy said it took 20 years," he said. "You don't know who to believe and it's just really unfortunate we didn't have any scientific data or sampling from the area to really prove the effects."

As for the Ixtoc's relationship to Deepwater Horizon, he surmises that so much dispersant was used on the oil that the marshes on the U.S. gulf coast would receive a "medium oiling" as opposed to Ixtoc's "heavy oiling" - in which mats of oil over a foot thick washed up. But the dispersants, of course, add a further layer of unknowns to the ecological legacy of the Deepwater Horizon spill.

For Ixtoc, though, the final chapters are finally nearing completion. Tunnell is sufficiently convinced that the tar he found on the reefs and rocky shore are from the Ixtoc spill and that those have degraded steadily over time, most quickly in areas with lots of waves and wind. All that remains is to determine whether the tar from mangroves is from Ixtoc or a more recent spill. The samples are currently being analysed at labs in Mexico.