Ixtoc I Oil Spill - Long-term Effects

Long-term Effects

The oil that was lost during the blow-out polluted a considerable part of the offshore region in the Gulf of Mexico as well as much of the coastal zone, which consists primarily of sandy beaches and barrier islands often enclosing extensive shallow lagoons.

The oil on Mexican beaches that the authors observed in early September was calculated to be about 6000 metric tons. Based on reports from various groups and individuals, five times that figure is thought to represent a fair estimate of what had landed on Mexican beaches. Investigations along the Texas coast show that approximately 4000 metric tons of oil or less than 1 percent was deposited there. The rest of the oil, about 120,000 metric tons or 25 percent, sank to the bottom of the Gulf.

The oil had a drastic impact on the littoral crab and on the mollusk fauna of the beaches which were contaminated. The populations of crabs, e.g. the ghost crab Ocypode quadrata, were almost totally eliminated over a wide area. The crab populations on coral islands along the coast were also reduced to only a few percent of normal about nine months after the spill.

One study found that the most persistent issues were pollution of estuaries and coastal lagoons lining the bay, and especially the effects on breeding and growth of several food fish species.

Juan Antonio Dzul was a teenager when the Ixtoc 1 oil rig collapsed in June 1979 in the Gulf of Mexico, 70 miles (100 km) from the fishing town of Champotón where he grew up and still lives. The memory of the huge spill that followed is etched on his mind. "The oil covered the reefs and washed up on the shore. Fish died and the octopuses were buried under the oil that filled the gaps between the rocks where they live," he recalled in a phone interview. “Even today you can find stains on rocks a few centimetres deep, and if you stick something metal in them the smell of oil still escapes.”

The oil washed ashore, a foot deep in some places, as it was pushed north by prevailing winds and currents until it crossed the Texas border two months later and eventually coated almost 170 miles (270 km) of US beaches. The beach that caused most international concern in Mexico was Rancho Nuevo, a key nesting ground for critically endangered Kemp's Ridley sea turtles which had already lumbered up the sand in their hundreds to lay eggs. By the time the eggs hatched, the oil was lapping at the shore.

Fishing was banned or restricted by Mexican authorities in contaminated areas north and south of the well. Fish and octopus catches dropped by 50 to 70% from the 1978 levels. Some larger species with longer life spans took years to recover from the Ixtoc spill. It wasn't until the late-1980s that the population of Kemp's Ridley turtles, which lay a couple of hundred eggs a year, as opposed to the millions produced by shrimp, started recovering. The immediate losses from an oil spill continue to ricochet through larger species for generations.

There is much less information on the impact of the Ixtoc I spill on benthos (bottom dwellers). The best studies were on the Texas coast over 1000 km from the spill. Massive kills can occur when oil reaches the benthos in sufficient quantity. The only indication of a massive kill may be the remains of the dead organisms, but if they lack hard parts there will be little evidence.

A report prepared for the US Bureau of Land Management concluded with respect to the spill's effect on US waters:

In spite of a massive intrusion of petroleum hydrocarbon pollutants from the Ixtoc I event into the study region of the South Texas Outer Continental Shelf during 1979-1980, no definitive damage can be associated with this or other known spillage events (e .g ., Burmah Agate ) on either the epibenthic commercial shrimp population (based on chemical evidence) or the benthic infaunal community. Such conclusions have no bearing on intertidal or littoral communities, which were not the subject of this study.