It's Not So Slick When Oil Ends Up in the Sea

About 29 million gallons of petroleum enters the oceans off North America each year, shows a new study by the National Research Council. The report finds that about 85 percent of that pollution can be blamed not on massive oil spills, but on the lesser amounts released by airplanes, swept into polluted rivers and from the largest culprits: recreational boats and runoff from the land.

The amount of petroleum released into North American and global waters is less than previously thought, the committee found. At the same time, however, new studies show that the environmental effects of a major oil spill are longer lasting than once thought and that even small amounts of petroleum can seriously damage marine life and ecosystems.

"Oil spills can have long lasting and devastating effects on the ocean environment, but we need to know more about damage caused by petroleum from land based sources and small watercraft since they represent most of the oil leaked by human activities," said James Coleman, chair of the committee that wrote the report.

"This doesn't mean we can ignore hazards from drilling and shipping, however," Coleman cautioned. "Although new safety standards and advances in technology reduced the amount of oil that spilled during extraction and transport in the last two decades, the potential is still there for a large spill, especially in regions with lax safety controls."

About 47 million gallons seep naturally from the seafloor into the North American oceans, more than all human sources of petroleum pollution combined. That puts North America in a better position than the world as a whole: worldwide, about 210 million gallons of petroleum enter the sea each year from human caused petroleum sources, with an additional 180 million gallons coming from natural seepage, the report says.

Of the human caused petroleum pollution entering the oceans around North America, less than eight percent comes from oil tanker or pipeline spills, says the report by the National Academies' National Research Council (NRC), titled "Oil in the Sea: Inputs, Fates, and Effects."

The report, which relies on data from a variety of sources, is said to be far more accurate than the NRC's last such assessment in 1985.

Oily Waters

Oil slicks visible from the air and birds painted black by oil get the most public attention, but it is consumers of oil -- not the ships that transport it -- who are responsible for most of what finds its way into the ocean, the NRC says.

Oil exploration and extraction are responsible for only three percent of the petroleum that enters the sea, with their effects concentrated where oil drilling rigs are at work in the Gulf of Mexico and in waters off southern California, northern Alaska, and eastern Canada.

The bulk of the 29 million gallons from humanmade sources comes from individually small source that, combined, account for about 25 million gallons of ocean petroleum pollution.

For example, oil runoff from cars and trucks is increasing in coastal areas where the population is growing and roads and parking lots are expanding. More than one half of the land based oil contamination along the North American coastline occurs between Maine and Virginia, where there are dense seaside populations, many cities, several refineries, and high energy use, the report notes.

Rivers polluted by oil in wastewater or the improper disposal of petroleum products are also a major source of oil entering the sea.

Older two stroke engines still found on many recreational boats and jet skis were purposely designed to discharge gasoline and oil. Land runoff and recreational boating account for nearly three-quarters of the petroleum released into the sea each year through human consumption.

Other sources of oil from human activities include military and commercial jets that occasionally jettison excess fuel over the ocean and ships that release oil from their engines while in port or at sea.

The impact of an oil spill on marine life is not directly related to the size of the spill, since even a small spill in an ecologically sensitive area can have long term impacts, the NRC found. A spill's influence also depends on the type and amount of toxics present in the petroleum product being released.

The riskiest toxics are a class of organic compounds known as polycyclic aromatic hydrocarbons, or PAHs. Growing evidence suggests that PAHs and other toxic compounds can have adverse effects on marine species even at very low concentrations. This means chronic releases from runoff and recreational boating may inflict more damage than previously thought, and that the effects of large spills may last as long as residual oil persists in the area.

Gulf of Mexico Impacted

The Gulf of Mexico is the most heavily impacted of North America's ocean waters, the NRC learned. About 20 percent of the land based petroleum entering North American coastal waters ends up in the Gulf of Mexico.

The Gulf also receives most of the oil and gas that is emitted by recreational boats and jet skis, and oil drilling rigs concentrated in the Gulf spill thousands of gallons each year.

The amount of petroleum released during oil drilling has dropped in recent years, but the threat of a spill cannot be ignored, the NRC warns. The report recommends that the U.S. Minerals Management Service promote extraction techniques that minimize accidental or intentional releases of petroleum.

Other federal agencies, including the Department of Transportation and the U.S. Environmental Protection Agency (EPA) should also continue to work with state environmental agencies and industry to minimize the potential for spills from pipelines and other coastal petroleum facilities.

While new shipping standards have helped reduce oil spills and deliberate discharges from tankers and other ocean going vessels, about 2.7 million gallons of petroleum still spill into North American waters while being transported to market. The report cautions that large tanker spills are still possible, particularly in areas without stringent safety procedures and inspections.

To better monitor how much oil consumers and industry are depositing in the ocean, the NRC recommends that federal agencies work with state and local environmental bureaus to develop a system for documenting sources of runoff. The report also calls on the EPA to continue efforts to phase out older, inefficient two stroke engines, which power many jet skis and other small watercraft.

The report also says federal ocean management agencies should try to develop more accurate techniques for estimating the amount of oil that seeps into the ocean from geologic formations beneath the seafloor. This would help researchers distinguish the effects of petroleum released by natural processes versus human activities, and study how marine life responds to the introduction of oil.

Altered Ecosystems

Where oil seeps naturally into the ocean, local marine ecosystems have been altered, the report says. For example, in seepage areas in the Santa Barbara Channel off California, there is little biodiversity, with just bacteria and a few invertebrate species surviving in the petroleum slurry.

Research conducted in the wake of the EXXON Valdez spill in 1989 shows that large oil spills can be devastating to the marine environment. They kill fish, mammals, birds and their offspring, destroy plant life, and reduce the food supply for organisms that survive.

Spills also disrupt the structure and function of marine communities and ecosystems, although more research is needed to better understand how spills affect overall populations, the NRC says.

Less is known about how chronic releases from sources such as land runoff and inefficient two stroke engines on boats and jet skis affect marine ecology. The report calls for the federal government, in cooperation with academia and industry, to launch a major research effort aimed at better understanding how chronic releases of petroleum affect the marine environment, particularly when organisms in already polluted waters are exposed to the multiple toxics found in oil.

The NRC report is available online at


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