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May 23, 2002

Tanker spills not the major source of ocean pollution
it is consumers of oil -- not the ships that transport it -- who are responsible for most petroleum that enters U.S. waters says a new report fromthe National Academies' National Research Council.

Nearly 85 percent of the 29 million gallons of petroleum that enter North American ocean waters each year as a result of human activities comes from land-based runoff, polluted rivers, airplanes, and small boats and jet skis, says the report. Less than 8 percent comes from tanker or pipeline spills. Oil exploration and extraction are responsible for only 3 percent of the petroleum that enters the sea. Another 47 million gallons seep into the ocean naturally from the seafloor.

"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 M. Coleman, chair of the committee that wrote the report, and Boyd Professor, Coastal Studies Institute, Louisiana State University, Baton Rouge. "This doesn't mean we can ignore hazards from drilling and shipping, however. 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."

To better monitor how much oil consumers and industry are depositing in the ocean, federal agencies should work with state and local environmental bureaus to develop a system for documenting sources of runoff, the report says.

In addition, the U.S. Environmental Protection Agency should continue efforts to phase out older, inefficient two-stroke engines, which power many jet skis and other small watercraft.

The committee's calculations of how much petroleum is added to the sea each year were based on data from a variety of sources. The accuracy of these data is much improved since the Research Council's last assessment in 1985. 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 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 report says.

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 to accommodate it. Rivers polluted by oil in waste water or the improper disposal of petroleum products are a significant source of oil in the sea as well. In addition, 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 25 million gallons of petroleum released into the sea annually through the consumption of petroleum.

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.

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 says.

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.

The U.S. Coast Guard and U.S. Maritime Administration should work with shipowners domestically and internationally through the International Maritime Organization to expand and enforce shipping standards that already have contributed to a decline in oil spills and operational discharges, the report adds.

Annually, about 2.7 million gallons of petroleum spill into North American waters while being transported to market. However, the report cautions that large tanker spills are still possible, especially in areas without stringent safety procedures and inspections. The U.S. Department of Transportation and EPA also should continue work with state environmental agencies and industry to assess and minimize the potential for a significant spill from pipelines and other coastal facilities.

The exploration and extraction of oil and natural gas introduces 880,000 gallons of petroleum to North American waters each year. These leaks are 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 amount of petroleum released during extraction has dropped significantly, but the threat of a spill cannot be ignored, the report says. To that end, the U.S. Minerals Management Service should continue to work with state environmental agencies and industry to promote extraction techniques that minimize accidental or intentional releases of petroleum.

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.


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 adverse effects, the report says. A spill's influence also depends on the type and amount of toxins present in the petroleum product being released. The riskiest toxins 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.

Significant research has been conducted in recent years -- particularly in the wake of the EXXON VALDEZ spill -- confirming 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 report says. To aid this research, a federal rapid-response team should be created to rush to oil spills and collect real-time data.

Where oil seeps naturally into the ocean, local marine ecosystems have been significantly altered, the report says. For example, in seepage areas in the Santa Barbara Channel off California, there is little diversity among organisms, which consist mainly of bacteria and a few invertebrate species.

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, especially when organisms in already polluted waters are exposed to the multiple toxins found in oil. Studying the small, chronic releases that occur at oil-drilling sites may aid this effort.

Worldwide, about 210 million gallons of petroleum enter the sea each year from the extraction, transportation, and consumption of crude oil and the products refined from it, with an additional 180 million gallons coming from natural seepage, the report says.

The study was sponsored by the U.S. Minerals Management Service, U.S. Geological Survey, U.S. Department of Energy, U.S. Environmental Protection Agency, National Oceanic and Atmospheric Administration, U.S. Coast Guard, U.S. Navy, American Petroleum Institute, and the National Ocean Industries Association. A committee roster follows.

The report OIL IN THE SEA: INPUTS, FATES, AND EFFECTS is available on the Internet at

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