Oil and Pollution in the Ocean

The Ocean Studies Board has summarized several past reports on the impact of oil and other pollutants in the ocean in their Ocean Science Series booklet, Pollution in the Ocean, the PDF of which can be found here.

The 1989 oil spill from the grounding of the oil tanker Exxon Valdez, still the largest such spill in U.S. history, is infamous for the devastation it caused to the fragile marine wildlife in Alaska's Prince William Sound. The tanker spilled approximately 11 million gallons of its 53-million-gallon cargo of crude oil, killing an estimated 900 bald eagles, 250,000 seabirds, 2,800 sea otters, 300 harbor seals and uncounted fish and invertebrates. Massive cleanup efforts removed much of the visible crude oil within a year, but the slow release of the remaining oil has continued to affect populations of local marine plants and animals to this day.

Although alternative energy sources are being pursued, oil is expected to remain the dominant fuel for at least the next couple of decades. Energy demands continue to rise as population increases and the developing world becomes more industrialized. Worldwide petroleum consumption is projected to rise sharply over the next few decades, with the largest rate of growth in China, India, and other developing Asian nations.

The National Research Council report Oil in the Sea III: Inputs, Fates, and Effects (2003) developed a new methodology for estimating petroleum inputs to the sea from both natural and human sources. Oil inputs from human activities are categorized as those that originate from: (1) petroleum extraction, exploration, and production activities; (2) petroleum transportation, including tanker spills and (3) petroleum use, including runoff from highways and discharges from recreational vehicles.

Although people often associate oil in the ocean with tanker accidents, natural seeps are the largest single source of oil in the sea, accounting for about 60 percent of the total in North American waters and 45 percemt worldwide. Seeps form when crude oil oozes into the water from geologic formations beneath the seafloor. Oil and gas extraction activities are often concentrated in regions where seeps form.

Oil SourcesThese pie charts show the relative contribution of the average, annual releases (1990- 1999) of oil into the marine environment from natural seeps and from human activities associated with the extraction, transportation, and use of oil.

New technologies have reduced oil pollution from ships and platforms. Historically, oil and gas exploration, petroleum production, and transportation-related spills have been significant sources of oil in the oceans. The second-largest marine spill in the world was a 1979 "blowout" of a Mexican exploratory oil well that released about 140 million gallons of crude oil into the open sea in the southern Gulf of Mexico. During the past decade, however, improved production technology and safety training of personnel have dramatically reduced both blowouts and daily operational spills. Today, accidental spills from platforms represent about 1 percent of petroleum discharged in North American waters and about 3 percent worldwide.

Although the amount of oil transported over the sea continues to rise, transportation-related spills are down. The U.S. Oil Pollution Act of 1990, enacted in response to the Exxon Valdez disaster, required older vessels to be phased out. Most tankers now have double-hulls or segregated tank arrangements that dramatically reduce spillage. Transportation spills now account for less than four percent of the total petroleum released in North American waters and less than 13 percent worldwide.

Petroleum runoff and recreational vehicle discharge have a major environmental impact. The conclusion of Oil in the Sea III, perhaps surprising to many, is that oil from individual cars and boats, lawn mowers, jet skis, marine vessels, and airplanes contribute the most oil pollution to the ocean. This includes land runoff from oil slicks on urban roads and hydrocarbons deposited from the atmosphere. According to the report's estimates, use-related oil pollution dwarfs that from oil and gas production activities, accounting for about 87 percent of the oil from human activity in North American waters.

Advances in technology are helping to reduce inputs of oil from vehicles. For a long time, some recreational vehicles, for example, outboard motorboats, used inefficient "two-stroke engines" that discharged significant amounts of oil into coastal environments. These engines began to be replaced with more efficient engines in 1990 when the U.S. Environmental Protection Agency (EPA) regulated "non-road engines" under the Clean Air Act.

Clean-up strategies require careful study. There are no easy solutions to cleaning up oil spills. Available methods include the use of biological agents that help break down the oil, use of materials that absorb oil, and gelling agents that make oil easier to skim from the surface. People also physically clean up spills by using high-pressure water hoses on shores and cleaning oil off of animals.

The National Research Council report Understanding Oil Spill Dispersants: Efficacy and Effects (2005) assesses the scientific questions related to the use of dispersants, a group of chemicals that act like soap to help dilute large oil spills. They work to reduce the oily contamination of wildlife and shoreline habitats by allowing the oil to be dispersed into the surrounding waters. However, in semi-enclosed coastal areas, the oil may not be diluted sufficiently by dispersants to reduce its toxicity to marine life.

The report concludes that decisions about whether and when to use dispersants require a very site-specific assessment of a complex array of variables, including the type and volume of the oil spill, and the weather, water depth, degree of turbulence, and relative abundance and life stages of marine species in the region. The report recommends that relevant state and federal agencies, industry, and international partners develop and implement focused studies to support decision making about the use and anticipated effectiveness of dispersants for a given spill.

The impact of an oil release depends more on its location than its size. Similar to the real estate maxim, the impact of oil is not so much about the amount released but more about the "location, location, location." Even a relatively small amount of petroleum can seriously harm marine life and habitat if it occurs in an area where the oil cannot be contained or dispersed. Unfortunately, many spills take place in coastal areas that are home to sensitive ecosystems such as mangroves and salt marshes that support a wide range of fish, birds, and animals—some of them endangered. In addition, car runoff and recreational vehicle discharges can occur in sensitive coastal environments. More than half of the oil pollution in North America is estimated to flow to coastal waters between Maine and Virginia, a region with densely packed urban areas.

Other NRC reports that also relate to oil in the ocean include:

Spills of Emulsified Fuels: Risks and Responses (2001)

The Oil Spill Recovery Institute: Past, Present, and Future Directions (2003)