Expert Report

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Even a small amount of oil in the sea can have severe effects on marine life depending on the location and timing of its release. Changes in regulations and industry practices following the Exxon Valdez spill in 1989 have helped to dramatically reduce oil inputs from petroleum transportation and extraction, but most oil that enters the sea does not come from oil exploration, extraction, or spills. In fact, 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 watercraft. This report, which is the third in a series, presents the most up-to-date estimates of major oil sources and makes recommendations to help policy-makers prioritize next steps for prevention and response.

Key Messages

  • Land runoff and two-stroke engines account for nearly three quarters of the petroleum introduced to North American waters from activities associated with petroleum consumption. This is particularly significant because, by their very nature, these activities are almost exclusively restricted to coastal waters.
  • Activities associated with oil and gas exploration or production introduce, on average, an estimated 3,000 tonnes (880,000 gallons) of petroleum to North American waters, and 38,000 tonnes (11,000,000 gallons) worldwide, each year.
  • Although the VOC released during the extraction, transportation, and consumption of petroleum appear to have short residence times in the marine environment, their impact on air quality may be significant.
  • Although there is now good evidence for the toxic effects of oil pollution on individual organisms and on the species composition of communities, there is little information on the effects of either acute or chronic oil pollution on populations or on the function of communities or ecosystems.
  • Areas surrounding natural seeps are extremely important natural laboratories for understanding crude oil behavior in the marine environment, as well as how marine life responds to the introduction of petroleum.
  • In North America, the largest and best known natural seeps appear to be restricted to the Gulf of Mexico and the waters off of southern California, regions that also have extensive oil and gas production.
  • Much more needs to be learned about how petroleum interacts with marine sediment and how it is transported or dispersed by ocean and coastal processes such as waves and currents.
  • Natural seepage of crude oil from geologic formations below the seafloor to the marine environment off North America is estimated to exceed 160,000 tonnes (47,000,000 gallons), and 600,000 tonnes (180,000,000 gallons) globally, each year.
  • Oil and gas extraction activities are often concentrated in regions where seeps form.
  • Releases associated with the consumption of petroleum make up nearly 70 percent of the petroleum introduced to the world�s oceans from anthropogenic sources and nearly 85 percent of the total petroleum input from anthropogenic sources to North American waters.
  • Releases from oil and gas extraction can include accidental spills of crude oil from blow outs, surface spills of crude from platforms, or slow chronic releases associated with the disposal of water produced from oil or gas-bearing formations during extraction (referred to as produced water) or oil-bearing cuttings created during the drilling process.
  • Releases that occur during the consumption of petroleum, whether by individual car and boat owners, non-tank vessels, or runoff from increasingly paved urban areas, contribute the vast majority of petroleum introduced to the environment through human activity.
  • Research on the cumulative effects of multiple types of hydrocarbons in combination with other types of pollutants is needed to assess toxicity and organism response under conditions experienced by organisms in polluted coastal zones
  • Spills from transportation activities may release a wide variety of petroleum products (not just crude oil) each of which behaves differently in the environment or contain different concentrations of toxic compounds like PAH.
  • The estimates for land-based sources of petroleum are the most poorly documented, and the uncertainty associated with the estimates range over several orders of magnitude.
  • The potential for large spills from aging pipelines and other coastal facilities is especially disconcerting, as these facilities often lie near sensitive coastal areas.
  • The seepage of crude oil to the environment tends to occur sporadically and at low rates.
  • The threat posed by even a minor spill in a sensitive area remains significant.
  • These compounds rapidly volatilize into the atmosphere and thus appear to have a short residence time in marine waters.
  • These releases are concentrated in areas of petroleum production in the Gulf of Mexico and the waters off of southern California, northern Alaska, and eastern Canada.
  • These releases from petroleum extraction activities that take place near shore or even on shore can pose significant risks to sensitive coastal environments
  • These spills can occur anywhere.
  • Unlike other sources, inputs from consumption occur almost exclusively as slow, chronic releases. Furthermore, because the vast majority of the consumption of petroleum occurs on land, rivers and waste- and stormwater streams represent the most significant source of petroleum to the marine environment.
  • VOC are also released from tankers underway or involved in loading and offloading activities, and they contribute to the total load of hydrocarbons input to the sea.
  • Volatile organic compounds (VOC) commonly associated with, or dissolved in, petroleum are released during extraction activities and also contribute to the total load of hydrocarbon input to the sea. These compounds, however, rapidly volatilize into the atmosphere and thus appear to have a short residence time in marine waters.
  • With a few notable exceptions (e.g., the Exxon Valdez, North Cape, and Panama spills), there have been a lack of resources to support studies of the fates and effects of spilled oil. Much of what is known about the fate and effect of spilled oil has been derived from a very few, well-studied spills.
  • through anthropogenic activities to North American waters and less than 22 percent worldwide.