FIGURE 2-9 Relative average, annual input (1990-1999) of petroleum hydrocarbons (kilotonnes) to North American (A) and worldwide (B) marine environment from sources associated with the consumption of petroleum.

offshore facilities, and marine vessels. Because of their relatively high volatilities and low solubilities, only a small fraction (about 0.2 percent) of VOC released to the marine atmosphere are deposited on the ocean surface. It is estimated that total deposition of petroleum hydrocarbons resulting from VOC release is 21,000 tonnes per year into North American waters and 52,000 tonnes per year, worldwide. The inputs represent estimates of the wet and dry aerosol deposition and gas absorption. Although the net loadings of total petroleum hydrocarbons are negative, due to outgassing of the lighter weight fraction, it is important to note that this category contributes 10 percent of the PAH loadings to the sea. It is difficult to evaluate the impacts, however, because very little is known about the role that air-sea interactions play on the long-term fate of volatile petroleum hydrocarbons. It will be necessary to first obtain a better understanding of the likely concentrations before potential impacts can be evaluated.

Purposeful Jettisoning of Aircraft Fuel

With the expansion of aircraft travel during the past two decades, as well as international flights into and out of North America, the release of unexpended fuel over the coastal ocean has become an increasing source of petroleum hydrocarbons in the marine environment (Table 2-2). The two major sources of aircraft releases are deliberate discharge due to emergency conditions aboard the aircraft (emergency jettisoning) and normal operational releases including the release of partially burned fuel in inefficient engines or inefficient operating modes and the emptying of fuel injection bypass canisters. Modern aircraft have takeoff weights that exceed their landing weights, sometimes by as much as 150 tonnes. Emergency jettisoning of fuel is infrequent but not rare. Reporting such releases is required but is not enforced or monitored. To avoid jettisoning fuel over residential areas, most releases of this type occur over preassigned areas with little human habitation, commonly lakes or coastal waters offshore of coastal airports. It is estimated that 1,500 tonnes of petroleum per year are released over the marine environment in North America and 7,500 tonnes per year worldwide from this source.

Trends in Consumption-Related Inputs

The spatial distribution of consumption-related inputs into North American waters reflects the regions where refinery production and urban areas are highest, namely the northeast corridor, with 39 percent of the consumption-inputs, and the Gulf of Mexico with 16 percent of the consumption-related inputs (see Chapter 3). The distribution also reflects the dominance of land-based inputs into coastal waters.

Over half of the land-based inputs for North America are estimated to occur in the nearshore region between Maine and Virginia, a region rich in estuarine and coastal resources. Land-based sources are generally the largest single source of oil input to the sea for all coastal regions, except for regions with seeps, the Arctic, and the western Pacific. Yet, the long-term fate, bioavailability, and effects of land-based inputs are poorly understood. Assessment of potential impacts is further complicated by the co-occurrence of other contaminants, such as chlorinated hydrocarbons and metals.

Consumption of oil overwhelms all other sources of oil input into coastal waters. Even for offshore waters, consump



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement