be zero, with illegal discharges reported as spills). A wide range of crude oils and refined products are included in these inputs.
As with spills associated with extraction of petroleum, the impacts from transportation-related spills are very much linked to the spill conditions and location. The release of petroleum over short periods can have significant impacts, depending on the location, time of year, environmental conditions, and effectiveness of containment and recovery actions. Depending on the petroleum type, loss to the atmosphere due to evaporation and volatilization will account for 10 percent (for heavy fuels) to 80 percent (for light, refined products) of the spill volume. The inputs do not account for any oil removal during the response, although recovery of 20 percent of the spill volume is considered to be a good effort. Much has been learned in the last decade about the fate and effects of oil spills, yet many questions remain, particularly about sub-lethal effects associated with oil residues remaining once cleanup efforts have been terminated.
Once petroleum hydrocarbons have been extracted, transported to refineries, and refined, they are delivered to the consumer. The six major sources of petroleum hydrocarbon releases to the marine environment include land-based sources (river discharge and runoff), two-stroke vessel discharge, non-tank vessel spills (≥100 GT), operational discharges (both ≥ 100 GT and < 100 GT), gross atmospheric deposition, and aircraft dumping. The volumes of oil and other petroleum products from spills or releases associated with consumption dwarf input from all other anthropogenic activities (Figure 2-2A and 2-2B). As mentioned earlier, North America consumes the vast majority of energy worldwide; thus, discharge of by-products from various energy uses remains high for North American waters.
Land-based river-runoff discharges are the largest anthropogenic source of petroleum hydrocarbon pollution in the marine environment, accounting for 54,000 tonnes per year in North American waters and 140,000 tonnes worldwide (Table 2-2, Figures 2-9 and 2-10). This input is quite significant because a high percentage is discharged directly into coastal and estuarine waters. Major sources include urban runoff, petroleum refinery wastewater, municipal wastewaters, and non-refining industrial wastes. As the population of coastal regions increase (Fig. 2-11), urban runoff has become more polluted by expansion in the numbers of cars, asphalt-covered highways and parking lots, municipal wastewater loads, and the use and improper disposal of petroleum products.
During periods of economic growth in North America, the population spends larger sums of money on recreational marine craft and has more free time to use these small vessels. Recreational use of two-stroke engines in many outboard motors and personal watercraft (e.g., jet skis) has increased significantly during the past two decades. In 1990, heightened awareness of the large numbers and the design inefficiencies of these engines led the U.S. Environmental Protection Agency to begin regulating the “non-road engine” population under the authority of the Clean Air Act. Inputs from use of two-stroke engines in coastal waters are large in areas of high coastal populations. Discharges from two-stroke engines account for an estimated 5,600 tonnes per year into North American waters (data were insufficient for worldwide estimates; Table 2-2, Figure 2-9). The bulk of the input is gasoline, which is thought to rapidly evaporate and volatilize from the water surface. However, very little is known about the actual fate of the discharge. Questions regarding the amount of petroleum residing in the water column or along the surface for biologically significant lengths of time remain. Together, land-based runoff and discharges by two-stroke engines account for nearly 22 percent of the total petroleum released to the marine environment in North America by all sources (collectively, they represent nearly 64 percent of the total anthropogenic load). This is of particular concern because these discharges occur entirely in coastal environments.
Spills from non-tank vessels ≥100 GT represents a relatively small amount of discharge, contributing 1,200 tonnes per year in North America and 7,100 tonnes worldwide (Table 2-2). In contrast, non-tank vessel operational discharges are a major source of petroleum hydrocarbons delivered to global marine waters, which is estimated to be 270,000 tonnes and represents the second highest input of petroleum hydrocarbons into the marine environment (Table 2-2). These sources include machinery space bilge oil, fuel oil sludges, and oily ballast. The International Convention for Prevention of Pollution from Ships (MARPOL 73/78) regulates, worldwide, the design, construction, and operation of commercial vessels of 100 gross tonnes or more, with the goal of reducing or eliminating the discharge of oil and other pollutants into the sea. These regulations have significantly decreased the load, and in 1990, compliance with MARPOL 73/78 ranged from 80 to 99 percent (by class).
VOC that enter the marine environment are generated primarily by sources such as internal combustion engines, power generating plants, industrial manufacturing facilities,