incompleteness of the data and the fact that the smaller spills, under 10,000 gallons (34 tonnes), comprised about 13 percent of the U.S. totals, the international spill quantities were increased by 25 percent to obtain the minimum estimate, by an additional 10 percent to obtain the best estimate, and further increased by 25 percent to obtain the maximum estimate. Results are summarized in Table E-21.

The North American and international spill estimates are combined to provide worldwide estimates (Tables 2-2 through 2-6). The best estimate for total spillage worldwide is 110,000 tonnes (30 million gallons) per year. The 1985 report (National Research Council, 1985) and the 1990 study (IMO, 1990) both used data from the International Tanker Owners Pollution Federation Ltd. (ITOPF) to estimate the quantity of oil entering the marine environment from tanker accidents. In the 1990 study, the spillage was averaged for the 10-year period from 1981 to 1989, establishing an annual average of 114,000 tonnes per year. In the 1990 report no adjustments were made for the deficiencies in the database, so care should taken when comparing these figures.

There are inputs to the sea from deliberate and continual releases of fuel from aircraft. There are two sources: deliberate discharge due to emergency conditions aboard the aircraft, and normal operation releases including the release of partially burned fuel in inefficient engines or inefficient operating modes and emptying of fuel injection bypass canisters. Modern aircraft have take-off weights exceeding their landing weights, sometimes by as much as 150 tonnes. For example, a 747 can carry as much as 220,000 L of fuel weighing about 175,000 kg or 175 tonnes. If a fully laden 747 jettisoned its fuel because it was required to return to an airport, it could dump as much as 150 tonnes of the fuel to enable it to land safely. Fuel dumping is infrequent but not rare. One airport reported on 16 fuel dumps in one year out of 7,000 flights conducted [Canadian Environmental Assess

Front Matter (R1-R12)

Executive Summary (1-4)

1. Introduction (5-18)

2. Understanding the Risk (19-62)

3. Input of Oil to the Sea (63-88)

4. Behavior and Fate of Oil (89-118)

5. Biological Effects of Oil Releases (119-158)

References (159-182)

Appendix A: Committee and Staff Biographies (183-188)

Appendix B: Definitions and Conversions (189-190)

Appendix C: National Seepage of Crude Oil into the Marine Enviornment (191-192)

Appendix D: Oil and Gas Extraction (193-202)

Appendix E: Inputs of Petroleum Hydrocarbons into the Ocean Due to Transportation Activities (203-218)

Appendix F: Inputs into the Sea from Recreational Marine Vessels (219-220)

Appendix G: Spills from Coastal Facilities (221-222)

Appendix H: Atmospheric Deposition and Air-Sea Exchange of Petroleum Hydrocarbons to the Ocean (223-232)

Appendix I: Estimating Land-Based Sources of Oil in the Sea (233-252)

Appendix J: Methods Used to Estimate PAH Loadings to the Marine Environment (253-254)

Appendix K: Regulatory Framework (255-258)

Index (259-265)