per day. Advancements in the design of engines and pumps and the fitting of containment has reduced the quantity of bilge oil generation in modern ships, and a rate of 5 gallons per day was applied for this evaluation. The number of tankers was taken from the Lloyd’s Register data for 1999, and the installed power was estimated based on the distribution of tanker sizes. Assuming 350 days per year operation, the estimated total bilge oil generation from the world’s tanker fleet is 19,200 tonnes per year. MARPOL requires that the oily water effluent be discharged overboard through an oil-water separator and oil discharge monitoring system, that is set to alarm and shut down when the oil content exceeds 15 ppm. Assuming a 15 ppm oil content for bilge discharges, it is estimated that less than 0.2 percent of bilge oil is discharged overboard. Thus, if all tankers comply with MARPOL regulations, the total worldwide bilge oil discharge would be (19,200 tonnes) × (0.002), or 38 tonnes per year.

Assumed compliance with MARPOL regulations is as follows: 99 percent of tankers greater than 125,000 DWT, 95 percent of tankers 20,000 to 125,000 DWT, and 90 percent of tankers less than 20,000 DWT. Assuming non-compliant tankers discharge 100 percent of the bilge oil into the oceans, the total calculated bilge oil discharge for both MARPOL compliant and non-compliant tankers is 1,130 tonnes per year.

According to Lloyd’s Register data there were 79,547 non-tankers above 100 GT in size operating commercially worldwide in 1999. These consisted of 38,732 commercial vessels with the main propulsion plants averaging 7,500 HP, and 40,815 other vessels with an average power of about 500 HP. Similar to tankers, a bilge oil generation rate of 5 gallons/20,000 HP was applied. Vessels between 100 GT and 400 GT, that comprise 54 percent of the non-tanker fleet, are not required to have oily water discharge equipment installed. Although these vessels are not permitted to discharge bilge effluent, it is believed that there is a significant level of non-compliance. Therefore, 15 percent of the commercial vessels and 30 percent of the other vessels were assumed not to comply with the MARPOL requirements. The total calculated worldwide bilge oil discharge for both non-compliant and compliant vessels other than tankers is 15,600 tonnes per year.

Based on 1998 data collected by INTERTANKO (unpublished), the world annual use of fuel oil for marine applications is estimated to be 130 million tonnes of heavy residual fuel oil and 40 million tonnes of distillate fuel. Heavy fuel oils contain between 1 percent and 5 percent sludge or waste oil, which cannot be burned as fuel and therefore must be disposed of by other means. A value of 1.5 percent is applied for these calculations. Diesel fuel oil does not produce any appreciable quantity of sludge and therefore is discounted from further consideration here. Thus, the total production of sludge from ships is estimated as (130 million tonnes) × (0.015), or 1,950,000 tonnes per year.

MARPOL prohibits the discharge of sludge at sea. The 1990 study estimated that 10 percent of tankers and 25 percent of non-tankers disposed of sludge at sea. Recognizing improvements in vessel operations and enforcement regimes and the increased use of shoreside waste reception facilities, for these calculations non-compliance is taken as 5 percent for tankers and 15 percent for non-tankers. On this basis, total discharge of sludge at sea is estimated at 260,000 tonnes per year.

Ballast discharges from fuel oil tanks are considered to be negligible. Placing seawater in fuel tanks as ballast water introduces contaminants into those tanks, increasing engine maintenance and the risk of malfunction. The practice is avoided whenever possible.

As shown below, the total calculated operational discharge from vessels worldwide is 272,000 tonnes. Overall, the estimated discharge has not changed significantly since the 1985 report. Discharges from machinery space bilges have declined, due to improved machinery, higher levels of compliance, and the requirements for oily water separator and monitoring systems for vessels greater than 400 GT. The estimate for sludge discharge has increased, in part due to the poorer quality of modern fuels, which results in higher sludge content.

The worldwide best estimate is 270,000 tonnes. The extent of compliance is very difficult to determine, yet it has a major influence on the estimated operational discharge. Due to the high level of uncertainty, a range from 90,000 tonnes per year (one-third of the best estimate) to 810,000 tonnes per year (three times the best estimate) was assumed.¹⁶

Based on an analysis of transit miles of ships trading in U.S. waters and the size of their power plants, the generation of bilge oil on vessels greater than 100 GT in size transiting United States waters was estimated to be 2,820 tonnes. Rec

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)