Changes in groupings of subcategories make direct comparison with 1985 study impossible.

Land-based (river and runoff)

Municipal & industrial wastes

Significant differences in data quality, assumptions, and methodology make comparison meaningless.

The large numbers suggested by both studies, although not directly comparable, suggest that land-based sources of petroleum pollution to coastal environments is a significant environmental concern at a variety of scales.

Municipal wastes

Grouped with all land-based sources in current report.

Non-refinging industrial wastes

Grouped with all land-based sources in current report.

Urban runoff

Grouped with all land-based sources in current report.

River runoff

Grouped with all land-based sources in current report.

Recreational marine vessels

Not accounted for in 1985 study.

Large number calculated during current study suggests this may be an important source of petroleum pollution, especially given the environmental sensitivity of the coastal areas where these vessels most commonly operate.

Spills (commercial vessels ≥100 GT)

Nontanker accidents

Both studies used national databases as the foundation for the resulting estimate. Thus, the results should be comparable at two significant figures.

The decrease from 20,000 tonnes per year to 7,100 tonnes is significant and reflects the substantial steps taken to reduce the incidence of transportation-related spills worldwide.

Operational discharges (vessels ≥100GT)

Bilge and Fuel oils

Differences in data, assumptions, and methodology make comparison of little value.

Operational discharges (vessels <100GT)

1985 study did not differentiate based on vessel size.

Atmospheric deposition

Atmosphere

Differences data, assumptions, and methodology make comparison of limited value.

Large numbers calculated in both studies suggest this may be a significant input of petroleum (especially PAH) to the marine environment

Jettisoned aircraft fuel

Not accounted for in 1985 study.

Large number (7,500 tonnes worldwide) suggests that this source may generate significant loading at local scales.

Ocean dumping

Not accounted for in current study.

Ocean disposal of wastewater treatment/sewage sludge has been banned in the United States and elsewhere, but may be locally significant where practiced. However, given the large uncertainty already associated with estimates of land-based sources (2 orders of magnitude), calculating the additional loads to each region or worldwide from sludge disposal was deemed to be of limited value.