A Quantitative Assessment of the Sources and Fate of Petroleum Compounds in the Marine Environment [and Discussion]

Petroleum is complex, containing many thousands of compounds ranging from gases to residues boiling about 400 $^\circ$C. Most (usually more than 75%) are types of hydrocarbons. Crude oils differ markedly in detailed composition, even during the lifetime of a single well, while distillates and petroleum products are enriched with certain compounds. Thus petroleum-derived inputs vary considerably in composition; it is essential to bear this in mind when quantifying them in general terms such as an 'oil' or 'total petroleum hydrocarbons' measurement. However, to place the gross inputs in their proper perspective in an assessment of potential environmental effects, it is equally important to identify quantitatively those components that are potentially harmful or have long residence times. Additional sources of hydrocarbons such as other fossil fuels, combustion and the biosphere must also be distinguished, providing difficult analytical problems where the contribution of petroleum-derived constituents is small. Much less information is available on the non-hydrocarbon components. Estimates of the total oil input to U.K. waters are, at best, approximate and range from 40 to 100 kt or more per year. Some contributions are more speculative than others, particularly the atmospheric input. Usually, environmental effects are of local concern and it is more realistic and more meaningful to appraise the quantity and quality of the inputs on a local rather than a national or global basis. Such appraisal identifies potential 'hot-spots' or areas of concern to which the results of studies on the distribution of hydrocarbons can be related broadly. The complexity of the inputs is matched by the range of properties of the components and the physical, chemical and biochemical processes that contribute to the distributive pathways and determine the fate of the inputs.