production discharges, or a land-based facility. In these cases, there may be a strong gradient from high to low oil concentration as a function of distance from the source. In other cases, such as land-based runoff and atmospheric inputs, the origin of the oil is a non-point source, and environmental concentration gradients of oil compounds may be weak. Chronic exposures may also result from the incorporation of oil into sediments in which weathering of oil is slow and from which nearly fresh oil may be released to the water column over extended periods. In recent years, it is the long-term effects of acute and chronic oil contamination that have received increasing attention (Boesch et al., 1987)

Petroleum hydrocarbon inputs into North American and worldwide marine waters were computed, based on various databases, for several major categories. Three activities— extraction, transportation, and consumption—are the main sources of anthropogenic petroleum hydrocarbon pollution in the sea. Each of these activities poses some risk of oil release, and as greater amounts of petroleum hydrocarbons are imported into North American waters, the risk increases. The categories are listed in Table 2-2. Details of the methods used, discussion of databases, and computation and distribution of sources are discussed in Appendixes C, D, E, F, G, H, and I. Table 2-2 and Figures 2-2A and 2-2B summarize the sources and inputs for North American and worldwide waters (see Chapter 3 for greater details). Table 2-3 summarizes conclusions about the intercomparability of the data, methods, and assumptions used develop these estimates with those reported by the NRC in 1985 and what significance if any, can be attached to changes in those estimates.

The acute toxicity of petroleum hydrocarbons to marine organisms is dependent on the persistence and bioavailability of specific hydrocarbons. The ability of organisms to accumulate and metabolize various hydrocarbons, the fate of metabolized products, the interference of specific hydrocarbons (or metabolites) with normal metabolic processes that may alter an organism’s chances for survival and repro