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EXECUTIVE SUMMARY

Many previous studies of oil toxicity used high oil concentrations and water-soluble fractions (WSF). The aim of this study was to approximate field conditions, in which weathering and chemical dispersions remove the volatile fractions and change droplet size. The objective was to discover whether reducing monoaromatics and diaromatics reduced toxicity.

The study measured the relative toxicity of fresh Prudhoe Bay crude (PBC) oil and two distillation fractions ("Stage I" and "Stage II") and their chemical dispersions to adult and larval shrimp and fish. The hydrocarbon compositions of the three oils, the WSF of the oils, and chemical dispersions were measured. Tissue content of aromatics was measured at points of zero mortality and 50% mortality. Distribution of oil droplet sizes in chemical dispersions of fresh PBC and Stage II oils were compared.

Distillation of fresh PBC oil produced a "Stage I" oil containing no significant amounts of monoaromatics (benzene and alkylbenzenes) but with the diaromatics unchanged. Further distillation produced a "Stage II" oil which contained only aromatics of three rings (phenanthrenes) and greater. Saturated hydrocarbons of corresponding boiling points were also removed.

Bioassays on adult shrimp (Pandalus danae) with dispersed oils showed that the removal of monoaromatics (Stage I) reduced toxicity about sevenfold. The water-soluble fractions (WSF) of Stage I oil and both WSF and dispersions of Stage II oil were not toxic to shrimp. Shrimp larvae were about four times more sensitive to the WSF of fresh PBC oil than adults, but were no more sensitive to dispersed whole oil.

Uptake of naphthalenes and phenanthrenes by adult shrimp provided evidence that correlated with the toxicity to Stage I dispersed oil and the lack of mortality in dispersions of Stage II oil. Toxicity to fresh PBC oil was probably a combination of these components of the oil measured in the tissues and monoaromatics not quantified in tissues.

Adult sand lance (Ammodytes hexapterus) mortality did not correlate with the aromatic content of the oils, but appeared to be affected by dispersed oil droplets of all three oils to about the same degree. The fish are more resistant to dispersed oil than the shrimp (higher toxicity index). However, when latent mortality is considered, the data show that the fish may be more sensitive than shrimp to dispersed oil.

Larval herring (Clupea harengus pallasi) were not much more Sensitive to dispersed oils than adults and lance, but mortality is not a good measure of impacts on these larvae because they exhibit a long moribund period. Haddock larvae (Melanogrammus aeglefinus) were about five to seven times more sensitive to dispersions of fresh PBC oil than to dispersed Stage I oil. They were more sensitive to both dispersions than herring larvae, but indices were close to those of shrimp adults and larvae.