American Petroleum Institute

Toxicity of Dispersed and Undispersed Prudhoe Bay Crude Oil Fractions to Shrimp, Fish, and Their Larvae
 N PUBL 4441

Annotation

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.