Are aromatic hydrocarbons the primary determinant of petroleum toxicity to aquatic organisms?

Aromatic components of oil, particularly polycyclic aromatic hydrocarbons (PAHs), are generally assumed to be the toxic fraction of spilled petroleum. We evaluated this assumption by analyzing the chemistry and toxicity of water accommodated fractions (WAFs) prepared from three environmentally weathered middle distillate oils differing in aromatic content. Oil toxicity was determined in short-term growth and survival tests with the mysid shrimp, Mysidopsis bahia. Median lethal concentrations (LC50s) ranged from 0.9 to 1.5 mg l(-1) total petroleum hydrocarbons (TPH), and growth-inhibiting concentrations (EC20s) ranged from 0.13 to 1.1 mg l(-1) TPH, Toxicity of the three oils expressed as mu g l(-1) Sigma PAH (sum of 40 PAH analytes; parent and alkyl homologues) ranged from 2.2 to 9.2 mu g l(-1) (LC50s) and from 0.32 to 5.7 mu g l(-1) (EC20s). The test oil with the lowest aromatic content, expressed as either mu g l(-1) PAH or mu g l(-1) naphthalenes in WAF had the greatest toxicity. The test oil WAF with the lowest total PAH concentration also had the lowest concentrations of single PAH analytes measured at concentrations greater than the detection limit. The results of this study demonstrated that low aromatic content oil can be highly toxic and that PAHs were not the major determinant of the toxicity of the three weathered middle distillate oils. (C) 1999 Elsevier Science B.V. All rights reserved.