OIL DISPERSION INCREASES THE APPARENT BIOAVAILABILITY AND TOXICITY OF DIESEL TO RAINBOW TROUT (ONCORHYNCHUS MYKISS)
ALLISON SCHEIN,† JASON A. SCOTT,† LIZZY MOS,‡ and PETER V. HODSON*†
†School of Environmental Studies, Queen’s University, Kingston, Ontario K7L 3N6, Canada
‡Hemmera, 4th Floor, 19 Bastion Square, Victoria, British Columbia V8W 1J1, Canada
(Received 9 July 2008; Accepted 11 September 2008)
Abstract—Diesel is a complex mixture containing polycyclic aromatic hydrocarbons, which persist after a spill, pass readily from water into tissues, and are toxic to early life stages of fish. The bioavailability and chronic toxicity of hydrocarbons dissolved into water from floating diesel (water-accommodated fraction) and chemically dispersed diesel (chemically enhanced water-accommodated fraction) were measured by the extent of ethoxyresorufin-O-deethylase (EROD) induction in juvenile rainbow trout (Oncorhynchus mykiss) and by the severity of blue sac disease in embryos. The water-accommodated fraction of floating diesel was virtually nontoxic to embryos at nominal concentrations up to 1,000 mg/L, causing only small weight changes. Liver EROD induction in juvenile trout was only observed at the highest nominal water-accommodated fraction concentration (10,000 mg/L). Chemical dispersion increased the bioavailability and toxicity of diesel to trout by 100-fold. Diesel chemically enhanced wateraccommodated fraction induced EROD activity, caused blue sac disease, and impaired development and growth of embryonic trout at nominal concentrations as low as 10 mg/L; 88% mortality occurred at 100 mg/L. However, when total hydrocarbon concentrations were measured, differences between dispersed and undispersed diesel disappeared, with a median lethal concentration of 8 mg/L of total hydrocarbons and sublethal median effective concentrations ranging from 1.3 to 6.1 mg/L. Dispersion of diesel by highenergy mechanical mixing was recently reported to cause acute lethality to juvenile trout between 40 and 200 mg/L. Therefore, dispersion of oil by any means increases the bioavailability and apparent toxicity of diesel to fish embryos without changing