PREDICTING THE AQUATIC TOXICITY OF CRUDE OILS

Abstract

ABSTRACT Aquatic toxicity information is critical to provide scientifically defensible estimates of ecological impact and natural resource injury to aquatic organisms resulting from a petroleum spill. For most crude oils, the availability of aquatic toxicity information is a significant data gap. As part of Chevron's oil-specific properties summary sheet project, a series of marine fish (silversides, top smelt) and invertebrate (mysid shrimp) acute toxicity tests on five crude oils with extensive chemical analysis (e.g., VPH C6–C9, CROSERF VOCs, EPH C10–C32, PAHs) of exposure concentrations have been performed. Acute toxicity studies were conducted under standard test guidelines. ASTM D 6081 procedures were used to prepare individual water extracts, also called water-accommodated fractions (WAFs), of each test concentration to which the test organisms were exposed. WAF preparation and testing was done in tightly closed containers with minimal headspace to reduce volatilization and maintain stable exposure levels of dissolved hydrocarbons as much as possible. Also, WAFs were replenished daily with fresh test solution. Since toxicity results are expressed as the mean exposure concentration of a particular subset of the petroleum compounds in the WAF that resulted in 50% lethality in the test species, the LC50 values in μg/L will vary depending on which subset is used to describe the effect of the oil on the aquatic organisms. Additionally, since the aquatic organisms are exposed to a mixture of hydrocarbons in the WAF, LC50 values expressed as one subset's concentration are not independent of the presence of other petroleum constituent types. The results indicate that generally invertebrates (i.e., mysid) are more sensitive than fish. LC50s expressed as total polycyclic hydrocarbons (PAHs) showed the least variability—96-hour LC50s for total PAHs ranged from 19–36 μg/L and 30–128 μg/L for mysid and fish, respectively.