Atlantic herring (Clupea harengus) embryos were exposed to water accommodated fractions (WAFs; oil dissolved in water) and chemically enhanced water accommodated fractions (CEWAFs; oil dispersed in water with Corexit 9500A) of Medium South American (MESA) crude oil. The CEWAF was approximately 100-fold more toxic than WAF based on nominal loadings of test solutions (% v/v). In contrast, the ratio of WAF and CEWAF toxicity expressed as measured oil concentrations approximated 1.0, indicating that the higher toxicity of CEWAFs was caused by an increase in exposure to hydrocarbons with chemical dispersion. In a second experiment, the chronic toxicity of Corexit 9500A and chemically dispersed heavy fuel oil 7102 (HFO 7102) to rainbow trout (Oncorhynchus mykiss) embryos was compared to chemically dispersed Nujol, a nontoxic mineral oil. Dispersant alone was toxic, but caused different signs of toxicity than HFO 7102. Nujol at a dispersant-to-oil ratio of 1:20 was nontoxic, suggesting that dispersant was sequestered by oil and not present at toxic concentrations. In contrast, the same nominal loadings of dispersed HFO 7102 caused concentration-dependent increases in toxicity. Both experiments suggest that chemically dispersed oil was more toxic to fish embryos than solutions created by mechanical mixing due to the increased exposure of fish to petroleum hydrocarbons and not to changes in hydrocarbon toxicity. The Nujol control discriminated between the toxicity of oil and chemical dispersant and would be a practical addition to programs of dispersant testing.

No abstract

The toxicity of Orimulsion-400 (PDVSA-BITOR), an emulsion of 70% bitumen in 30% water, was tested during the embryonic development of Atlantic herring (Clupea harengus) and mummichog (Fundulus heteroclitus) in duplicate experiments. Air injection and different salinities were included in the herring assays to examine their effects on Orimulsion-400 toxicity. Water-accommodated fractions (WAFs) of no. 6 fuel oil were tested in the mummichog assays to compare Orimulsion-400 toxicity with that of a heavy fuel oil. Concentrations of Orimulsion-400 as low as 0.001% (v/v) were harmful to both species. In herring, the more sensitive of the two species, this concentration produced 100% abnormal larvae. Similar abnormalities, including pericardial edema and spinal deformities, the same signs of toxicity caused by heavy fuel oils and polycyclic aromatic hydrocarbons (PAHs), were produced in both herring and mummichog. Fish exposed to Orimulsion-400 also suffered from increased mortality, reduced heart rates, premature hatch, and reduced lengths compared to control fish. Orimulsion-400 was approximately 300-fold more toxic than the WAFs of no. 6 fuel oil. Salinity had few clear effects on Orimulsion-400 toxicity, but aeration of test solutions greatly reduced toxicity by causing bitumen to coalesce and float. Aeration also removed toxic chemicals such as PAHs. The present study suggests that in the event of a spill, Orimulsion-400 could impair fish recruitment, but that strong wave action would reduce toxicity by accelerating the removal of emulsified bitumen from the water column.

No abstract