A microscale test to measure petroleum oil toxicity to mummichog embryos

A test was developed to compare the toxicity of different petroleum oils to mummichog (Fundulus heteroclitus) embryos. Fertilized eggs were incubated for 11 days at 22.5degreesC directly on the surface of oil-contaminated sand without a superficial water layer. The mortality rates, the stage of development, and the prevalence of malformations were determined. No effect was found in controls incubated on sand with water and mineral oil as compared with controls on sand with water alone. Two weathered oils, an Alaska North Slope crude oil (ANCO) and a Mesa light crude oil (MLCO), produced similar symptoms of toxicity: retarded growth and development, pericardial edema, hemostasis, hemorrhages, and spinal deformities. These symptoms are consistent with those observed in other fish species exposed to petroleum oils, suggesting that the results of the bioassay would be applicable to other species. MLCO was more embryotoxic than ANCO. The minimal oil concentrations causing a significant reduction in body length were 4.5 mug oil/g sand for MLCO and 12.7 mug oil/g for ANCO, indicating the assay is sensitive. The slopes and the intercepts of the relationships between concentration and growth did not differ in three dose-response experiments conducted with each oil, indicating that the assay is reliable. Finally, the bioassay is less costly than other available options to assess the toxicity of petroleum oils to marine fish embryos. Further work to improve the standardization of the assay will involve comparison of the toxicity of petroleum oils with reference toxicants and selection of a standard substrate. (C) 2002 Wiley Periodicals, Inc.