Evaluation of artificially-weathered standard fuel oil toxicity by marine invertebrate embryogenesis bioassays

Abstract

Weathering of petroleum spilled in the marine environment may not only change its physical and chemical properties but also its effects on the marine ecosystem. The objective of this study was to evaluate the toxicity of the water-accommodated fraction (WAF) obtained from a standard fuel oil following an environmentally realistic simulated weathering process for a period of 80d. Experimental flasks with 40gL−1 of fuel oil were incubated at 18°C with a 14hlight:10hdark photoperiod and a photosynthetically active radiation (PAR) intensity of 70μEm−2s−1. Samples were taken at four weathering periods: 24h, 7, 21 and 80d. WAF toxicity was tested using the sea urchin (Paracentrotus lividus) and mussel (Mytilus galloprovincialis) embryo–larval bioassays and the aromatic hydrocarbons levels (AH) in the WAF were measured by gas chromatography/mass spectrometry. In contrast with the classic assumption of toxicity decrease with oil weathering, the present study shows a progressive increase in WAF toxicity with weathering, being the EC50 after 80d eightfold lower than the EC50 at day1, whereas AH concentration slightly decreased. In the long term, inoculation of WAF with bacteria from a hydrocarbon chronically-polluted harbor slightly reduced toxicity. The differences in toxicity between fresh and weathered fuels could not be explained on the basis of the total AH content and the formation of oxidized derivatives is suggested to explain this toxicity increase.