John Wiley & Sons, Ltd.

Acute toxicity of chemically and mechanically dispersed crude oil on juvenile sea bass (Dicentrarchus labrax): Absence of synergistic effects between oil and dispersants

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The goal of this experiment was to assess the relative acute toxicities of mechanically and chemically dispersed oil (Crude Arabian Light) in controlled conditions. Juvenile sea bass (Dicentrarchus labrax) were exposed to four commercial formulations of dispersants (Corexit EC9500A, Dasic Slickgone NS, Finasol OSR 52, Inipol IP 90), to mechanically dispersed oil and to the corresponding chemical dispersions. Acute toxicity was evaluated at 24, 48, 72, and 96 hours through the determination of lethal concentrations (LC10, LC50 and LC90) calculated from measured total petroleum hydrocarbon concentrations; Kaplan Meyer mortality analyses were based on nominal concentrations. Animals were exposed to the dissolved fraction of the oil and to the oil droplets (ranging from 14.0 to 42.3 µm for the chemical dispersions). Kaplan Meyer analyses demonstrated an increased mortality in the case of chemical dispersions. This difference can mainly be attributed to differences in TPH since the chemical lethal concentrations were not reduced when compared to mechanical lethal concentrations (except after 24 hours of exposure). The ratios of lethal concentrations of mechanical dispersions over the different chemical dispersions were calculated in order to enable a direct comparison of the relative toxicities of the dispersions. The results ranged from 0.27 to 3.59 with a mean ratio close to 1 (0.92). These results demonstrate an absence of synergistic effect between oil and chemical dispersants in an operational context. This article is protected by copyright. All rights reserved

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