Comparative toxicity of eight oil dispersants, Louisiana sweet crude oil (LSC), and chemically dispersed LSC to two aquatic test species

Abstract

The present study describes the acute toxicity of eight commercial oil dispersants, South Louisiana sweet crude oil (LSC), and chemically dispersed LSC. The approach used consistent test methodologies within a single laboratory in assessing the relative acute toxicity of the eight dispersants, including Corexit 9500A, the predominant dispersant applied during the DeepWater Horizon spill in the Gulf of Mexico. Static acute toxicity tests were performed using two Gulf of Mexico estuarine test species, the mysid shrimp (Americamysis bahia) and the inland silversides (Menidia beryllina). Dispersant-only test solutions were prepared with high-energy mixing, whereas water-accommodated fractions of LSC and chemically dispersed LSC were prepared with moderate energy followed by settling and testing of the aqueous phase. The median lethal concentration (LC50) values for the dispersant-only tests were calculated using nominal concentrations, whereas tests conducted with LSC alone and dispersed LSC were based on measured total petroleum hydrocarbon (TPH) concentrations. For all eight dispersants in both test species, the dispersants alone were less toxic (LC50s: 2.9 to >5,600 µl/L) than the dispersant-LSC mixtures (0.4-13 mg TPH/L). Louisiana sweet crude oil alone had generally similar toxicity to A. bahia (LC50: 2.7 mg TPH/L) and M. beryllina (LC50: 3.5 mg TPH/L) as the dispersant-LSC mixtures. The results of the present study indicate that Corexit 9500A had generally similar toxicity to other available dispersants when tested alone but was generally less toxic as a mixture with LSC.

Hydrocarbon-Degrading Bacteria Exhibit a Species-Specific Response to Dispersed Oil while Moderating Ecotoxicity

“…The observed increase in toxicity associated with the uninoculated dispersed oil is consistent with the literature, and numerous studies have shown dispersant-oil mixtures to be significantly more toxic than dispersants alone (14,(19)(20)(21)62). Like Rico-Martínez et al (14), we saw a synergistic effect of Corexit 9500A, with Macondo crude oil increasing the toxicity to the marine rotifer B. manjavacas relative to Corexit alone or to physically dispersed crude oil.…”

“…Furthermore, the EPA required British Petroleum (BP) to assess the toxicity of dispersed oils using the Brachionus rotifer test following the DWH oil spill (18). In another study, Hemmer et al (19) showed that dispersant-crude oil mixtures were more toxic than dispersants alone to mysid shrimp (Americamysis bahia) and inland silverside fish (Menidia beryllina). Other studies observed that dispersed oil and dispersant constituents showed higher toxicity than crude oil alone in coral species (20,21).…”

Lethal and sublethal effects of oil, chemical dispersant, and dispersed oil on the ctenophore Mnemiopsis leidyi

“…However, knowledge of dispersant toxicity is useful, as these compounds are regulated in part based on their toxicity to several estuarine model species, which may or may not be representative of gelatinous marine species. Indeed, the dispersant Corexit EC9500A in the present study was more toxic to M. leidyi than to a model estuarine crustacean, the mysid Americamysis bahia (48 h LC 50 = 38 mg l −1 , Hemmer et al 2011). Mortality studies with Corexit and other common coastal zooplankton such as the copepods Acartia tonsa (Avila et al 2010) and L. aestiva (Cohen et al 2014) reported LC 50 s similar to those found for M. leidyi.…”

Science in support of the Deepwater Horizon response

“…Results indicate that none of the dispersants tested displayed biologically significant endocrine-disrupting activity (30); dispersants alone were less toxic than dispersant-oil mixtures. SLC oil alone was generally similarly toxic to both test species as dispersant-oil mixtures, and the toxicity of Corexit9500A was generally similar to the toxicities of other available dispersants (31).…”