Oil and oil dispersant do not cause synergistic toxicity to fish embryos

Abstract

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.

Diluted bitumen causes deformities and molecular responses indicative of oxidative stress in Japanese medaka embryos

“…Overall, the effect on medaka embryos of dilbit exposure corresponded to the effects of exposure of fish embryos to various crude oils (Wu et al, 2012Olsvik et al, 2011, refined oils such as heavy fuel oil (Martin et al, 2014;Incardona et al, 2011b), diesel fuel (Schein et al, 2009), and individual PAH and alkyl PAH (Incardona et al, 2006, 2011aTurcotte et al, 2011Lin et al, 2015). The greater apparent toxicity of dilbit CEWAF relative to WAF corresponded to previous observations that chemical dispersion increases the amount of oil that is bioavailable and toxic to fish embryos without any clear indications of interactive toxicity (Adams et al, 2014a). Thus, it appears that the risks of dilbit toxicity to developing fish embryos differ little from those of conventional oils.…”

“…Our study revealed that a reduced capacity of the antioxidant response was further influenced by exposure to Corexit ® , although the potential interactions between PAHs and the components of this dispersant cannot be ruled out. The apparent enhanced toxicity of chemically-dispersed oil has been previously attributed to the introduction of additional fine oil droplets into water which increases the exposure of fish to PAHs without any obvious synergistic toxicity between dispersant and oil (Adams et al, 2014a;Ramachandran et al, 2006Ramachandran et al, , 2004. In the present study, effects on swim bladder inflation of the dispersant control (nujol CEWAF) fish suggests that dispersant may also be bioavailable and toxic to fish embryos in the absence of dilbit.…”

“…The greater prevalence of swim bladder effects in medaka exposed to CEWAF of dilbit and nujol may indicate a direct effect of the active ingredients of the dispersant; dispersants are used to promote interactions between oil and water. While the greater toxicity of CEWAF to trout embryos has been attributed mainly to the greater exposure to dissolved petroleum hydrocarbons that partition from stable suspensions of oil droplets to water (Adams et al, 2014a), the increased occurrence of the swim bladder defects in the CEWAF treatment may represent an additive effect of dispersant. Medaka are physoclistic, as are percids and sunfishes, having a distinct gas gland for maintaining swim bladder inflation and buoyancy.…”

“…An alternative method (Adams et al, 2014a) measured total petroleum hydrocarbons by fluorescence spectrometry (TPH-F, mg/L), and provided data quickly and inexpensively. Immediately after daily renewal of test solutions, aliquots of 1.5 mL of each solution were diluted 50:50 in 1.5 mL of anhydrous ethanol.…”

The influence of heart developmental anatomy on cardiotoxicity-based adverse outcome pathways in fish

“…2). These effects range from outright embryonic heart failure and mortality at relative high PAH exposures (Adams et al, 2014a;Adams et al, 2014b;Esbaugh et al, 2016;Incardona et al, 2014;Incardona et al, 2013;Jung et al, 2013;Jung et al, 2015;Madison et al, 2015;Martin et al, 2014;McIntyre et al, 2016a;McIntyre et al, 2016b;Sørhus et al, 2015), to more subtle effects on heart shape and delayed impacts on cardiovascular performance at lower concentrations (Hicken et al, 2011;Incardona et al, 2015). These latter, protracted physiological impacts likely contributed to the delayed mortality and poor population recruitment previously observed both in 1) mark-recapture studies with pink salmon (Oncorhynchus gorbuscha) exposed to crude oil during embryogenesis (Heintz, 2007;Heintz et al, 2000) and 2) the losses of wild pink salmon spawned in shoreline habitats that were oiled in the aftermath of the 1989 Exxon Valdez disaster (Rice et al, 2001).…”