Elsevier

Aquatic Toxicology

Volume 95, Issue 3, 27 November 2009, Pages 230-238
Aquatic Toxicology

Characterization of the metabolic actions of crude versus dispersed oil in salmon smolts via NMR-based metabolomics

https://doi.org/10.1016/j.aquatox.2009.09.006Get rights and content

Abstract

With maritime transport of crude oil from Alaska to California, there is significant potential for a catastrophic spill which could impact migrating salmon. Therefore, this study compared the lethal and sublethal metabolic actions of the water-accommodated fraction (WAF) and the chemically enhanced WAF (CEWAF, via Corexit 9500) of Prudhoe Bay crude oil in smolts of Chinook salmon (Onchorhyncus tshawytscha). After 96-h exposure to the CEWAF, the resulting LC50 was some 20 times higher (i.e., less toxic) than that of the WAF. Muscle and liver samples from surviving fish were collected and low-molecular weight metabolites were analyzed using one-dimensional 1H and projections of two-dimensional 1H J-resolved NMR. Principal component analysis (PCA), employed to analyze NMR spectra and identify most variance from the samples, revealed age-related metabolic changes in the fish within the replicated studies, but few consistent metabolic effects from the treatments. However, ANOVA results demonstrated that the dose–response metabolite patterns are both metabolite- and organ-dependent. In general, exposure to either WAF or CEWAF resulted in an increase of amino acids (i.e., valine, glutamine and glutamate) and a decrease of both organic osmolytes (i.e., glycerophosphorylcholine) and energetic substrates (i.e., succinate). The simultaneous increase of formate and decrease of glycerophosphorylcholine in the liver, or the decrease of glycerophosphorylcholine in muscle, may serve as sensitive sublethal biomarkers for WAF or CEWAF exposures, respectively. In conclusion, dispersant treatment significantly decreased the lethal potency of crude oil to salmon smolts, and the NMR-based metabolomics approach provided a sensitive means to characterize the sublethal metabolic actions.

Introduction

Currently all salmon species, as well as migratory steelhead trout, are classified as “threatened” under the U.S. Federal Endangered Species Act. While they are struggling to recover from the combined effects of over-fishing, habitat decline and pollution, there is serious concern that marine oil spills and associated response activities near rivers where these species spawn may impact smolts entering the ocean. In particular, there is concern that dispersant application could increase the toxicity of crude oil as, due to sea conditions, dispersants are the only response option available for central and northern California waters during most of the year (S.L. Ross, 2002). Therefore, information on the relative toxicity of dispersed versus non-dispersed oil is needed by spill responders.

While other studies have investigated the toxicity of oil to the alevins and embryos of Chinook salmon (Onchorhyncus tshawytscha), and the fry of Alaskan pink salmon (O. gorbuscha; Rice et al., 1975, Rice et al., 2001, Swartz, 1985, Heintz et al., 2000) and coho salmon (O. kisutch; Stickle et al., 1982, Thomas et al., 1987, Thomas et al., 1989), there is currently little available information on the impacts of oil or dispersed oil on salmon smolts. Therefore, this investigation compared the adverse actions of the water-accommodated fraction (naturally dispersed; WAF) versus the chemically enhanced water-accommodated fraction (dispersed with Corexit 9500; CEWAF) of unweathered Prudhoe Bay crude oil (PBCO) in the smolts of Chinook salmon.

Impacts were assessed via both lethality as well as more advanced sublethal metabolic endpoints via NMR-based metabolomics. This post-genomic approach combines the metabolic profiling capabilities of NMR with multivariate statistical techniques (Lindon et al., 2000, Nicholson et al., 2002), and has been used for biomarker development in chemical risk assessment, disease diagnosis, and toxic action mechanism characterization (Viant et al., 2003, Rosenblum et al., 2005, Ekman et al., 2006, Lin et al., 2006, Bundy et al., 2009). It is capable of reproducibly profiling potentially hundreds of low-molecular weight endogenous metabolites (Viant et al., 2009), including glycolytic and TCA intermediates, as well as high-energy phosphagens such as phosphocreatine, thus providing a thorough assessment of sublethal metabolic actions as well as overall health and reproductive capability. Such information may effectively contribute to spill response decision-making in the event of a coastal spill.

Section snippets

Animals

Chinook salmon smolts (O. tshawytscha; ∼6 cm FL) were obtained from the California Department of Fish and Game (DFG) Feather River Hatchery and acclimated to ambient seawater conditions (∼33‰, 11–14 °C) prior to use at the DFG Marine Pollution Studies Laboratory. Two cohorts were obtained for use (in May and June, 2005); fish from the first were used in the first three WAF and first two CEWAF experiments, while fish from the second were used in the fourth WAF and the last two CEWAF experiments (

Acute toxicity of WAF and CEWAF

No significant TC differences were found between treatment slopes (ANCOVA F values all ≤0.15), so flush rates in all experiments were similar. Flush rates within all WAF or CEWAF experiments were also not statistically different (p = 0.46). The range of temperature, pH, and DO of the natural seawater that flushed the exposures during the experiments were 11.6–15.8 °C, 7.47–7.95, and 3.68–7.58 mg/L, respectively.

The percentage survival after 96 h at a series of exposure concentrations is summarized

Relative toxicity of WAF and CEWAF

Surfactant-based dispersants may enhance the acute toxicity of spilled oil to migrating fish by increasing its dispersion, and thus pelagic availability, potentially decimating populations via reduced recruitment (Tjeerdema et al., 1991). However, based on THC, the mean 96-h LC50 for the WAF of PBCO (7.46 mg/L) was some 20-fold lower than that for the CEWAF (155.93 mg/L), suggesting that hydrocarbon bioavailability to smolts may have been reduced under dispersed conditions—and may be attributed

Acknowledgements

Funding was provided by the NOAA/UNH Coastal Response Research Center (Grant No. NA17OZ2607, Project No. 04-843), the DFG Office of Spill Prevention and Response (Grant No. PO475011), and DFG's Oil Spill Response Trust Fund through the Oiled Wildlife Care Network, Wildlife Health Center, UCD School of Veterinary Medicine (Grant Nos. 18091, 18092 and 18093). MRV thanks the NERC for an Advanced Fellowship (NER/J/S/2002/00618). The authors thank Wen, Chio-ni for figure preparation, and both J. de

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