Environmental Science

NMR Metabolomic Studies Highlight Detrimental Effects of Sub-Lethal Oil Pollution

“…exposure to sublethal levels of oil altered and disrupted multiple metabolic pathways in both the plasma and liver metabolome of cormorants”

Metabolomics simultaneously studies all the metabolites in the cells of living organisms. This has been made feasible by the development of powerful high-frequency nuclear magnetic resonance (NMR) technologies. Metabolomics is now a widely-used research tool across many disciplines. It provides a unique chemical fingerprint that can be used to assess responses to external conditions. As it shows changes in the metabolism and metabolic pathways of a biological system, which are closely linked to phenotype, this information can provide basic functional information on physiological state.

The Deepwater Horizon (DWH) oil spill in April 2010 was the largest offshore marine oil spill in the world, covering 112,100 km2. It resulted in unprecedented loss of human life and economic and environmental impacts. The active spill continued for several months, resulting in repeated sub-lethal exposure to oil along 2,100 km of US shoreline in Louisiana, Mississippi, Alabama and western Florida.

It has been suggested that the damage to wildlife was lessened by the fact that the oil was more biodegradable and less toxic than other oils due to its chemical makeup. However, various studies have shown that birds exposed to the oil experienced changes in hematologic parameters, effects on multiple organs, including the heart, feather damage, and increased heat loss and energetic demands.

Most recently, a metabolomic study, evaluated the effect of external sub-lethal exposure to the DWH oil spill on the double-crested cormorant. Plasma and liver samples were obtained from an external oil dosing study and analysed using one dimensional proton nuclear magnetic resonance spectroscopy (1D 1H NMR) and from control cormorants that had not been exposed to the oil. A total of 49 metabolites involved in energy, fatty acid, amino acid and nucleoside metabolism were investigated in the plasma and liver tissue samples.

The metabolomic analysis of the plasma samples revealed significant negative effects on the metabolic profiles of cormorants repeatedly exposed to the oil. In some cases, such as plasma level of methionine, changes occurred after only two external exposures (26 g cumulative) to the oil. Significant changes in metabolites of energy metabolism and fatty acid and amino acid metabolic pathways were observed as well as several metabolites essential to the one-carbon metabolism pathway. Increased production of ketone bodies was apparent, suggesting that the birds were using lipids as an alternative energy source despite carbon resources being readily available. Hepatic bile acid metabolism was also altered. Alteration in several liver metabolites indicated impairment of mitochondrial energy metabolism among birds with oil exposure.

The authors indicated that the changes they observed in the cormorants exposed to repeated sub-lethal doses of oil from the DWH spill would be detrimental to reproduction, migration, and survival of the birds.

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Dorr BS, et al. Effects of Repeated Sublethal External Exposure to Deep Water Horizon Oil on the Avian Metabolome. Scientific Reports 2019; 9:Article number 37. https://www.nature.com/articles/s41598-018-36688-3#ref-CR21