Mass Spectral Analysis of Water Column Samples from a Single Depth Profile Near the Deepwater Horizon Oil Spill

The Deepwater Horizon oil spill is the largest offshore oil spill in history, spilling an estimated 4.9 million barrels of oil. Additionally, over 1.8 million gallons of dispersants have been applied, both through underwater and surface applications. The depth and volume of this spill as well as the underwater dispersant applications likely allowed for the dissolution of oil components into the water column during transport to the ocean surface. We examined the water-soluble components of dissolved organic matter, oil, and dispersants at various depths and locations within 10km of the wellhead in order to assess the degree of oil dissolution into the water column. Here we present results from analysis of four samples from a depth profile collected 1.16km from the wellhead. We used ultrahigh resolution negative-ion mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, a technique that has been used to characterize both DOM and crude oil. We compared oil from the wellhead with the composition of different extracts from the water samples and observed hundreds of compounds which are present in both the original oil and the water column. The oil compounds contained in the extracts were similar for all four depths. Compounds within the heteroatom classes N and O were most abundant in the source oil, while oil compounds in the formula classes O2 and SO3 were enhanced in the water samples. Compounds from these classes may be good markers for tracing the impact of this spill in the Gulf of Mexico ecosystem.