Vanadium/Nickel Ratio as a Proxy for Oil Contaminated Sediments in the Northern Gulf of Mexico
Puspa Lal Adhikari
Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, Louisiana
Vanadium and Nickel are typically abundant in crude oil and accumulate in bottom sediments contaminated with oil. They form a strong bond with high molecular weight organic compounds. Addition or subtraction of more liable portions of crude oil may change their concentrations but the V/Ni ratios remain same. Thus, their ratios have been used to fingerprint and also as an internal marker of microbial degradation of crude oil contamination. After the Deepwater Horizon oil spill, a number of studies have been conducted, mainly looking for the environmental impacts of the oil released in the Gulf of Mexico waters. However, none of the published studies have used V/Ni ratios to fingerprint oil pollution in the deep ocean sediments. This study estimates V/Ni ratios and also correlates their concentrations with TPH in the contaminated sediments in and around the spill sites. A linear plot of Vanadium versus Nickel for contaminated sediments samples should have a constant slope similar to the V/Ni ratio of the source oil. If it remains similar, the V/Ni ratio can be used as proxy for crude oil contamination. Using this ratio as tracer of oil pollution is relatively easier, faster and less expensive than the traditional organic-compound based approaches. Also, Vanadium and Nickel are more persistent than the associated organic fraction. Thus they can be used to understand the long term transport, accumulation and the rate of degradation of oil, even when the oil fractions have degraded beyond our ability to carry out compound specific source oil fingerprinting.
AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects