Characterizing the composition and biogeochemical behavior of dispersants and their transformation products in Gulf of Mexico coastal ecosystems

Darrel Sparks (PI), P. Lee Ferguson (co-PI), Anne E. McElroy (co-PI), and Bruce J. Brownawell (co-PI)
Funding Agency: 
Gulf of Mexico Research Initiative

The use of chemical dispersants is a key emergency response option available to mitigate impacts of large oil spills on sensitive coastal or surface water ecosystems and resources. Long controversial, the relative merits of dispersant use came under intense scrutiny when approximately 1.84 million gallons of Corexit® series dispersants were used during the Deepwater Horizon (DH) oil spill that occurred in the Gulf of Mexico (GOM) in 2010. Despite recent and intense investigation, many questions remain concerning the hazards posed by large-scale dispersant application in marine oil spills. Importantly, the transformation, fate, and transport of crude oil components released to the marine environment through accidental spills has been well studied over many years, but the fate of dispersants applied to mitigate spills of oil in the sea is largely unknown. Our research addresses toxicity, sorption, and occurrence in seafood of dispersant components and transformation products, questions that have not been well addressed in the past. To date there has been insufficient effort investigating microbial degradation of dispersants, their toxicity and their interaction with particulate matter. Comprehensive examination of these processes will improve the understanding of dispersant fate and potential effects in the GOM, and will help to drive development of safer and more effective dispersants which will ultimately lead to protection of the GOM ecosystem. The over-arching goals of the our research are to improve the knowledge base on dispersant behavior in the coastal marine environment and to increase understanding of the processes that controlled dispersant fate and biological exposure in the GOM following the DH oil spill. The tools developed and information gained from this project will be critical for more informed comparative assessments of the safety of different dispersants based on their specific ingredients. The specific aims of the research are to:

  1. Characterize the persistence of the complex mixture of components in Corexit® 9500 and a range of other surfactants that are presently used in alternative commercial formulations approved for use in the GOM, and elucidate resulting persistent degradation products; this will be conducted in aerobic incubations with GOM seawater; through coordination with the Tulane University dispersant GoMRI consortium, similar tests with more promising surfactant/dispersants developed during the project period will also be conducted.
  2. Identify toxic transformation products of dispersants produced under aerobic conditions in seawater under Aim 1; transformation products will be isolated and characterized with novel toxicity identification and evaluation (TIE) approaches on degraded dispersant mixtures.
  3. Assess the particle reactivity of dispersant components to evaluate phase partitioning that controls bioavailability and possible loss to sediment reservoirs in the GOM; sorption of dispersant chemicals, and identified transformation products (from #1 & #2) to surficial GOM sediments and suspended particles will be determined.
  4. Develop tools and evaluate the migration of potentially toxic dispersant transformation products into marine organisms used for human consumption through incorporation of results from (#1 and #2) into improved methods for determining dispersant component residues and Itransformation products in seafood from the GOM in freshly collected and archived samples.