Characterization of a Microbial Community in Response to MTBE Contamination in Marine Sediment

On March 9, 2015, the Carla Maersk, which was carrying 216,049 barrels of methyl tertiary-butyl ether (MTBE) outbound for Venezuela, was struck port side by the bow of the Conti Peridot. An unspecified amount of MTBE spilled into the Port of Houston. MTBE has an exceptionally high water solubility and a large volume of the contaminant likely diluted and dispersed throughout the channel. MTBE was the most common fuel oxygenate because of its low cost, ease of production, and favorable transfer and blending characteristics. After only a few years of intense use, MTBE has become one of the most frequently detected groundwater pollutants in the United States. A potential fuel oxygenate alternative is tert-butyl alcohol (TBA). TBA can be found with MTBE in gasoline as a manufacturing by-product. It is also a key intermediate in the degradation of several dialkyl ethers used as fuel oxygenates, including MTBE, which is formed via cleavage of the ether bond. MTBE and TBA are difficult to remediate based on chemical and physical properties and need special consideration in site characterization and remedial design. Some treatment technologies that have been widely used for MTBE and TBA groundwater remediation includes groundwater pump and treat, air sparging, in situ chemical oxidation, phytoremediation, natural attenuation and bioremediation. Marine sediment samples were collected from the Port of Houston at four different locations. Two locations were approximately the same geographical location as Morgan’s Point where the spill occurred, and two additional locations were selected further downgradient of the shipping channel where MTBE was likely to travel due to boat traffic. In addition, six different locations from the Gulf of Mexico were provided by Battelle for background comparison. These six locations from Battelle will provide data on the typical composition of marine microbial communities and will allow for comparison to microbial communities that had been exposed to MTBE for several months. To the possibility of native bioremediation, each site would be amended with a different terminal electron acceptor and either MTBE or TBA as the amended electron donor. To characterize how the microbial community responds to MTBE contamination in marine sediment, and to identify specific microbial processes that will attenuate MTBE, DNA was extracted from all samples, PCR amplified, and sequenced using Illumina MiSeq high throughput sequencing technology. The samples are prepared for sequencing but the results are for future work. Looking at the Houston MTBE control for the four sites, it can be seen that each concentration after 55 days were either equal or greater than 100%. This indicates that no chemical reactions resulting in non-biological degradation occurred. All four sites for the Houston MTBE and Fe(III) and Houston TBA and Fe(III) amended bottles remain at a concentration near 80%, although each bottle has a steady linearly decreasing concentration over the 55 days. Houston MTBE and nitrate bottles showed mixed results. Sites two and four remain at approximately 100% of the initial concentration while sites one and three both degraded at nearly the same rate to a final concentration of 79% and 76%, respectively, of initial concentrations. Overall, site three seemed to show the most potential for degradation of the four Houston sites. Because only one bottle was used instead of duplicates or triplicates in this study, it could be due to the selective nature of the sampling. In other words, site three may have had a higher population of MTBE degrading microorganisms then the other sites. Additionally, given the physical and chemical properties of MTBE, it is possible that MTBE spilled at site four traveled with water quickly before settling at site three