Abstract
Concentrations of total Hg in sediments near six drilling sites in the Gulf of Mexico were elevated well above average background values of 40–80 ng/g. The excess Hg was associated with barite from discharged drilling mud. In contrast with total Hg, concentrations of methylmercury (MeHg) in these sediments did not vary significantly at nearfield (<100 m) versus farfield (>3 km) distances from the drilling sites. Observed variability in concentrations of MeHg were related to local differences in redox state in the top 10 cm of sediment. Low to non-detectable concentrations of MeHg were found in nearfield sediments that were anoxic, highly reducing and contained abundant H2S. At most drilling sites, nearfield samples with high concentrations of total Hg (>200 ng/g) had similar or lower amounts of MeHg than found at background (farfield) stations. Higher values of MeHg were found in a few nearfield sediments at one site where concentrations of TOC were higher and where sediments were anoxic and moderately reducing. Overall, results from this study support the conclusion that elevated concentrations of MeHg in sediments around drilling sites are not a common phenomenon in the Gulf of Mexico.
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Acknowledgments
The authors thank Steve Viada, Al Hart, Frank Johnson and Woody Powell from Continental Shelf Associates, Inc., for logistical support in the field and with data compilation and statistics. Special thanks to Joe Smith, Mary Boatman, Mike Parker, Jim Ray and other reviewers of this study. This paper was originally presented as SPE 80569 at the SPE/EPA/DOE Exploration and Production Environmental Conference, held in San Antonio, Texas, USA, 10–12 March, 2003. This research was funded through the Synthetic Based Muds Research Group.
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Trefry, J.H., Trocine, R.P., McElvaine, M.L. et al. Total mercury and methylmercury in sediments near offshore drilling sites in the Gulf of Mexico. Environ Geol 53, 375–385 (2007). https://doi.org/10.1007/s00254-007-0653-6
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DOI: https://doi.org/10.1007/s00254-007-0653-6