Total mercury and methylmercury in sediments near offshore drilling sites in the Gulf of Mexico |
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Authors: | John H Trefry Robert P Trocine Michelle L McElvaine Robert D Rember Lucas T Hawkins |
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Institution: | (1) Department of Marine and Environmental Systems, Florida Institute of Technology, Melbourne, FL 32901, USA;(2) International Arctic Research Center, University of Alaska, Fairbanks, AK 99775, USA;(3) Frontier Geosciences Inc., Seattle, WA 98109, USA |
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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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Keywords: | Sediment Mercury Methylmercury Offshore oil Gulf of Mexico |
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