This paper presents results from a study of concentrations of total mercury (Hg) and methylmercury (MeHg) in seabed sediments near six offshore drilling sites in the Gulf of Mexico. Surface (0-2 cm) and subsurface (2-20 cm) sediment samples for this study were collected within three zones at each drilling site: <100 m (nearfield), 100-250 m (midfield) and >3 km (farfield). Total Hg levels in sediments from this study range from 11-92 ng/g (parts per billion, dry weight) for all farfield (background) samples and 25-558 ng/g for all nearfield samples. Concentrations of total Hg are significantly higher at nearfield stations than at farfield stations for five of the six drilling sites due to inputs from drilling discharges. Concentrations of MeHg range from 0.11-1.05 ng/g for all farfield sediments and <0.03-2.7 ng/g for all nearfield sediments. In contrast with results for total Hg, concentrations of MeHg in surficial (0-2 cm) sediments from all six drilling sites do not vary significantly between nearfield and farfield stations. Statistical comparisons of MeHg levels in nearfield versus farfield sediments at the six drilling sites, along with data from two of those sites that show lower levels of MeHg in some nearfield sediments than in farfield sediments, suggest that elevated levels of MeHg in sediments around drilling sites are not a widespread phenomenon in the Gulf of Mexico.

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