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Abstract Surface sediment samples were collected from five platforms in the Gulf of Mexico during the Gulf of Mexico Offshore Operations Monitoring Experiment (GOOMEX), a Minerals Management Service funded study, and analyzed for total mercury. While this study was reported in 1995, new interest in the report was sparked by several newspaper articles using the results to link mercury in drilling discharges with mercury in fish. As part of the study program, sediment samples were collected from near the platform and far from the platform. Total mercury ranged from not detected to 3.5 parts per million in the sediments. The highest values were from near a single platform where discharges are shunted to within ten meters from the bottom. Tissue samples, including shrimp, crabs, fish livers, and fish stomach contents, were also collected as part of the project and analyzed for total mercury. Statistical comparison of the results indicated that the samples did not differ significantly between near field and far field. This presentation includes a background discussion of the issue of mercury as a global pollutant and puts into perspective the contribution from oil and gas activities around platforms.
Introduction Are drilling muds a source of mercury in the seafood we eat? This question was raised in January of 2002 when a series of newspaper articles appeared in the Mobile Register suggesting that oil and gas activities in the Gulf of Mexico were adding mercury to the environment. The added mercury was proposed as a source of mercury in fish consumed by local residents in Mobile, Alabama. Results from a Minerals Management Service (MMS) study, Gulf of Mexico Offshore Operations Experiment (GOOMEX), were used to demonstrate that this is true. However, the results of the study were not correctly interpreted. This report will present those results in the context of the global issue of mercury in the environment.
What is Mercury? Mercury is a naturally occurring element whose chemical symbol is Hg. The symbol Hg comes from the Greek word hydrargyrum, meaning watery silver. This term applies to mercury, since it is the only metal that occurs as a liquid under conditions at the surface of the Earth. Mercury is also commonly known as quicksilver. As an element, mercury does not serve any function in biological systems like other trace elements such as copper or zinc. In other words, you won't find mercury listed on your vitamin bottle.
Why the Concern about Mercury? Mercury is widely used in industrial products and some industrial processes because it is an excellent conductor of electricity. The properties of mercury also make it useful in pressure and vacuum gauges. At standard temperature and pressure, mercury readily becomes a gas. Some forms of mercury are easily taken up by organisms and concentrated in their bodies. Mercury acts as a neurotoxin at higher levels. The mercury is more concentrated in predators such as swordfish, sharks, panthers, eagles, and humans. The primary source of mercury poisoning in humans is from eating fish.
Where is Mercury found in the Environment? On the Earth's surface, mercury can occur in solid, liquid, or gaseous forms. Mercury can occur as elemental mercury, inorganic mercury, or organic mercury. Elemental mercury, Hg, in liquid form is the silvery fluid used in thermometers. As a gas, elemental mercury is in the air we breathe. Inorganic mercury, Hg, can form a dissolved salt in water or occurs as the mineral cinnabar, HgS. Mercury also can combine with small, organic molecules, such as methane, to form organic mercury compounds like methylmercury.
Since mercury can exist in so many forms on the Earth's surface, it moves through the environment along many complex pathways. As a gas, mercury can travel from a source to many thousands of miles away. Rain removes mercury from the atmosphere to the surface of the Earth. Rivers also transport mercury to the lakes and streams where fish live. To get into the fish we eat, mercury must first be converted to the organic methylmercury form.
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