Mercury in the Gulf of Mexico:
Do Offshore Oil & Gas Facilities Contribute?

Some forms of mercury, particularly methylmercury, can harm virtually all types of life when they are present at high levels. Humans are exposed to methylmercury primarily through consumption of fish and shellfish, which has led to concern about mercury levels in the tissues of commercial and recreational seafood. Concerned about food safety, the American Petroleum Institute (API) commissioned Battelle to review the current literature on sources of mercury in the Gulf of Mexico and on the potential contribution of offshore oil and gas operations to levels of the metal in seafood.

Dr. Jerry Neff from Battelle, who recently prepared an extensive report for the API considered naturally occurring sources of mercury, as well as human activities that add the metal to the environment. A key finding is that the amount of mercury entering the Gulf of Mexico from all offshore oil and gas facilities is very small when compared to other sources. Furthermore, the mercury associated with drilling discharges is insoluble and unlikely to be absorbed by marine organisms, including the bacteria that make methylmercury. This indicates that mercury from offshore platforms in the Gulf does not get into the marine food chain that provides fish for human consumption.

The U.S. Environmental Protection Agency (EPA) recently estimated that nearly 350,000 pounds of mercury is released to the U.S. atmosphere each year from human activities – primarily emissions from coal-fired power plants, municipal waste incinerators, oil and gas powered commercial/industrial boilers, as well as automobiles. An estimated 55,100 pounds of mercury per year of mercury is deposited from the atmosphere to the surface waters of the Gulf of Mexico in rainfall and dry deposition; an additional 48,500 pounds of mercury per year flows into the Gulf from the Mississippi River. Smaller amounts of mercury come from other rivers, run-off from land, and commercial activities near the coast and offshore. This atmospheric deposition is the largest source of mercury in waters of the Gulf, according to Dr. Neff.

On the other hand, the amount of mercury contributed by offshore oil and gas operations is estimated at 346 pounds per year, which is about one-third of one percent of the mercury that enters the Gulf from the air and the Mississippi River. Studies conducted at more than 30 oil and gas facilities indicated that the concentration of total mercury in sediments near most of these platforms is at or near natural background concentrations. In fact, sediments from coastal waters of the western Gulf, where there have been extensive oil and gas operations for the past 60 years, contained lower concentrations of mercury than sediments from the eastern Gulf, where nearshore oil and gas operations have been more limited.

These data indicate that offshore oil and gas activities do not significantly contribute to mercury concentrations in Gulf of Mexico sediments. Furthermore, total mercury concentrations in the tissues of marine invertebrates and fish from the Gulf are similar to what is found in the same or similar species from other marine waters in the U.S. and other parts of the world, including places where there has been much less, or no, oil and gas activity. The methylmercury in the edible tissues of recreational and commercial fishery products harvested from the Gulf of Mexico does not come from discharges from offshore oil and gas wells.

For more information contact Dr. Jerry Neff at (781) 952-5229, neffjm@battelle.org.