Mercury and Fish Farms
The Truth About Mercury and Fish Farms
The Dangers of Mercury
Mercury is a dangerous neurotoxin that can affect the brain, heart and immune system, especially for children and developing fetuses. Chronic exposure to mercury can cause problems such as learning disabilities and developmental delays.1 The greatest source of mercury exposure to people is from consuming fish.2 U.S. Environmental Protection Agency scientists estimate that one in six women of childbearing age already has enough mercury in her body to put her child at risk should she become pregnant, regardless of seafood consumption.3 
Questions Raised: Fish Farms, Oil Rigs and Mercury
A recent study by a team of Canadian researchers examined whether one possible ecological effect of salmon farm pollution is increased mercury contamination in surrounding wild-caught fish populations. The researchers sampled fish caught in the traditional fishing grounds of indigenous people and found that mercury was significantly higher in wild fish caught near the salmon farms than far from them. This was attributed to fish-farm pollution, which may be altering the food web, forcing wild fish to eat more highly contaminated organisms. The researchers also believe that the fish-farm pollution might be tainted with mercury and might be altering water chemistry to make the mercury in surrounding sediments more easily absorbed by aquatic organisms.4
Recent reports have highlighted a connection between oil and gas rigs and elevated mercury levels in surrounding sediments and wild-caught fish. Data from a 1996 U.S. Department of Interior Minerals Management Service study of three rigs in the Gulf of Mexico revealed that sediments within a few hundred feet of two rigs had mercury levels many times higher than base levels in Gulf of Mexico sediments.5 Data also indicated that shrimp and fish caught beneath the rig with the most contaminated sediments had average mercury levels that were two to five times higher than those caught around the least contaminated rigs.6
Scientists attribute the mercury contamination in and around the rigs to drilling ‚muds,”7 which are a mercury-rich mixture of the sediments and materials that cool and lubricate drill bits that bore into the ocean and are ultimately discharged into the ocean.8
In 2001, federal guidelines limited the amount of mercury in drilling muds,9 but approximately 1,600 pounds of mercury are still legally dumped into the Gulf of Mexico from the 1,091 new wells drilled each year.10 High levels of mercury remain in sediments 12 years after drilling has stopped.11
The environment around oil and gas rigs alone may be sufficient to transform the mercury found in drilling muds into a form that can contaminate fish and other organisms,12 but research is also needed to determine whether waste from fish-farms placed near these rigs could further stimulate the process, leaving wild-fish populations at higher risk of mercury exposure.
Whether they are standing alone or placed near oil rigs, fish farms may expose wild-caught fish to higher levels of mercury. These fish could enter the human food supply and threaten public health. These issues need to be studied before any large fish farms are permitted in federal waters including on or within one mile of oil and gas rigs.
Footnotes
1 U.S. Environmental Protection Agency, Report to Congress, Volume V: Health Effects of Mercury and Mercury Compounds, December 1997.
2 U.S. Environmental Protection Agency, Report to Congress,Volume VII: Characterization of Human Health and Wildlife Risks from Mercury Exposure in the United States, December 1997.
3 Mahaffey, K., Cliffner, R.P., and Bodurow, C., ‚Blood Organic Mercury and Dietary MercuryIntake: National Health and Nutrition Examination Survey, 1999 and 2000,” Environmental Health Perspectives, 112(5) 562-570, April 2004; Mahaffey, K.R., ‚Methylmercury Epidemiology Update,” Slide presentation given at the National Forum on Contaminants in Fish, San Diego, January 2004.
4 Dubruyn, A.M., Trudel, M. Eyding, N.A., Harding, J., McNally, H., Mountain, R., Orr, C., Urban, D., Verenitch, S., Mazumder, A., Ecosystemic Effects of Salmon Farming Increase Mercury Contamination in Wild Fish, Environ. Sci. & Technol. Published on Web 4/19/2006.
5 Ben Raines, ‚Mercury contamination at some rigs on par with Superfund sites” Mobile Register, April 14, 2002, analyzing data from Kennicutt, M. C., Green, R. H., Montagna, P., and Roscigno, P. F., 1996. Gulf of Mexico Offshore Operations Monitoring Experiment (GOOMEX), Phase I: Sublethal responses to contaminant exposure – introduction and overview. Canadian Journal of Fisheries, Aquatic Sciences. 53: 2540-2553.
6 Raines, ‚Rig shrimp test high for mercury” Mobile Register, January 27, 2002. analyzing data from Kennicutt, M. C., Green, R. H., Montagna, P., and Roscigno, P. F., 1996. Gulf of Mexico Offshore Operations Monitoring Experiment (GOOMEX), Phase I: Sublethal responses to contaminant exposure , introduction and overview. Canadian Journal of Fisheries, Aquatic Sciences. 53: 2540-2553.
7 Treffrey, J.H., Trocine, R.P., McElvaine, M.L., Rember, R.D., Concentrations of Total Mercury and Methylmercury in Sedimwnt Adjacent to Offshore Drilling Sites in the Gulf of Mexico, 2002.
8 U.S. Environmental Protection Agency, Environmental Assessment of Final Effluent Guidelines for Synthetic-Based Drilling Fluids and other Non-Aqueous Drilling Fluids in the Oil and Gas Extraction Industry (EPA-821-B-00-014, December 2000).
9 40 C.F.R §§ 435.10-435.47 See also, Effluent Limitations Guidelines and New Source Performance Standards for the Oil and Gas Extraction Point Source Category; OMB Approval Under the Paperwork Reduction Act: Technical Amendment; Final Rule, 66 Fed. Reg. 6850-6919 (Jan. 22, 2001); Oil and Gas Extraction Point Source Category; Final Effluent Limitations Guidelines and Standards for the Coastal Subcategory; Final Rule, 61 Fed.Reg. 6085-66130, (December 15, 1996).
10 U.S. Mineral Management Service, Gulf of Mexico Program, “Estimate of Annual Metric Tons of Mercury Discharged with Barite.”
11 Ben Raines, ‚A Trail of Misleading Mercury Information,” Mobile Register, May 19, 2002.
12 Gill, G., “Chemistry of Mercury to Methylmercury” presentation at Mercury Forum, May 20-21, 2002.