Harmful Substances Watch: Mercury

Fish have made this heavy metal quite famous, and restricted intake of fish has been recommended by a wide variety of public health organizations due to risk of mercury contamination. But do you know your mercury-and-fish limits? Canned tuna is the most likely source of mercury exposure for U.S. consumers who eat fish. Just how much can you eat each week and still stay safe?

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Like all environmental toxins, mercury can be found in great variety of locations and amounts. Some oceans are lined with ores that contain natural mercury deposits. The Mediterranean Sea, for example, contains cinnabar (mercury sulfide) deposits that can leech into the water and find their way into Mediterranean fish. Tuna from the Mediterranean tends to be higher in mercury than tuna from the Atlantic or the Pacific for this reason.


Human activities, however, can be an equally significant source of mercury contamination. Over 100 tons of mercury are released annually into the air by U.S. industries - primarily coal-fired power plants, municipal waste combustion facilities, and incinerators that handle medical waste. Mercury also finds it way into landfills across the country in the form of fluorescent light bulbs, thermostats, and electrical components (including components still used in automobiles).

Once deposited in the soil or in the air, mercury can be transported by natural ecological forces to groundwater, rivers, and oceans. This movement of toxins through our environment (along pathways called "transfer vectors") can bring mercury into the natural habitat of fish thousands of miles away from the original site of contamination.

When it comes to canned light tuna, a good ballpark guideline for safe mercury intake can be based on body weight alone. For every 10 pounds of weight, allow yourself just under one ounce (technically, 0.95 ounces) of canned light tuna per week. If you weigh 150 lbs., for example, limit yourself to 14 ounces (or approximately 2 cans) of tuna. For canned albacore tuna, however, this restriction becomes much greater, because canned albacore averages substantially more mercury than canned light. With albacore, for every 10 pounds of weight, allow yourself only 1/3rd of an ounce per week. In this case, if you weigh 150 pounds, restrict yourself to 5 ounces (less than one can) per week.


While body weight can give you an initial ballpark estimate for restricting your canned fish intake, it's important to note that your body and your lifestyle are unique. You may have other important sources of mercury exposure, and you may have unique metabolic needs when it comes to detoxification of mercury inside your cells. For these reasons, a truly personalized assessment of your mercury exposure and mercury risk can be helpful for planning your fish intake (and other dietary decisions as well).

Several health organizations, including the U.S. Environmental Protection Agency (EPA), have issued advisories cautioning pregnant women (and women considering pregnancy) against excess consumption of mercury-containing fish. For the latest EPA advisory, click here.


References:

1. Adams DH. (2004). Total mercury levels in tunas from offshore waters of the Florida Atlantic coast. Mar Pollut Bulletin 49(7-8):659-63.
2. Hood, E. (2003). A diet rich in fish. High-end consumers face more mercury risks. Environ Health Perspect 111(4):A233.
3. Kraepiel AM, Keller K, Chin HB et al. (2003). Sources and variations of mercury in tuna. Environ Sci Technol 37(24):5551-8.
4. Schober SE, Sinks TH, Jones RL, et al. (2003). Blood mercury levels in US children and women of childbearing age, 1999- 2000. JAMA 289(13):1667-74.
5. Storelli MM, Stuffler RG, and Marcotrigiano GO. (2002). Total and methylmercury residues in tuna-fish from the Mediterranean sea.
6. Food Addit Contam 19(8):715-20.
7. Sunderland EM. (2007). Mercury exposure from domestic and imported estuarine and marine fish in the U.S. seafood market. Environ Health Perspect 115:235-242.

Related Topics:

• WebMD Video: Mercury and Seafood
• Canned Tuna: Avoid if Pregnant?

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Everyday Toxins

Can you name something we depend on each day for our health and well-being that can also serve as the source of more than 100 harmful substances? Answer: everyday drinking water.

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It's difficult to come up with a comprehensive list of potentially toxic substances found in ordinary, everyday drinking water. That's because there are literally thousands of potential toxins and toxic sources. Every year, approximately 150 million tons of solid waste are dumped into our nation's 7,500 municipal landfills. Over time, toxins found in this solid waste can make their way down into the groundwater and eventually pass over into our drinking supply. Waste incinerators, manufacturing waste, and use of treated sewage sludge as an agricultural fertilizer are other common sources for toxic contamination of our drinking water.

The U.S. Environmental Protection Agency (EPA) sets standards -- and routinely monitors -- over 80 different toxic substances commonly found in our drinking water. Many of these substances are common agricultural pesticides, like alachlor, atrazine, or lindane. Others are heavy metals, like cadmium or lead. Also found are plastics like styrene or vinyl chloride. More than 1,000 potentially toxic substances have been found in drinking water from water supplies throughout the United States, and some toxins, like the pesticide atrazine, are found in virtually all city and county-regulated water supplies.

What you can do about all of these toxins is quite simple: you can choose your drinking water carefully, and treat it as an all-important aspect of your diet when it comes to quality. Even if you live in a region where watersheds are fairly clean, you are likely to need some type of home water-filtering system, unless you'd prefer to buy high-quality bottled water. We like solid-block carbon filters (especially the kind that can be installed under the sink). Reverse osmosis filters are also an excellent way to achieve high-quality drinking water.

When it comes to bottled water, we like natural mineral and spring waters (especially those bottled in glass rather than plastic). When water is allowed to naturally percolate down through the soil, it can pick up substantial amounts of many minerals, including minerals like calcium and magnesium that we often have difficulty optimizing in our diet. For this same reason, we typically avoid distilled water, because too many of these beneficial minerals get removed during the distilling process.

For more complete information about drinking water contaminants, click here.

References:

1. Environmental Working Group. (2005). A National Assessment of Tap Water Quality. National Tap Water Quality Database. December 2005 Report. Available online here.
2. Lubick, N. Emerging DBPs in drinking water. Environ Sci Technol. 2006 Dec 1; 40(23):7112-3.
3. Manassaram, D. M.; Backer, L. C., and Moll, D. M. A review of nitrates in drinking water: maternal exposure and adverse reproductive and developmental outcomes. Environ Health Perspect. 2006 Mar; 114(3):320-7.
4. Rodriguez-Mozaz, S.; de Alda, M. J., and Barcelo, D. Monitoring of estrogens, pesticides and bisphenol A in natural waters and drinking water treatment plants by solid-phase extraction-liquid chromatography-mass spectrometry. J Chromatogr A. 2004 Aug 6; 1045(1-2):85-92.
5. Sinclair, C. J.; Boxall, A. B.; Parsons, S. A., and Thomas, M. R. Prioritization of pesticide environmental transformation products in drinking water supplies. Environ Sci Technol. 2006 Dec 1; 40(23):7283-9.
6. Squillace, P. J.; Scott, J. C.; Moran, M. J.; Nolan, B. T., and Kolpin, D. W. VOCs, pesticides, nitrate, and their mixtures in groundwater used for drinking water in the United States. Environ Sci Technol. 2002 May 1; 36(9):1923-30.
7. Thacker, P. D. Pollutants persist in drinking water. Environ Sci Technol. 2005 Feb 1; 39(3):58A-59A.
8. Vieira, V.; Aschengrau, A., and Ozonoff, D. Impact of tetrachloroethylene-contaminated drinking water on the risk of breast cancer: using a dose model to assess exposure in a case-control study. Environ Health. 2005; 4(1):3.

Related Topics:

• Toxins in Dust Raise Risk of Asthma
• Environmental Illness: Toxins in our Environment

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