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Mercury and Fish Consumption









Holly Meehl


Questions Addressed

            What is mercury? Why is mercury in fish? How is mercury bad for you? How much fish can I eat without being negatively affected by mercury and still obtain all the health benefits of fish? If I’m pregnant how does mercury pose a threat to my baby? What are other risks of eating fish? Why is it good to eat fish?



            Since the beginning of mankind, people have used fish as a main source of food. Groups of people living near or on water were easily able to obtain a meal due to the delicacies that swam below. Today, people still enjoy fish and it is the staple form of nourishment for many societies. Seafood is especially enjoyed in America, from crab cakes in Maryland, to crawfish in New Orleans. Studies have shown that fish is a good source of protein and fat, and is a healthy option for a meal. Yet there is another side to the health aspects of fish. All seafood contains levels of mercury in their systems, and over time scientists have discovered that mercury is bad for humans. This paper will discuss how and where mercury forms and how mercury can affect humans due to our consumption of fish. For some people the health benefits of eating fish will outweigh the threat of mercury poisoning, yet others must seriously weigh the risks before biting into their fifth piece of sushi.

What Is Mercury and How Does it Get into Our Fish

            Mercury is a reactive heavy metal that can either come naturally from the earth in places like volcanoes, or from manmade structures. Mercury comes from humans through coal-fired electric plants, gold mining, the burning of garbage and waste, the making of chlorine, and institutional boilers. There are different ways people can become exposed to mercury. One way is if you break a product containing elemental mercury, such as a thermometer. You could also come into contact with it if you are using compounds that contain mercury. However, the most common way people come into contact with mercury is through eating fish and ingesting organic mercury or methylmercury (MeHg). Mercury gets into our fish because it is released into air from the man-made sources listed above and then can enter lakes, ponds, rivers, and oceans through rainwater. Once in the water it is converted by microbial activity into methylmercury. This methylmercury is then absorbed into the muscle tissue of the fish, and thus into our bodies when we eat fish. Larger, longer living fish thus have greater amounts of mercury inside them because they have been in the water longer and also have more body mass for the mercury to absorb into.

(Mozaffarian, D., Rimm, E., 2006)

(Mergler, D., Anderson, H., Chan, L., Mahaffey, K., 2007)


Why is Mercury Bad for You?


            For adults, large amounts of mercury ingestion can affect the brain and or kidneys. Symptoms of mercury poisoning can include tremors, irritability, shyness, disturbances in vision or hearing, or memory problems. When a pregnant woman consumes too much MeHg through fish, the mercury can cross the placenta and affect the brain development of her unborn child. When a fetus has such contact with MeHg it can affect how the baby learns, moves, and behaves later in life.







Pregnant Women and Mercury Levels:  A Study

            A scientific study was recently done on pregnant women and their levels of mercury in their hair and how such levels affected their unborn children. 1022 Inuit children from the Faeroe Islands who were born in 1986-1987 were chosen as part of the study. Their mothers’ diet was high in pilot-whale blubber and meat, which contains large amounts of methylmercury. The researchers measured the level of MeHg in the women’s hair at the end of their pregnancy, and consequently, due to their diet, the women’s hair contained large amounts of MeHg. The researchers then returned to the Faeroe Islands once the children were around seven years of age and subjected them to several tests. It was found that the high level of MeHg in the mother’s hair directly correlated with greater impairments of language, attention, and memory in these children.

            Yet, another study was done called the Seychelles Child Development Study, in which the same study was completed. The mother’s mercury levels were tested after their pregnancy, and the researchers performed tests on the children once they were older (around their ninth birthday.) In contrast to the Faeroe Island study, this study found a weak association between high levels of MeHg in the women’s hair and the child’s ability to perform on a speed and coordination test. The scientists concluded that prenatal exposure to MeHg did not present children with neurodevelopment risks. However, the amount of fish that the Seychellois women consumed was much less than that of the Faeroe Island women. The women from Seychelles ate the typical amount of fish a woman should eat while pregnant (a maximum of 12oz. with restrictions on certain types of fish.) Because the Faeroe women’s diet of whale meat is very high in MeHg levels, and is not typically normal for pregnant women around the world, their children’s impairments later in life made sense. Most women do not typically eat this amount of fish high in mercury, especially while pregnant, and this is why these mothers’ children had problems later in life.

(Lyketsos, C., 2003)


Benefits of Eating Fish: N-3 Fatty Acids

Fish contain fats called n-3 fatty acids (omega-3 fatty acids) which can be good for the body. The two types of these fatty acids which are the best for humans are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA.) A recent study showed that moderate intake of fish i.e. 1-2 servings per week or around 250-500mg/d of EPA and DHA is shown to reduce death in adults due to coronary heart disease by 36%. Researchers have also seen cases where DHA can be beneficial to the neurodevelopment of an unborn child. In fourteen trials it was shown that high levels of DHA consumption in pregnant women improved a child’s vision later in life. Another eight trials estimated that if pregnant women increased their DHA consumption by 50% between their 5th and 6th month of pregnancy it would later raise mental processing scores in their young children. Other positive associations have been seen between the increase of DHA during pregnancy and the result of raised behavioral attention scores, visual recognition memory, and language comprehension in the child’s infancy. This shows that essentially a certain amount of fish consumption is beneficial to pregnant women as well as adults.  

(Mozaffarian, D., Rimm, E., 2006)


Eating Fish and Getting Cancer?

Another possible risk for adults in relation to fish intake is cancer due to the PCBs (synthetic organochlorine compounds previously used in industrial and commercial processes) and dioxins (dibenzofurans which are organochlorine by-products of waste incineration). These are emitted into the air and could enter the bodies of fish. Although such emissions have decreased by 90% since 1987 they remain in the environment for a long time, and thus in the fish we eat today. However, studies have been done which show that there is little evidence of fish intake and an increased risk of cancer. No direct correlation has been found with cancer risk and fish consumption, and therefore the benefits of eating fish for adults outweigh such a risk.

(Mozaffarian, D., Rimm, E., 2006)

Mercury Maps: A study

            A mercury maps study marked the mercury levels of certain bodies of water in the U.S. and then created an equation to find the reduction of mercury air deposition needed in each area.  Because mercury gets into our water and fish through the air, such a reduction would result in lower mercury levels in the bodies of water and the fish we eat. Yet some bodies of water had to be left out of the study due to the presence of POTWs (Publicly Owned Treatment Works), and/or pulp and paper mills, and/or the presence of mercury mines, gold mines, or chlor-alkali facilities. These places contain non-air sources of mercury that would significantly affect the study’s results. Below is a chart marking where the amounts of mercury reduction needed in each area. Clearly Maine, Florida, and bodies of water along the Mississippi River have high levels of MeHg with a necessary reduction of over 75% needed. The areas marked in yellow are the areas where the non-air sources of mercury mentioned above are located and thus could not be included in the study.

Map showing the percent reduction in mercury required to meet the fish tissue mercury criterion


General Guidelines of What Fish to Eat and How Much

            The American Heart Association suggests eating fish at least twice a week because it is such a great source of protein and omega-3 fatty acids.  Here is a chart which lists common fish and shellfish eaten in America with their amounts of mercury and their amount of Omega-3 fatty acids.


Mean mercury level in parts per million (ppm)

Omega-3 fatty acids
(grams per 3-oz. serving)

Canned tuna (light)









Salmon (fresh, frozen)












Flounder or sole   





















Mahi mahi






Fresh or frozen tuna



Red snapper



Orange roughy




Here are a list of fish with the highest levels of mercury, about 1 ppm (parts per million.)


Mean mercury level in
parts per million (ppm)

Omega-3 fatty acids
(grams per 3-oz. serving)







Tilefish (golden bass or golden snapper)



King mackerel




It is advised that women who are pregnant or want to become pregnant should not include any of these types of fish in their 12oz per week limit. Also young children should not consume any of these fish due to the risk of impairment to their neurodevelopment. All other adults can eat up to 7oz of these fish per week. Adults in general can eat up to around 14oz of fish per week containing mercury levels around 0.5 ppm.



            From the evidence observed it can be concluded that mercury is the biggest threat for pregnant women and their children. Neurological damage could occur in a child whose mother ate over 12oz of high level mercury fish while pregnant. Such cases were seen in the study involving the Faeroe women and their children. However, fish can also be beneficial to pregnant women due to the consumption of DHA. If pregnant women simply watch how much fish they eat and do not surpass the 12oz level or eat fish on the restricted list their children should be safe and perhaps benefit from a fish encompassing diet. Adults do not have to worry about the risks of mercury poisoning through fish unless extremely large amounts of high mercury fish are consumed. The benefits for adults far outweigh the risks because fish is a good source of fat and protein and is even seen to prevent coronary heart disease.






General Sites to Learn About Mercury


Works Cited

American Heart Association. 2008. Fish, Levels of Mercury and Omega-3 Fatty Acids. Retrieved

January 20, 2008. From

Department of Health and Human Services: Agency for Toxic Substances and Disease Registry. 1999. “Public Health Statement for Mercury.” Retrieved February 10, 2008. From

Donna Mergler, Henry A Anderson, Laurie Hing Man Chan, Kathryn R Mahaffey, et

al. (2007). Methylmercury Exposure and Health Effects in Humans: A Worldwide Concern. Ambio, 36(1), 3-11.  Retrieved February 10, 2008, from Sciences Module database. (Document ID: 1246377131).

Lyketsos, C. “Should pregnant women avoid eating fish? Lessons from the Seychelles.” The

Lancet. Volume 361, Issue 9370, 17 May 2003, Pages 1667-1668. Retrieved January 27, 2008. From Science Direct.

Mozaffarian, Darius, Eric Rimm. Fish Intake, Contaminants, and Human Health: Evaluating the

            Risks and Benefits. A clinical review. The Journal of the American Medical Association.

2006;296:1885-1899. Retrieved January 22, 2008.

“Report: Fish Mercury Risk Underestimated.” 2001. with Retrieved

January 20, 2008. From

Rhode Island Department of Health. 2008. Office of Environmental Risk Assessment: Mercury

In Fish. Retrieved January 20, 2008 From

U.S. Environmental Protection Agency. 2005. “Mercury Maps: Linking Air Deposition and Fish

            Contamination on a National Scale.” Retrieved February 4, 2008. From






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