Seafood & the Health Concerns of Mercury Bioaccumulation
It is nearly impossible to debate that fish and seafood have become a cornerstone of much of the American diet. This resurgence in popularity has been spurred by growing numbers of medical studies and nutritional claims touting the health effects gained by fish consumption. An already stalwart marketplace in Europe and Asia working hard to meet the increasing demand has only bolstered this. There was much seafood to be had at one time, caught as needed from uncontaminated waters in a sustainable way without the faintest worry or health concern able to meet the demand of the world’s population. However, in the last thirty to forty years, seafood stocks have been over-trawled, over-farmed, and waters have been contaminated making the remaining stock young, small, weak, and poisoned. The most notable contaminant raising consumer controversy is mercury, but knowing how much and which variety of seafood can be safely consumed are more difficult to discern.
First, the historical changes that led to there being few fish left in the sea to be guiltlessly consumed without worry of neurotoxins are a fairly simple chain of reactions. An industrial boom of various growth and technologies led to increases in population, in turn leading to higher demand for all food, including seafood and fish. This increased demand coupled with more technology led to bigger, faster ships that could collect fish in new and more efficient ways, deeper in the ocean, with larger hauls. These larger hauls were enabled by advances in refrigeration and sped to market shelves by both truck and plane. Medical advances and the increasing ease of communication led to the broadcast that fish and seafood provided heart health benefits in a low fat, high protein, and nutrient-rich package. Fish contain the sought after omega-3 fatty acids and have been shown to reduce negative forms of cholesterol when part of a balanced diet (Stibich).
Not so suddenly, the waterways have been commercially scavenged to the point that certain ocean stock are depleted to the point of projected ecosystem collapses from which some stocks will be unlikely to return. The National Oceanic and Atmospheric Association (NOAA), “in their annual Fisheries of the United States publication, reports that the total amount of seafood consumed by the U.S. in 2005 was 4.8 billion pounds, an amount greater than all national totals except those of Japan and China” (Damassa). Of that 4.8 billion pounds, per capita consumption weighed in at 16.2 pounds of fish and shellfish per person (7.3 kg) in 2005, markedly higher than the 2001 total of 14.8 pounds (6.7 kg) per person, “This trend is particularly relevant in light of a growing U.S. population and recent studies that predict global fisheries may collapse by mid-century if they are not managed more sustainably” (Damassa). Despite media coverage of the oft stigmatized aquaculture practices associated with negative environmental penalties, shrimp varieties continued to be the most consumed by Americans proving worrisome for the future of the species and its ecosystem.
Tragically, in this windfall of global progress, the waterways and oceans became polluted, in large part directly due to human actions such as mining, industrial outputs such as solid waste and combustion byproducts, and general waste dumping. Mercury, an element found in nature has become more and more abundant in nature through its tendency to leech into waterways and therefore, directly into the food chain. It has become noted as an irreversible bioaccumulator in the very fish and seafood a large portion of the world has been relying on for their heart healthy nutrients, everyday existence, cultural identities, and livelihoods. Fish and seafood store the mercury in their bodies that they encounter in polluted water and sediment. They also store mercury from sources ingested by consuming algae, plankton, and other fish. This mercury then becomes abundant in their flesh and builds up throughout their lifespan. Coupled with overfishing all stocks for larger, more popular and commercially viable predator fish such as swordfish and tuna, those which had bioaccumulated more mercury in their flesh size and lifespan, the average consumer is increasingly being served a larger portion of contamination. This contamination then in turn bioaccumulates in human consumers in the same method as it did in the seafood or fish, however, it has far more pronounced health effects, especially depending on the level of risk of that the consumer.
Most often contamination is found in the form of methylmercury (MeHg), “a potent neurotoxin that is among the most widespread contaminants affecting our nation’s aquatic ecosystems” (Brumbaugh, 7). This form of mercury contaminant is found almost entirely in seafood and fish sources taken into the human body via diet. It is extremely toxic and dissolves in water. Methylmercury impairs the neurological development of the at risk populations of the unborn, infants, and children under the age of six. These neurological impairments may affect cognitive thinking, memory, attention, language, and fine motor and visual spatial skills. “The National Research Council, in its 2000 report on the toxicological effects of methylmercury, pointed out that the population at highest risk is the offspring of women who consume large amounts of fish and seafood. The report went on to estimate that more than 60,000 children are born each year at risk for adverse neurodevelopmental effects due to in utero exposure to methylmercury” (U.S. Geological Survey, http://www.usgs.gov/themes/factsheet/146-00/).
Therefore, an advisory also was also issued for pregnant and nursing women as well as those women of childbearing age who might become pregnant. The mother may show no symptomatic effects of mercury ingestion or contamination and still there will be a display of marked disabilities in the fetus. In turn, as a result of several studies on maternal and child health effects, most notably the Faroe Islands study published in 2004 by researchers at Harvard School of Public Health, the federal government has issued advisories and guidelines concerning the type of fish to avoid as well as the portion sizes acceptable to be consumed (Wright, 1). This advisory, issued in March 2004 as a joint proclamation by the Food and Drug Administration and the Environmental Protection Agency contains the following three main directives to at risk populations:
“1. Do not eat Shark, Swordfish, King Mackerel, or Tilefish because they contain high levels of mercury.This does not mean that the general adult population is safe from the threat of mercury, however. Adults, especially the elderly, can experience ill effects of too much mercury in their diet. Just as mercury bioaccumulates in fish and seafood, it may also accumulate in the adult human’s nervous system causing varied symptoms. Disorientation, impaired vision, speech, coordination, hearing, and walking may all occur, however, these are frequently linked to other health issues, leaving mercury poisoning to be an elusive diagnosis. More damaging levels of methylmercury can even lead directly to kidney and brain damage, some of which can be irreversible.
2. Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury.
• Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.
• Another commonly eaten fish, albacore ("white") tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.
3. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don't consume any other fish during that week.” (http://www.cfsan.fda.gov/~dms/admehg3.html)
There are federal fish advisories as well as those issued by state and local governments individual to different bodies of water, different species of fish, as well as distinctive contaminants such a methylmercury, dioxins, PCBs (polychlorinated biphenyls), and other organic contaminants. Almost all states, especially those who are part of the coastal water system hold updates and advisories, however, it is important to remember that methylmercury can be a more deceptive contaminant which cannot be lessened in the fish unlike other compounds that may only accumulate in certain areas such as skin, organs, or scales. “Younger fish tend to have lower concentrations of mercury than older, larger fish within the same waterbody. Mercury concentrates in the muscle tissue of fish. So, unlike PCBs, dioxins and other organic contaminants that concentrate in the skin and fat, mercury cannot be filleted or cooked out of consumable game fish” (U.S. Geological survey, http://www.usgs.gov/themes/factsheet/146-00/).
Therefore, it is up to each consumer to stay abreast of advisories and be informed about their dietary choices. A severe lack of regulation exists throughout the marketplace, both from a national and global standpoint. “Eighty percent of seafood consumed in the U.S. is currently imported” (Damassa), leaving much to the imagination concerning poaching, catch methods, freshness, and sustainable sources. According to the American Dietetic Association, variety is really the key to consumption. “For the majority of people who consume commercial fish, eating a variety of seafood, especially oily or dark meat species with higher levels of omega-3s, one or two times per week is enough” (Welland, 33). That way both the health effects can be gained, but with a high level of information, contaminants can be avoided for the most beneficial outcome.
Bibliography
Brumbaugh, William G., et. al. (Septermber 2001) “A National Pilot Study of Mercury Contamination of Aquatic Ecosystems Along Multiple Gradients: Bioaccumulation in Fish,” Biological Science Report, U.S. Department of the Interior, U.S. Geological Survey, (USGB/BRD/BSR-2001-0009)
Damassa, Tom (2-17-2007) “Recent Trends in U.S. Fisheries and Seafood Consumption.” Fisheries of the United States 2005, National Marine Fisheries Service, Fisheries Statistics Division, NOAA, Silver Spring, MD [Accessed 7- Dec-2008]
Rados, Carol. (May 2004) “FDA, EPA Revise Guidelines on Mercury in Fish.” FDA Consumer Magazine. http://www.fda.gov/fdac/features/2004/304_fish.html [Accessed 1-Dec-2008.]
Stibich, Mark, Ph. D. “The Best Types of Fish for Health.” About.com. http://longevity.about.com/od/lifelongnutrition/a/fish_mercury.htm [Accessed 5-Dec-2008]
Wright, Liz Borod. (October 21, 2005) “How Safe is a Seafood Diet? Experts Disagree on Toxic Hazards From Consuming Fish” ABC News. http://abcnews.go.com/Health/Diet/story?id=1189930&page=1 [Accessed 5-Dec- 2008]
U.S. Department of Health and Human Services and the U.S. Environmental Protection Agency. (March 2004) “What You Need to Know About Mercury in Fish and Shellfish” http://www.cfsan.fda.gov/~dms/admehg3.html [Accessed 6-Dec-2008]
U.S. Geological Survey. (October 2000) “Mercury in the Environment” http://www.usgs.gov/themes/factsheet/146-00/ [Accessed 2-Dec-2008]
Welland, Diane, MS, RD. (November 2008) “Holy Mackerel! Go Fish for an Ocean of Omega-3 Benefits” Today’s Dietitian, Vol. 10, No. 11, pages 28-33.
Not quoted specifically in this paper, however the inspiration for all my interest in seafood:
Grescoe, Taras. (2008) Bottomfeeder: How to Eat Ethically in A World of Vanishing Seafood. New York, NY: Bloomsbury.
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