Fish Consumption
Most of us know that fish can contain mercury and that eating too much of certain species can harm your health. But, do you know how to eat fish safely to protect yourself and your family?
The mercury in fish is methylmercury, which is one type of organic mercury. Organic mercury is particularly harmful to all living beings because it can enter any cell in the body. Mercury is a neurotoxin and fetuses, infants and young children (under 6) are most vulnerable to its effects as their brains are still developing. The National Academy of Sciences (NAS) reports that “Chronic, low-dose prenatal methylmercury exposure from maternal consumption of fish has been associated with…poor performance on neurobehavioral tests, particularly on tests of attention, fine-motor function, language, visual-spatial abilities (e.g. drawing) and verbal memory”. In adults, symptoms of mercury poisoning include fatigue, pain, numbness, stomach upset, memory loss, confusion and insomnia.
In our environment, mercury comes from both natural sources (deposits, volcanic eruptions, etc) and from man-made sources (burning of coal and other fossil fuels, cement plants, some chlor-alkali plants, incinerators, disposal of mercury-containing products, artisinal gold mining, etc.). Today, about 2/3 of the mercury in our environment is from human activities. Mercury from any of these sources pollutes our atmosphere, soil and water. In sediments, microorganisms convert elemental mercury into methylmercury, which is absorbed or ingested by aquatic plants and animals. Because mercury bioaccumulates, the larger fish that are high on the food chain are usually the most contaminated with mercury.
Because mercury bioaccumulates in humans as well, you need to pay attention to guidelines on what is safe to eat. To add complexity to this task, the guidelines are not consistent between federal agencies. SafeMinds advocates for using the most stringent guidelines, particularly if you are pregnant or nursing. The Food and Drug Administration regulates commercially sold fish and has set a standard that it can contain no more than 1 mg/kg of mercury which is equivalent to 1part per million (ppm) of mercury. However, the FDA has largely allowed the fishing industry to monitor itself and independent testers have found fish available for sale that exceed this level.
The EPA regulates fish caught from lakes nationwide and has established a reference dose of mercury for the public of 0.1mcg/kg body weight/day. This limit, later supported by the NAS, has an uncertainty factor of 10 built in and is designed to keep a person’s blood mercury below 4-5mcg/liter, a level at which there are unlikely to be any statistically significant effects on children based on results from research in the Faroe Islands.
According to the EPA, women who are pregnant, planning to become pregnant or nursing, and young children should not consume more than 3mcg of mercury a week for every 10 pounds that they weigh. So for example, a 60 pound child, should not eat more than 18mcg of mercury a week, which is equivalent to about one third of a can of white (albacore) tuna (averages 10mcg/ounce so 60 mcg in a 6 ounce can) or about one can of light (skipjack or yellowfin) tuna (averages 3.3mcg/ounce or 20mcg in a 6 ounce can). These women and children should avoid swordfish, shark, king mackerel, tilefish, ahi, marlin and other large predatory fish entirely. This warning also includes large lake fish like jack, walleye and bass caught in waters that are under a mercury advisory.
For everyone else, there is no hard data, but you can probably consume up to three times this amount safely. Keep in mind that sushi is often made with predatory fish species and that the frequency that you eat fish is as important as the species that you eat. Consider, also, that you may have mercury exposure from air pollution and dental amalgam, in particular, which add to your body’s total load.
If the above calculations make your head spin, the National Resources Defense Council has two excellent tools on their Website. One is a mercury calculator, which will help you determine how much fish is safe to eat. The other is a list for you to print out and take to the grocery store that categorizes fish and seafood according to its relative safety. Another simple rule of thumb is to not eat fish that are bigger than your dinner plate.
Finally, remember that the amount of mercury in fish is not static, mercury can vary from fish to fish within the same species and studies are continuing to show health effects at lower and lower levels of mercury. At the same time, our environment is becoming more contaminated. As of 2006, the EPA lists mercury advisories on lakes and rivers in 48 states. As of 2006, 23 states have statewide mercury advisories for all freshwater lakes and rivers. Twelve states have mercury advisories for their coastal waters. A recent study has shown that mercury levels in the North Pacific Ocean have risen approximately 30% in the past 20 years (Sunderland et al. 2009). In order to protect yourself and your family, be sure to keep an eye out for updates to these advisories.
For Further Reading:
“Diagnosis: Mercury – Money, Politics and Poison” by Jane M. Hightower, MD
“Bitter Sea: The Human Cost of Minimata Disease” by Akio Mishima
Both books are available through the SafeMinds Amazon store.
