Mercury in Fish

Mercury is one of the most toxic heavy metals. Fish and seafood caught closer to industrial areas are more likely to have higher levels of mercury and other contaminants. Adults wigh levels of mercury in their tissues experience symptoms of muscle weakness, fatigue, headaches,irritability, hair loss, inability to concentrate, numbness and tigling around lips, fingers and toes, problems with vision, hearing, speaking, and balance. High levels of mercury increase risk for heart disease, while decreases one's level of selenium, an important antioxidant. Selenium is also important to recycle glutathione, a critical antioxidant to the liver's ability to neutralize many toxins. In extreme cases, mercury toxicity can lead to tremors, coma, and even death.

Fish absorb mercury from the organisms they feed on. The older and the larger a fish, the higher the level of mercury it contains. Nearly all fish contain some mercury, but predator fish and large-sized species, for example tuna, are usually high in methyl mercury, a highly toxic form. Nursing mothers, and young children should avoid eating high-mercury fish such as swordfish, tilefish, and king mackerel, and select small ocean or farm-raised fish. From 8 to 16 servings (a serving of fish is 3 to 6 ounces) of fish that are not high in mercury per month. Pregnant women should avoid fish and sea food, for mercury can easily cross the placenta, and disrupt the development of the baby's brain and nervous system.


Mercury Levels in Commercial Fish and Seafood
As measured in maximum parts per million (ppm)

Shark 4.54ppm
Tilefish (Gulf of Mexico) 3.73
Swordfish 3.22
King Mackerel 1.67
Halibut 1.52
Snapper 1.37
Lobster 1.31
Tuna (Fresh/Frozen) 1.30
Grouper 1.21
Monkfish 1.02
Bass (Salt water) 0.96
Marlin 0.92
Tuna (Canned) 0.85
Orange Roughy 0.80
Pollock 0.78
Spanish Mackerel (S. Atlantic) 0.73
Bluefish 0.63
Crab 0.61
Tilefish (Atlantic) 0.53
Cod 0.42
White Croaker (Pacific) 0.41
Squid 0.40
Butterfish 0.36
Anchovies 0.34
Perch (Freshwater) 0.31
Whitefish 0.31
Catfish 0.31
Spiny Lobster 0.27
Oyster 0.25
Scallops 0.22
Salmon (Fresh/Frozen) 0.19
Mackerel (N. Atlantic) 0.16
Herring 0.14
Mullet 0.13
Trout (Fresh Water) 0.13
Talapia 0.07
Pickerel 0.06
Shrimp 0.05
Crawfish 0.05
Haddock 0.04
Sardine 0.04
Perch (Ocean) 0.03

Sources:
US Department of Health and Human Services
and US Environmental Protection Agency

Dr. Laurie Steelsmith. Natural Choices for Women's Health(New York: Three Rivers Press, 2005, pp. 25-29).