Mercury is a natural element that is found in very small quantities in air, water and all living things. Mercury can find its way into food in a number of ways including: natural recycling, volcanic activity, burning of fossil fuels, and pollution. There has been an increased concern about mercury in seafood as they should be.
Mercury levels in the northern Pacific Ocean have risen about 30 percent over the past 20 years and are expected to rise by 50 percent more by 2050 as industrial mercury emissions increase, according to a 2009 study led by researchers at the U.S. Geological Survey and Harvard University.
Mercury-containing plants and tiny animals are eaten by smaller fish that are then gobbled up by larger fish, whose tissue accumulates mercury. That’s why larger, longer-living predators such as sharks and swordfish tend to have more of the toxin than smaller fish such as sardines, sole, and trout.
A group of scientists and policy analysts pointed out that a 6-ounce serving of salmon contains about 4 micrograms of mercury vs. 60 micrograms for the same portion of canned albacore tuna—and 170 micrograms for swordfish.
When you eat seafood containing methylmercury, more than 95 percent is absorbed, passing into your bloodstream. It can move throughout your body, where it can penetrate cells in any tissue or organ.
The Food and Drug Administration lists these fish with some of the highest levels of mercury:
- shark
- swordfish
- some varieties of tuna
- orange roughy
- marlin
- king mackerel
- tilefish
To avoid mercury, the FDA recommends limiting yourself to approximately 12 ounces of fish, or two meals, per week. Some of the most commonly eaten fish low in mercury include canned light tuna, salmon, pollock, catfish and shrimp. The FDA also notes that white albacore tuna has a higher mercury content than canned light tuna. Limit albacore tuna to one meal, or 6 ounces, per week.
As far as shell fish and other seafood is concerned, some of the least amount of mercury is found in:
- scallops
- clams
- shrimp
- oysters
The Natural Resources Defense Council has a list of fish that contain the lowest levels of mercury. These include:
- anchovies
- catfish
- flounder
- hake
- haddock
- herring
- salmon
- trout
- whitefish
- pollock
- sardines
While all of these fish are low in mercury, NRDC notes that farmed salmon should be avoided because it can contain high levels of another chemical with serious long-term health effects -- PCBs (Polychlorinated biphenyl). The NRDC also recommends avoiding haddock and flounder because these fish are low numbers due to extensive fishing.
