Mercury Content of Fish

Do you ever worry about the mercury content of fish and food safety? I do. My family and I consume a lot of fish. Most of us are avid anglers, and we catch fish often. We usually eat what we catch, too, so you can understand my concern about mercury in fish and how it relates to fish consumption. My husband and I catch mostly saltwater fish, while the sons-in-law and the grandsons engage mostly in freshwater fishing, especially for largemouth bass. They sometimes go saltwater fishing with us, too. In years past, before the big mercury content of fish scare, we might eat fish every day of a two-week beach vacation. We no longer do that because of food safety issues. When we spend time at the beach now, we’ll eat fish only once or twice during our stay, and we’ll freeze the rest of our catch to eat later. Frozen is never quite as tasty as fresh, but spreading out our fish consumption is safer. Below is some information about food safety and the mercury content of fish.

Mercury is a heavy metallic element that’s usually observed in liquid form. Man has been using mercury for thousands of years, dating back to ancient Egypt. It’s been used for a number of reasons – to improve overall health, to heal broken bones, in cosmetics, in salves, and to provide immortality. During the middle ages, alchemists used mercury in their attempts to turn base metals into gold. In more recent times, mercury has been used in thermometers, in dental fillings, as a topical antiseptic, in the production of fluorescent lights, in eye drops, in nasal sprays, and as a preservative in vaccines.

Today, mercury is used in some types of cosmetics, telescopes, neon signs, argon lamps, mercury-vapor lamps, in the mining of gold, in batteries, and in steel and other metal production. By far, however, the biggest use of mercury is found in coal-fired power plants.

There are some definite environmental issues with mercury. About half of the mercury in the atmosphere comes from natural sources, especially from erupting volcanoes and widespread forest fires. There’s no real way to control these occurances. The other half, however, come from human inventions and activity. Mercury seeps into the air, soil, and water from landfills, coal plants, steel plants, and hazardous waste incinerators and kilns.

The effects of pollution, including mercury pollution, are world-wide environmental issues. Exposure to mercury can cause devastating effects in humans and animals. In animals, mercury poisoning has been reported in seals, where the toxin damaged the animals’ immune systems. In humans and in animals, exposure to mercury has been linked to damage to the kidneys, the nervous system, the digestive tract, and the cardiovascular system. It is especially dangerous for young children, babies, and developing fetuses. Again, the problem of mercury pollution spans the globe, from the Great Lakes to our oceans to remote peaks in the Andes Mountains.

Methylmercury is an organic compound which contains mercury ions, and it’s very toxic to the environment. In fact, it’s the most toxic form of mercury. Unlike mercury, there are few natural sources for methylmercury. Most of it comes from human activities – the burning of inorganic mercury wastes and fossil fuels. Inorganic mercury is converted into methylmercury by organisms that don’t require oxygen. Such anaerobic organisms can be found in soil, in freshwater lakes and rivers, and in seawater. Humans, mammals, and birds can get methylmercury poisoning from eating fish with high concentrations of the toxic compound.

For years, people assumed that most freshwater fish were safe to eat and that it was only large saltwater fish that contained dangerous levels of mercury. There’s some basis for this belief, based on the way mercury breaks down. When methylmercury winds up in fresh water sources, like streams, rivers, and lakes, the molecules stick to decaying vegetation and decaying fish and animals. With the help of sunlight, a chemical process occurs that makes the methylmercury break down.

In saltwater sources like oceans, bays, and inlets, the salt poses a problem. The saltiness in saltwater comes from sodium and chloride. When methylmercury enters salt water, the molecules attach themselves to chloride, making it much harder for the sun’s rays to break down the mercury. As a result, methylmercury lasts longer in seawater, making it more readily available to saltwater fish. Unfortunately, recent evidence shows that the mercury content of fish from numerous freshwater sources is now dangerously high, too.

Freshwater fish were once thought to be safe from methylmercury, but that’s not the case now. In a study that was aired on ABC News, over 1,000 freshwater fish were tested for mercury. The fish came from some 300 different streams. Scientist were shocked to find that every single fish contained mercury. What was even more alarming was that about 25% of the tested fish contained dangerous levels of mercury – above the levels deemed safe by the EPA. Generally speaking, freshwater fish with the highest levels of mercury include largemouth bass, smallmouth bass, great northern pike, char, walleye, brook trout, rainbow trout, brown trout, pickerel, and some species of catfish. It seems that the mercury content of fish is increasing and spreading.

Saltwater fish are prime victims for concentrations of methylmercury. This is especially true of big predators that consume large numbers of other fish and shellfish. Some of the worst culprits as far as saltwater fish are concerned include sharks, king mackerel, swordfish, bluefin tuna, blackfin tuna, barracuda, bluefish, cobia, little tunny, seabass, and tilefish. For fish caught in tidal rivers, check the river’s levels of mercury by consulting the local Fish and Game. They’ll most likely be able to give you some food safety guidelines about consuming local fish species, along with specific mercury content of fish involved.

Large predators generally contain the highest levels of mercury. Have you ever wondered why this is so? Think about the food chain in lakes and oceans. Practically all fish species, including shellfish, have at least some traces of mercury in their bodies. Predators feed on shellfish and smaller fish, so the larger predatory species are consuming more mercury. The longer a predatory fish lives, the more methylmercury it consumes, and the bigger it grows. Which fish do anglers usually target? The answer is: large predators. That’s why most fishing lures are made to resemble fish and shellfish. I’ve never seen any lures or jigs made to look like algae. Nope, we fisherfolk are usually after the big boys – the very ones that usually contain the most mercury. Catch and release, anyone?

Mercury poisoning occurs when high levels of the element or of its compounds, including methylmercury, build up in an individual through the consumption of mercury-rich foods like affected fish. The toxicity can also be a result of inhaling mercury vapors or from exposure to mercury spills. Symptoms of mercury poisoning include increased heart rate, high blood pressure, vision problems, speech difficulties, and hearing loss. Individuals affected may also experience tingling, burning, and numbness of the extremities, along with lack of muscle coordination. The skin sometimes turns pink, develops a rash, or peels. Mercury poisoning can cause irreversible damage to the heart, lungs, brain, kidneys, and immune system. For developing fetuses, mercury can inhibit brain and nervous system development, leading to a host of later problems.

It’s always important to follow food safety guidelines, and that is certainly true with the mercury content of fish. If you’re fishing, get a copy of the state guidelines for fish consumption for the area in which you’re angling. This information is often provided by the state’s game and fish commission. It’s important to realize that some areas are more heavily polluted by mercury and methylmercury than others. Sometimes even bodies of water within the same state vary greatly when it comes to mercury levels. It’s always best, however, to play it safe. Women in their childbearing years, nursing mothers, and children under the age of six would do best to limit their seafood consumption to shellfish. Other saltwater fish choices that are usually safe in small amounts – up to one or two meals per week, depending on location – include pollock, pompano, tilapia, snapper, flounder, croaker, canned light tuna, haddock, salmon, and cod. Generally safe freshwater species include bluegill, redbreast, crappie, warmouth perch, and redear sunfish. Again, it’s important for you to check the safety of the specific area or body of water. By using up-to-date food safety guidelines, you can largely avoid the harmful mercury content of fish.