Many people eat fish as part of a healthy diet, but certain varieties contain high levels of mercury, which may be dangerous for developing fetuses and young children.
Good news is that most popular fish species contain low amounts of mercury and pose little threat to most individuals. According to FDA recommendations, pregnant women should consume 8-12 ounces of seafood low in mercury each week.
1. Salmon
Mercury levels in wild and farm raised salmon are extremely low; according to the Food and Drug Administration (FDA), their mercury content falls well under their weekly recommendation of six ounces for adults. Salmon also provides omega 3 fatty acids, protein and vitamin D benefits – essential elements for pregnant women and children during gestation and lactation.
Fish can accumulate mercury as they live and consume other fish, with larger predatory fish typically having higher mercury levels due to eating more. This process is called biomagnification. Mercury pollution builds over time in the environment; consequently, areas near sources such as coal-fired power plants may experience fish with elevated mercury concentrations.
Mercury does not readily leave the body, meaning these fish could continue accumulating it as they grow and consume other fish species. That’s why eating various kinds of seafood including smaller species with shorter lifespans may help protect you.
To reduce mercury exposure, the best approach is to consume a wide range of fish species – particularly smaller and younger species with shorter lifespans – in your diet. Avoid specific species known for having high mercury levels such as shark, marlin, king mackerel, orange roughy tilefish from Gulf of Mexico and southern Atlantic and tuna (bigeye, albacore and yellowfin species), as well as shad, herring and anchovy (Note: Women who are pregnant, breastfeeding or planning to become pregnant within one year have specific recommendations from FDA). For more information visit Smart Seafood Buying Guide with charts detailing each seafood option available from these.
2. Shrimp
Mercury is a toxic element that can harm humans and their nervous systems. Mercury can be found both as gaseous elemental mercury and its organic form methylmercury in the environment, with elemental mercury found in air, soil and water sources and bacteria turning it into methylmercury that plants and animals absorb through food sources such as fish consumption – larger fish eaters tend to accumulate greater levels of this toxin than smaller ones; common sources include shark, swordfish, king mackerel and tilefish which pregnant women, nursing mothers as well as children should avoid.
At present, most fish and shellfish are relatively low in mercury content. Small fish such as anchovies, sardines, salmon, catfish, flounder, haddock, mullet plaice and pollock; shrimp cod clams mussels as well as canned tuna and salmon contain relatively minimal levels of mercury – providing you with all the vital nutrients essential to health. Eating an array of these species will give your body all it needs for proper functioning.
Pregnant women, nursing mothers and young children should consume up to 12 ounces (2 average meals) a week of lower mercury fish such as shrimp, canned light tuna salmon or catfish. If you catch your own fish, make sure that it complies with local advisories before eating it. One week of increased fish intake won’t have much of an effect on methylmercury levels in your body; simply reduce how much fish you eat the following week. Selenium found in some seafood can help bind with mercury to reduce its toxic effects and may explain why people who regularly eat shrimp don’t experience symptoms associated with mercury poisoning such as headache, dizziness, numbness or clouded thinking.
3. Tuna
Anyone who’s ever read a seafood guide knows the ominous warning that certain fish contain high levels of mercury. That’s because industrial processes that release mercury into the ocean convert it into methylmercury that is absorbed by phytoplankton and spread up through food chains before larger predators such as tuna eat those smaller fish to gain even more methylmercury in their flesh.
Larger and longer-living fish tend to contain higher mercury levels due to spending more time near areas where methylmercury production occurs, which explains why shark, swordfish and fresh tuna all tend to have greater mercury concentrations than canned tuna and smaller species such as cod.
Avoiding tuna altogether would not be recommended; it provides essential omega 3s and protein. Instead, we should focus on choosing lower mercury options like salmon and shrimp as ways of mitigating risks.
However, you can avoid the worst forms of mercury found in canned tuna by opting for wild-caught, low mercury fish such as Wild Planet’s skipjack tuna which boasts a mercury level of just 0.067ppm – more than 14 times lower than FDA action limits and considered “Best Choice” by the Environmental Protection Agency.
Wild Planet controls the average mercury levels in their canned tuna and conducts annual third-party testing to verify their products are mercury free. Furthermore, fresh yellowfin, albacore, and bigeye tuna have average mercury levels 6-8 times lower than FDA’s action limit and could provide you with alternatives that meet these criteria.
4. King Mackerel
Mercury that enters the ocean can quickly convert to methylmercury, which diffuses into phytoplankton and is consumed by smaller fish before eventually reaching tuna, which contains 10 million times as much mercury than water itself! Furthermore, mercury levels in larger fish such as tuna can quickly accumulate into levels that pose serious health threats for people who consume them.
Although avoiding high mercury fish such as swordfish, shark and king mackerel is advised, eating lower mercury seafood such as cod and salmon is still an effective way to get omega 3 fatty acids that promote healthy fetal and infant development and brain function. It’s important to remember, though, that even such low mercury fish could contain mercury if improper storage or processing procedures were applied during processing.
Consuming seafood from licensed sources can help ensure any heavy metals are eliminated and not consumed by consumers, and properly storing seafood reduces risks of bacteria contamination and food-borne illness.
Zumpano recommends restricting mackerel consumption to Atlantic and Mediterranean varieties that contain inflammation-fighting omega-3s but are low in mercury content, such as Atlantic or Mediterranean mackerel. She cautions against eating Spanish mackerel from Spain’s western Atlantic waters and Gulf of Mexico, along with orange roughy and Chilean sea bass from this area – opting for alternatives like shrimp or pollack instead if necessary.
5. Tilefish
Tilefish (commonly referred to as golden snapper or the clown of the sea) may look tempting with its firm texture and lobster-like flavor; however, this fish should be avoided due to high mercury levels. According to the Environmental Defense Fund’s seafood selector tool, tilefish caught near oil rigs in the Gulf of Mexico had elevated mercury levels whereas fish caught further away showed much lower mercury concentration.
Most ocean fish, such as shrimp, canned light tuna and salmon, contain low mercury concentrations. However, certain species such as shark, swordfish and king mackerel contain higher mercury concentrations; pregnant women and children should avoid these fishes to protect their health. Both the FDA and EPA advise pregnant women and children avoid these types of species altogether.
Airborne mercury enters oceans where microorganisms convert it to methylmercury, which accumulates up the food chain and collects in aquatic habitats. Eating fish containing high concentrations of methylmercury may lead to health issues in humans including neurodevelopmental delays for infants and toddlers; mild amounts may cause lips, fingers or toes tingling while severe exposure can result in hearing or vision problems, paralysis and even death.
Mercury enters the environment through multiple sources, but most comes from coal-fired power plants as a byproduct of combustion, with emissions also coming from wastewater treatment plants and incinerators. Regulations have been put in place to control these potential sources and thus limit how much mercury ends up in fish, as well as through biomagnification, into humans. Other contributors of mercury pollution include gold mining waste products, paper mill waste and leather tanning waste. Countries like Japan have implemented regulations which limit mercury in waterways and groundwater supplies.