Sushi is a popular dish that originated in Japan and has gained worldwide popularity. It consists of vinegared rice combined with various toppings and fillings, such as raw seafood, vegetables, and eggs. While sushi can be a nutritious meal, there are concerns about mercury levels in some types of sushi. Mercury is a heavy metal that can accumulate in certain fish and shellfish at levels high enough to cause health problems for humans when consumed regularly.
Quick Answers
– The fish highest in mercury are king mackerel, marlin, orange roughy, shark, swordfish, tilefish, and bigeye and ahi tuna.
– Salmon, pollock, catfish, tilapia, shrimp, anchovies, clams, and crab tend to be low in mercury.
– Mercury levels vary by species and size/age of fish. Larger, longer-lived predatory fish accumulate the most mercury.
– Pregnant women, nursing mothers, and young children are advised to avoid high mercury fish and eat a variety of lower mercury seafood.
– Adults should also limit consumption of high mercury fish to no more than once per week.
– Cooking and processing does not destroy mercury in seafood. Mercury levels found in the raw product remain after cooking.
Mercury in Fish and Seafood
Mercury is present naturally in the environment but human activities like coal burning and gold mining have increased levels in waterways. Mercury builds up in the aquatic food chain, bioaccumulating in predator fish that eat many smaller contaminated fish over their longer lifespans. The bigger the fish and the higher on the food chain, the higher the mercury concentration. This is why large predatory fish like tuna and swordfish tend to have much higher mercury than smaller fish like sardines and anchovies.
The most common form of mercury found in fish is methylmercury, which is the most toxic and readily absorbed by the human body. Consuming fish with high levels of methylmercury can affect the developing nervous system, especially in fetal and child development. That is why the US FDA and EPA provide guidelines for limiting mercury exposure from seafood consumption. They advise children, pregnant women, and nursing mothers to completely avoid fish with the highest mercury levels.
Fish High in Mercury
The fish that tend to be highest in mercury are:
King mackerel – This large predatory fish has average mercury levels around 0.73 ppm, one of the highest averages among common seafood.
Marlin – Another large predatory sport fish popular for its meat, marlin (particularly blue marlin) has mercury concentrations from 0.48-1.45 ppm.
Orange roughy – This deep sea fish lives up to 150 years, allowing it to accumulate significant mercury over its lifespan. Levels around 0.55 ppm.
Shark – Long living apex predators, shark meat contains average mercury concentrations between 0.98-1.45 ppm.
Swordfish – Another elongated-bodied predatory fish, swordfish contains mercury levels ranging 0.97-1.45 ppm.
Tilefish (Gulf of Mexico) – With mercury levels averaging 0.45-1.45 ppm, tilefish caught in the Gulf of Mexico has one of the highest recorded averages. Atlantic tilefish are lower.
Bigeye and ahi tuna – Large tuna varieties used for sushi like bigeye and yellowfin (ahi) can have elevated mercury levels around 0.58-1.09 ppm. Skipjack and canned light tuna are lower mercury options.
Mercury Levels by Species
Here are the typical mercury level ranges for some common types of seafood:
| Fish Type | Mercury Level (ppm) |
|---|---|
| King mackerel | 0.73 |
| Marlin | 0.48-1.45 |
| Shark | 0.98-1.45 |
| Orange roughy | 0.55 |
| Bigeye tuna | 0.58-1.09 |
| Swordfish | 0.97-1.45 |
| Tilefish (Gulf of Mexico) | 0.45-1.45 |
| Ahi tuna | 0.38-0.76 |
| Chilean sea bass | 0.28-0.57 |
| Grouper | 0.27-0.64 |
| Bluefish | 0.23-0.84 |
| Snapper | 0.06-0.64 |
| Halibut | 0.14-0.26 |
| Tuna (canned light) | 0.12 |
| Pollock | 0.11 |
| Salmon | 0.01-0.29 |
| Tilapia | 0.013 |
| Sardines | 0.013 |
| Anchovies | 0.012 |
As shown, larger predatory fish like shark, swordfish, and bigeye tuna as well as long-lived fish like orange roughy and tilefish have some of the highest recorded mercury levels. Smaller fatty fish and shellfish tend to accumulate less mercury.
Mercury in Tuna for Sushi
For sushi, the tuna varieties with the most concerns about mercury are bigeye tuna and yellowfin/ahi tuna. These tuna can exceed 0.5 ppm mercury. Albacore tuna is also moderately high in mercury while skipjack and canned light tuna are lower mercury options for pregnant women and children.
Here are the mercury facts on tuna commonly used for sushi:
Bigeye tuna – Used for sashimi and higher end sushi, bigeye tuna contains approximately 0.58-1.09 ppm mercury. This is one of the highest levels for tuna.
Yellowfin/Ahi tuna – Yellowfin tuna is also known as ahi, a favorite for sushi and poke bowls. Its mercury content ranges 0.38-0.76 ppm, considered moderately high.
Albacore tuna – Used for white tuna sushi, albacore tuna has mercury around 0.35 ppm, approaching high.
Bluefin tuna – The expensive delicacy for sushi traditionally has about 0.31-0.45 ppm mercury. Some research shows levels may be declining.
Skipjack tuna – The most common tuna for canned light tuna has lower mercury levels around 0.144 ppm. A better sushi choice for pregnant women.
So for sushi, skipjack and some albacore are safer tuna choices. Bigeye, yellowfin, and bluefin tuna are higher in mercury and intake should be limited, especially for pregnant women and children.
Mercury in Common Sushi Fish
Here are the typical mercury levels for fish commonly used in sushi:
| Fish | Mercury Level (ppm) |
|---|---|
| Bigeye tuna | 0.58-1.09 |
| Yellowfin/Ahi tuna | 0.38-0.76 |
| Albacore tuna | 0.35 |
| Bluefin tuna | 0.31-0.45 |
| Salmon | 0.01-0.29 |
| Halibut | 0.14-0.26 |
| Red snapper | 0.06-0.64 |
| Squid | 0.05-0.17 |
| Octopus | 0.01-0.072 |
| Shrimp | 0.001 |
This makes it clear that for sushi, the bigeye, yellowfin/ahi, albacore and bluefin tuna varieties are substantially higher in mercury content. Pregnant women and children should avoid them and choose lower mercury sushi options like salmon, shrimp, squid, and octopus.
Health Concerns
For most adults, occasional intake of fish with mercury levels under 0.5 ppm is not a significant concern. However, regular consumption of high mercury fish can increase risk for neurological problems and damage to the brain, nerves, kidneys, lungs, and heart. Extremely high mercury poisoning causes sensory impairment, lack of coordination, and even death.
That is why women who are pregnant, nursing, or planning pregnancy are advised to completely avoid high mercury fish that typically exceed 0.5 ppm. It is especially crucial to minimize mercury exposure during early pregnancy when the fetal brain and nervous system is developing most rapidly.
After birth, developing children are still vulnerable to mercury’s effects on neurological development and function. Children should consume low mercury seafood options until at least age 12. Albacore tuna should also be avoided for young children due to its moderate mercury level.
While adults are generally less sensitive, regular intake of high mercury fish is still not advised. Adult men and women who are not pregnant/nursing should limit consumption of high mercury fish to no more than one 6 oz portion per week. This helps reduce risk from excessive mercury accumulation over time.
Symptoms of Mercury Poisoning
In high doses, whether through large repeated fish meals or industrial exposure, mercury is clearly toxic. Here are symptoms of mercury poisoning to be aware of:
– Impaired peripheral vision
– Lack of coordination, poor dexterity
– Numbness or tingling in hands, feet, mouth
– Muscle weakness
– Dizziness
– Trouble hearing or ringing in ears
– Slurred speech or trouble speaking
– Memory problems
– Emotional changes like irritability
– Fatigue
– Headaches
– Abdominal pain
– Fever
If anyone experiences these symptoms frequently after eating a lot of high mercury fish, they should contact a doctor. Severe mercury poisoning requires immediate medical treatment.
Avoiding Mercury in Fish
The key ways to limit mercury exposure from seafood include:
– Check advisories – Follow local seafood advisories about high mercury fish to avoid, especially for pregnant/nursing women and children
– Choose low mercury fish – Consume low mercury fish more often like salmon, tilapia, shrimp, pollock, cod, catfish, anchovies, and trout
– Eat a variety – Vary the types of seafood you eat which helps minimize any one source of contaminants
– Limit intake of high mercury fish – For adults, keep consumption of high mercury fish like tuna under 12 ounces per week
– Purchase smaller fish – Larger, older fish of the same species accumulate more mercury over their lifespan
– Avoid riskiest fish – Completely avoid fish that tend to be very high in mercury like shark, swordfish, king mackerel, and tilefish if pregnant or a child
– Check labels – Canned tuna and other processed seafood should have safe mercury levels but check labels to be sure
– Grill, broil, bake – Avoid deep frying which can increase the concentration of mercury
Following these precautions allows you to eat fish regularly for its nutritional benefits while minimizing potential harm from contaminants like mercury.
Conclusion
Some types of sushi do contain higher levels of mercury that warrant caution, especially for pregnant women, nursing mothers, young children, and those who eat fish frequently. Bigeye tuna, yellowfin/ahi tuna, and bluefin tuna tend to have the highest mercury concentrations among sushi fish. Safer sushi choices include salmon, crab, shrimp, squid, tobiko, and octopus. In general, larger and longer living predatory fish accumulate the most mercury while smaller fish, shellfish, and shorter lived fish have less. By following seafood advisories, varying your intake, and limiting consumption of high mercury fish, you can balance the health benefits and potential risks of sushi and fish consumption.
