Consuming too much mercury-contaminated fish can lead to serious consequences, including tremors, numbness, memory problems and muscle weakness. Sushi eaters should exercise extreme care when selecting their selections of seafood.
Smaller species at the lower levels of the food chain tend to accumulate less mercury, making shrimp, salmon and other seafood low on the food chain safe choices.
Tuna
Mercury is a toxic metal found throughout nature and oceans alike, both naturally and from human activity. Although some forms of mercury occur naturally, humans are also major sources of pollution that contributes to its presence. When humans burn fossil fuels, elemental mercury gets released into the air before eventually falling as rain. When in water it converts to methylmercury which then absorbs into plants and animals of ecosystem. Large fish such as tuna consume smaller ones which absorb even more methylmercury – so much so that just three servings can exceed your weekly mercury limit according to Consumer Reports.
Researchers employed atomic absorption spectrometry to conduct an in-depth examination of mercury levels found in sushi from restaurants that specialize in Japanese cuisine, focusing specifically on tuna, salmon and kani sushis from Japan. They investigated both organic and inorganic mercury; organic mercury (mHg+) predominated as its toxic form dominated the samples; its average concentration exceeded 88% of what the Provisional Tolerable Weekly Intake (PTWI; 1.6 mg/kg for adults and 20 g/kg for children) allowed.
This study investigated the frequency and types of sushi eaten among university community residents by interviewing 1289 individuals. On average, people reported consuming 5.06 fish-sushi meals monthly on average with some eating over 40 pieces at each meal – those who reported more sushi consumption were more likely to be Caucasians or Asians.
Even though mercury levels vary between tuna cans, it is still wise to consume seafood regularly. Seafood contains essential omega-3 fatty acids which aid brain development in infants while decreasing heart disease risk in adults. Incorporating lower mercury fish, like salmon or shrimp into your diet may reduce its impact.
According to the FDA, an adult without pregnancy or heart disease should be able to consume up to three 4-ounce servings of low-mercury fish per week without incurring risks. Pregnant women and those who may become pregnant in the near future should consume lower mercury fish such as tuna two or three times per week in a serving roughly equivalent to half a medium-size can of tuna.
Salmon
Mercury is an element that is toxic when consumed in large doses and neurotoxins such as mercury can have serious repercussions for pregnant women and young children, especially pregnant women and those contemplating becoming pregnant. Pregnant women should steer clear of fish with mercury contamination such as tuna sushi; alternatively, non-tainted salmon provides excellent protein sources as well as omega-3 essential fatty acids beneficial to heart health.
Mercury levels tend to be relatively low in marine ecosystems, yet bioaccumulate in species higher up the food chain. Mercury accumulates as it diffuses through phytoplankton into phytoplankton which in turn is consumed by small fish as well as larger predatory fish such as tuna and salmon; due to eating many smaller fish themselves they accumulate high amounts of mercury; therefore the United States Food and Drug Administration advises eating these species no more than twice weekly.
A recent DNA barcoding analysis conducted on sushi samples identified by DNA barcoding has found that some restaurants serve fish with higher mercury levels than those available in grocery stores, especially bigeye and bluefin tuna (in combination with yellowfin) that exceed what the Environmental Protection Agency considers safe levels.
Study authors propose that restaurants and other vendors of sushi disclose which species of tuna is being offered for sale to consumers to limit mercury intake, and for clearer labeling to help enable customers to make more informed choices.
An accurate, fast, and cost-effective method was recently developed and applied successfully for the determination of total mercury content in raw sushi. This technique uses thermal decomposition amalgamation atomic absorption spectrometry (TDA-AAS). A portion of the sample is burned off in nickel and quartz containers before its mercury is trapped by using a gold amalgamator at high temperatures; once trapped it’s measured using an atomic absorption cell. The method has demonstrated good accuracy after being validated on certified reference materials such as rice flour (NIST SRM-1568b), fish protein (NIST SRM-1568b), peach leaves, and oyster tissue samples from these certified references materials analyzed before starting testing the TDA-AAS method was established and successfully applied.
Shrimp
Sushi shrimp imported from Asia often contains mercury. Shrimp are high in protein and low in fat; however, they may be contaminated with antibiotics or industrial processes involving mercury contamination that leads to neurotoxin damage of both the brain and nervous system, including numbness or tingling in fingers and toes, memory loss and mental confusion at higher concentrations. According to FDA recommendations for pregnant women eating no more than 12 ounces per week of low mercury species of fish such as sushi shrimp.
The FDA’s methylmercury advisory was created to protect pregnant women and young children from the detrimental effects of exposure to mercury-contaminated fish, specifically bluefin tuna, by choosing lower mercury fish such as salmon, shrimp, whitefish and cod. Furthermore, pregnant and nursing mothers are advised to limit consumption of shark, king mackerel and swordfish since these contain excessive levels of mercury.
A study of 159 shrimp samples from 10 brands discovered mercury concentrations to be generally low and variable; however, total fat was related to mercury concentration levels; when total fat content in shrimp increased, mercury levels decreased and vice versa. Therefore, its authors recommend selecting shrimp high in total fat content in order to lower mercury intake.
Rutgers University and Robert Wood Johnson Medical School conducted a joint survey among 1,289 residents living in university communities to ascertain how much sushi they consumed; 92% responded that they did, eating an average of five fish or sushi meals each month. To assess this data further, scientists employed gas chromatography-mass spectrometry (GC-MS) analysis on shrimp samples to measure organic and inorganic mercury concentration levels; results revealed twice as much organic mercury than inorganic mercury content was present in shrimp.
GC-MS methods measure not only mercury but also other components like sulfides, chlorides, phosphorus and nitrates in sushi seafood as well as particle matter which is detrimental to human health and can contribute to respiratory diseases such as COPD.
Eel
Eel is a popular sushi dish, and many consumers believe that its omega-3 fatty acid content makes it healthy. Unfortunately, however, too often consuming it could result in mercury poisoning which damages the central nervous system as well as disrupting hormones and having negative side effects on mental wellbeing.
The FDA advises most adults to limit mercury-containing fish intake to no more than six ounces each week, with pregnant and trying-to-conceive women eating salmon and tuna lower in mercury for consumption during this timeframe. It is strongly suggested that people avoid high mercury seafood like swordfish, king mackerel, tilefish from the Gulf of Mexico tilefish and shark.
Consumers looking for information on mercury levels of their favorite seafood can visit the Natural Resources Defense Council website and access a list of low and high mercury seafood; additionally, their app called Safe Sushi provides users with helpful insights when choosing sushi dishes.
Sushi may contain harmful contaminants other than mercury, including antibiotics and polychlorinated biphenyls – two known carcinogens – such as antibiotics and polychlorinated biphenyls that may contribute to cancer, birth defects or neurological disorders. Furthermore, frozen fish from Asia contains these same contaminants, while raw or undercooked seafood sushi contains even more.
Assuming you enjoy eating sushi safely, the key to enjoying it safely is limiting your consumption of sauces and condiments such as eel sauce. Eel sauce contains 335 mg of sodium per tablespoon while 7 grams of sugar make this choice especially dangerous to one’s health. Opting for low sodium/mercury fish options such as those provided at restaurants that practice good hygiene is best as this ensures it was freshly made prior to being delivered to customers.