#3 Sushi Health Risk—Toxins, with 10 Tips to Protect Yourself

Wednesday Oct 9 | BY |
| Comments (2)

Toxins in Sushi

In addition to parasites and bacteria, sushi may also be contaminated with toxins.

After talking about parasites and bacteria in former posts, now it’s time to talk chemicals. Considered by many to be the biggest concern when consuming sushi, chemicals can be difficult to detect or to track, yet they may pose significant health risks.

“Far from being a healthy alternative to the sandwich,” writes Dr. Danny Penman in the Daily Mail, “sushi contains a cocktail of chemicals, heavy metals and pesticides which can potentially lower intelligence, reduce fertility and even lead to cancer.”

“People think they’re improving their health by eating sushi,” says Professor David Carpenter, an environmental health scientist at the University of Albany, New York, “but they are in fact poisoning themselves.”

Is it really that bad? Here’s what we found.

Danger #1: Mercury

Probably the most well known potential toxin in sushi is mercury. (Dr. Williams talked about the dangers of mercury in a former post.) Predatory fish are known to contain more of the toxic metal than other fish, with “high mercury” defined as more than 0.3 parts per million by the Environmental Protection Agency (EPA).

According to the organization’s “Guide to Mercury in Sushi,” the Ahi (yellowfin tuna), Aji (horse mackerel), swordfish, blue marlin, young sea bass, albacore tuna, and similar fish contain the most mercury. (You can find the complete list of mercury in sushi here.) Clams, shrimp, flatfish, trout, salmon, octopus, freshwater eel (Unagi), and other similar options were low in mercury.

The EPA notes that mercury is especially dangerous for fetuses, infants, and children, which is why pregnant women are warned to avoid sushi and other forms of high-mercury fish. The metal can affect a growing brain and nervous system, which can impact cognitive thinking, memory, attention, language, and fine motor and visual spatial skills.

Methylmercury poisoning can also create “pins and needles” in the hands and feet, lack of coordination, speech and hearing impairments, difficulty walking, and muscle weakness. Fortunately, data from biological monitoring by the Centers for Disease Control and Prevention (CDC) shows that so far, most people have blood mercury levels below that associated with possible health effects. (Dr. Williams notes that he believes arsenic is actually more of a health concern in today’s world than mercury.

Still, the danger is there, particularly if you enjoy sushi often. In December 2008, Broadway star Jeremy Piven suffered “shocking levels” of mercury in his system from eating too much sushi and Chinese herbs, forcing him to leave the Broadway play Speed-the-Plow. The attending physician at Beth Israel Medical Center in New York City checked his heavy metals and found mercury at a level “almost six times the upper limit of normal and allowable.” The doctor said it was the highest level he had ever seen, and noted that mercury can cause cardiac arrest, kidney failure, and psychiatric problems.

If you enjoy sushi on a regular basis, it may be wise to limit your consumption of high-mercury types. Pregnant women should completely avoid high-mercury fish, and may choose those in the low-mercury list for beneficial essential fatty acids one to two times a week.

Danger #2: Food Not Properly Handled

It’s important to know where your sushi is coming from. According to the Denver Department of Environmental Health, “fish that is not purchased from an approved source may not be properly acquired or handled prior to shipping and can contain toxins harmful to humans.” Two of the common ones are “ciguatera” and “scombroid.”

Ciguatoxins are produced by a marine algae microorganism, and affects fish that feed close to tropical reefs, including red snapper, grouper, triggerfish, jacks, and barracuda. Similar to mercury contamination, this toxin affects larger fish the most, as it’s passed upward through the food chain. Symptoms of poisoning include nausea, vomiting, and tingling fingers and toes. Seafood restaurants can avoid these types of toxins by purchasing fish from suppliers who can ensure the fish were not harvested at or near reefs.

Scombroid is formed when fish are not stored at the right temperature. Bacteria that may be present in the fish can then transform into the toxin when the fish are not kept cold enough. The toxin can cause allergic reactions like itching, rashes, and shortness of breath. Fish most often affected by this toxin include mackerel, tuna, mahi-mahi, and bluefish. Restaurants can prevent this toxin by maintaining proper storage temperatures (below 41 degrees Fahrenheit) from harvest to table.

Danger #3: The Rice

It’s not only the fish that can contain toxins. The rice, as well, can contain microorganisms that can cause food poisoning. In fact, the Minnesota Department of Agriculture states that rice is a leading cause of B. cereus emetic-type food poisoning in the U.S. The microorganism is frequently present in uncooked rice. Cooking destroys all but the spores, which can survive. If the rice is not served warm or properly cooled to store, the spores can germinate and multiply, producing the toxin. Again, it’s all about whether or not the establishment properly handles the food.

Rice can also be a source of arsenic. A 2012 study by Consumer Reports found that organic rice baby cereal, rice breakfast cereals, brown rice, and white rice contained arsenic, many at worrisome levels. “We found significant levels of inorganic arsenic, which is a carcinogen,” read a Consumer Reports press release, “in almost every product category, along with organic arsenic, which is less toxic but still of concern.” (You can find a chart summarizing the results here.)

Danger #4: Radioactive Cesium

In 2012, researchers from Stanford University reported that 15 Pacific bluefin tuna that migrated from Japan to the California coast had radioactive cesium levels 10 times higher than those found in the same type of fish before the nuclear disaster at Fukushima. The levels were still low, however, and considered only a small fraction of the naturally occurring radioactivity in tuna. Timothy J. Jorgensen, associate professor of radiation medicine at Georgetown University, noted the levels were much too small to have any impact on human health.

Danger #5: Pesticides and PCBs

A number of studies have found pesticides in our fish populations. In years past, manufacturers often dumped these chemicals into the ocean. The surrounding sea shelf off of Palos Verdes Peninsula in California was a popular dumping ground for 30 years, and was declared by the EPA as one of the “most hazardous dumping grounds in the nation.” The white croaker fish, which lives there, was named as “the most contaminated species along the Los Angeles and Orange County Coasts.” Plans are currently in progress to clean up the area.

A 2009 study published in Ecological Applications noted that for more than a decade, numerous pesticides have been detected in river systems of the western U.S. that support Pacific salmon and steelhead. A 2010 study found that Roundup increases incidence of disease in fish, increasing the production of parasites and significantly reducing fish survival.

Another 2009 study on contaminants in fish from the Aleutian Islands of Alaska, examined levels of polychlorinated biphenyls (PCBs—which are carcinogenic) and pesticides in the muscle tissue from nine fish species, and food the highest PCB levels in rock sole, and the highest pesticides in sockeye salmon. They noted that PCBs accumulate in marine mammals and fish.

There are a number of other examples of studies showing that the pesticides we’re using or have used in the past can show up in our fish. According to an analysis published in the Journal of the American Medical Association, if 100,000 people ate farmed salmon twice a week for 70 years, the extra PCB intake could potentially cause 24 extra deaths from cancer, but would present at least 7,000 deaths from heart disease (due to the healthy omega-3 fatty acids). They also noted that levels of PCBs and dioxins in fish are very low, similar to levels in meats, dairy products, and eggs.

Danger #6: Fish Fraud

A recent study by the ocean conservation group “Oceana” reported that roughly a third of the time, seafood sold at U.S. grocery stores, seafood markets, restaurants and sushi venues have been swapped for species that are cheaper, overfished, or risky to eat. Over the course of two years, the organization went to 21 states and purchased 1,247 pieces of fish, which they then submitted for DNA testing. Out of the samples tested, 401 were determined to be mislabeled.

What does this have to do with toxins? Well, if you’re buying a fish you believe to be low risk and getting something else, you could be at a higher risk for toxins than you think. The two most commonly mislabeled fish were snapper (which was actually rockfish, perch, or tilapia), and tuna, which was mostly replaced with “escolar”—an often-banned snake mackerel that can cause mild to severe gastric distress.

Even more concerning were the substitutions discovered at sushi restaurants. Out of 118 sushi venues, 95 percent sold fish that varied from menu identification. Snapper, tuna, and yellowtail were incorrectly labeled in every case.

Non-sushi restaurants performed better, with just over half selling incorrectly labeled fish. Grocery stores were the best of the three, with only 27 percent selling seafood that mismatched the label.

How to Reduce Your Risk

After reading about all these potential dangers, you may be worried about ever eating sushi again! Though eating any food is never completely risk-free, the overall risk with sushi, despite these dangers, is low. You can take the following additional precautions to reduce your risk.

  1. Rinse the rice: If you’re making sushi at home, you may be able to cut your exposure to arsenic by rinsing raw rice thoroughly before cooking. Use a ratio of 6 cups water to one-cup rice for cooking, and drain the excess water afterward. This is how rice is cooked in Asia and lowers toxins more than the modern technique of cooking rice in water that is entirely absorbed. Using more water has been shown to remove about 30 percent of the inorganic arsenic content.
  2. Think about cutting back: If you frequently eat sushi and are concerned about the toxins, consider cutting back and enjoying it only occasionally as part of a varied diet.
  3. Eat small: In general, smaller fish are lower in potentially dangerous metals and toxins. Eat the larger fish only once in awhile.
  4. Purchase whole fish: These are easier to identify than slices or cuts of fish. You’re more likely to get what you think you’re getting.
  5. Don’t be cheap: If prices for sushi look too good to be true, you may be getting something else than you think you are. Don’t trust bargain deals when it comes to your health.
  6. Ask questions: Ask your fish vendor or server what kind of fish you’re getting. Was it wild-caught or farm raised? Where did it come from? You may not get all the answers, but you can tell how careful your vendors are about quality.
  7. Choose your poison: Saltwater fish are typically lower in pesticides than fresh water fish, so if you’re concerned about pesticides, go for ocean fish. Realize, however, that ocean fish can be higher in toxic metals—so go smaller, as the bigger fish carry higher levels.
  8. Look for signs of health: Healthy fish have clear eyes, bright red gills, no slime, no fish smell, a firm and elastic belly area, and scales that do not come off easily. A sour odor, off color, sunken eyes, ice crystals, and paper wrapping that is moist or slimy indicates the fish was probably not stored at the proper temperature.
  9. Go reputable: Those places that are known for good sushi are the places to go. Eat only dishes prepared by reputable cooks in commercial kitchens that are meticulously clean.
  10. Use it right away: If you buy sushi in grocery stores, eat it right away. Your freezer is not cold enough to keep it safe. Never eat sushi that has been sitting around at room temperature.

For more help in choosing safe and sustainable sushi, see Canada’s Sustainable Sushi Guide (super handy and easy to follow), and the Environmental Defense Fund Sushi Selector.

How do you avoid toxins in sushi? Please share any tips you may have.

* * *

“2 Investigators: Is Your Sushi Safe?” CBS News, October 27, 2011, http://chicago.cbslocal.com/2011/10/27/2-investigators-is-your-sushi-safe/.

Christina Frangou, “An Informal Poll of Gastroenterologists on Sushi: Do Those Who Treat Also Eat?” Gastroenterology & Endoscopy News, April 2006, http://www.gastroendonews.com/ViewArticle.aspx?d_id=187&a_id=6700.

Dr. Danny Penman, “Sushi—the raw truth,” Daily Mail, April 4, 2006, http://www.dailymail.co.uk/health/article-381958/Sushi–raw-truth.html.

“Guide to Mercury in Sushi,” NRDC, http://www.nrdc.org/health/effects/mercury/sushi.asp.

“Mercury: Health Effects,” EPA, http://www.epa.gov/hg/effects.htm.

Alexis Chiu, “Jeremy Piven’s Doc: Star Stricken by Toxins from Sushi,” People, December 18, 2008, http://www.people.com/people/article/0,,20247781,00.html.



“Arsenic in your food,” Consumer Reports, November 2012, http://www.consumerreports.org/cro/magazine/2012/11/arsenic-in-your-food/index.htm.

Dan Childs, “How Fukushima May Show Up in Your Sushi,” ABC News, May 28, 2012, http://abcnews.go.com/blogs/health/2012/05/28/how-fukushima-may-show-up-in-your-sushi/.

“Forget Radioactive Sushi, Our Fish are Already Polluted with Pesticides,” Grub Street Los Angeles, April 18, 2011, http://losangeles.grubstreet.com/2011/04/forget_radioactive_sushi_our_f.html.

“Palos Verdes Shelf,” EPA, http://www.epa.gov/region9/superfund/pvshelf/.

Kat Kinsman, “Nationwide study casts a wide net over seafood fraud,” Eatocracy, February 21, 2013, http://eatocracy.cnn.com/2013/02/21/seafood-fraud-study/.

David H. Baldwin, et al., “A fish of many scales: extrapolating sublethal pesticide exposures to the productivity of wild salmon populations,” Ecological Applications, 19:2004-2015, http://www.esajournals.org/doi/abs/10.1890/08-1891.1.

“New study shows Roundup pesticide kills fish; U.S. heading toward OKing more ‘Roundup-Ready’ genetically engineered farm acreage,” InvestigateWest, March 3, 2010, http://www.invw.org/node/958.

Sara Hardell, et al., “Levels of polychlorinated Biphenyls (PCBs) and Three Organochlorine Pesticides in Fish from the Aleutian Islands of Alaska,” PLOS One, August 25, 2010; 5(8):e12396, http://www.plosone.org/article/info:doi/10.1371/journal.pone.0012396.

Mozaffarian D, Rimm EB. Fish intake, contaminants, and human health: evaluating the risks and the benefits. JAMA. 2006; 296:1885-99. http://www.ncbi.nlm.nih.gov/pubmed/17047219?dopt=Citation.

“Fish: Friend or Foe?” Harvard School of Public Health, http://www.hsph.harvard.edu/nutritionsource/fish/.

Colleen M. Story

Colleen M. Story

Colleen M. Story, a northwest-based writer, editor, and ghostwriter, has been creating non-fiction materials for individuals, corporations, and commercial magazines for over 17 years. She specializes in the health and wellness field, where she writes and ghostwrites books, e-books, blogs, magazine articles, and more.

Colleen is the founder of Writing and Wellness. Her fantasy novel, “Rise of the Sidenah,” was released with Jupiter Gardens Press in September 2015. Her literary novel, “Loreena’s Gift,” is forthcoming in spring 2016 from Dzanc Books. She lives in Idaho. www.colleenmstory.com


Comments are closed for this post.

  1. I used to eat sushi quite often but don’t at all anymore… the biggest issue is the mercury in the fish. Rice isn’t as big of a deal as heavy metal toxicity imo!

    Thanks for writing this Colleen!

    David Benjamin

  2. Libby says:

    Yes Colleen, I have heard of this before, but only briefly. Our family still eats a fair bit of rice but the only fish we eat now is when we catch it ourselves. Living in Australia we have access to clean waters so this is a blessing. Although in saying this, I still enjoy sushi now and then but will ensure that I only get it from reputable places.

    Comments are closed for this post.