Mercury in Fish - Questions and Answers

Consumption Advice

Canned Tuna

Health Benefits of Eating Fish

Health Risks of Mercury Exposure

The Science


Consumption Advice

Why has Health Canada updated its advice pertaining to mercury in fish?

Health Canada's review, initiated in 2004, of Canadian fish consumption habits and consumption advisories concluded that the risk management approach for mercury in commercial fish required revision. This conclusion was based largely on new data that the Canadian Food Inspection Agency (CFIA) and Health Canada collected on the mercury levels in fish available for sale in Canada, as well as a comprehensive review of Canadian fish consumption patterns. Emphasizing the nutritional benefits of fish consumption as part of Health Canada's advice was also deemed necessary. Similar reviews of the risk management of mercury in fish have also been conducted by other international organizations.

What is the consumption advice?

Canadians are advised to limit consumption of fresh/frozen tuna, shark, swordfish, escolar, marlin, and orange roughy. In general, you can eat up to 150 g per week of these fish species combined. However, women who are or may become pregnant and breastfeeding mothers can eat up to 150 g per month. Young children between 5 and 11 years of age can eat up to 125 g per month. Very young children between 1 and 4 years of age should eat no more than 75 g per month of these fish species.

Separate advice is applicable only to canned albacore (white) tuna. This advice does not apply to light tuna. Women who are or may become pregnant and breastfeeding mothers may consume up to 300 g a week of albacore tuna. This is equivalent to about two 170-g cans of albacore tuna per week. Children between the ages of 5 and 11 years of age may consume 150 g (about one 170-g can per week) and children 1 to 4 years of age may eat 75 g (about ½ of a 170-g can per week). Note that there are approximately 120 grams of tuna meat in a 170-g can of tuna after the liquid is drained.

I've heard mention of escolar in the news. What is the issue?

Escolar naturally contains a type of oil that is not digestible. When ingested, the oil can pass through the digestive tract unaltered. This can result in short-term effects including nausea, oily diarrhea and cramps. While no long-term health effects have been observed, it may be more of a health issue for people with existing medical conditions (e.g. irritable bowel syndrome). Therefore, those who like to eat escolar may wish to limit the portion size. More information is available from Health Canada's Fact Sheet on Escolar.

The advice covers children between 1 and 11 years of age. What about infants?

Infants less than 1 year of age are also covered by the advice although it is considered unlikely that an infant could consume enough fish to be exposed to an unacceptable amount of mercury. If you decide to feed your infant any of the fish described in the advice, ensure that the amount is less than 40 g per week of canned albacore tuna or less than 40 g per month of the other types of fish listed in the advice (fresh/frozen tuna, shark, swordfish, marlin, orange roughy and escolar ).

Is there consumption advice for other types of fish?

There are no recommended consumption limits for any other types of retail fish in Canada besides fresh/frozen tuna, shark, swordfish, escolar, marlin, orange roughy, and canned albacore (white) tuna. It is recommended that Canadians eat a variety of healthy foods every day, such as fish, in accordance with Canada's Food Guide.

Are there any advisories for sport fish?

Sport fisheries are usually the responsibility of provincial and territorial governments, although within federal parks, sport fisheries are the responsibility of Parks Canada. If you plan to consume sport fish, consult the appropriate government authority to determine if there are any consumption advisories for the lake or river from which the fish were caught. Environment Canada maintains a webpage listing current Provincial and Territorial Consumption Advice for Sport Fish.

Why do advisories differ from country to country?

Fish consumption advice varies between countries because the fish consumption habits and the fish species that are consumed may differ between countries. Consumption advisories can also take into account other measures taken to protect consumers, such as the establishment of maximum levels for contaminants and enforcement activities. Health Canada's advice is based on the most up-to-date information related to the Canadian context. It is subject to regular revisions and updates in view of any new information gathered by Health Canada's scientists. However, the general consumption advice from various regulatory agencies remains consistent: people can enjoy the health benefits from eating fish by making informed choices.

How is Health Canada making Canadians aware of the updated fish consumption advice?

The updated advice that was issued in 2007 has been disseminated to various provincial, territorial, and federal health professional associations including: Canadian Pediatric Society, Society of Obstetricians and Gynecologists of Canada, Dieticians of Canada, Canadian Medical Association and their provincial/territorial counterparts, Family Physicians of Canada, Canadian Nurses Association, Canadian Practical Nurses Association, Canadian Association of Midwives, Canadian Association of Naturopathic Doctors, and Chinese Medicine and Acupuncture Association of Canada.

The advice is available on Health Canada's Mercury in Fish website. Also, Health Canada officials have issued information to, and conducted interviews with, the media on this subject.

Can fish have more than one common name?

Yes. The same fish species may be referred to by different names by different groups, organizations, jurisdictions, or countries. The Canadian Food Inspection Agency (CFIA) has developed a "Fish List" that lists the common and scientific names of a given fish species.

Why is there specific advice for women who are or may become pregnant and young children?

Methylmercury that enters a woman's body can be distributed from the maternal blood to a developing fetus through the placenta. The consumption advice for women who are or may become pregnant and young children is more restrictive than for the general population because the developing fetus and young children are considered to be more susceptible than adults to the adverse health effects of methylmercury.

What if I have consumed more than the recommended amounts of the fish listed in the advice?

Safety factors and conservative assumptions were built into the consumption advice. If you occasionally eat more than the recommended amounts of the fish listed in the consumption advice your exposure to mercury in fish will still be below the level that would be considered unsafe, even to an unborn child.

Why isn't salmon covered in the advice? I've heard a lot about it in the news.

The levels of mercury in the muscle tissue of salmon are very low. Separate studies have identified other chemicals, such as polychlorinated biphenyls (PCBs), in the fat of both wild-caught and farmed salmon. These chemicals can be found in most fish and in many other foods, but at low levels that do not cause concern for human health.

Canned Tuna

No advice has been given on canned albacore tuna consumption for the population in general. Should people in this group be concerned about the amounts of canned albacore tuna that they eat?

Some people who are actively trying to increase the amount of protein in their diet find canned tuna to be a convenient and inexpensive source of protein. If you have been choosing canned albacore tuna as your main protein source, you might consider reducing the amount of canned albacore (white) tuna that you consume. An adult member of the "population in general" could eat up to six 170-g cans of canned albacore tuna (as long as they were not eating any of the predatory fish listed in the Health Canada advice). The best approach, however, is to choose a variety of different protein sources throughout the week. Consistent with Canada's Food Guide, Health Canada encourages Canadians to eat a variety of healthy foods every day.

Does the advice cover albacore tuna that is sold in vacuum-sealed pouches?

The advice applies to all ready-to-eat (pre-cooked) albacore tuna, regardless of package size or type. Albacore (white) tuna is most commonly available in 170-gram cans but other can sizes are also available. Pre-cooked tuna is also sold in vacuum-sealed pouches.

Why are there recommendations for canned albacore tuna but not others types of canned tuna?

All canned tuna, including albacore, is typically below the Canadian standard of 0.5 ppm total mercury. However, some people eat canned tuna as frequently as every day. If frequent consumers of canned tuna regularly choose canned albacore (white) tuna, their exposure to mercury could reach unacceptably high levels. The same concerns do not exist for canned "light" tuna because it contains less mercury than canned albacore tuna. Various species can be labelled as "light" tuna including skipjack, yellowfin, and tongol.

Why is the consumption advice for fresh/frozen tuna different from that for canned tuna?

Tuna that are used in canned products are typically younger and smaller fish and therefore tend to contain significantly less mercury than the larger tuna fish that are sold as fresh and frozen products.

Why is there consumption advice for fresh/frozen yellowfin tuna but not canned yellowfin tuna?

Some data suggest that yellowfin tuna steaks contain lower amounts of mercury than other species of tuna that are sold fresh/frozen, such as bigeye. As there are insufficient Canadian data for fresh/frozen yellowfin tuna and it is not always possible to know the species of fresh/frozen tuna that you are purchasing at the fish counter, the advice continues to cover all fresh/frozen tuna.

Health Benefits of Eating Fish

Should I stop eating fish?

No. By making informed choices about what types of fish are consumed and how often, mercury exposure from fish can be minimized while the health benefits associated with eating fish continue to be gained.

What are the nutritional benefits of fish?

Most fish contain some of the long chain omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Recent evidence has suggested that fish consumption and the associated intake of EPA and DHA from fish can help maintain healthy heart function. Consumption of fish has also been associated with reduced risk of sudden cardiac death in healthy people and there is evidence that regular consumption of fish by pregnant women and women who may become pregnant plays a role in normal fetal brain and eye development.
Some types of fish have higher levels of these beneficial fatty acids than others. Fish and shellfish that contain higher levels of these fatty acids and are also low in mercury include: anchovy, capelin, char, hake, herring, Atlantic mackerel, mullet, pollock (Boston bluefish), salmon, smelt, rainbow trout, lake whitefish, blue crab, shrimp, clam, mussel and oyster.

All fish are also a significant source of vitamin D and contribute valuable mineral nutrients to the diet such as selenium, iodine, magnesium, iron and copper.

Are there benefits of fish consumption to my unborn baby?

Yes. Studies suggest that regular consumption of fish helps the nervous system development of the fetus and young children. The benefit is increased by limiting exposure to mercury. Therefore, choose to consume types of fish that are low in mercury in order to obtain the greatest benefit from fish consumption during pregnancy.

Can I eat fish if I am breastfeeding?

Yes. Because the levels of mercury in breast milk are low, infants who breast feed are not considered to be at risk. Health Canada promotes breastfeeding as the best method of feeding infants as it provides optimal nutritional, immunological and emotional benefits for the growth and development of infants. Nursing mothers should follow the fish consumption advice outlined by Health Canada and, in instances where sport fish may be consumed, any advice that has been issued by the applicable government authority (usually provincial or territorial). Environment Canada maintains a webpage listing current Provincial and Territorial Consumption Advice for Sport Fish.

Health Risks of Mercury Exposure

What are the health effects of exposure to methylmercury, the form of mercury that is of most concern?

A wide range of adverse health effects have been observed in humans following methylmercury exposure, the severity largely depending on the magnitude of the dose and the duration of exposure. The predominant health affects in humans are associated with the impaired functions of the central and peripheral nervous systems. For example, elevated methylmercury exposure in a fetus or young child can cause a decrease in I.Q., delays in walking and talking, lack of coordination, blindness, and seizures. In adults, excessive methylmercury exposure can lead to personality changes, tremors, changes in vision, deafness, loss of muscle coordination and sensation, memory loss, intellectual impairment, and, in very extreme cases, even death.

Do long-term, low exposures to methylmercury have different health effects than short-term, high exposures?

Unlike short-term, high exposures to methylmercury, long-term (chronic) methylmercury exposure at low doses among adults may not result in readily observable symptoms. The possible long-term risks of low exposure to methylmercury (for example, possible effects on cardiovascular health) may be counteracted to some degree by the nutritional benefits of fish consumption.

The developing fetus is most sensitive to short-term (acute) methylmercury exposure. Fetal exposure to methylmercury may affect the developing nervous system at substantially lower doses than in adults. Epidemiological studies, including recent studies in fish-eating populations in the Seychelles and the Faroe Islands, have demonstrated that methylmercury exposure may have subtle impacts on fine motor function, attention span, verbal learning, and memory of children that were exposed to methylmercury in utero.

Is any exposure to methylmercury considered too much?

Not necessarily. Tolerable Daily Intakes (TDIs) of methylmercury that are based on an oral route of exposure are developed for food contaminants by Health Canada and other international organizations. A TDI is defined as the amount of a chemical that a person can be exposed to on a daily basis over a lifetime without appreciable risk of adverse health effects. Health Canada developed a TDI for methylmercury for women of childbearing age, pregnant women, and young children of 0.2 micrograms per kilogram body weight per day (0.2 μg/kg bw/day). Health Canada employs the methylmercury TDI for adults of the general population that was developed by the Joint FAO/WHO Committee on Food Additives, which is 0.47 micrograms per kilogram body weight per day (0.47 μg/kg bw/day). 

Health Canada supports the Joint FAO/WHO Committee on Food Additives opinion for methylmercury, that for adults of the general population, intakes up to two times higher than its existing provisional tolerable weekly intake, which is 1.6 μg/kg bw/week or 0.23 μg/kg bw/day,  would not pose a risk to neurotoxicity.

The Science

What is mercury?

Mercury (chemical symbol, 'Hg') is a naturally occurring metal in soil, rocks, and water bodies. It can also be released into the environment as a result of human activities including coal-fired power generation, metal mining, and waste incineration. Mercury can exist in three different chemical forms: elemental (Hg or Hg2+), inorganic (combined with elements such as sulfur, chlorine, or oxygen), and organic (combined with carbon or hydrogen).

How does methylmercury differ from other forms of mercury?

Methylmercury is an organic form of mercury and is very toxic at high exposure levels. Methylmercury is the most common form of mercury in fish and is present in some types of fish at concentrations that have the potential to impair human health. In humans, methylmercury is readily absorbed into the bloodstream and distributed throughout the body to locations including the brain and, in pregnant women, the developing fetus.

Is mercury only found in fish?

Traces of mercury have been measured in a wide variety of foods including dairy products, meats, poultry, eggs, pasta, fruits, and vegetables. However, the levels of mercury in these foods are very low relative to the levels found in fish and these foods only contribute a small amount of mercury to the diet. The most common source of human exposure to mercury is the consumption of certain types of fish.

Why do certain fish contain more mercury than others?

Traces of mercury, largely in the form of methylmercury, can be found in nearly all fish species, although the levels are higher in some fish than in others. Fish bioaccumulate methylmercury in their muscle tissues primarily as a result of eating plants and other organisms that contain methylmercury. Methylmercury then biomagnifies through the food chain when predators, such as piscivorous fish (fish that eat other fish), eat organisms that have already bioaccumulated methylmercury in their muscle tissues. Over time, fish, particularly top predators, that regularly consume prey that contains methylmercury will have greater tissue concentrations of methylmercury than either their prey or the surrounding environment. Shark and swordfish are examples of piscivorous fish that are high in the food chain and contain high concentrations of methylmercury.

What are the concentrations of mercury in fish?

The Canadian Food Inspection Agency (CFIA) conducts routine monitoring of the mercury levels in numerous fish species at fish processing plants before the fish travel to commercial markets. A summary of these data is provided in Health Canada's health risk/benefit assessment document on mercury in fish.

What types of fish contain very low levels of mercury?

Fish that tend to contain very low levels of mercury include shellfish (for example oysters, clams, scallops, mussels), salmon, crab, shrimp, trout, herring, haddock, pollock (Boston bluefish), sole, flounder, lobster, Atlantic mackerel and lake whitefish.

Does cooking reduce the amount of mercury in fish?

No type of common cooking method (for example, frying, poaching, grilling) reduces the total concentration of mercury in a fish. Mercury is bound to proteins in a fish's muscle and cannot be removed through cooking.


Are there any standards (maximum limits) for the amount of mercury permitted in retail fish?

A standard (maximum limit) of 0.5 parts per million (ppm) total mercury in retail fish, with three exceptions, has been in place in Canada for many years. Health Canada has recently made a small change to this standard and implemented a two-tiered standard for total mercury in retail fish. Now there is a standard of 0.5 ppm total mercury in all retail fish (including all canned tuna) except fresh/frozen tuna, shark, swordfish, escolar, marlin, and orange roughy. A 1.0 ppm standard for total mercury has been established for fresh/frozen tuna, shark, swordfish, escolar, marlin, and orange roughy; these fish are also subject to consumption advice. Both standards are enforced by the Canadian Food Inspection Agency (CFIA).

Why are there two different standards for mercury in fish?

Health Canada and CFIA's scientists continue to find that the total mercury levels in the majority of commercial fish species, including canned tuna, are below the 0.5 ppm standard for total mercury in commercial fish, which was first established in 1970. However, certain varieties of piscivorous (fish-eating) fish tend to contain more than 0.5 ppm total mercury. Although these types of fish are higher in mercury they are normally consumed less frequently than other types of fish and therefore are not considered to be a significant source of mercury to the average diet. Rather than prevent the sale of these piscivorous fish, fresh/frozen tuna (not including canned tuna), shark, swordfish, escolar, marlin, and orange roughy are permitted to be sold as long as they contain less than 1.0 ppm total mercury. These fish are also subject to consumption advice.

Why does the standard cover total mercury when methylmercury is of concern?

Total mercury is the sum of all chemical forms of mercury, including methylmercury. Analyzing fish tissues for total mercury is less expensive than analyzing for the individual chemical forms of mercury, such as methylmercury. Since fish tissues are commonly analyzed for total mercury, Health Canada has developed standards based on total mercury levels. This approach is acceptable given that most of the mercury present in fish tissue is in the form of methylmercury.

What happens to fish if its mercury level exceeds the standards?

The Canadian Food Inspection Agency (CFIA) regularly tests fish and shellfish from fish processing plants to determine if they meet the Canadian standards for total mercury. If a fish contains higher mercury levels than what the Canadian standards permit, more testing is done on fish from the same lot or batch. Fish that are found to violate the Canadian standards for total mercury are not permitted to be sold in Canada.

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