# Fishy Business: Are there really dangerous levels of mercury in Tuna or not? **URL:** \ **Category:** Factual Questions\ **Created:** [October 2, 2010, 6:27pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858 "2010-10-02T18:27:38Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![HyenaThePirate](https://avatars.discourse-cdn.com/v4/letter/h/ecd19e/32.png) [@HyenaThePirate](https://boards.straightdope.com/u/HyenaThePirate)\ **Post date:** [October 2, 2010, 6:27pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/1 "2010-10-02T18:27:38Z")
Deciding that it was high time I reversed years of bad eating habits and whip myself into a shape that the ladies find more appealing, I recently purchased several cases of delicious canned tuna to put on my ruffage. After my coworkers and friends noticed I was eating tunafish every day for lunch (in one form or another) several of them expressed concern that I was poisoning myself to death. Apparently, a person should consume no more than 2 cans of tuna per WEEK due to some sort of high mercury content that is now found in ocean faring fish, specifically tuna. At first, I was a bit skeptical. I am not unversed in the chemical sciences, and it seems to me that any tuna containing enough mercury to harm me (a full bodied and voluptuous human male) would have killed the fish LONG before it had a chance to find its way into a can and subsequently onto my dinner plate. Attempting to do a little research, I discovered the usual internet debate where psuedo experts argue with psuedo intellectuals over heavily opinionated beliefs. Yet, I haven’t seen any official releases from any of the numerous agencies that I imagine would have carefully warned us consumers (or the tuna fishing industry) for that matter about this potential danger. An examination of the cans themselves provided no warning label one would usually find on a product that generally protect the company from liability should their product escalate your departure from life far earlier than it should have been. So what’s the deal? Is it safe to eat more than two cans of tuna per week, or is this just a bunk claim from people who might have an ulterior motive by ridding the office of my daily fish-stinking diet? ---
**Author:** ![Baracus](https://avatars.discourse-cdn.com/v4/letter/b/2bfe46/32.png) [@Baracus](https://boards.straightdope.com/u/Baracus)\ **Post date:** [October 2, 2010, 7:59pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/2 "2010-10-02T19:59:29Z")
> [@HyenaThePirate](#): > > Yet, I haven’t seen any official releases from any of the numerous agencies that I imagine would have carefully warned us consumers (or the tuna fishing industry) for that matter about this potential danger. You can get some “official” information from the [FDA and EPA](http://water.epa.gov/scitech/swguidance/fishshellfish/outreach/factsheet.cfm). Long story short, the primary danger and advice seems to be geared towards children and pregnant women. Eating tuna every day _will_ elevate your blood mercury levels, but apparently it is not that big of a deal at normal consumption levels. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [October 2, 2010, 8:39pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/3 "2010-10-02T20:39:10Z")
From Wikipedia > [@](#): > > Mercury content in tuna can vary widely. For instance, testing by Rutgers University found that a can of StarKist had 10 times more mercury than another can of exactly the same kind of tuna. Tuna is in many ways a particularly healthy food; I think the benefits far outweigh the risks for middle-aged men, but, as a tuna-eating middle-aged man, perhaps I’m just an optimist! > [@HyenaThePirate](#): > > … it seems to me that any tuna containing enough mercury to harm me (a full bodied and voluptuous human male) would have killed the fish LONG before it had a chance to find its way into a can and subsequently onto my dinner plate. I guess mercury isn’t excreted, so just accumulates. Tuna are very high up the food chain so get a lot, but tuna-eating humans are even higher up the food chain. But I’ve no idea about this really. The only reason I quoted you here was to ask for further details about “voluptuous human male.” 😃 ---
**Author:** ![constanze](https://avatars.discourse-cdn.com/v4/letter/c/f9ae1b/32.png) [@constanze](https://boards.straightdope.com/u/constanze)\ **Post date:** [October 2, 2010, 8:52pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/4 "2010-10-02T20:52:52Z")
You claim that you are not “unversed in the chemical science”, but in this case, you should look up some biology instead: the effect of mercury on the body is not immediate poisioning (like arsenic), which would cause the fish to die before you, rather, it’s a slow process affecting the inner organs. Most critical is the effect on the brain, thus the warning for pregnant and small children, but it can also have negative effects on your body. If you don’t mind loosing some statistical years of your life, then keep on eating tuna fish instead of other fish or other methods of improving your health. That wil prove that you aren’t swayed by “psuedo experts”. Also, good look complaining to, or suing, the fish companies. They don’t have to worry about risks because ocean fish is regulated differently than meat. Since there are no maximum limits of heavy metals, they don’t have to measure them or put it onto the packaging. They only have to adhere to certain hygienic rulse during preparations, but not to the contents of the fish. You are eating it at your own risk. Are you at least paying attention to dolphin-safe tuna? ---
**Author:** ![KlondikeGeoff](https://avatars.discourse-cdn.com/v4/letter/k/3e96dc/32.png) [@KlondikeGeoff](https://boards.straightdope.com/u/KlondikeGeoff)\ **Post date:** [October 2, 2010, 9:37pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/5 "2010-10-02T21:37:30Z")
Just to give you an idea of the scope of the problem, not so long ago a Japanese thermometer factory had to shut down. Turned out all the mercury was contaminated by tuna fish. ---
**Author:** ![HyenaThePirate](https://avatars.discourse-cdn.com/v4/letter/h/ecd19e/32.png) [@HyenaThePirate](https://boards.straightdope.com/u/HyenaThePirate)\ **Post date:** [October 3, 2010, 3:53am UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/6 "2010-10-03T03:53:07Z")
> [@constanze](#): > > You claim that you are not “unversed in the chemical science”, but in this case, you should look up some biology instead: the effect of mercury on the body is not immediate poisioning (like arsenic), which would cause the fish to die before you, rather, it’s a slow process affecting the inner organs. Most critical is the effect on the brain, thus the warning for pregnant and small children, but it can also have negative effects on your body. If you don’t mind loosing some statistical years of your life, then keep on eating tuna fish instead of other fish or other methods of improving your health. That wil prove that you aren’t swayed by “psuedo experts”. > Also, good look complaining to, or suing, the fish companies. They don’t have to worry about risks because ocean fish is regulated differently than meat. Since there are no maximum limits of heavy metals, they don’t have to measure them or put it onto the packaging. They only have to adhere to certain hygienic rulse during preparations, but not to the contents of the fish. You are eating it at your own risk. > > Are you at least paying attention to dolphin-safe tuna? Yes I do try to buy dolphin-safe tuna, and actually have been considering purchasing fresh tuna with that purpose in mind (apparently because canned tuna companies have such iffy track records on their “dolphin safety”). That is actually what prompted me to inquire seriously into all of this potential urban mythos. True, mercury isn’t going to drop you dead in moments after contact, but I think you might severely be understating it’s danger. There is a reason mercury is considered one of the most dangerous metals known to man. Mercury causes thousands of poisonings a year, many of them fatal, and much of it from what we might consider relatively small amounts. In the very least, much of the damage it causes is irreversible, and usually affecting all the body parts I kinda of like the most (I.e. my central nervous system, kidneys, and brain). From what I recall from chemistry class, as little as 1 ounce is enough to do serious, permanent damage. So when I think of the size of a tuna, and consider just how much of that tuna is contained in a tiny little can, I began to worry that if a two can a week limit is what is suggested, then how saturated must these fish be? I suppose the real answer I am looking for is how much tuna per week can I eat without inadvertently murdering myself. > [@septimus](#): > > But I’ve no idea about this really. The only reason I quoted you here was to ask for further details about “voluptuous human male.” 😃 What more can I say? I am a credit to our species and would make a fine edition to any top-rated intergalactic zoo. ---
**Author:** ![dzeiger](https://avatars.discourse-cdn.com/v4/letter/d/46a35a/32.png) [@dzeiger](https://boards.straightdope.com/u/dzeiger)\ **Post date:** [October 3, 2010, 4:47am UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/7 "2010-10-03T04:47:47Z")
IIRC, there are several different sizes and types of tuna–the longer-lived, larger ones will have a higher concentration of mercury since it accumulates over the fish’s life. I believe most canned tuna is the cheaper, shorter-lived types. It wouldn’t surprise me if there is some sort of loose correlation between how expensive the tuna is and the amount of mercury it contains. ---
**Author:** ![HyenaThePirate](https://avatars.discourse-cdn.com/v4/letter/h/ecd19e/32.png) [@HyenaThePirate](https://boards.straightdope.com/u/HyenaThePirate)\ **Post date:** [October 3, 2010, 6:19am UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/8 "2010-10-03T06:19:19Z")
> [@dzeiger](#): > > IIRC, there are several different sizes and types of tuna–the longer-lived, larger ones will have a higher concentration of mercury since it accumulates over the fish’s life. > > I believe most canned tuna is the cheaper, shorter-lived types. It wouldn’t surprise me if there is some sort of loose correlation between how expensive the tuna is and the amount of mercury it contains. You raise an interesting point in that, sir. I would wager that the correlation wouldn’t be that loose I imagine, if what is suspected is actually happening with the mercury levels in these fish. Which lends to another question. Much evidence has been documented about the possibility of their sea-based diets as an attributing factor to the longer life spans of the asian races. If the mercury levels in these fish are truly a danger with prolonged exposure, then it stands to reason that at some point we should see a marked decline in the mortality rates of Japanese men and women, for example. Right? ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [October 3, 2010, 10:14am UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/9 "2010-10-03T10:14:24Z")
> [@HyenaThePirate](#): > > Which lends to another question. > Much evidence has been documented about the possibility of their sea-based diets as an attributing factor to the longer life spans of the asian races. > If the mercury levels in these fish are truly a danger with prolonged exposure, then it stands to reason that at some point we should see a marked decline in the mortality rates of Japanese men and women, for example. Right? Via Googling: > [@](#): > > Based on the results of our testing, consumers should avoid brands of light canned tuna that comes from Latin American countries, especially Ecuador and Mexico because of their astonishingly high average level of mercury. > > Our testing showed that on average Asian brands of tuna had the lowest mercury concentrations, especially that which came from Thailand. I’d post the URL, but I’ve no relevant expertise and, anyway, didn’t chance on a webpage explaining _the reason_ for the goegraphic bias. ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [October 4, 2010, 12:37pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/10 "2010-10-04T12:37:43Z")
> [@HyenaThePirate](#): > > You raise an interesting point in that, sir. > I would wager that the correlation wouldn’t be that loose I imagine, if what is suspected is actually happening with the mercury levels in these fish. > > Which lends to another question. > Much evidence has been documented about the possibility of their sea-based diets as an attributing factor to the longer life spans of the asian races. > If the mercury levels in these fish are truly a danger with prolonged exposure, then it stands to reason that at some point we should see a marked decline in the mortality rates of Japanese men and women, for example. Right? The Japanese have [paid a price](http://en.wikipedia.org/wiki/Minamata_disease) for releasing mercury into the ocean. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [October 4, 2010, 2:12pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/11 "2010-10-04T14:12:39Z")
> [@HyenaThePirate](#): > > . Apparently, a person should consume no more than 2 cans of tuna per WEEK due to some sort of high mercury content that is now found in ocean faring fish, specifically tuna. > > A Mercury is found in fish naturally. While there are cases of mercury contamination in areas, the gist of the issue is that the existence of mercury in fish, such as tuna, is nothing new. C_alifornia vs Tri-State Seafood, Delmonte, Bumble Bee_ 2006 Page 60: The Judge ruled that “there is no dispute that most of the methylmercury in the ocean exists completely independently of human activity.” Dr. Francois Morel, a noted Princeton University environmental scientist, testified that the percentage of mercury in tuna that originates from human sources “is either zero or 1.5 per cent.” Page 61: University of Connecticut marine scientist Dr. William Fitzgerald, the court wrote, testified that he “knows of no peer-reviewed study that has found an increase in methylmercury in ocean fish during the time period when atmospheric mercury levels have increased.” And the defense “presented scientific studies that show there has been no increase in the amount of methylmercury in ocean fish during the past 100 years.” Page 65: The court heard about a scientific study showing that that the mercury levels in tuna caught in 1998 “were nearly identical to (and in fact slightly less than)” the levels in fish caught back in 1971. This supports the court’s conclusion that “there is almost no anthropogenic [human-derived] methylmercury in the ocean.” Page 76: “There is evidence,” the court wrote, that mercury begins its natural journey up the food chain “in deep ocean hydrothermic vents … If hydrothermic vents are the source of methylmercury, then 100 percent of methylmercury in the ocean is naturally occurring.” In fact, according to Dr. Fitzgerald, “deep ocean vents produce enough methylmercury to account for about four times the amount of methylmercury that bioaccumulates in ocean fish each year.” Page 116: The final nail in a giant scare campaign: The court declares that “methylmercury in fish, including tuna, does not respond to human pollution, and is a natural part of the product’s environment.” ---
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [October 4, 2010, 2:13pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/12 "2010-10-04T14:13:24Z")
Here’s [one article](http://neuro.psychiatryonline.org/cgi/content/full/20/4/iv) reviewing the scientific literature on the effects of mercury. Quoting from the sections most relevant to the OP: > [@](#): > > The major route of exposure to methylmercury is through consumption of fish and marine mammals. Inorganic mercury, present in the environment as a result of emissions from both natural (e.g., volcanoes) and human (e.g., coal-burning power stations) sources, is converted to methylmercury within microorganisms in aquatic sediments, allowing it to enter the food chain. Biomagnification occurs at each ascending level of the food chain. Thus, the highest concentrations are found in muscles of longer-living aquatic predators (e.g., pike, shark), principally as a methylmercury cysteine complex.24 Industrial pollution is another source. It can result in localized areas in which the level of methylmercury in fish is very high, as happened in Minamata Bay in Japan. > … > Symptoms of acute exposure to methylmercury in adults (Minamata disease) may include impairments in all primary sensory modalities (blurred vision, with bilateral and symmetric constriction of the visual fields; bilateral deficits in hearing, with speech discrimination more impaired than pure tone; deficits in smell and taste; distal paresthesias with preserved or hyperactive tendon reflexes) as well as dysarthria and cerebellar ataxia. Psychiatric symptoms are common and include loss of volition and apathy, excessive interpersonal sensitivity, perseveration, and loss of inhibition.3,25,27 > … > Chronic exposure to methylmercury in adults is most commonly manifested in distal paresthesias.25 Touch threshold is increased in all areas of the body. Cerebellar ataxia is not usually seen, but sensory ataxia and pseudoathetoid movements may be present. The injury is to the somatosensory cortex, as indicated by preservation of tendon reflexes, normal conduction velocity in the sural nerve, and abnormality of the short-latency somatosensory evoked potential. A SPECT study compared rCBF in elderly patients with mild chronic methylmercury poisoning to age-matched healthy individuals.30 The groups had similar incidence of white matter abnormalities on MRI. There were no significant differences in cortical rCBF between the groups. Cerebellar atrophy was present in 27% of the patients with methylmercury exposure and none of the participants in the matched comparison group. Regional CBF was significantly decreased in cerebellum even in patients without visible atrophy. > … > Vulnerability to methylmercury poisoning is age-related, with susceptibility decreasing with increasing age.2 To summarize that a bit further: Acute exposure in adults causes neurological damage which results in all sorts of sensory and psychiatric problems. Mild chronic mercury exposure in adults can cause neurological damage that typically results in loss of coordination by damaging sensory neurons and the part of the brain that controls movement. “Chronic” exposure [in this particular study](http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T06-4PB75MD-4&_user=489286&_coverDate=11%2F15%2F2007&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_acct=C000022678&_version=1&_urlVersion=0&_userid=489286&md5=cd9180af166d25d9cd2366ef1eb4254b&searchtype=a) was defined as a group of adult individuals with methylmercury exposure from the Minimata incident over ~20 years and an average mercury level (measured in hair) of 24.8 ppm, declining to closer to ~10 ppm in the decades after the exposure. That’s still a very high exposure; studies that look at groups that eat lots and lots of seafood find hair mercury [around 2.4 ppm](http://www.ncbi.nlm.nih.gov/pubmed/20049129). So to answer the OP’s question, it’s hard to say. If you’re eating huge amounts of the tuna with the highest mercury concentrations, you’re probably getting enough mercury to cause neurological damage over time. At more modest consumption, with a bit of care to avoid mercury, you’re probably fine. Oh, and the amount of mercury which doesn’t cause any serious problems to a healthy adult can definitely cause problems for fetal and early childhood development. ---
**Author:** ![This\_Just\_In\_2](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@This\_Just\_In\_2](https://boards.straightdope.com/u/This_Just_In_2)\ **Post date:** [October 4, 2010, 3:39pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/13 "2010-10-04T15:39:36Z")
[From this website](http://en.wikipedia.org/wiki/Environmental_Defense_Fund), I see that canned tuna seems okay to “enjoy in moderation”. It really depends on where that fish came from, so read the label. From that website "Canned light tuna consists primarily of skipjack. These small tunas are resilient to fishing pressure because of their short life spans and rapid growth and reproduction rates. Most skipjack are caught by pole-and-line (a method of fishing that does relatively little ecological harm) or purse seine fleets (which can result in considerable bycatch). This highly migratory species is managed by international organizations." ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [October 4, 2010, 5:33pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/14 "2010-10-04T17:33:20Z")
> [@lazybratsche](#): > > So to answer the OP’s question, it’s hard to say. If you’re eating huge amounts of the tuna with the highest mercury concentrations, you’re probably getting enough mercury to cause neurological damage over time. At more modest consumption, with a bit of care to avoid mercury, you’re probably fine. > > Oh, and the amount of mercury which doesn’t cause any serious problems to a healthy adult can definitely cause problems for fetal and early childhood development. This sums it up pretty well. If you’re old enough to buy alcohol in the US and not going to be pregnant or breastfeeding (Hey, who knows what you reallly mean by ‘voluptuous’?), and you’re not exposed to mercury in some other way, then you’re probably fine. [Kids and women who are or will be sharing bodily fluids with kids should be careful, though.] ---
**Author:** ![wheresmymind](https://avatars.discourse-cdn.com/v4/letter/w/91b2a8/32.png) [@wheresmymind](https://boards.straightdope.com/u/wheresmymind)\ **Post date:** [October 4, 2010, 10:59pm UTC](https://boards.straightdope.com/t/fishy-business-are-there-really-dangerous-levels-of-mercury-in-tuna-or-not/555858/15 "2010-10-04T22:59:21Z")
> [@constanze](#): > > Are you at least paying attention to dolphin-safe tuna? Actually, “dolphin-safe” tuna is a pretty classic example of [unintended negative consequences stemming from good intentions](http://www.southernfriedscience.com/?p=6539). Basically, moderate amounts of dolphin by-catch were traded for tiny amounts of dolphin by-catch plus ENORMOUS amounts of fish by-catch, which is currently screwing with the trophic status of the ocean and killing lots of sharks (among other things). It’s up to society to decide whether 1 dolphin is more important than several thousand other fishes/sharks, but my guess is some people would think twice about “dolphin safe” if they saw the mountain of bycatch involved.