State of New Mexico > Environment Department > Surface Water Quality Bureau

Surface Water Quality Bureau
Monitoring & Assessment
Mercury in Fish
- A Foodsource FAQ -

Developed by the New Mexico Department of Health, 1991

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This FAQ compliments our Fish Consumption Advisories.  To review more, choose a link on the right...
Kris Barrios
Acting Program Manager
(505) 827-2621


This file was originally posted at this website in 1996.  The following text has not been modified since then, but the topic's contact information below has been updated.

Environment Department
Lead: Gary Schiffmiller
(505) 827-2470

Department of Game & Fish
Lead: Michael Sloane
(505) 476-8055

Department of Health
Lead: Heidi Krapfl
(800) 878-8992

Where can I find out if mercury has been found in the fish at the lake I'm planning to go to?

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The easiest thing to do is go to the lake an your fishing trip, and look for a mercury fish consumption advisory (health advisory) there. Information on the advisories will soon be available at vendors who sell fishing licenses. You can also call the Department of Game and Fish at (505) 327-7905 or (505) 827-7911, or the Environment Department at (505) 827-0187.

What do the fish advisories
tell me?

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The health advisories are prepared for each individual lake, based on the levels of mercury found in each species and size of fish there. They tell you what size fish are safe to eat for different groups of people.

Why are there different health advisories for different groups of people, like children, women who plan to have children, and pregnant women?

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These groups have more serious problems; with mercury, since mercury is especially dangerous to those whose brains are still developing (babies during pregnancy and children), and women can accumulate mercury before pregnancy and then the babies will become exposed from their mothers' bodies during pregnancy.

Has eating mercury-contaminated fish made anyone sick in New Mexico?

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At this moment, we have not had any people proven to be ill from eating mercury-contaminated fish in Now Mexico. However, because the symptoms could be mild, and similar to many other diseases like senility, Alzheimer's disease, etc., there could be ill people that we don't know about. There are no legal requirements to report mercury poisoning to the state health department.


How many fish would I have to eat to become ill?

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Eating more fish than the health advisories recommend could increase your risk of illness. People have become ill after eating fish with 300 micrograms per day an the average.(The frequency of eating fish and the lenqzh of time of exposure varied.)

To translate these numbers to the levels of mercury found in Now Mexico fish, eating just 1/4 pound per day of the larger fish containing mercury could give you the same dose of mercury as that associated with health effects.

Why do the health advisories tell me not to eat any of the Group IV fish?

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For some chemicals, such as mercury in drinking water, the legal limits for exposure are 1,000 times less than the amount known to cause illness. Applying that safety factor to the level of mercury in fish known to cause illness would suggest that you shouldn't eat 1/4 pound of the Group IV fish more frequently than every 1000 days (or once in three years). Because of individual differences in susceptibility, we recommend not eating any of these fish to be safe.

Shouldn't we find out if this is making people sick in New Mexico before we warn people about it?

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Trying to find people who are ill would be very expensive and difficult, and maybe impossible, even if it is happening. In the meantime, more people would go on getting exposed to mercury, wnen we have sufficient evidence from studies in other places that these levels of mercury can be potentially hazardous.

What kind of mercury is in fish?

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Mercury in fish is primarily methylmercury (organic).

Does it make a difference what kind of mercury I got exposed to?

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Any kind of mercury, inorganic or organic, can cause health problems. However, organic mercury is more serious because it is absorbed by the body more easily.

How did we first discover this problem?

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Some routine spot checking by the federal government first found the problem. We verified it, and continued testing other lakes in New Mexico.

Have enough fish been tested to be really sure of the level of mercury contamination?

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Yes, for the lakes for which we have issued health advisories. Mercury levels are strongly correlated with the length of the fish because longer fish are older and have had more time to accumulate mercury. Thus only four fish of different lengths from each species in a lake need to be tested in order to predict with great accuracy the levels of mercury in all the fish. However, we are testing more fish than this in order to verify our statistical models.

How long have New Mexico fish been contaminated with mercury?

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We really don't know. However, it is likely that they have been contaminated for a number of years. Previous tests (which were less accurate than the ones available now) indicate that some lakes may have had problems at least for several decades.

Why wasn't anything done about this earlier?

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High quality laboratory tests on mercury in fish have only been recently available, and these tests are very expensive to do. in addition, our scientific understanding of the health risks associated with mercury continues to grow.

What other parts of the country and the world have this problem?

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Health departments in at least 21 other states, two Canadian orovinces, and other countries have issued health advisories on freshwater fish in one or more of their lakes or rivers. Some of these include Colorado, Oregon, Wisconsin, Minnesota, Michigan, Arizona, and New York. Some jurisdictions forbid keeping any fish at all (they legally make streams or lakes catch-and-release).

Will New Mexico enact any regulations regarding fish with mercury contamination?

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At this time, we have no plans to legally restrict keeping fish, and will continue issuing health advisories as tests are completed. Under certain circumstances, we may consider asking that lakes be designated as catch-and-release.

Will the health advisories for a specific lake ever change?

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With additional testing, and more knowledge about the dangers of mercury, the health advisories could change. However, other states have found that their health advisories only need to be changed slightly each year.

Where is the mercury in the fish coming from?

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We don't know for sure, but we have not found any single source for it here in Now Mexico so far. Studies in other areas of the U.S. and the world have found that most of the mercury appears to be coming from the air and then deposits in lakes and on soil. The mercury gets into the air from industrial processes including smelters.

Another possibility is that mercury can be found naturally in different types of soils, and become washed into lakes with soil disturbances such as overgrazing, housing developments, road developments, etc.

Why would some lakes have a problem and others not?

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The factors which affect the amount of mercury which gets into the fish are not fully understood. However, some of them appear to be:


More acid lakes lead to more conversion of mercury to methylmercury, which is taken up by the fish more easily;


Recently formed lakes, especially those with submerged decaying vegetation such as trees, are more likely to convert mercury to methylmercury;

3. Smaller lakes may have the mercury more concentrated;

Rivers with swiftly moving water will usually have less concentrated mercury; and


Bigger fish, and species of fish which eat other fish, get larger amounts of mercury.

Is there anythinq that can be done to clean up the mercury?

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There is some research on this, but no good, cheap, safe, effective, and permanent way has yet been discovered.

Will cooking the fish get rid of the mercury?

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No, cooking will not eliminate the mercury. In fact, as the moisture is cooked out of the fish, the relative concentration of mercury actually increases.

Since mercury may be getting into the lakes from the air or soil, why is it at it dangerous to swim in the lake, camp in the campqround, or touch the fish?

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The levels of mercury in the water can be so small that they can't even be detected, and still accumulate over time in fish. So swimming or playing in the dirt does not appear to pose any health risk, and handling the fish does not expose you to any important amount of mercury either.

What kinds of health problems can mercury cause?

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The type of health problems depend an the amount, duration, and route of exposure. Serious problems can occur after exposures for short periods of time if the mercury levels are very high, or after more moderate exposures for a long period of time. The probability of developing health problems is influenced by personal factors such as age, sex, pregnancy, general health condition, etc.

The most serious problems are related to the brain and spinal cord, and include blindness, paralysis, brain damage, and death. Other parts of the body which can be damaged are the kidneys and respiratory tract. Heart and immune system damage have been found in animals exposed to mercury.

Does mercury cause cancer?

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At this time, most of the scientific evidence indicates that mercury does not cause cancer.

Does mercury cause birth defects?

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Yes, mercury has been proven to cause severe brain damage in infants when their mothers were exposed to it durinq pregnancy. Also, mercury can change chromosomes, and in animals, has been shown to damage the reproductive tract of males.

How long can mercury stay in my body?

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After a single exposure, you will have eliminated about half the amount of mercury in your body within approximately 2-1/2 months. However, with repeated exposures, the amount of mercury in your body will build up.

How does mercury get out of my body?

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Primarily through the feces (stools), although some is excreted through urine.

How can I find out if I have mercury poisoning?

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This requires an extensive physical exam by a doctor and many laboratory tests. Blood tests are more useful than hair tests, but both can be difficult to interpret in living human beings, because they are not completely accurate measurements of the amount of mercury in your body.

Who should have tests for mercury poisoning?

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Anyone who believes they may have had a lot of exposure to mercury, and who has medical problems of unknown cause which are the type that could be caused by mercury, should contact their physician to discuss further evaluation for possible mercury poisoning.

Why are mercury laboratory tests difficult to interpret?

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Laboratory tests for any chemical in our bodies are difficult to interpret for a number of reasons, including:


They don't necessarily tell you when the exposure occurred, whether it was recent or a long time ago, although with information about the length of time mercury remains in the body, we can make some guesses about the time of the exposure;


They don't tell you whether the exposure occurred once, or frequently;


They don't necessarily tell you the amount of exposure, although some guesses can be made based on the test results;


They don't tell you how you were exposed to mercury;


They don't necessarily tell you whether the symptoms you are experiencing are from the mercury; and


They don't necessarily tell you whether you will experience health problems in the future.

Is there anything I can take to get the mercury out of my body?

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There are several drugs which doctors can use to help speed up getting the mercury out of your body. However, these are dangerous themselves and should only be used when absolutely necessary (when someone is severely ill with mercury poisoning).

Is there any treatment for mercury poisoning?

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There is no treatment which can reverse any damage done to your body by mercury. However, by using special drugs to help clear the mercury out of your body, and supportive care, some health problems may partially improve.

How does the risk of mercury compare to other health risks?

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Compared to the risk of other chemicals, mercury is very dangerous. Many other chemicals have much less evidence of serious health effects compared to mercury. In addition, although other chemicals may be in the environment, exposure in sufficient ammmts to cause health effects is often rare.

However, the risks of tobacco smoke, traffic accidents, and radon, for example, are much higher than mercury, unless exposures to mercury are high for a large number of people.

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FOR MORE INFORMATION... (all links open in a new window)
bulleted item US Environmental Protection Agency
bulleted item Mercury
bulleted item Water Pollutants > Mercury
bulleted item US Geological Survey
bulleted item Mercury Contamination of Aquatic Ecosystems
bulleted item US Food and Drug Administration
bulleted item What You Need to Know About Mercury in Fish and Shellfish

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