Mercury: Fish to Avoid

Mercury: Fish to Avoid

How much mercury does this fish have?

Fish can be a part of a healthy diet (but are by no means essential to a healthy diet, so vegan friends keep on vegging out!).  Unfortunately, many popular fish are high in mercury.  Mercury is a heavy metal that we do not need in our systems to survive.  In fact, there is no safe amount of mercury that we know of.  As parents, we have an obligation to protect our children as much as possible.  One way to do this is to avoid feeding kids fish high in mercury.  Pregnant women also need to avoid mercury as much as possible, as mercury can cross the placental barrier.

Fish as a Source of Mercury

Preparing fish

While some mercury is naturally discharged into the environment, much mercury is added to the environment by human industry.  Industries often discharge large amounts of waste products into our water sources.  Elemental or inorganic mercury is discharged by industry into our oceans and is transformed by bacteria into methylmercury.  This methylmercury then accumulates in the aquatic food chain.  Thus, small animals eat the bacteria, bigger animals eat them, and as you move up the food chain more and more methylmercury accumulates in the fish. Pregnant women who eat this fish, or children whose parents feed them this fish, are at higher risk. (Read more here.)

Which Fish to Eat?

Grilled fish

Not all fish accumulate methylmercury equally.  Just as not all mammals eat the same things, not all fish eat the same things.  If the methylmercury processing bacteria aren’t in the food chain (or are less in the food chain), then the bigger fish will contain less mercury.

Unfortunately, overfishing has also done a lot of damage to the aquatic environment.  Some fish are being so overfished their populations are declining dangerously.  This isn’t a health or diet issue, but it is an environmental issue.  Because this is a nutrition blog, I’ll still list fish with dangerously low levels or with bad environmental fishing practices, but I will include the caveat of stars for those who wish to avoid them.

This list is from the Natural Resources Defense Council.

LEAST MERCURY

Enjoy these fish:
Anchovies
Butterfish
Catfish
Clam
Crab (Domestic)
Crawfish/Crayfish
Croaker (Atlantic)
Flounder*
Haddock (Atlantic)*
Hake
Herring
Mackerel (N. Atlantic, Chub)
Mullet
Oyster
Perch (Ocean)
Plaice
Pollock
Salmon (Canned)**
Salmon (Fresh)**
Sardine
Scallop*
Shad (American)
Shrimp*
Sole (Pacific)
Squid (Calamari)
Tilapia
Trout (Freshwater)
Whitefish
Whiting

MODERATE MERCURY

Eat six servings or less per month:
Bass (Striped, Black)
Carp
Cod (Alaskan)*
Croaker (White Pacific)
Halibut (Atlantic)*
Halibut (Pacific)
Jacksmelt
(Silverside)
Lobster
Mahi Mahi
Monkfish*
Perch (Freshwater)
Sablefish
Skate*
Snapper*
Tuna (Canned
chunk light)
Tuna (Skipjack)*
Weakfish (Sea Trout)

HIGH MERCURY

Eat three servings or less per month:
Bluefish
Grouper*
Mackerel (Spanish, Gulf)
Sea Bass (Chilean)*
Tuna (Canned Albacore)
Tuna (Yellowfin)*

HIGHEST MERCURY

Avoid eating:
Mackerel (King)
Marlin*
Orange Roughy*
Shark*
Swordfish*
Tilefish*
Tuna (Bigeye, Ahi)*

* Fish in Trouble! These fish are perilously low in numbers or are caught using environmentally destructive methods. To learn more, see the Monterey Bay Aquariumand the The Safina Center (formerly Blue Ocean Institute), both of which provide guides to fish to enjoy or avoid on the basis of environmental factors.

** Farmed Salmon may contain PCB’s, chemicals with serious long-term health effects.

Mercury: Dangerous for Kids’ Health

Mercury: Dangerous for Kids’ Health

There are so many ways we try to protect our children.  We hold their hands when they cross the street, we watch them as they play on the playground, and we buckle them into their car seats.  But how careful are we about how they eat?  One way we can protect our kids is to reduce their exposure to serious known toxins.  Exposure to toxic chemicals can affect children in very serious ways, as they are still growing and developing.* One of the most common toxic exposures is to a metal called mercury.

What is Mercury?

Mercury is a heavy metal that is naturally occurring in the environment.  In fact, it is so heavy that just one quarter cup of mercury at room temperature weighs nearly one kilogram!  (Just over two tablespoons weighs one pound.)  It is a silvery color that you may have seen in thermometers.  Even though mercury occurs naturally in the environment, it can also be propagated by certain industries and causes serious environmental and health consequences.

How Is Mercury Taken In?

Mercury is pernicious in that it can be taken in in many ways.  It can be inhaled, consumed, and absorbed through the skin.  It can also cross placental barriers and be prenatally absorbed by a fetus.  It is important to begin protecting your child from mercury exposure as soon as they are conceived.

What Exposes My Kids to Mercury?

Some children are exposed to extra mercury because they or their families are associated with certain employment that uses mercury.  Ironically, the health care sector used to be a major route of exposure, through use of mercury in instruments and cleaning supplies, but fortunately this is no longer common practice.  Mercury is still used heavily in the mining industry (especially gold mining), power plants, crematoria, and the charcoal industry.  If you or your child is not exposed to these industries, then your child’s exposure to mercury is likely to be environmental: food, air, water, and soil.  Let’s look at the main routes of exposure in turn.

Mercury Exposure in Food

This is the most common way children are exposed to mercury and one of the most easily preventable.**  Mercury accumulates in the seafood food chain.  This means that top seafood predators, such as tuna fish, are highest in mercury.  By knowing what fish are highest in mercury and which are lowest, you can ensure that your child is eating fish with low levels of mercury.

Be aware that fruits and vegetables grown in mercury heavy soil or in a mercury poisoned atmosphere are also themselves high in mercury.  Today, fertilizers no longer contain mercury as they used to, so most people in developed countries do not need to worry.  However, if your produce is being grown next to a power plant, a plant that produces mercury cell batteries, a gold mine (you wish, right?), a cemetery, or a crematorium, you should be aware that the mercury levels in your produce might be high.

Some preservatives also contain mercury.  This is a good reason to try to buy things fresh and prepare your own food as much as possible.   In many foods, even foods purporting to be all natural or pure, the only additional ingredient is a preservative.

Mercury has also been detected in certain foods that are the byproducts of mercury producing practices.  The most notable one is high fructose corn syrup.***  High fructose corn syrup is found is so many foods today that it is almost ubiquitous.  Aside from the fact that it is incredibly unhealthy in general, it is also a source of toxicity.

Mercury Exposure in Soil

Kids play outside (or at least mine do – and I hope yours do, too).  But because kids are digging in the dirt, getting filthy, and putting their hands in their mouths, they are also exposed to anything the soil contains, including mercury.  Environmental mercury can accumulate in soil just from being deposited from the air.  Soil can also contain mercury from decomposing wastes, as well as from fertilizers containing mercury (which fortunately is less common today – but used to be used more).****

Other Sources of Mercury Exposure

Some mercury exposure is due to the customs of certain cultures.  If you do not participate in these cultural practices, then you do not need to worry about these things.

Significant exposure can come from certain ayurvedic medicine.  Yes I know ayurvedic medicine is supposed to be healthy, but certain medicines and practices contain mercury and it can be really dangerous.*****  Other religions like Santeria or Espritismo also involve mercury in their rituals.******

Another significant cultural exposure to mercury comes in the form of skin lightening cosmetics, creams, lotions, and other products.  In some cultures, especially Asian cultures, light skin is seen as highly desirable and there is temptation to use products to lighten skin tone.  However, many of these products contain mercury, which can be very dangerous.*******

What Harm Does Mercury Cause?

In children, mercury poisoning generally manifests in the form of acrodynia, or “pink disease.”  It is called pink diseases because children’s hands, feet, cheeks, and lips turn pink and painful.  They can also begin to lose their hair, teeth, and nails.********   Other symptoms of mercury poisoning include confused vision, hearing, and speech, and a lack of coordination.

Mercury poisoning is very serious.  Mercury kills neurons in certain parts of the brain, which makes it especially dangerous for babies in utero.  It crosses both the placental and blood brain barriers and is not efficiently excreted, so it can accumulate in the unborn baby.  These babies are born with neurological problems that resemble cerebral palsy, spasticity, and other reflex, visual, and convulsive problems.  All pregnant women, for the sake of their unborn babies, should not risk mercury exposure.

How Much Mercury is too Much?

There is no known safe level of mercury to consume.  Let me repeat that.  There is NO safe amount of mercury to consume.

In other words, any mercury is too much mercury.

To protect your children, reduce their mercury intake as much as possible.

How Can I Protect My Kids From too Much Mercury?

There are certain things you can do to reduce your children’s exposure to mercury:

  • If you feed your children fish, ensure you are feeding them low mercury fish.
  • Reduce your kids’ intake of mercury containing food additives like preservatives and high fructose corn syrup.
  • Avoid keeping mercury containing products like mercury thermometers and fluorescent light bulbs in your house.  If you do keep these items in your home, ensure they are kept safe and not in danger of breaking.  If a mercury containing item does break, safely clean up the spill, keeping your kids far away at all times.  (If you are pregnant and one of these items breaks, please leave the area immediately and do not inhale in that area.   You should contact an approved toxic spill company to clean up the toxins and test the air, as airborne mercury is highly toxic.)
  • Do not use ayurvedic or other ritualistic remedies that may contain mercury.
  • Do not expose yourself or your children to skin lightening creams, lotions, etc.

(You many notice that not vaccinating is not on this list.  There is no scientific link between the trace amounts of mercury contained in vaccines and autism.**********  In fact, elemental liquid mercury injected is less harmful than mercury in its other forms taken in through food, skin, or air exposure.***********)

Conclusion

I hope this information is useful.  I will follow up soon with more information on what fish and seafood are safest and most dangerous to consume, as well as more information about how children are exposed to mercury through seafood consumption.

*Jarosinska D, Gee D. Children’s environmental health and the precautionary principle.Int J Hyg Environ Health. 2007;210:541–6.

*Selevan SG, Kimmel CA, Mendola P, Pronczuk-Garbino J. Children’s health and the environment – a global perspective. WHO press; Geneva: 2005. Windows of susceptibility to environmental exposures in children; pp. 17–26.

*Weiss B. Vulnerability of children and the developing brain to neurotoxic hazards.Environ Health Perspect. 2000;108(Suppl 3):375–81.

**Al-Saleh IA. Health implications of mercury exposure in children. Int J Environ Healthc.2009;3:22–57

***Dufault R, LeBlanc B, Schnoll R, Cornett C, Schweitzer L, Wallinga D, et al. Mercury from chlor-alkali plants: measured concentrations in food product sugar. Environ Health.2009;8:2.

****United Nations Environment Programme-Chemicals . Global Mercury Assessment.Geneva: 2002. Available at: http://www.unep.org/gc/gc22/Document/UNEP-GC22-INF3.pdf.

*****Dargan PI, Gawarammana IB, Archer JRH, House IM, Shaw D, Wood DM. Heavy metal poisoning from ayurvedic traditional medicines: an emerging problem? Int J Environ Healthc. 2008;2:463–74.

******U.S. Environmental Protection Agency . Task force on ritualistic uses of mercury-EPA/540-R-01-005. Washington, DC: 2002.

*******Al-Saleh I, Al-Doush I. Mercury content in skin-lightening creams and potential hazards to the health of Saudi women. J Toxicol Environ Health. 1997;51:123–30.

*******Hursh JB, Clarkson TW, Miles EF, Goldsmith LA. Percutaneous absorption of mercury vapor by man. Arch Environ Health. 1989;44:120–7.

********Palmer RB, Godwin DA, McKinney PE. Transdermal kinetics of a mercurous chloride beauty cream: an in vitro human skin analysis. J Toxicol Clin Toxicol. 2000;38:701–7.

*********Bjørklund G (1995). “Mercury and Acrodynia” (PDF).Journal of Orthomolecular Medicine 10 (3 & 4): 145–146.

**********Doja A, Roberts W (2006). “Immunizations and autism: a review of the literature”. Can J Neurol Sci 33 (4): 341–6.

***********Clarkson TW, Magos L (2006). “The toxicology of mercury and its chemical compounds”. Crit Rev Toxicol 36 (8): 609–62.