Mercury in Fish: Why You Should Be Concerned and What To Do

A major review of mercury contamination of fish carried out by four scientific groups, published in the internationally recognised Swedish environmental journal Ambio concludes that:
* On average, three times more mercury is falling from the sky today than before the Industrial Revolution 200 years ago as a result of the increasing use of mercury and industrial emissions.
* The uncontrolled use of mercury in small-scale gold mining is contaminating thousands of sites around the world. These activities alone contribute more than 10 percent of the mercury in the Earth's atmosphere.
* Little is known about the behavior of mercury in marine ecosystems and methylmercury in marine fish, the ingestion of which is the primary way most people at all levels of society worldwide are exposed to this highly toxic form of mercury.
* Methylmercury exposure now constitutes a public health problem in most regions of the world.
* Methylmercury levels in fish-eating birds and mammals in some parts of the world are reaching toxic levels, which may lead to population declines in these species and possibly in fish populations as well.
There is now solid scientific evidence of methylmercury's toxic health effects, particularly to the human foetus and new evidence that methylmercury exposure may increase the risk of cardiovascular disease, particularly in adult men.

However, before you throw your fish away the benefits of omega 3 may outweigh the risks in pregnancy, according to a paper published in the Lancet last month by Professor Joseph Hibbeln. A survey of 11,875 pregnant women found that those who ate less than 340 grams (3 servings) of seafood per week in pregnancy had more adverse outcomes. Beneficial effects on child development were recorded in those with maternal seafood intakes of more than 340 g per week, suggesting that advice to limit seafood consumption could actually be detrimental.

What to do?
Certain fish are a good source of omega 3's, plus protein. Fish, especially larger fish like tuna, swordfish and marlin, store the mercury which we then ingest. The chart below lists in order of best to worst the best fish to eat in terms of the greatest amount of omega 3 with the lowest amount of mercury. Farmed salmon may have significantly lower amounts of omega 3 compared to wild salmon because the amount of omega 3 in the fish depends to a large extent on the quality of its diet.

	omega 3 g/100g	mercury mg/kg	omega3/ mercury
fresh wild salmon	2.7	0.05	54.0
canned sardines	1.57	0.04	39.3
canned and smoked salmon	1.54	0.04	38.5
fresh mackerel	1.93	0.54	35.7
trout	1.15	0.06	19.2
fresh tuna	1.5	0.4	3.8
cod	0.25	0.11	2.3
fresh sole	0.1	0.05	2.0
canned tuna	0.37	0.19	1.9
marlin	*2	1.1	1.8
swordfish	*2	1.4	1.4
*estimated

Larger fish like tuna tend to be higher in mercury so don't eat tuna more than once a week. Since canned tuna has much less of the omega-3's left after the canning process, stick with fresh tuna. Marlin and swordfish and best consumed once a month max. Eat salmon, small mackerel or sardines instead. Generally speaking, the larger the fish the more the mercury.

It also helps to limit other sources of mercury. Childhood vaccinations no longer contain thimerisol, an ingredient that contains mercury, which is now used instead in flu vaccines!

However, there are ways to detoxify mercury thus reducing its effects on you. The most potent mercury detoxifier is selenium. A daily intake of 50 to 100mcg may provide significant protection. Seafood provides selenium, as do seeds and nuts. While Brazil nuts are supposed to be high, some analyses show very little. Make sure your multivitamin is providing at least an additional 30mcg.

Mercury may also be detoxified by a sulphation/methylation process that involves B6, B12, folic acid and zinc. A theory is emerging in autism that exposure to mercury, plus abnormal methylation, may lead to brain damage. Both homocysteine and oxidants are capable of damaging the brain. The symptoms of mercury toxicity include headaches, memory loss and psychosis. That's why hatters, who polished top hats with mercury, went mad.

Consequently, ensuring you have a good intake of antioxidants, especially selenium, and a good intake of B vitamins (especially B6, B12 and folic acid) and zinc, plus a low homocysteine level, may help protect you from the dangers of mercury.

Ultimately, the problem of mercury contamination will be curtailed by the international community reducing industrial exposure in developing countries.

Wishing you the best of health,


Patrick Holford

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