By Dr. Matsen

We’ve all heard that eating fish is crucial to good health due to its anti-inflammatory omega 3 oils and brain-boosting EPA and DHA oils. However, conflicting claims say fish is bad because its mercury content can create a multitude of mild to serious health problems. How do you make sense out of this contradiction?

Mercury Background

Mercury is a heavy metal that can indeed create a myriad of health problems, particularly in the developing brains of fetuses and infants, but also in adults. Symptoms of mercury poisoning might include: fatigue; eczema and skin rashes; excess salivation; mood swings; muscle weakness; memory loss; impairment of the peripheral vision; disturbances in sensations such as pins and needles; numbness—usually in the hands feet and sometimes around the mouth; lack of coordination such as when writing; impairment of speech, hearing, and walking; and mental disturbance. In practice, virtually any symptom or disease can be associated with mercury toxicity.

Mercury occurs naturally in rock and soil in tiny amounts but is much more concentrated in cinnabar ore, a reddish mineral associated with alkaline hot springs and that can contain over 12% mercury sulphide. The Romans mined mercury from cinnabar ore in Spain; convicts who had been given the death sentence were used to do the mining, since their chance of survival in these toxic mines was indeed slim. Mercury is also found to lesser degrees in coal and gas deposits.

Mercury is the only heavy metal that’s liquid at room temperature and it also vaporizes readily at higher temperatures. For example, when coal is burned to create electricity, the mercury in the coal vaporizes into the atmosphere. During the winter, it cools, condenses, and falls back to earth. During the summer, mercury might heat up enough to vaporize again into the atmosphere. In this way, mercury from the tropics can work its way towards the poles over a number of summers. Once mercury arrives in a climate that’s always cool, it accumulates there and begins to work its way into the food chain.

How Mercury Gets into Fish

Mercury vapour is far more absorbable than metal mercury but bacteria in water can methylate metal mercury making it very absorbable as well. Fish living behind dams can be high in mercury if the flooded soil contains mercury, since bacteria can methylate it so that it begins its journey up the food chain into fish. Big fish that eat little fish absorb and retain the mercury from the little fish. Interestingly, while methyl mercury doesn’t affect the fish that ingests it, mammals (including whales, dolphins, and humans) that eat mercury-containing fish can be strongly affected. The ability of mercury to vaporize and migrate towards colder climates makes fish from the polar oceans very likely to be high in mercury. However, fish from high-altitude fresh-water lakes would be equally prone to high mercury levels, and these fish are even more likely to be toxic to mammals due to a difference in the mineral content of lake water compared to ocean water.

Ocean waters are high in selenium which binds to and neutralizes some of the mercury in ocean fish, thereby reducing its toxic impact on mammals that might eat it. Fresh- water lakes, however, are typically low in selenium, thus making fish from high-altitude fresh-water lakes potentially more mercury-toxic to humans than ocean fish.

Several lakes in B.C. contain fish known to be high in mercury. These are: Jack of Clubs Lake (gold smelter pollution near Wells): Pinchi Lake (mercury mining in World War II) which is located farther west; and Williston Lake (dam), located  farther north. Lake trout and bull trout in these lakes are considered unsuitable for human consumption because they contain more than the 0.5% mercury level deemed safe by Health Canada. However, be warned that most high-altitude lakes in B.C. have yet to be tested for mercury levels.

Degrees of Mercury in Ocean Fish

The mercury levels in ocean fish have been tested thoroughly. Generally the larger, older, and more predatory a fish is, the more likely it will have higher levels of mercury. Swordfish, marlin, barracuda, big eye tuna (ahi), tilefish, and shark (including B.C.’s spiny dogfish) are highest in mercury as they’re on the top of the ocean food chain and it’s best to avoid eating these.

Tuna, in general, are commonly listed to be completely avoided but this is an erroneous generalization as tuna is a large family of fishes with a wide range of mercury levels. Skipjack and yellowfin are short-lived members of the tuna family that are low in mercury. These are labeled in cans as “light” tuna. Albacore or “white” tuna is moderately high in mercury and is considered safe for occasional adult use but not for pregnant or breastfeeding women or young children. However, albacore tuna that pass by the west coast of Vancouver Island in the late summer are immature at 3 to 5 years of age, and considerably lower in mercury than older albacore from more southerly waters. If you can find a local commercial tuna fisherman you can get all the benefits of healthy tuna fish oils with low risk of mercury.

The same principle of younger fish containing less mercury applies to black cod (sablefish) and halibut as well. Both of these fish can live to an age and a size where they can become high in mercury. If bought direct from a local commercial fisherman it might be possible to select from younger, safer fish. With halibut, 25 pounds or less would be much safer than the larger fish.

A big mistake a sport fisherman might make is to intentionally go after the biggest halibut which could be a fish weighing hundreds of pounds. A fish this big is guaranteed to be high in mercury and if consumed in quantity, could easily lead to health problems. It would be wise to release a fish this big, partly for personal health reasons, but also to help maintain the stock. Virtually all halibut over 70 pounds are females and the bigger the female, the more numerous the eggs; for example, a 50 pound female halibut produces 500,000 eggs, while a 250 pound fish can produce 4,000,000 eggs per year. It only makes sense to let the big ones go.

This concept of the largest fish being the females with the most eggs also applies to ling cod. Ling cod, like Atlantic and Pacific cod and hake and pollock, are fast- growing fish. This makes them low in mercury content, except for the largest ones (over 36 inches), which are always females that can carry up to 500,000 eggs per year. Like halibut, it makes sense to throw these big female ling cod back.

Short-lived, very low mercury fish include herring, sardines (the larger ones are known as pilchards), sole, flounder, and salmon. Pacific salmon live from 2 to 5 years, depending on the species, and are very low in mercury and very high in health-promoting oils.

Fish from the north Atlantic have more mercury than north Pacific fish because the prevailing westerly winds take the mercury from the U.S. coal-burning plants to the Atlantic. However, the recent increase in coal-burning plants in Asia could eventually raise the levels of mercury in north Pacific fish. Fortunately there is one fish in the north Pacific that can compensate somewhat for increasing mercury levels. That fish is the pink salmon.

Pink salmon, like chum salmon, deal with predators by producing great volumes of fish that saturate predators so that some will survive. However, while chum might take 4 years to mature, pinks do so in just 2 years. What better way to avoid mercury accumulation in a progressively more polluted planet than take advantage of this fast-growing mercury-free pink salmon loaded with its health- giving oils?

The Alaskans have seen the opportunity of the pink salmon’s propensity for population production and seized it by developing Sea Ranching. They hatch out young pink fry (and chum) by the hundreds of millions and release them into the ocean where they fend for themselves. This has resulted in millions of mature pinks returning two years later. So many pinks returned in some years that they’ve flooded the world market and have been unable to sell them all.

In B.C., the use of Salmon Farms—raising Atlantic salmon in enclosed net pens—has actually interfered with the production of pink salmon. Being very small when they leave the rivers and creeks, pinks are vulnerable to being attacked and destroyed by sea lice that thrive around salmon farms. Since these deadly farms are throughout Johnstone Strait and Queen Charlotte Strait, it makes it very difficult for young pinks from Georgia Strait and the Fraser River to get to their northern high seas feeding grounds via this route. While the chemical called Slice has been used successfully to kill sea lice on fish from salmon farms, it also kills prawns, crab, shrimp, and krill (incidentally all these are low in mercury) and Slice’s toxicity to humans hasn’t been fully identified. This chemical approach to dealing with sea lice will likely create more health problems down the road.

Testing for Mercury

To measure one’s short-term exposure to mercury, blood testing can be done. Results should be less than 5 micrograms per liter of blood which equates to 5 parts per billion. (Some labs use a different scale in which 0 to 18 nmol/l is considered normal.)

If the blood reading is higher than 5 parts per billion, one needs to completely eliminate the fish containing high levels of mercury such as swordfish, marlin, barracuda, big eye (ahi) tuna, tilefish, and shark. Also, drastically reduce the moderately high mercury fish such as black cod (sablefish), halibut, and albacore tuna, as well as fresh-water fish. The best fish to use would be sardines, herring, sole, flounder, wild salmon, cod (Atlantic, Pacific, or ling), pollock, hake, and “light” canned tuna.

The blood should be retested to make sure the mercury circulating through the body comes back to normal levels that are less than 5 parts per billion. However, there is usually another, deeper layer of mercury that doesn’t show on blood, hair, or urine testing. It’s called the body burden of metals and is the body’s accumulation of mercury (and other metals) that has been taken out of circulation and stored away in the organs and tissues of the body over the years. German chemist Alfred Stock speculated in the 1920’s on mercury being hidden away deep in the body and the Swedes verified this with autopsies in the 1970’s and 1980’s. This discovery led Sweden to completely ban mercury that had long been used in amalgam fillings, vaccines, thermometers, contact lens solutions, nasal sprays, etc.

The test for the deeper body burden of metals is called a DMPS Challenge and is done by Medical or Naturopathic doctors trained in chelation. DMPS is a sulfur compound that, when injected into the body, pushes “hidden” metals out of storage into circulation where it can be identified and quantified. Most of this metal is eliminated through the urine which is then sent to a lab for analysis. Saturating the body with a sulfur compound such MSM (1 capsule 2 times per day for 4 weeks) prior to a DMPS Challenge seems to give better results. Having seen hundreds of results of DMPS Challenges (including my own) it is clear that most everyone has been storing away mercury deep in their systems since earliest childhood, even before birth.

The mercury in our environment may be rising, but fortunately it can be identified and eliminated, and in so doing, also eliminate a very wide range of health complaints.