Avoiding mercury contamination in fish

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Barely a week seems to go by without the publication of a report or study extolling the health-boosting virtues of fish. Good news about fish abounds, it appears, so it’s no surprise that many of us are making a concerted effort to eat more of it. However, recent news that some fish species, including tuna, may be contaminated with mercury appears to have sent quite a ripple of disquiet amongst fish lovers. Because mercury has the potential to damage the nervous system of developing foetuses and small children, women who are pregnant, planning pregnancy or breast feeding have been advised to limit their consumption of tuna and to exclude some other types of fish altogether. After years of riding a tide of positive publicity, could it be that the chips are up for fish?

Mercury’s presence in the sea is the result of its natural release from the earth’s crust and industrial pollution. Not surprisingly, this metal has the propensity to makes its way from seawater into the fish that inhabit it. However, not all species of fish are as prone to mercury contamination as others. Through a phenomenon known as bioconcentration, mercury concentrations tend to increase the higher up the food chain you go. Basically, what this means is that the bigger the fish, the more tainted it is likely to be. Tuna, a firm favourite in this country in both fresh and canned forms, is one big fish well known to be prone to pollution with mercury, as is whale, marlin, swordfish and shark.

Research performed over the last 20 years has suggested that eating fish tainted with mercury can interfere with the neurological development of foetuses and small children. Some of the evidence for this has come from a study performed in Faroe Islanders, the diet of whom is traditionally rich in whale meat contaminated with mercury. Researchers have discovered that increasing levels of mercury in this population are associated with impairment in language, attention, memory and movement in children. As a result of this and other research, the Food Standards Agency here in the UK has recommended that women who are pregnant, planning pregnancy or breast feeding should limit their consumption of tuna to two medium-sized cans or one fresh tuna steak per week. They have also recommended complete abstinence from shark, marlin and swordfish for these women and all children under the age of 16.

My personal feelings that avoiding fish likely to be contaminated with mercury makes good sense. However, let us not forget that the omega-3 fats found in certain species of fish are known to promote health, and actually help neurological development in the growing foetus and during childhood. As it happens, while tuna is often classified as an oily fish, tests reveal it’s omega-3 content is actually really quite low. The best ploy, I think, is to shift emphasis away from tuna, towards fish that offer more in the way of healthy omega-3 fats, and less in the way of mercury. For those looking for a direct swap, I recommend salmon, either fresh or in tinned form. Other options include trout, mackerel and herring. While tuna may be of the menu for many, the good news is there’s plenty more fish in the sea.

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