By Lisa M. Belisle, MD, MPH
Originally published May 2007, Parent & Family

When I was young, I would sit on the dock near the family camp, threading my father’s fishhooks with freshly dug worms, as he cast out into the waters of Little Sebago. For me, late spring and summer (if we were lucky) meant fish on the grill. Fish-eating is a healthy habit to have: fish is filled with heart and brain-friendly omega-3-fatty acids, as well as zinc, iron, and vitamins A, B and D. It is also a good source of protein for those limiting their red meat intake.

Lately, however, fish has come into question due to concerns about mercury—a troubling toxin, especially for pregnant women, infants and children. Even finding less contaminated fish has become a problem, due to decreases in the fish supply.

How do we balance the benefits of finned food with a need to keep mercury out of our meals—and keep our fish population protected in the process?

The Menace of Mercury

Mercury occurs in trace amounts in coal and certain types of rocks. It is released from its natural sources by coal-burning power plants and through manufacturing processes. At one time, it was also used for thermometers, blood pressure cuffs and certain types of equipment. This is less common now, although some everyday items such as energy-saving light bulbs still contain mercury.

Unfortunately, mercury does not breakdown readily in the environment. Schools that once used mercury in their science labs have found decades-old mercury stored in abandoned cabinets. Industrial sites that deal with this substance have been known to have high levels in their trash for years.

When rain passes through contaminated industrial trash or smokestack air, it carries mercury with it into the groundwater, and then into rivers and streams. Once there, mercury is converted by bacteria into an even more toxic form called methyl mercury. Smaller organisms absorb methyl mercury and are consumed by larger organisms. Larger organisms, such as fish and birds, are eaten by humans. In addition to eating mercury-contaminated food, living creatures can also absorb it through the skin or lungs.

Unfortunately, mercury is very toxic to living creatures--especially small living creatures, such as infants and children. Mercury is also easily passed from pregnant or nursing mothers to their babies. Mercury (even in very small amounts) is poisonous to brain and nerve cells, but can also cause damage to the digestive system, respiratory system, kidneys and eyes. In a University of North Carolina study, 21% of women aged 16 to 49 had unacceptably high mercury levels. This is troubling information given that these are prime child-bearing years.

Minimizing Mercury Exposure

Because fish is a nutrient-rich food, it makes little sense to avoid eating it entirely. Instead, the U.S. Food and Drug Administration recommends:

• Not eating shark, swordfish, king mackerel, or tilefish—especially women and children.
• Limiting weekly consumption to two servings (12 ounces, or 2 average meals) of fish with low mercury levels such as shrimp, canned light tuna, salmon, pollock, and catfish. (Fish sticks and fish sandwiches are usually made from products that are lower in mercury).
• Limiting weekly consumption of albacore ("white") tuna to no more than one serving (6 ounces, or one average meal), and eating no other fish that week.
• Checking advisories about the safety of fish caught locally. In Maine, there are strict limits on eating freshwater fish, which can be found at www.maine.gov/dhhs/eohp/fish.

The group Physicians for Social Responsibility also reminds us that:

• Children’s servings should be smaller than those eaten by adults. One to two ounces is an appropriate serving size for a toddler, while older children may eat 2-3 ounces. A serving size is equal to the size of the individual’s palm.
• When cooking fish, especially the types that are known to have more mercury, we should trim away fatty parts, using cooking methods that allow fat to drain off (such as broiling, grilling, roasting or steaming) and throwing away any fat drippings that accumulate. (FMI, visit www.mercuryaction.org.)

The Supply/Demand Dilemma

Fish consumption has risen dramatically in the past two centuries—leading to a decreased supply of fish due to overfishing. The cod population off Nova Scotia has decreased by 98% since the 1850’s. Farm-raised fish can be a good alternative. Approximately one third of all fish on the market are farm-raised. According to the Monterey Bay Aquarium, the main considerations in choosing fish responsibly are:

• which species are raised,
• how they are raised and
• where the farm is located.

For more information on responsible fish eating—and a “Seafood Watch Pocket Guide,” visit www.mbayaq.org. Choosing fish responsibly ensures that there will always be fish available for us to eat. Eating less-contaminated fish ensures that we are getting the health benefits of fish without exposing ourselves (and our children) to unnecessary risk. As long as we are smart about our choices, we can still favor fish on the grill—and delight in days of summer fishing with our fathers.