Fish have always been upheld as a healthy, low-fat alternative to beef and pork. Many varieties, particularly small and oily fish (e.g., herring, sardines, Atlantic mackerel), are high in omega-3 fatty acids like EPA and DHA, which are essential fats that cannot be synthesized by humans.
Though fish intake has leveled out as a whole in the United States, the FAO reports that the consumption of fish has expanded globally over 4 percent in 2010 to $218BN annually despite the fact that over 80 percent of our world’s fish stocks have been fully exploited. Those of us who are sushi lovers often find ourselves eating fish more than average.
Anyone who consumes fish needs to not only take into account depleted fish stocks, but also contaminant risk, such as mercury and PCBs. Now that more studies have linked mercury, a known neurotoxin, to adverse health affects ranging from lethargy to hair loss in adults to even more severe damage in children, consumers are becoming more informed on how and what they consume.
“Fish get mercury from their environment,” says Dr. Michael Gochfeld at a conference at the Department of Medicine at Stony Brook University Medical Center. “About one third of mercury is from natural activities, like volcanoes but two thirds is caused by humans, particularly from burning coal.”
According to the EPA, The U.S. is estimated as the third highest producer of anthropogenic mercury emissions, but that’s only a small portion of the global emissions. Asia produces about 53% of the mercury emissions and approximately half of the mercury deposits in the United States are from atmospheric deposits from Asia.
“Mercury rains down in its inorganic form and gets taken up by planktonic organisms into the base of the water column,” explains Gochfeld. “When in an anoxic environment, there are sulfate-reducing bacteria that get poisoned by it. These organisms are capable of methylating the mercury to monomethyl mercury and they do this to jettison the mercury from their bodies. It gets released into the environment and becomes a problem for larger fish and of course for humans.”
“All fish contain mercury,” says Timothy Fitzgerald, Environmental Defense Fund scientist focusing on sustainable seafood programs. “The mercury level in fish is one of the biggest things that drive exposure in people (between 30-40% of the mercury exposure in the U.S. comes from eating tuna). Who you are – whether you are a child or adult or pregnant mother, how much you weigh, how much you are eating, and at what frequency matters. The exposure is all about the dose.”
Once mercury is taken up in fish or humans, it tends to associate with protein because protein is where most of the sulfur resides. In the fish, this is in the filet, which is the part we typically eat. “Mercury is taken up quite quickly in the gut and gets redistributed to all tissues,” explains Dr. Jane Hightower, internist and author of Diagnosis: Mercury: Money, Politics and Poison. “Over 95% of the mercury in your body that you eat will be absorbed and within 2-3 days you can get distribution throughout the body.”
“Mercury clears from the body very quickly,” asserts Fitzgerald, “especially compared to other toxins like PCBs and dioxins, which can stay in the body for decades. One estimate that I saw is at a rate of 1 percent/day if you are not taking in any more mercury. That means on average you can get rid of 50% of your mercury load in 2 months.” But this of course is if you don’t continue to recontaminate your body by eating more fish, cautions Hightower.
“The hardest part is diagnosing it,” says Fitzgerald. “The symptoms look like so many other things.” Hightower, who started noticing symptom patterns in her patients in 2000 agrees: “The symptoms from mercury poisoning are highly variable. The most common is fatigue, trouble with concentration, muscle and joint pain, trouble thinking, and hair loss. Those are the symptoms that you get with the lower levels of exposure. If you get these symptoms, you may put yourself at risk for more permanent health issues such as brain and nerve damage.”
What’s clear now is that every fish has mercury and with forty-four states with fish advisories, it is imperative for people to reconsider their consumption patterns. The latest findings from the Environmental Health Perspectives report also reveals that mean mercury concentrations in the Food and Drug Administration’s Monitoring Program guidelines differ by 20 percent or more for 33 out of 58 seafood items, putting more people at greater risk for exposure.