Mercury in fish: the list that puts tuna and mackerel in doubt

Mercury in fish: the list that calls tuna and mackerel into question

A canned tuna lover discovers a list that places his favorite food in the group of fish to avoid because of its high mercury content. The table, released by the Natural Resources Defense Council (NRDC) and picked up by El Mostrador, classifies species into three tiers: those whose consumption is discouraged (king mackerel, barracuda, red snapper, shark, swordfish, tilefish and tuna), those that should not exceed three servings a month (bluefish, grouper, Gulf mackerel, Chilean sea bass, canned albacore tuna and yellowfin tuna) and those limited to six a month (sea bass, carp, Alaskan pollock, halibut, lobster, mahi mahi, monkfish, snapper, canned tuna, bonito or sea trout, among others). The problem, they point out from the start, is that the source is not a health agency: the NRDC is an American wildlife advocacy group, and its guide relies on data from the FDA and the EPA, but its main mission is not public health.

Canned tuna, in the spotlight

Alarm spreads among those who admit to eating a lot of canned fish. "Given that I overdo it with canned tuna and mackerel... What effects does mercury have?" asks one participant. The answer he gets is blunt: "Neurological, basically." From there unfolds a catalog of symptoms ranging from hair and tooth loss to irreversible brain damage, with references to historical poisonings such as Minamata. Some point out that organic mercury, such as dimethylmercury, is never eliminated from the body and that any amount is potentially harmful. Others tone it down: "To ingest the same amount of mercury as Qin Shi Huang by eating canned tuna, you'd have to eat several million cans."

The discussion soon turns to the credibility of the list. Some participants argue that the NRDC acts more to protect threatened species than to safeguard human health. Others defend that its data come from the FDA and the EPA, two US federal agencies, which lends it credibility. The controversy is not resolved: while some call for epidemiological studies showing a real increase in poisoning from fish consumption, others demand data proving that mercury in fish has increased compared with past decades.

Where does the mercury that ends up in fish come from?

According to claims in the thread, the main source of emissions is coal-fired power plants, which release mercury into the atmosphere; it ends up settling in rivers and oceans, where it turns into methylmercury and accumulates up the food chain. Large, long-lived fish, such as tuna or swordfish, concentrate more of it because they eat other fish that have already accumulated it. That is why small species, such as sardines, show much lower levels. However, the NRDC list also includes freshwater fish such as carp or perch, which raises the question of why inland ecosystems are affected too.

Concern about where fish comes from mixes with antiestéticar of radioactivity. Several messages mention FAO area 61, which corresponds to the northwest Pacific, as an area to avoid because of the Fukushima accident. "Can you see the FAO 61 area thing on the cans?" asks one participant. The answer is that some brands do specify the catch area: Orbe and Alopécico sardines indicate they come from FAO 27, the northeast Atlantic. The advice repeated most often is to read the label and go for small, locally sourced fish.

Fillings, vaccines and other sources of mercury

The conversation drifts toward other routes of exposure. One participant claims that silver-colored dental amalgams continuously release mercury vapor and that there are "dozens of studies" linking them to allergies, migraines, memory loss or tachycardia. The claim is not checked against health sources and remains just one more opinion in the thread. Thimerosal, a mercury-based preservative once used in some vaccines, is also mentioned as a possible cause of autism, a hypothesis the scientific community has repeatedly rejected. The article does not endorse any of these claims: they are included as part of the debate, not as proven facts.

Fed up with food warnings

The overall tone drifts toward fatigue. "You can't eat fish because it has mercury, you can't drink milk because no animal drinks milk as an adult, you can't eat wheat or corn because it's genetically modified..." sums up one participant. The most repeated conclusion is that you have to eat something and zero risk does not exist. Others point out that mercury is not the only problem: farmed salmon, panga and contaminated sunflower oil have had their own warnings. One participant's final question sums up the general feeling: "What fish are we left with?"

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The NRDC list is not binding, but it has prompted more than one person to review their diet. The available evidence suggests that mercury accumulates in large predators and that small species are safer. What remains unresolved is whether the risk justifies changing habits or whether this is just a new twist in food hypochondria.