Mercury (Hg) is a neurotoxin that is released into the environment by both natural and anthropogenic causes. It makes its way into aquatic sediment where it is converted to methylmercury (MeHg) by sulfate-reducing bacteria. Methylmercury is more lipid soluble tan elemental mercury and is therefore more easily transferred between organisms through consumption and makes it way up the food chain, primarily the aquatic food chain.
Because of this, MeHg is more dangerous as an environmental pollutant than elemental mercury. It can also be stored in body tissues for many years. Therefore the tissues of long-lived predatory organisms contain much more methylmercury than organisms at lower trophic levels because they consume and store more methylmercury over their lifetime. Because many species of sharks are at the top of the food chain and are long-lived compared to many species of bony fish their meat contains a great deal more methylmercury than other seafood options. Eating sharks and other top marine predators may be dangerous. Mercury is a neurotoxin and the ingestion of Hg or MeHg contaminated food may lead to severe health problems. In a tragic event in the 1950s thousands of people were paralyzed and 100 died after eating contaminated fish from Minamata Bay, Japan. Mercury had bioaccumulated in the fish of Minamata Bay from discharges of a nearby chemical company.
Several governmental worldwide organizations have outlined acceptable levels of methylmercury in fish. These levels signify the maximum amount of mercury an adult could potentially tolerate in a seafood item without significant negative risks to their health. According to the Codex Alimentarius and the United States Food and Drug Administration (US FDA) acceptable methylmercury levels in predatory fish is 1.0 mg/kg. Japan has set this level at 0.3 mg methylmercury/kg.
Allowable total mercury levels according to the European Community are 0.5 mg/kg. These allowable levels are significantly lower than the consumption of shark meat allows as shark tissue is highly concentrated with both Hg and MeHg. A 2007 study released by the US FDA that measured mercury concentrations in sharks between 1991 and 2007 found an average total mercury concentration of 0.979 ppm (±0.626) with the highest levels of sharks sampled found to be 4.54 ppm (4.54 mg/kg). As ppm is convertible to mg/kg in a 1:1 ratio, this average concentration of 0.979 mg/kg is significantly higher than the established allowable European Community level of 0.5 mg total mercury/kg. A study at Mote Marine Laboratory in Sarasota, Florida looked at methylmercury concentrations in nine species of sharks in coastal waters. Samples averaged 0.88 ppm, or 0.88 mg/kg with some concentrations as high as 2.87 ppm, or 2.87 mg/kg. The average level of 0.88 mg/kg is dangerously close to the máximum allowable limits set by both the Codex and Alimentarius of 1.0 mg methylmercury/kg and far surpass limits established by Japan of 0.3 mg/kg. Also, according to the same study, one-third of the samples studied had methylmercury levels that were higher than the 1.0 mg/kg established allowable levels. Mercury and methylmercury levels in shark meat are significantly higher tan suggested consumption levels and therefore may pose severe risk to human health if consumption continues.
In Mexico, 23,000 tons of shark meat are consumed annually. The meat is widely sold in supermarkets across the country but is labeled as with simply, “shark steak,” “cazon,”.” Because of this, Mexican consumers may not be aware that they are eating shark at all, let alone the health risks associated with the consumption of these products. If “shark meat” is alluded to at all, the species name is not given. As some shark species contain higher levels of mercury, it is essential that consumers have access to this information in order to safeguard their health.
To mitigate the issue of shark meat consumption in Mexico, Nakawe Project, in partnership with Turtle Island Restoration Network , is launching:
“Got Mercury ?” campaign.
The primary goal of this project is to educate Mexican citizens about the health risks associated with eating sharks, principally related to mercury as a toxin. By reaching out to Mexican citizens and providing them with the education and tools to understand the toxins shark meat contains, we hope to reduce the amount of shark meat consumed in Mexico.
Calculate Mercury Content in Fish & Seafood by TIRN
Eating seafood high in mercury is hazardous to your health, especially for women and children. Our “Got Mercury?” calculator below helps you make healthier seafood choices. Just enter your weight, the seafood type, the amount of seafood you will eat during a week, and click the “calculate” button to see the mercury content in fish.