Shark mercury

Lyle, J.M. 1984. Mercury concentrations in four carcharhinid and three hammerhead sharks from coastal waters of the Northern Territory. Austral. Jour. Mar. Freshwater Res. 35 441 -451. 

Silva, P., F.H. Epstein, and R.J. Solomon. 1992. The effect of mercury on chloride secretion in the shark (,Squalus acanthias) rectal gland. Comp. Biochem. Physiol. 103C 569-575. 

Although the rate of mercury input to the ocean s surface waters has increased as a result of anthropogenic activities, it is not clear that the relatively high MMHg concentrations now seen in the larger fish, e.g., tuna, shark, and swordfish, are the result of pollution. Measurements of mercury levels in preserved fish collected over the past 100 years have proven inconclusive due to small sample sizes and contamination effects. 

The primary concern with organic mercury is methyl mercury in fish. Children and women of childbearing age should be cautious about consuming fish known to accumulate mercury such as tuna, shark, swordfish, and pike. Local fish consumption advisories should be followed. 

There are several different types of organic mercury, but by far the most important in terms of health effects is methyl mercury. When atmospheric mercury is deposited on the ground or in the water, it is converted to methyl mercury by bacteria. Mercury compounds are very toxic and this is the bacteria s way to detoxify mercury. Small animals then consume the bacteria, along with the methyl mercury and bigger animals in turn consume the smaller animals, thus increasing the concentrations of methyl mercury. Methyl mercury accumulates in the larger carnivorous animals, most important of which are fish such as tuna, pike, and shark. 

It should also be remembered that fish high in the food chain, such as tuna, swordfish, and shark accumulate toxic substances like mercury or PCBs. Mercury affects the nervous system and is a proven reproductive hazard. Table 13.4 lists examples of marine animals that may be toxic. 

Fish Tuna, shark, sword fish Mercury Neurotoxic, reproductive effects ... 

If you choose to eat fish, realize that the more you eat, the more mercury your baby will ingest. And, so far, scientists haven t come up with a how-much-is-too-much figure with regard to fetal brain damage and lowered IQ. It seems like the least harmful way to eat fish, then, is to follow the FDA s suggestions avoid shark, swordfish, king mackerel, and tilefish. The EPA and some countries, including... 

For some reason there isn t the same amount of black-and-white government information on what is and isn t safe to consume when breastfeeding as when pregnant. Talk to your doctor about specifics, but sushi gets the thumbs up. Continue to stay away from fish high in mercury like swordfish, shark, and tuna (for more on this, see Part 2, Food ). 

Penedo de Pinho, A., J.R.D. Guimaraes, A.S. Martins, P.A.S. Costa, G. Olavo, and J. Valentin. 2002. Total mercury in muscle tissue of five shark species from Brazilian offshore waters Effects of feeding habit, sex, and length. Environ. Res. Section A 89 250-258. 

P. Krystek, R. Ritsema, Determination of methylmercury and inorganic mercury in shark filets, Appl. Organomet. Chem., 18 (2004), 640-645. 

What about the mercury contamination of fish It s true that mercury, a heavy metal, becomes concentrated in the fatty tissues of fish. That s particularly true for tilefish, swordfish, king mackerel, and shark, all of which contain 1 part per million or more of mercury. But, as reported in the November 28,2002, issue of the New England Journal of Medicine, many if not most fish do not have appreciable amounts. Fresh and frozen tuna have 0.32 parts per million (ppm) and canned tuna drops down to 0.17 ppm. Pollack has 0.20 ppm. In both salmon and shrimp, mercury is not detectable. 

A 12.5 kg sample of shark meat contained 22 mg of methyl mercury, CHsHg". Is this amount within the legal limit of 1.00 ppm of methyl mercury in meat ... 

Silva, P Mount Desert Island Biological Salsbury Cove, ME Mercury in chloride transport in shark rectal gland and rabbit thick ascending limb. NIEHS... 

Typical mercury concentrations in large carnivorous freshwater fish (e.g., pike) and large marine fish (e g., swordfish, shark, and tuna) have been found to exceed 1 g/g (ppm) (EPA 1984b Fairey et al. 

Recreational and Subsistence Fishers. Methylmercury concentrations in sport fish can be at least an order of magnitude higher than in commercial fish purchased in a supermarket (see Section 5.4.4). Therefore, recreational and subsistence fishers, including some Native American peoples who consume locally caught fish from mercury-contaminated waterbodies or consume long-lived predatory oceanic species such as shark and swordfish, can be exposed to higher mercury concentrations than individuals who consume similar amounts of commercially marketed fish from a variety of sources (Ebert et al. 1996 ... 

Hueter RE, Fong WG, Henderson G, et al. 1995. Methylmercury concentration in shark muscle by species, size and distribution of sharks in Florida coastal waters. In Porcella DB, Wheatley B, eds. Mercury as a global pollutant. Proceedings of the Third International Conference Whistler, British Columbia, July 10-14, 1994. Boston, MA Kluwer Academic Publishers, 893-899. 

The food web that exists primarily in the water column may be impacted by methyla-tion of reactive mercury species. Concentrations of methylmercury in predatory piscivorous marine fishes that inhabit coastal waters (such as sharks) may exceed 1 mg kg Most of this methylmercury is thought to be transferred through and accumulated in the food web, as methylmer-cuty is very bioavailable. Almost 100% of the mercury found in fish muscle tissue is... 

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