Methylmercury in fish tissue

R. Rai, W. Maher, F. Kirkowa, Measurement of inorganic and methylmercury in fish tissues by enzymatic hydrolysis and HPLC-ICP-MS, J. Anal. Atom. Spectrom., 12 (2002), 1560-1563. 

H. E. L. Palmieri, L. V. Leonel, Determination of methylmercury in fish tissue by gas chromatography with microwave-induced plasma atomic emission spectrometry after derivatization with sodium tetraphenylborate, Fresenius J. Anal. Chem., 366 (2000), 466-469. 

L. Yang, Z. Mester, R. E. Sturgeon, Determination of methylmercury in fish tissues by isotope dilution SPME-GC-ICP-MS, J. Anal. At. Spectrom., 18 (2003), 431-436. 

Uthe, J.F., Solomon, J. and Grift, B. (1972) Rapid semimicro method for the determination of methylmercury in fish tissue. JAOAC, 55, 583-589. 

In species-unspecific isotope dilution techniques, an isotopically enriched standard solution is added post-column, and the data evaluation is performed as described in Section 7.3.4 for CE coupling. Species-unspecific isotope dilution for HPLC coupling has been described for the determination of Cd, Cu and Zn in metallothioneins extracted from eel liver, while Fe, Cu and Zn were determined in proteins separated from human serum. This technique has also been applied to iodine determination in humic substances,as well as selenium speciation in human serum. Species-specific isotope dilution using HPLC-ICP-MS has been described for selenium analysis, the analysis of organotin species in sediments, methylmercury in fish tissue, trimethyllead in water, and chromium speciation. Overviews to this topic have been published, e.g. by Heumann and Hill. ... 

The US Environmental Protection Agency has set a criterion of 0.3 mg methylmercury per kg in fish tissue that should not be exceeded to protect the health of consumers of noncommercial freshwater/estuarine fish. 

Methylmercury partitions strongly into the lipid-rich tissues of fish hence, it becomes highly bioconcentrated. Assume the BCF for fish is 106 liters/kg (i.e., assume an equilibrium partitioning model is an acceptable approximation to the real world). What fraction of the methylmercury in a lake would actually be in fish tissue, if the lake had a volume of 106 m3 and contained a metric ton (1000 kg) of fish ... 

The general population is most commonly exposed to mercury primarily from two sources (1) eating fish and marine mammals (e.g., whales, seals) that may contain some methylmercury in their tissues or (2) from the release of elemental mercury from the dental amalgam used in fillings. It is not known how much of the elemental mercury released from dental amalgam is inhaled as a mercury vapor, how much is breathed out, how much is swallowed in a liquid form, or how much is converted into a mercuric salt that is either swallowed of directly absorbed into the oral mucosa. Exposure to mercury, however, does not... 

A variety of methods exist for the extraction, clean-up and subsequent analysis of methylmercury in samples. Most methods involve a solvent extraction, often with toluene, of the methylmercury from the sample, followed by separation by gas chromatography with an electron-capture detector. The specific details for methylmercury extraction from fish tissue are shown in Figure 5.10. A similar approach can also be applied for the extraction and analysis of methylmercury from sediment. A summary of the methods used for the determination of methylmercury in fish and sediment matrices is given in Table 5.2. This has also been recently reviewed [13]. 

Specific chapters then focus on different projects on speciation analysis. Chapter 4 deals with interlaboratory studies on methylmercury in fish and sediment Chapter 5 describes the collaborative projects to certify organotins in sediment RMs and mussel tissues Chapter 6 gives an overview of the certification project on trimethyllead in simulated rainwater and urban dust Chapter 7 describes the certification project on arsenic species in fish tissues Chapter 8 focuses on the intercomparison and tentative certification of Se(IV) and Se(VI) in simulated freshwater Chapter 9 deals with a feasibility study to stabilize Cr species in solution followed by the certification of Cr(III) and Cr(VI) in lyophilized solutions and welding dust Chapter 10 gives a review of methods used for A1 speciation Chapter 11 develops the overall collaborative project to standardize single and sequential extraction procedures for soil and sediment analysis, followed by interlaboratory studies and certification of soil and sediment reference materials. 

The largest pool of methylmercury in freshwater biota is found in fish tissues, and fly larvae are alleged to play an important role in mercury cycling from feeding on beached fish carcasses, as judged by observations on... 

Once methylmercury is formed it enters the food chain by rapid diffusion and firm binding to proteins in aquatic biota and attains its highest concentrations in the tissues of fish at the top of the aquatic food chain due to biomagnification through the trophic levels. The main factors that affect the levels of methylmercury in fish are the diet/trophic level of the species, age of the fish, microbial activity and mercury concentration in the upper layer of the sediment, dissolved organic carbon (DOC) content, salinity, pH, and redox potential. 

Uthe et al 2 have described a rapid semi-micro method for determining methylmercury in fish and crustacean and aquatic mammal tissue. The procedure involves extracting the methylmercury into toluene as methylmercury bromide, partitioning the bromide into aqueous ethanol as the thiosulphate - complex, re-extracting... 

The unexpectedly high concentrations of mercury found in water and in fish tissues result from the formation of soluble monomethylmercury ion, CHjHg, and volatile dimethylmercury, (CH3)2Hg, by anaerobic bacteria in sediments. Mercury from these compounds becomes concentrated in fish lipid (fat) tissue and the concentration factor from water to fish may exceed 10. The methylating agent by which inorganic mercury is converted to methylmercury compounds is methylcobal-amin, a vitamin Bj2 analog ... 

What is a realistic detection limit for the analytical method employed All methods have finite limits of detection, and these limits vary widely. For example, a report indicating that the methylmercury concentration in fish tissue is "not detected" means little if the detection limit of the measurement method is an order of magnitude higher than the allowable level of mercury in fish. 

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