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The content, chemical form, and distribution of mercury and selenium in edible tissue were determined for several samples of fish and other marine animal organisms (mollusks, crustaceans and pods). For most fish samples, except Pacific blue marlin, 53 to 94% of the total mercury content was present as methylmercury, being notably higher in freshwater species. Other marine organisms, except shrimp, contained only 29 to 47% methylmercury. For all samples, a significant part of the total selenium content (4 to 47%) was present as selenate (Se VI). Tissue selenium levels did not correlate with corresponding mercury levels. In freshwater and older processed (canned) marine fish, except marlin, 55 to 80% of the total mercury content was water-extractable. For non-processed (fresh) and newly-processed marine samples, only 22 to 47% was extractable. On a percentage basis, inorganic mercury was generally more extractable than methylmercury. For all fish samples, except marlin, 55 to 60% of the total selenium content was water-extractable, while only 35 to 45% was extractable for other marine species. On a percentage basis, Se VI was more extractable than selenite (Se IV) and selenide (Se II).

The content, chemical form and distribution of mercury and selenium were determined for several samples of canned tuna. Samples represented albacore, bluefin, skipjack and yellowfin species, and were packed in either water or vegetable oil. Recently-processed samples (less than one year old) and much older samples (8-29 years old) were examined. Methylmercury was the predominant mercury form in all samples, comprising 57.4-94.7% of the total mercury content. For these samples, 7.6-44.8% of the total selenium content was present as selenate. There was no apparent effect of packing medium, species or sample age on the methylmercury and selenate percentages. Although the total selenium content exceeded that of total mercury, there was no apparent correlation between the total levels of both elements. Sample age influenced the level of water-extractable mercury and selenium in canned tuna. For recently canned samples, an average of 27.0% of the total mercury and 55.6% of the total selenium content were water-extractable. However, for the older samples, the corresponding respective average extractable levels were 46.4 and 48.2%. For both categories, inorganic mercury and selenate were more extractable, on an average percentage basis. In addition, an average of 7.2% of the total mercury content was benzene-extractable.

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Specific environmentally significant arsenic compounds are determined by capillary gas-liquid chromatography. Inorganic (arsenite, arsenate) and organic (monomethylarsonate, dimethylarsinate) arsenicals are measured as the corresponding methylthioglycolate derivatives, which are simultaneously separated on wide-bore borosilicate glass and fused-silica columns under conditions of temperature programming. Inorganic arsenate and arsenite cannot be differentiated by the derivatization technique. Flame-ionization and electron-capture detection are evaluated. A simple and rapid sample preparation procedure is used for water, urine, blood, and tissue.