Predators, mercury

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

In a report from the U.S. EPA (1980), fish contained between 10,000 and 100,000 times the concentration of methyl mercury present in ambient water. In a study of methyl mercury in fish from different oceans, higher levels were reported in predators than in nonpredators (see Table 8.2). Taken overall, these data suggest that predators have some four- to eightfold higher levels of methyl mercury than do nonpredators, and it appears that there is marked bioaccumulation with transfer from prey to predator. 

While methylmercury occurs naturally in tlie environment, it is reasonable to expect that methylmercury levels have increased in modem times as a result of increased inorganic mercury concentrations. Whether methylmercmy concentrations have increased to a similar extent as inoiganic mercuiy is not known. It is clear, however, that elevated fish mercuiy concentrations can currently be found in remote lakes, rivers, reservoirs, estuaries, and marine conditions, typically in predators such as sportfish at the top of food webs. As of 2003, 45 states had fish consumption advisories related to mercuiy, and 76% of all fish consumption advisories in the United States were at least partly related to mercury (USEPA 2004a). The number of advisories is increasing with time, although this is due at least partly to more sites being sampled (Wiener et al. 2003). 

For threatened or endangered species, or species of special concern, it is often necessary to analyze specimens that have died of causes not directly attributable to mercury. Bird eggs that have been abandoned or flooded out may be used for analyses. However, if the eggs were pushed out of the nest by parents that are incnbating the rest of the clntch, the reason for rejection of the egg must be considered in order to properly interpret mercury residue levels. Similarly, birds killed by predators may be suitable for analysis, but the internal tissues of sick or emaciated birds should not be nsed for residue analysis because in some studies, error has resulted from remobilization of mercury (Ensor etal. 1992 Sundlof etal. 1994). 

Chapter 4). Because wildlife (in particular, top-level predators) are the integrators of a mercury signal that has already been integrated across several media (air, water, sediments, and fish), the fourth objective is most challenging, and will require careful attention in overall network development. 

Arnold BS. 2000. Distribution of mercury within different trophic levels of the Okefenokee swamp, within tissues of top level predators, and reproductive effects of methyl mercury in the Nile tilapia (Oreochromis niloticus). PhD dissertation. University of Georgia. 

Fimreite N, Fyfe RW, Keith JA. 1970. Mercury contamination of Canadian prairie seed eaters and their avian predators. Can Field-Nat 84 269-276. 

Webber HM, Haines TA. 2003. Mercury effects on predator avoidance behavior of a forage fish, golden shiner (Notemigonus ctysoleucas). Environ Toxicol Chem 22 1556-1561. 

Hogan LS, Marschall E, Folt C, Stein RA (2007) How non-native species in Lake Erie influence trophic transfer of mercury and lead to top predators. J Great Lakes Res 33 46-61... 

Table 3.3 Results of EDI/PNEC evaluations of HCB and mercury predators.

High mercury levels in terminal food chain predators hke tuna fish have caused considerable worry. It has been found that tuna contain larger than average amounts of selenium.1- 10 Discuss the possible role of selenium with respect to the presence of mercury. ... 

Amouroux D., Donard O. F., Krupp E., Pecheyran C., Besson T., and Fitzgerald W. F. (2003) Isotopic fractionation of mercury species in top predators fishes (tuna and whale) from world ocean preliminary results. In Abstracts ofASLO Aquatic Sciences Meeting, Salt Lake City, UT, USA, 8—14 February. 

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