Marine mammals tend to have much higher mercury concentrations than 

 other marine organisms, with particularly high concentrations being found in the 

 hver (Law et al. 1991). As a general rule, mercury accumulation in marine 

 mammals increases with age, although there was no significant correlation 

 between age and mercury concentrations in these dolphins, the six animals with 

 the highest levels of mercury were all at least five years old. Mercury is a highly 

 toxic, nonessential metal, (Thompson, 1990), particularly in one of its organic 

 forms (methyl mercury) and is believed to affect the central nervous system. 

 Methylation of mercury, due to the action of aquatic microorganisms could be 

 followed by bioaccummulation up the food chain through the diet of marine 

 mammals. In addition, mercury may exhibit toxicity by combining with 

 sulfhydryl groups inhibiting enzyme systems (Doull, 1980). 



Selenium is an essential metal within a narrow range — above that range it 

 is quite toxic (Cooper, 1967). Selenium concentrations were elevated in die two 

 animals which also had high mercury levels. This finding is not unexpected 

 because, as in other species, selenium generally covaries with mercury (Muir et 

 al. 1988). The selenium concentrations in liver samples of stranded dolphins 

 were similar to the concentrations reported earlier for this species (Geraci 1989). 

 Selenium, like mercury, may have an inhibiting effect on activities of many 

 sulfhydryl enzymes, but is also believed to have an important protective action 

 against the toxic effects of mercury, by readily complexing with methyl mercury. 

 To what extent selenium may have a protective effert against mercury in these 

 dolphins remains to be studied. 



Chlorinated Hydrocarbons in Blubber and Liver 



Although the levels of CHs were relatively low in most of these dolphins, 

 some of the animals had concentrations of these contaminants at levels of possible 

 toxicological concern. In general, the concentrations of contaminants in these 

 stranded dolphins were consistent with previously published data of stranded 

 dolphins. Three of the dolphins have concentrations of PCBs (77, 78 and 120 

 ^g/g) in their blubber tissue higher than a level of toxicological concern (SO 

 ^g/g) for marine mammals suggested by Wagemann and Muir (1984); three 

 additional animals had concentrations of PCBs > 40 p.g/g in blubber tissue. 



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