DISCUSSION 



The stranding of approximately 350 bottlenose dolphins along the 



Gulf Coast raised concerns about the health and survival of this species of marine 

 mammals as well as the quality of the environment in which they live. These top 

 predators in the marine food chain can accumulate high concentrations of 

 contaminants in their tissues and organs. Of the metals analyzed, only mercury 

 and selenium appeared to have concentrations high enough to be of possible 

 concern. In addition, elevated concentrations of CHs in some of the dolphins may 

 be of concern. 



Metals in Liver and Kidney 



The suite of metals (Appendix Al, A2) were chosen for analysis to allow 

 monitoring and evaluation of their synergistic and antagonistic characterictics 

 with respect to some of the known toxic contaminants. The range of 

 concentrations of metals found in ttitsc Gulf Coast dolphins, especially in livers, 

 was wide (e.g. mercury, 0.18-117 jig/g and selenium, 0.70-34.9 ^g/g). The 

 differences in concentrations are probably associated with several factors — 

 including diet, exposure to anthropogenic and natural sources, as weU as age, sex 

 and reproductive cycle. 



Elevated l«»vels of mercury and s'^hnium in two of ^h^-se 'dolphins may be 

 of concem. The limit of tolerance for mercury in mammalian liver tissues has 

 been suggested to be approximately l(X)-400 jig/g (Wagemann and Muir, 1984). 

 Accordingly, the elevated levels of mercury found in livers from two of these 

 dolphins (> 1(X) ^g/g) are of concem because of potential biological effects. 

 Additionally, two more dolphins had mercury levels (~ 40 P-g/g) that were 

 considerably higher than the remaining animals. Geraci (1989) also reported 

 elevated levels of mercury in dolphins from the previous stranding (range, 0-110 

 p.g/g; n = 59). Interestingly, the concentrations of mercury were approximately 

 ten times higher in liver than in kidney (Figure 2) — the reverse of what is 

 normally found in terrestrial mammalian species (Doull, 1980). This anomoly 

 may be of sigiiiflcance because the predominant form of mercury found in the 

 liver (methyl mercury) may add to the burden of organic pollutants that can 

 accumulate in this organ. 



66 



