However, the differences in analytical methods and quality assurance measures 

 make it difficult to rigorously compare contaminant concentrations among data 

 from various researchers. 



Even dolphins stranded in the same area had a wide variablity of the 

 concentrations of CHs (Tables 4, 5), indicating the source of contaminants was 

 not related to their stranding sites. For example, among the 10 Galveston area 

 dolphins, 7 were among those with the lowest PCB and DDT concentrations in 

 blubber while the other 3 were among the highest (Figure 3). A knowledge of 

 migratory and feeding patterns of these animals, together with data on age. sex, 

 and reproductive status, would be essential to help explain the observed 

 contaminant variability. Also, analyses of stomach contents of these animals may 

 shed some light on immediate sources of contaminants. 



Of the 209 PCB congeners, only a few of fliese are demonstrably or 

 potentially toxic and of these few, the planar (non-ortho substituted) congeners 

 may account for most of the toxicity exerted by PCTBs in the environment 

 (McFarland and Clarke, 1989 and Safe, 1984). Several recent studies report the 

 presence of low levels of these planar PCBs in a variety of marine mammals 

 (McFarland and Clarke, 1989 and Tanabe, et al. 1987). Preliminary results 

 from the analysis of blubber (Figure 4) of these dolphins showed the presence of 

 low concentrations of a number of planar PCBs (Krahn et al. unpublished data). 

 Funlicr analyses arc needed to evaluate toxicological implications of these initial 

 analyses. 



Two dolphins had higher concentrations of DDTs than of PCBs in the 

 blubber samples, similar to results reported by O'Shea, et al. (1980) for two 

 California bottlenose dolphins with elevated concentrations of DDTs. These 

 anomalies are interesting as most researchers report PCB concentrations to be 

 higher than DDTs in tissues of marine mammals and fish. The profile of CHs 

 (i.e. PCBs vs. DDTs) in California bottlenose dolphins reported by O'Shea et al. 

 (1980) is similar to patterns observed from sites in southem California where 

 fish, invertebrates and sediment sampled in our field surveys for the National 

 Benthic Surveillance Project (NBSP) of NOAA's Status and Trends Program 

 (NS&T) show relatively high proportions of DDTs. Most other U.S. sites 

 sampled for the NBSP show contaminant profiles in which concentrations of 



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