provisions for collection of multiple species at several stations and we have sufficient data from 

 this and other programs to address this issue. 



The collection of different species of bivalves might complicate the comparison of analytical 

 results and further analysis of the data. Fortunately, some species have been found to coexist at 

 the same locations (Figure 12 and Table 12). The chemical analysis of these species will assist in 

 the decision whether or not it is appropriate to compare trace organic concentrations encountered in 

 different organisms and/or the limitations of such comparisons. The following species-by-species 

 sections discuss the similarities and differences in the concentrations of the total HCHs, DDTs, 

 chlordanes and PCBs, on a dry weight basis, among the different species listed in Table 12. This 

 comparison is not comprehensive because we do not have data for age, sex, or reproductive stage 

 which may differ for the various species sampled and these factors do influence tissue 

 concentration of contaminants. 

 Anadara tuberculosa, Anadara similis and Protothaca grala 



These organisms have been collected from under the roots of mangroves in several 

 stations, including Colombia, Costa Rica, and Ecuador. Figures 13 and 14 compare the 

 concentrations of total HCH, DDTs, chlordanes and PCBs encountered in Anadara tuberculosa, 

 Anadara similis and Protothaca grata.. Results indicate that the concentrations measured in one 

 species are, in general, accompanied by similar concentrations in the other species. Concentrations 

 of total HCHs, chlordane, DDTs and PCBs differ by less than a factor of three between these 

 species and indicating no preferential uptake and retention of analytes by either of the two Anadara 

 species. The same analysis, however, seems to indicate that Protothaca grata tends to accumulate 

 these trace organic contaminants to a slightly greater extent than both Anadara species. The 

 observed differences are very small and too few samples were analyzed to detect with any certainty 

 systematic differences between species. 

 Crassostrea rizhophorae, Isognomon alatus, Anomalocardia brasiliana, Mytella 



falcata and Mytella guayanensis 



Although not all these organisms were found at the same sites, they all were collected in 

 areas were Crassostrea rizhophorae was also found. Crassostrea rizhophorae and Isognomon 

 alatus were found attached to the roots of mangroves in Jamaica. In Brazil, Crassostrea 

 rizhophorae was collected within one hundred meters from the areas where Anomalocardia 

 brasiliana, Mytella guayanensis or Mytella falcata were sampled. 



Figure 15 indicates that Crassostrea rizhophorae does not accumulate HCHs, DDTs, 

 chlordanes and PCBs to the same extent, compared to Isognomon atatus and Mytella falcata,. The 

 concentrations, however, do not differ by more than a factor of three. No clear differences can be 



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