10-31 

 The Cause of the Observed Trace-Metal Distributions 



Obviously both oyster and mussel tissue composition are influenced 

 by the trace-metal content of the particles they ingest. There should 

 then be a relationship between the chemical properties of the particles 

 of the surrounding water and the sediments and the compositions of the 

 tissues. Consequently, the chemical composition of the ingestible 

 particles could be inferred from two environmental indicators : the 

 composition of the sediments at the sediment-water interface, and the 

 composition of the bulk water (including the fine-grained particles) 

 associated with the organisms. 



Considering the trace-metal maps for the top five cm of Long 

 Island Sound sediment cores (Figures 10-5-7) , there is a marked similarity 

 between the areas of high metal concentrations in the sediments and high 

 concentrations in the mussels and oysters. Similarly, a comparison of 

 the Ni concentrations in mussels (Figure 10-21) with the coastal distri- 

 bution of rti'in unfiltered Long Island Sound water (Figure 10-22) also 

 shows a marked correlation. [Nickel is the only element analyzed in the 

 mussel study which has also been extensively analyzed in water samples 

 from along the Connecticut coast (Turekian, 1971) ] . I conclude that 

 the primary source of the metals found in elevated levels in the soft 

 tissues of mussels and oysters is the suspended organic-rich debris in 

 the Sound. -—This is accentuated where a significant source of metal- 

 bearing organic-rich particles from human activities is introduced by 

 direct supply or secondary resuspension. Therefore, a strong correlation 

 exists between high metal concentrations in all components of the coastal 

 system -- water, sediment and organisms and the proximity of freshwater 

 stream and sewer discharges. 



Redistribution of particulate material from point and in part 

 non-point ( i.e., atmospheric) injections occurs in the sediments of the 

 Sound. Siibsequent dilution of this high-metal-content particulate 

 matter with indigenously produced, low-metal-content planktonic debris 

 plus material from "cleaner" sediments in the Sound acts to obscure 

 point sources. This occurs within a relatively short distance (one - two 

 miles) from the point of injection. 



