all the clams used in our previous bioassays. This work was done 

 outside the scope of our original research proposal and is of a very 

 prel iminary nature. 



The preliminary results support the hypothesis of differential 

 resistance. The clams from the Sanitary and Ship Canal showed virtually 

 no impairment of filtering performance in response to porewater from the 

 place where they where taken or to the Calumet Sag porewater (see 

 below). The clams from Swan Lake were sensitive (36% decline in filter- 

 ing performance) to porewater from the Sanitary and Ship Canal, while 

 they had only a slight negative response, comparable to the Cal-Sag 

 clams, to the Cal-Sag porewater. The Ship Canal porewater was not 

 tested on the Cal-Sag clams. 



SOURCE OF CLAMS 

 CS318.5 

 SS317.0 

 Swan Lake 



SOURCE OF POREWATER 



SS317.0 CS318.5 



-0.17 



-0.08 0.00 



-0.36 -0.13 



43 



