the porewater contains a pH-sensitive toxicant that is not affected by 

 chelation with EDTA, as heavy metals would be (Tables 4.2 and 4.4). 

 Second, toxicity to both C. dubia and the fingernail clam M. transversum 

 is associated with total ammonia concentrations in sediment porewater 

 (Table 4.3, and Figures 4.1, 4.2, and 4.3). Third, removal of ammonia 

 by treatment with zeolite removes the toxicity (Table 4.5). Finally, H. 

 transversum is known to be sensitive to un-ionized ammonia at levels 

 that are likely to occur in the porewaters. 



Not all the toxicity found in the upper Illinois Waterway was 

 associated with ammonia. Porewaters from the Calumet Sag Channel 

 (CS307.4) and the lower Des Plaines River (DP277.0) contained visible 

 signs of oil and grease and toxicity associated with PAHs (including 

 naphthalene) and other compounds found in petroleum. 



4.5 Sensitivity of Recolonizing Clams 



Much to our surprise, we found several species of fingernail 

 clams, including Muscuh'um transversum, at several sites in the upper 

 Illinois Waterway: the Chicago Sanitary and Ship Canal (SS317.0), the 

 North Branch of the Chicago River (CR325.4), and the Calumet Sag Channel 

 (CS318.5). Biologists from the Long Term Resource Monitoring (LTRM) 

 Station at Havana also reported finding fingernail clams in mud they 

 happened to bring up on their sampling nets and boat anchors. 



We wondered if these clams had acquired some resistance to the 

 toxicants in the sediments, so we tested their responses to a sediment 

 sample from the Chicago Sanitary and Ship Canal (SS317.0) and another 

 from the Calumet Sag Channel (CS318.5). At the same time, we tested 

 clams from Swan Lake on the lower Illinois River, where we had obtained 



42 



