EXECUTIVE SUMMARY 



In a brief span of 3 years, 1955-1958, several abundant species of aquatic 

 insects, snails, and fingernail clams practically disappeared from a 170-km reach 

 of the Illinois River, from Hennepin on the north to the mouth of the Sangamon 

 River on the south. The declines of the fingernail clam, Musculium transversum, 

 were particularly spectacular: from average densities of 21,000 animals per square 

 meter to zero in Peoria Lake and backwater lakes near Havana. The declines had 

 drastic repercussions on the ducks and fish that fed upon the invertebrates. The 

 lesser scaup duck, or bluebill, virtually stopped using the Illinois River as a major 

 migration route, and there was a decline in the condition and growth of bottom- 

 feeding fish, including sport fish, -such as channel catfish, and commercially 

 important species, such as common carp. 



The situation changed very little into the 1980s, despite improvements in 

 water quality (e.g., higher disolved oxygen levels attributable to improved waste 

 treatment in the Chicago-Joliet area and Peoria). This lack of recovery was espe- 

 cially puzzling because the- invertebrates are capable of rapidly recolonizing 

 barren areas; seed populations are available in spring-fed areas of Peoria Lake and 

 in tributaries and these organisms have short, rapid life cycles. 



We found that porewater from Illinois River sediments contains a toxic 

 factor that inhibits the filtering ability of the clam, and the toxicity increases 

 upstream, peaking near Lockport. We observed the same pattern of sediment 

 toxicity with a different test organism, also representing a class of important food 

 organisms for fish and waterfowl: the water flea, Ceriodaphnia dubia. In contrast, 

 the porewater actually stimulates an alga and bacteria, but this is not surprising 

 because of the great physiological differences among plants, bacteria and animals. 



Toxicity greatly decreased when the porewater was made slightly more acid 

 and porewater became nontoxic when filtered through a resin that removed 

 ammonia. Removal of heavy metals with a chelating agent had no effect on toxic- 

 ity. All the evidence points to ammonia as the culprit, especially since toxicity in 

 all tests correlated highly with the concentration of ammonia, which is known to 

 be toxic to aquatic animals. Since ammonia is a nutrient for plants and certain 

 types of bacteria, the presence of ammonia likewise could explain the stimulation 

 of these organisms. 



Although ammonia appears responsible for the major upstream-downstream 

 pattern in toxicity, there were two sites where the porewater contained visible 

 signs of oil and the toxicity was associated with petroleum hydrocarbons, includ- 

 ing PAHs (polycyclic aromatic hydrocarbons) such as naphthalene. 



During the course of this study, several species of fingernail clams, includ- 

 ing M. transversum, reappeared in the Chicago area waterways and in the Illinois 

 River at Peoria and Havana. There are at least four possible explanations for this 

 surprising reappearance of clams in the same general areas where the porewaters 

 tested toxic. First, we found that clams recolonizing the upper Illinois are more 

 resistant to ammonia than the clams from the lower Illinois, where the organisms 

 were obtained for all of the early bioassays. Second, our previous research demon- 

 strated that the surface layers of sediment in some areas are less toxic than layers 

 a few centimeters deeper. Toxicity may have been overestimated in tests where 

 surface and deep layers of sediment were mixed prior to testing. Third, toxic 

 episodes may be brief and infrequent, allowing organisms to colonize in between 

 episodes. Fourth, the distribution of toxicity in sediments may be extremely 

 patchy, so that healthy organisms are found adjacent to barren areas. If the latter 

 two hypotheses prove to be true, acute toxicity in the Illinois River has changed 

 recently from a widespread problem to a more localized or episodic problem. 

 Reduction of toxicity in surface sediments may reflect recent reductions in 

 ammonia loading from sewage treatment plants in the Chicago area, although it is 

 not clear whether the sources of ammonia in the porewaters are effluents, the 

 deeper layers of sediments, or both. 



