tify specific toxic compounds in complex mixtures (Figure 1.3; Mount and 

 Anderson-Carnahan 1988; Mount and Anderson-Carnahan 1989; Mount 1988). 



TIE procedures use toxicity-based fractionation schemes to charac- 

 terize and identify compounds in aqueous samples that exhibit toxicity 

 to aquatic organisms. Although TIE cannot be used on bulk sediments, it 

 can be applied to the aqueous fraction (porewater). Previous studies 

 (Adams et al . 1985; Swartz et al . 1985; Knezovich and Harrison 1988; 

 Connell et al . 1988; Swartz et al . 1988, Di Toro et al . 1992) have shown 

 a correlation between toxicity or bioaccumulation of a number of contam- 

 inants by benthic macroinvertebrates, on the one hand, and porewater 

 concentrations on the other. The TIE procedures are designed to address 

 multiple toxicant interactions as well as matrix effects on bioavail- 

 ability. The major strength of TIE is that it allows direct relation- 

 ships to be established between toxicity and chemical analyses. TIE is 

 a phased approach that is designed to isolate, identify and confirm the 

 presence of acutely toxic compounds. TIE methodology for identification 

 of chronically toxic compounds is currently under development (USEPA 

 1992). Phase I of TIE consists of a series of chemical and physical 

 manipulations designed to remove or render biologically unavailable 

 generic classes of compounds (Figure 1.4). Phase II uses information 

 from Phase I to focus appropriate analytical methods on toxic fractions. 

 Phase III consists of methods designed to verify that the suspected 

 toxicant is the actual toxicant. TIE methodology has been applied to 

 sediments from the Great Lakes (Ankley et al . 1990) and the Calumet Sag 

 Channel of the Illinois River system (Schubauer-Berigan and Ankley 

 1991). We applied these techniques to sediments from the Illinois River 

 System in an effort to identify the substance or substances responsible 

 for the declines of the benthic invertebrates. 



