262 



than have been demonstrated on other contaminants, and the costs of 

 constructing and operating such systems are likely to be higher. 



For many contaminants, however, the most difficult problems are 

 encountered in determining contaminant effects thresholds. A range of 

 methods have been developed for estimating the human health and 

 ecological risks associated with varying levels of sediment contamination. 

 However, more research must be completed to develop reliable 

 methodologies for determination of ecological and human health effects 

 thresholds. 



