metals. However, in a Swedish estuary following dredging, there was an over- 

 all increase in concentrations of Hg, Cd, Zn, Pb, and Ni in the benthic fauna. 

 The elevated level was starting to return to normal after 1.5 yr (Rosenberg 

 1977). 



Hydrocarbons present at sublethal levels in dredged material have the 

 potential to interfere with the olfactory senses of marine animals and affect 

 food location, escape from predators, selection of habitat, and sex attraction 

 (Diaz and Boesch 1977). Due to the many variables that affect the toxicity of 

 potential contaminants, we agree with Hirsch et al . (1978) that whole sediment 

 bioassays should be used to predict the toxicity of dredged material at the 

 disposal site. We further urge that many of these tests consist of long-term 

 evaluations of subtle sub-lethal effects. 



In the course of our review, we have identified a significant data gap 

 relating to contaminant availability and toxicity to the biota. While there 

 is considerable information about the impact of individual contaminants on 

 aquatic and terrestrial organisms, the bioavailability and toxicity of the 

 contaminants found in dredged material is still relatively unknown. Few 

 studies have been conducted within the context of dredged material disposal 

 situations and, further, most tests have failed to measure synergistic ef- 

 fects. Contaminated dredged material usually contains many contaminants 

 and, therefore, synergistic effects could very well be the rule. 



Fate of deposits of dredged material: Post-disposal movement of dredged 

 material has been shown to range from no movement (Gordon 1974), to moderate 

 dispersal from the disposal area (Bassi and Basco 1974), to almost complete 

 displacement from the disposal area (Maurer et al . 1974). In pipeline dredg- 

 ing, much of the dredged material may leave the disposal area at the time of 

 disposal in the form of fluid mud (Bassi and Basco 1974). Material discharged 

 from hopper dredges or from barges is less likely to be widely dispersed. 



Factors affecting dispersal include grain size and other characteristics 

 of the dredged material, currents, tides, storms, bottom topography, shipping 

 traffic, and depth. Saila et al . (1972) discussed dispersion occurring at a 

 dump site in Rhode Island Sound. Holliday (1978) summarized the processes 

 affecting the fate of dredged material and Holliday et al . (1978) discussed 

 models for predicting the short-term fate and long-term transport of dredged 

 material. Mathematical models of both short-term and long-term transport of 

 dredged material have been developed (Krone and Ariathurai 1976, Ariathurai et 

 al. 1977). 



Changes in circulation: Deposits of dredged material have the potential 

 to alter estuarine circulation patterns, tidal prisms, and water exchange 

 rates. In turn, these can decrease freshwater flow through the estuary, de- 

 crease saltwater penetration, sharpen salinity gradients, affect temperatures, 

 alter nutrient budgets, and affect other physical or chemical parameters. 

 These in turn affect living organisms (Odum 1970, May 1973b). Changes may be 

 \/ery subtle and difficult to predict. 



A classi 

 near Brownsv 



ic example of impacts of circulation changes occurred in South Bay 

 ille, Texas. Dredged material from the Brownsville ship channel 



32 



