(a) the greatest detrimental impact on benthos resulted from burial in 

 excess of 0.5 m (1.6 ft); 



(b) benthic repopulaticn was by horizontal migration; 



(c) population density had not recovered in the center of the disposal 

 area S mo after disposal; 



(d) because of invasion of opportunistic species, species diversity was 

 greater in the center of the disposal area 9 mo after disposal; 



(e) at 9 mo both species density and diversity were greater at the mar- 

 gins of the disposal area than reference areas; and 



(f) effects of the disposal operation were confined to the immediate 

 disposal site area. 



For additional discussion of impacts on benthic organisms see the DMRP 

 synthesis reports by Hirsch et al . (1978) and Wright (1978). 



Contaminants: Dredged material from harbors or other heavily industrial- 

 ized areas may contain substantial amounts of heavy metals, oils and greases, 

 pesticides, PCBs, and other toxic substances. These elements and compounds 

 tend to be tightly bound to clay particles. Release to the water column is 

 limited and controlled by complex chemical reactions such as pH and redox 

 potential and by the presence of iron and sulfides. Therefore, most contami- 

 nants remain with the bottom sediments where they pose a long-term potential 

 hazard to the ecosystem. 



The uptake and biological significance of toxicants, such as PCBs, 

 kepones, petroleum hyrocarbons, and heavy metals are not usually well under- 

 stood. Haider and Johnson (1977) found significant uptake of PCB's by fathead 

 minnows ( Pimephales promelas ) from sediments via the water column. However, 

 patterns are not consistent and generalizations are difficult to make at this 

 time. These toxicants persist as residues in tissue due to bioaccumulation 

 (Stern and Walker 1978). Neff et al . (1978), in the laboratory, obtained an 

 uptake of heavy metals 26.5% of the time from 135 exposures involving eight 

 metals and five benthic invertebrates. It does appear that uptake of heavy 

 metals is not nearly as common as once suspected but further research is 

 needec'. Blom et al . (1976), Brannon et al . (1976), Chen et al . (1976), Khalid 

 et al . (1977), and Lee et al . (1977) provide state-of-knowledge discussions. 



Pesticides, PCBs, and kepones biomagnify in organisms as these compounds 

 pass to higher trophic levels (Nathans and Bechtel 1977, Horn et al . 1979). 

 With the exception of mercury, biomagnification is much less common with heavy 

 rietals or petroleum hydrocarbons. 



The presence of contaminants in dredged material indicates a pccential 

 for uptake, but there are many documented instances in which organisms exposed 

 to contaminated materials did not exhibit uptake. Many factors control up- 

 take. Sodium chloride, for instance, inhibits the availability of many heavy 



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