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sediments in such ways as to be unavailable to any but microorganisms. It 
is the objective of special care measures of disposal to increase the con- 
ditions within the sediment mass that will promote continued sequestering. 
SOME ECOLOGICAL CONDITIONS THAT SUPPORT OCEAN DUMPING OF POLLUTED DREDGED 
MATERIALS 
SEQUESTRATION OF POLLUTANTS 
In general the dumping of dredged material in the marine environment 
creates conditions in the mound that induce immobilization of toxic metals 
and many organic compounds. This is particularly true when the dredged 
material contains substantial amounts of fine particles and is enriched by 
naturally occurring organic matter (Gambrell et al., 1977). Also, it 
should be noted that several physicochemical conditions that immobilize 
pollutants of interest to the present discussion are augmented by some 
“special care" disposal measures discussed hereinafter. First, however, it 
may be helpful to examine the sequestering effect that these physicochemi- 
cal conditions have on particular pollutants. 
SELECTED POLLUTANTS 
Mercury 
Uptake and accumulation accompanying mercury contamination have been docu- 
mented for pelagic and benthic organisms. It appears, however, that this 
uptake by aquatic organisms is predominantly from water rather than bioac- 
cumulation in food webs (Gambrell, et al., 1978). Fortunately elutriate 
tests on a number of sediments have shown that very few release mercury in 
significant amounts (Brannon et al., 1978). 
The following physicochemical conditions can effectively immobilize mercury 
in sediments: (1) humic materials, (2) sulfide, (3) clays, especially 
montmorillonites, (4) reducing conditions, and (5) pH around 7.0. Many of 
these conditions are met in ordinary disposal of dredged material in the 
