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Evidence is that many marine organisms accumulate most toxicants primarily 
from the water column or interstitial water. Many toxicants once disposed 
in dredged material are not readily available in either medium. "Special 
care" measures of disposal can enhance immobilization of, say, toxic metals 
to a high degree. 
Persistence. As used in environmental management, persistence refers 
to the property of toxic substances to resist degradation by the activity of 
such organisms as bacteria or fungi or by natural physicochemical factors 
for substantial periods of time. Obviously, metals and metal compounds may 
be very persistent. But many of these are immobilized by conditions of 
dredged material disposal. Among organics, the organochlorines, are quite 
persistent. But contrary to a still commonly held view they will not remain 
permanently in the marine environment. Even the PCBs are amenable to bio- 
degradation, albeit for some with high chlorine numbers the process is very 
slow. The best procedure, then, is to sequester them removed from the biota 
either permanently or for long periods of time by one or another "special 
care" disposal methods. 
SOME ECOLOGICAL CONDITIONS THAT SUPPORT OCEAN DUMPING OF POLLUTED DREDGED 
MATERTALS 
Taking conditions affecting the immobilization of mercury, cadmium, and 
chlorinated hydrocarbons in dredged material one finds several factors that 
work equally well on all three. For example, mercury is immobilized (ab- 
sorbed) in sediments by clays (especially montmorillonites), as are cadmium 
and DDT; humic materials and other organics are important immobilizers; 
sequestering is enhanced generally by reducing conditions and a pH near 
neutral. Most of these conditions are met in ordinary disposal of dredged 
material (in the mound) in the open ocean, but "special care" measures can 
enhance the effects. 
NATURE AND APPLICATION OF SPECIAL CARE MEASURES 
Obviously special care measures will apply to methods of disposing of 
