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(e) The life stage of the organism. 
Other factors will determine the availability of the toxicant to exert its 
effects upon the organism. For instance, much of the dredged material re- 
moved during harbor and channel maintenance dredging is high in organic 
matter and clay and is both biologically and chemically active. It is usu- 
ally devoid of oxygen, may contain appreciable sulfide, and is near neutral 
pH. These sediment conditions favor effective immobilization of many pol- 
lutants. For example, organic matter and especially sulfide can effective- 
ly immobilize mercury and lead, especially in a reducing and near neutral 
pH condition. These conditions are usually found when dredged material is 
disposed in a low-energy hydraulic regime, and is favored by mounding or 
placement in a low-energy depression and capped with clean material (see 
Special Care Disposal Measures in this report). It should be noted then 
that some laboratory tests, of the availability of, say, metals when a 
dredged material is disposed in the ocean are not an accurate measure of 
field effects. ; 
The difference between acute vs. chronic toxicity is generally, but not 
always, attributable to the amount of toxicant present within the organism. 
Acute responses of organisms are relatively easy to observe, whereas chron- 
ic responses are not. Acute responses generally involve dysfunctign of a 
vital process, such as respiration or heart function. Chronic responses on 
the other hand more likely will affect the reproductive capacity or fecun- 
dity of the organism. 
Fortunately, all organisms have the ability to accommodate to the intake of 
a wide range of toxicants. They achieve this accommodation by sequestering 
the toxicant in their storage tissues or by a process of detoxification and 
depurative elimination carried out by the liver, lungs, kidneys or, in some 
cases, the skin. This process of depuration is time-dependent. Hence 
amelioration of impacts of even highly polluted dredged material can be 
achieved by reducing the frequency of dumping and the amount dumped on each 
occasion (see section on Multiple Capping and Depuration in this report). 
