particle-size distribution, and angularity. In addition, other factors, 
which were uncontrolled and not coyered in this study, must be considered 
when dealing with natural sediments. These factors may include sorbed 
toxic metals, high biochemical oxygen demand, and nutrient content. 
Concentration-response curves were established to predict mortality 
for selected estuarine fish exposed to suspended particles. Lethal con- 
centrations of fuller's earth causing a 10-percent mortality in 24 hours 
of exposure (24-hour LC,q) ranged from 0.57 g 17! for Atlantic silversides 
CO BALS ied seeps mummichogs. Fish exposed to fuller's earth were clas- 
sified as tolerant (24-hour LCj9 = 10 g ee): sensitive (24-hour LCj9 
> 16 > 1.0 g 17!), or highly sensitive (24-hour LGiigh le Om ealwea)eaaeihe 
use of lethal concentration levels causing 10- or 50-percent mortality 
over a defined period of exposure (hours or days) to establish suspended 
solid criteria is customary and useful. However, this procedure ignores 
the biologically significant sublethal effects of suspended solids on 
estuarine Organisms. 
The tolerances of various estuarine fish can be generalized. 
The most lethal effects of suspended mineral solids were found in: (a) 
Fish in the lower trophic levels (anchovies, Atlantic silversides, and 
juvenile white perch), (b) juvenile fish, and (c) species with high oxy- 
gen requirements. Species with very low oxygen requirements only succumb 
to very heavy concentrations of suspended solids, or not at all. These 
degrees of tolerance tend to be correlated with species habitat preferences. 
Pelagic (open water) and littoral (shoal water) fish were all affected by 
suspensions of solids, but to widely varying degrees. Benthic (bottom- 
dwelling) species that live in or at the mud-water interface were the 
least affected. 
Dredging and dredged material deposition (particularly open-water 
disposal) should be timed and located, if possible, to: (a) Avoid spawn- 
ing grounds and times, and also areas used by juvenile fish; (b) avoid 
areas used by lower trophic level fish, particularly filter-feeders; and 
(c) avoid areas used by pelagic and littoral fish with high oxygen require- 
ments. 
Adequate knowledge of local conditions at dredging and dredged material 
disposal sites is essential for preproject decisionmaking; i.e., species 
present (seasonal and resident), habitat preference, life history stages, 
sediment types, sediment chemistry, sediment concentrations, and probable 
duration of exposure. 
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