Sediment was maintained in suspension during the test period by con- 
tinuous agitation with a submersible pump and aeration by injection of 
compressed air. The control tank received the same pumping and aeration 
treatment. 
Fuller's earth (Fisher F-90, technical grade), kaolinite (Hydrite-10, 
Georgia Kaolin Company, Elizabeth, New Jersey), and resuspended bottom 
sediments from the upper Patuxent River estuary were used in the bioassay 
experiments. Concentrations in the experimental tanks were determined by 
weight. Replicate 5-milliliter samples were drawn from test and control 
tanks and dried. The difference between the weight of the dried control 
sample and the dried test tank sample represented the added sediment 
load in grams per liter (g ie 
Fish were exposed to suspended solids in 27-liter polyethylene tanks. 
Temperatures were maintained within +1.5° Celsius by immersing the test 
tanks in a circulating water bath. Tanks were monitored for fish mortality, 
temperature, pH, and dissolved oxygen. 
Lethal concentrations (LC) of suspended solids causing 10-, 50-, and 
90-percent mortality of test fish were determined by normit analysis 
(personal communication, McErlean, Environmental Protection Agency, 1969), 
a modification of probit analysis (Berkson, 1953). 
2. Bioassays Using Mineral Solids. 
Tests using commercial preparations of the mineral solids, kaolinite 
and fuller's earth, were conducted using 14 fish species from two locations 
(Table 1). Six species were from Delaware Bay (bay anchovy, Anchoa 
mitehtlit; Atlantic silverside, Menitdta menidta; croaker, Mtcropogon 
undulatus; weakfish, Cynoscton regalis; bluefish, Pomatomus saltatrix; and 
cusk eel, Rissola marginata). Eight species were from the Patuxent River 
estuary, Maryland (spot; toadfish, Opsanus tau; mummichog; hogchoker, 
Trinectes maculatus; menhaden; white perch; striped bass, Morone saxattlis; 
and striped killifish). Bioassay tests for the Delaware Bay fish were 
conducted at the University of Delaware Bayside Laboratory, Lewes, 
Delaware; tests for the Patuxent River estuary fish were conducted at the 
University of Maryland Hallowing Point Field Station, Prince Frederick, 
Maryland. 
Fish were collected by otter trawl or haul seine and transported in 
water to holding facilities. Bayside Laboratory holding facilities con- 
sisted of 140-liter polyethylene tanks immersed in temperature-controlled 
water baths. Water quality at Bayside was maintained by a combination of 
aeration and filtration in a closed-system recirculating unit. Hallowing 
Point holding facilities consisted of 250-liter polyethylene tanks immersed 
in temperature-controlled water baths. An inline protein skimmer device 
was used to maintain water quality in the closed system. 
All fish were starved for 2 to 5 days before testing. Hydrite-10 and 
fuller's earth were analyzed for particle size, organic content, and 
