between LC,, and LCgg. The range of concentration between LC)q and LCqo 
did not necessarily reflect the sensitivity of the species as indicated 
by the 24-hour LCso Values For example, the LC,g to LCgg range for white 
perch was 28.76 g 171; spot, with a 24-hour LCsq more than twice that of 
white perch (20. 34 versus 9.85 g 171) had an LCjg to reoe range of only 
18.54 g 1” 1, Similarly, Wey anchovies (LC59 = 4.71 g 1°~) had an LCj9 
to LCgg range of 7.29 g 1-1; the more sensitive Atlantic silverside 
Ween) 2240) g le) had ani LGig to) LGqg range of 9.43 9 1e.. 
White perch and spot exposed to fuller's earth for varying times 
showed an overall reduction of LCj9, LCs59, and LCg9, with increasing dura- 
tion of exposure (Table 4). These values were plotted logarithmically 
and are presented as toxicity curves (Figs. 2 and 3) (Sprague, 1969) and 
as concentration mortality curves (Figs. 4 and 5). 
Table 4. LCj,9, LCs5q, and LCgg values for white perch and spot, 
with increasing duration of exposure to fuller's 
earth. 
Duration of 
bioassay 
¢h) 
INot tested. 
2. Bioassays Using Resuspended Natural Sediments 
Lethal concentrations of natural sediments during 24-hour exposures 
were determined for white perch,: spot, menhaden, and striped killifish, 
and compared with the 24-hour LC values for fuller's earth (Table 5). 
Table 5. Comparison of 24-hour LC values of fuller's earth and 
natural Patuxent River, Maryland, sediments. 
Sediment 
Species 
LCj9 | Natural Sie 
Fuller's earth BSH I 
LC59 Natural 128.2 
Fuller's earth 38.18 
LCo9 | Natural 169.3 
Fuller's earth 
