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BULLETIN OF BUREAU OF FISHERIES 
Chloride of lime, or bleaching powder 
This substance is of uncertain composition as usually found. Its lethal properties as regards 
aquatic life are largely dependent upon the amount of chlorine which is liberated when the bleaching 
powder is added to the water. The potential amount of chlorine available in the sample under 
question must be known before its toxicity can be estimated. Much confusion exists in the pre- 
vious reports because of that fact and consequently no limits are given here. 
Chromic acid, H 2 Cr04 
Chrome tannery wastes. M. M. E., 100 p. p. m. in hard water did not kill goldfish, Carassius 
auratus, in 100 hours’ exposure; the same amount in very soft water killed goldfish in 30—35 minutes. 
Citric acid, (COOH)CH 2 C(OH)(COOH)CH 2 COOH 
Wastes from industries using citrus fruits. M. M. E., 894 p. p. m. in hard water killed goldfish, 
Carassius auratus , in 4-28 hours; 625 p. p. m. in hard water was not lethal to goldfish in 100 hours 
exposure; 120 p. p. m. in soft water killed cladocerans, Daphnia magna, in 24-72 hours. 
Cobaltous chloride, CoCl 2 
Pigment works; chemical industries. M. M. E., 1,000 p. p. m. in hard water killed goldfish, 
Carassius auratus, in 30-32 hours; 10 p. p. m. in soft water fatal to some goldfish in 168 hours; 
others survived exposure to this amount for longer periods. 
Copper, Cu 2 
See various cupric compounds. As Moore and Kellerman (1905) have pointed out and as 
is discussed here under the action of heavy metals, the amount of copper required to produce lethal 
results varies greatly with the water, and particularly the carbonates. These writers state that 
“in water containing carbonates, if the amount of dissolved C0 2 is very low the basic carbonate of 
copper formed may be considered insoluble; if, however, the water should contain a fair amount 
of C0 2 it would bring the copper carbonate at least partially into solution.” Copper compounds 
are used as algicides and occur in many industrial wastes. 
Cresol, general formula C 6 H,i(OH) (CH3) 
A mixture of the various isomeric compounds of this group. The mixture and the individual 
compounds occur in gas wastes in varying proportions and the mixture is used in various sheep 
dips and other preparations for the disinfecting of livestock. Both gas wastes and dipping vats 
have on occasion been the sources of stream pollution by this substance. This mixture and two 
of the component isomers are discussed below. 
Cresol 
Adams (1927), 10 p. p. m. in Nile River water killed cladocerans, Daphnia sp., and copepods, 
Cyclops sp.; Demyanenko (1931), 17-20 p. p. m. lethal for fishes. 
Orthocresol 
Shelford (1917), 55-65 p. p. m. in tap water killed orange-spotted sunfish, Lepomis humilis, 
in 1 hour; M. M. E., 10-20 p. p. m. in hard water killed goldfish, Carassius auratus, in 3-5 days. 
Paracresol 
Shelford (1917), 80-90 p. p. m. in tap water killed orange-spotted sunfish, Lepomis humilis, 
in 1 hour; Southgate, Pentelow, and Bassindale (1933), 6.2 p. p. m. in tap water caused trout, 
Salmo irideus, to float helpless on their backs in 1 hour 40 minutes, if the water carried circa 10 
p. p. m. of dissolved oxygen and in 13 minutes if the water carried only 3 p. p. m. dissolved oxygen. 
